Gradient domestication seedling raising and high-survival cultivation method for saline-alkaline tolerant taxodium zhongshanha

Abstract

The invention relates to the field of agriculture and forestry planting, and discloses a gradient domestication seedling raising and high-survival cultivation method for saline-alkaline tolerant taxodium zhongshanha. Comprising the following steps: determining a soil conductivity range allowed by a target root zone according to conductivity distribution of a 0-80cm soil layer of a target saline-alkali afforestation land; in the nursery garden, container matrixes are arranged into a first matrix layer, a second matrix layer and a third matrix layer from top to bottom to form an increasing conductivity gradient, irrigation liquid with different conductivity is adopted for irrigation and water supplementation in a staged mode, and the conductivity of the second matrix layer is stabilized within the range; planting holes are dug in the afforestation land, a salt elimination layer and a salt elimination channel are arranged to be communicated with a drainage ditch, the upper portion of the salt elimination layer is sequentially backfilled with a buffer layer, a transition layer and outer-layer original saline-alkali soil, and after container seedlings and root clusters are subjected to field planting and planting, maintenance is conducted according to an irrigation system to maintain the conductivity of the buffer layer and the transition layer to be not higher than the upper limit of the range.

Description

Technical Field

[0001] This invention relates to the fields of agriculture and forestry planting, specifically to a method for the gradient domestication and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides. Background Technology

[0002] Saline-alkali land is widely distributed in coastal mudflats, low-lying areas along rivers and lakes, and some inland salinized areas. Influenced by factors such as groundwater depth, evaporation, and rainfall, soil salinity often varies vertically and migrates and redistributes with seasonal changes, easily leading to salt return phenomena in the surface layer or root zone. Salt accumulation affects seedling water and nutrient absorption, inhibits root growth, and consequently causes problems such as prolonged seedling establishment time and unstable survival rates in the early stages of afforestation.

[0003] Metasequoia glyptostroboides is highly adaptable and has a certain application basis in the greening and ecological restoration of saline-alkali land. However, in actual afforestation, the salinity of soil varies greatly in different plots and at different depths, and the root environment changes rapidly after seedling planting. If the salinity of the nursery substrate differs significantly from that of the root zone in the afforestation site, or if the root distribution fails to adapt to the salinity level of the target root zone, root elongation may be restricted and water absorption capacity may decrease after planting, affecting subsequent growth.

[0004] Existing afforestation methods in saline-alkali land typically involve soil replacement, application of organic fertilizers or soil conditioners, irrigation and leaching, and the construction of drainage ditches to reduce surface salinity or improve salt drainage conditions. In terms of seedling management, standardized substrate formulas, conventional irrigation, and hardening-off methods are commonly used. While these practices can improve local conditions to some extent, the connection between nursery seedling cultivation, transplanting, and post-planting care is not sufficiently refined. On the one hand, the seedling stage often lacks targeted treatment based on differences in soil salinity, making it difficult to ensure root distribution matches the target root zone. On the other hand, the composition and layering of backfill soil at planting, as well as the selection of post-planting irrigation methods, rely heavily on experience. There is a lack of unified control over the salt drainage structure and the soil conductivity in the root zone, easily leading to localized salt accumulation or salt return, thus affecting survival rate and forest stability. Therefore, we propose a gradient acclimatization and high-survival-rate cultivation method for salt-tolerant Metasequoia glyptostroboides. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a gradient acclimatization and high survival rate cultivation method for salt-tolerant Metasequoia glyptostroboides, thereby solving the technical problems existing in the prior art.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] A gradient acclimatization and high survival rate cultivation method for salt-tolerant Metasequoia glyptostroboides includes the following steps:

[0008] S1: Based on the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site, determine the target distribution depth range of the Metasequoia glyptostroboides root system and the allowable soil electrical conductivity range in the target root zone;

[0009] S2: In the nursery, the container substrate is set up from top to bottom as a first substrate layer, a second substrate layer and a third substrate layer. The first substrate layer uses an improved substrate with an electrical conductivity lower than the lower limit of the soil electrical conductivity range allowed by the target root zone. The second substrate layer uses a substrate with an electrical conductivity within the range allowed by the soil electrical conductivity of the target root zone. The third substrate layer uses a substrate with an electrical conductivity higher than that of the second substrate layer, so as to form an increasing electrical conductivity gradient from top to bottom in the container.

[0010] S3: Plant the Metasequoia glyptostroboides seedlings in the container substrate. In the early stage of acclimatization, use a low conductivity irrigation solution to irrigate from the top of the container. In the middle and late stages of acclimatization, use an irrigation solution with a higher conductivity than the irrigation solution in the early stage of acclimatization to replenish water from the bottom of the container or the side hole. By adjusting the irrigation frequency and the amount of water per irrigation, the conductivity of the second substrate layer is stabilized within the soil conductivity range allowed by the target root zone, so as to obtain Metasequoia glyptostroboides container seedlings with roots penetrating into the second substrate layer and the third substrate layer.

[0011] S4: Excavate planting holes in the saline-alkali afforestation area, lay a coarse-grained material salt drainage layer at the bottom of the planting hole, and connect the salt drainage layer to the drainage ditch through the salt drainage channel. Backfill the salt drainage layer in sequence with a buffer layer, a transition layer and an outer layer of native saline-alkali soil. The buffer layer is made of improved soil with an electrical conductivity within the allowable range of soil electrical conductivity in the target root zone and basically equivalent to the electrical conductivity of the second matrix layer. The transition layer is a mixed soil with an electrical conductivity between that of the buffer layer and the outer layer of native saline-alkali soil.

[0012] S5: Place the container seedling of Metasequoia glyptostroboides along with its root ball into the planting hole, so that the root neck of Metasequoia glyptostroboides is located above the buffer layer and the lower part of the root ball enters the buffer layer and the transition layer. After covering with soil and compacting, a plant is formed.

[0013] S6: After planting, water and maintain the planted plants according to the preset irrigation system. In the early stage of afforestation, use large amounts of water for frequent irrigation, and work with the salt drainage layer and the salt drainage channel to allow the salt in the soil above the planting hole to migrate to the salt drainage layer and the soil layer below it. In the later stage of afforestation, use medium water for frequent irrigation or small amounts of water to maintain the electrical conductivity in the buffer layer and the transition layer of the planting hole not higher than the upper limit of the allowable electrical conductivity range of the target root zone.

[0014] Preferably, the step of determining the target root distribution depth range of Metasequoia glyptostroboides and the allowable soil electrical conductivity range of the target root zone based on the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site includes:

[0015] Within each hectare of the saline-alkali afforestation land, select 3 to 5 sample points, and at each sample point, divide the soil layer 0 to 80 cm below the surface into 4 soil layer segments at a depth interval of 20 cm.

[0016] At least three soil samples were collected horizontally within each soil layer segment. The soil samples were mixed evenly to form a mixed soil sample. The soil conductivity of each mixed soil sample was measured using a soil conductivity meter at 25 degrees Celsius to obtain the soil conductivity value of each soil layer segment in the 0-80cm soil layer.

[0017] The determination of the target depth range of the root system of Metasequoia glyptostroboides includes:

[0018] Based on the cultivation experiment results of Metasequoia glyptostroboides under different soil electrical conductivity conditions, a critical value for soil electrical conductivity is predetermined. The critical value for soil electrical conductivity is the upper limit of soil electrical conductivity that allows Metasequoia glyptostroboides to grow normally.

[0019] In the 0-80CM soil layer, each soil layer segment with a soil conductivity value less than or equal to the critical soil conductivity value is selected. Adjacent soil layer segments with soil conductivity values ​​not greater than the critical soil conductivity value are merged to form a continuous depth interval, and the continuous depth interval is taken as the target distribution depth range of the Metasequoia glyptostroboides root system.

[0020] The determination of the permissible soil electrical conductivity range for the target root zone includes:

[0021] The soil electrical conductivity values ​​of each soil layer within the target distribution depth range of the Metasequoia root system are arithmetically averaged to obtain the average soil electrical conductivity value.

[0022] 0.8 times the average soil electrical conductivity value is taken as the lower limit of the allowable soil electrical conductivity range of the target root zone, and 1.2 times the average soil electrical conductivity value is taken as the upper limit of the allowable soil electrical conductivity range of the target root zone.

[0023] Preferably, the container substrate setting step includes:

[0024] Select a seedling container with an open top, leave a 2-5cm space from the bottom to the top of the container without substrate, and fill the remaining space with the first substrate layer, the second substrate layer and the third substrate layer in sequence;

[0025] The first substrate layer, the second substrate layer, and the third substrate layer are filled into the seedling container from top to bottom. The thickness of the first substrate layer is 5-10 cm, the thickness of the second substrate layer is 10-20 cm, and the thickness of the third substrate layer is 5-10 cm.

[0026] Preferably, the first matrix layer is formed by mixing peat, perlite and saline-alkali soil treated by leaching with clean water in a mass ratio of 1:1:1 to 2:1:1;

[0027] The second matrix layer is formed by mixing humus, garden soil and partially improved saline-alkali soil in a mass ratio of 1:1:1 to 2:1:2;

[0028] The third matrix layer is formed by mixing coarse sand, garden soil and unmodified saline-alkali soil in a mass ratio of 1:1:1 to 2:1:2.

[0029] The soil electrical conductivity values ​​of the first matrix layer, the second matrix layer, and the third matrix layer were determined by sampling and measuring each matrix layer at 25°C. The soil electrical conductivity value of the first matrix layer was less than the lower limit of the allowable soil electrical conductivity range for the target root zone, the soil electrical conductivity value of the second matrix layer was within the allowable soil electrical conductivity range for the target root zone, and the soil electrical conductivity value of the third matrix layer was greater than that of the second matrix layer.

[0030] Preferably, the step of planting the Metasequoia seedlings in the container substrate includes:

[0031] Planting holes are pre-formed in the first substrate layer. After the roots of the Metasequoia glyptostroboides seedling are spread out, they are placed in the planting holes, so that the root neck of the Metasequoia glyptostroboides seedling is located near the junction of the first substrate layer and the second substrate layer. The lower end of the seedling roots enters the second substrate layer. The substrate from the first substrate layer is used to backfill the holes and the seedling is gently pressed to fix it.

[0032] The step of irrigating the container from above with a low-conductivity irrigation solution during the early stages of acclimatization includes:

[0033] The period from the completion of planting of Metasequoia glyptostroboides seedlings to 30-45 days after planting is considered the early acclimatization period. Irrigation solution with an electrical conductivity lower than the lower limit of the allowable soil electrical conductivity range of the target root zone is selected and slowly poured from above the container, so that the irrigation solution seeps down into the first substrate layer and the second substrate layer along the direction of gravity.

[0034] Irrigation is carried out every 3 to 5 days during the early stage of acclimatization, with the volume of irrigation liquid each time being 0.1 to 0.3 times the total volume of the seedling container, so as to keep the first substrate layer in a low electrical conductivity state.

[0035] Preferably, the step of using an irrigation solution with a higher electrical conductivity than the irrigation solution used in the early stages of acclimatization to replenish water from the bottom or side holes of the container, and stabilizing the electrical conductivity of the second substrate layer within the allowable soil electrical conductivity range of the target root zone by adjusting the irrigation frequency and the amount of water applied per irrigation includes:

[0036] The seedling stage 30 to 45 days after planting is considered the mid-to-late stage of acclimatization. During this mid-to-late stage, irrigation solution with a conductivity greater than that of the irrigation solution in the early stage of acclimatization and within the allowable soil conductivity range of the target root zone is added to the third substrate layer through the drainage hole at the bottom of the container or the side hole located on the lower side wall of the container.

[0037] Irrigation is carried out every 5 to 7 days during the middle and late stages of acclimatization. The volume of irrigation liquid for each irrigation is 0.1 to 0.3 times the total volume of the seedling container. During the irrigation interval, soil electrical conductivity is sampled and measured in the second substrate layer periodically. The irrigation frequency or the volume of single irrigation liquid is adjusted according to the measurement results to keep the soil electrical conductivity in the second substrate layer within the allowable range of the target root zone.

[0038] Preferably, the step of digging planting holes and laying a coarse-grained desalination layer in saline-alkali afforestation land includes:

[0039] Planting positions are arranged along the row direction according to the predetermined spacing between plants. Planting holes are dug at each planting position. The plane of the planting hole is approximately circular or approximately square. The diameter or side length of the opening of the planting hole is 60-90cm and the depth of the planting hole is 60-100cm.

[0040] A coarse-grained material is laid along the entire bottom surface of the planting hole to form the salt drainage layer. The coarse-grained material is one or a mixture of several of the following: gravel, pebbles, or sintered ceramsite with a particle size of 5 to 20 mm. The thickness of the salt drainage layer is 10 to 20 cm.

[0041] A salt drainage channel is provided on one side of the salt drainage layer. The salt drainage channel extends along the direction of the planting row or in a direction that intersects with the planting row and connects with the drainage ditch between the rows or at the edge of the plot. The salt drainage channel is filled with the same coarse-grained material as the salt drainage layer.

[0042] Preferably, the step of backfilling a buffer layer, a transition layer, and an outer layer of native saline-alkali soil sequentially above the salt drainage layer includes:

[0043] The buffer layer is backfilled above the salt drainage layer. The thickness of the buffer layer is 20-40cm. The buffer layer is formed by improved soil, which is soil obtained by mixing garden soil, organic fertilizer and desalinated saline-alkali soil.

[0044] The transition layer is backfilled above the buffer layer. The thickness of the transition layer is 20-30cm. The transition layer is a mixed soil formed by mixing the improved soil used in the buffer layer with the original saline-alkali soil taken out during excavation at a mass ratio of 1:1 to 1:2.

[0045] The outer layer of native saline-alkali soil is backfilled above the transition layer. The outer layer of native saline-alkali soil is the saline-alkali soil that was stripped from the ground surface and piled up separately when the planting hole was dug.

[0046] The soil electrical conductivity of the buffer layer and the transition layer was determined by sampling and measurement, which included:

[0047] Several soil samples were taken from each of the improved soil used to form the buffer layer, the mixed soil used to form the transition layer, and the original saline-alkali soil of the outer layer, and mixed evenly to form a mixed soil sample. The soil conductivity of each mixed soil sample was measured using a soil conductivity meter at 25°C to obtain the soil conductivity values ​​of the improved soil for the buffer layer, the mixed soil for the transition layer, and the original saline-alkali soil of the outer layer.

[0048] The soil conductivity value of the improved soil in the buffer layer is adjusted to be within the allowable soil conductivity range of the target root zone and is basically equivalent to the soil conductivity value of the second matrix layer. The soil conductivity value of the mixed soil in the transition layer is controlled to be between the soil conductivity value of the improved soil in the buffer layer and the soil conductivity value of the outer primary saline-alkali soil.

[0049] Preferably, the step of placing the containerized Metasequoia glyptostroboides seedling along with its root ball into the planting hole includes:

[0050] A planting hole matching the size of the root ball of the Metasequoia glyptostroboides container seedling is dug at the center of the upper surface of the buffer layer. The planar shape of the planting hole is the same as or similar to that of the planting pit. The diameter or side length of the planting hole is 2-5 cm greater than the diameter or side length of the root ball. The depth of the planting hole is such that the bottom of the root ball is located near the junction of the buffer layer and the transition layer and enters the transition layer.

[0051] Remove the completed Metasequoia glyptostroboides container seedlings from the seedling container, remove the outer shell of the container without damaging the root system and substrate, keeping the root ball intact, and place the root ball into the planting hole, so that the Metasequoia glyptostroboides root neck is 5-10 cm below the upper surface of the buffer layer.

[0052] The soil compaction step includes:

[0053] The improved soil used to form the buffer layer is used to backfill the voids around the root ball, and the mixed soil used to form the transition layer is used to backfill the voids below and around the root ball and between the transition layer and the root ball. The thickness of the backfilling layers is 10-15 cm.

[0054] After each layer of improved soil or mixed soil is backfilled, the backfill soil is compacted by manual treading or by a special compaction tool until the buffer layer and transition layer above the planting hole are flush with the surface of the surrounding buffer layer and transition layer. After the backfill soil is compacted, the outer layer of original saline-alkali soil is filled around the planting hole to form the surface.

[0055] Preferably, the step of using large amounts of water for infrequent irrigation in the early stages of afforestation, in conjunction with the salt drainage layer and the salt drainage channel, includes:

[0056] The first two to three months of the first growing season after the planting of Metasequoia glyptostroboides trees are considered the initial stage of afforestation.

[0057] During each irrigation in the early stage of afforestation, clean water is injected from the ground surface into the planting hole so that the soil moisture content in the depth range corresponding to the buffer layer and transition layer in the planting hole is close to saturation. The amount of water for each irrigation is calculated as 0.4 to 0.8 times the volume of the planting hole for each Metasequoia glyptostroboides.

[0058] The irrigation interval during the initial stage of afforestation is 10 to 20 days. During each irrigation, the salt drainage channel is kept connected to the drainage ditch so that the irrigation water seeps into the salt drainage layer from the buffer layer and the transition layer and then flows into the drainage ditch through the salt drainage channel.

[0059] The steps of using multiple applications of medium-sized or small amounts of water to maintain the soil electrical conductivity in the buffer layer and transition layer of the planting hole at a level not exceeding the upper limit of the allowable soil electrical conductivity range for the target root zone in the subsequent stages of afforestation include:

[0060] The period from the end of the initial afforestation phase to the end of the second growing season is considered the subsequent afforestation phase. During this phase, surface irrigation is carried out using either multiple applications of medium-grade water or frequent small applications of water. For multiple applications of medium-grade water, the amount of water used each time is calculated as 0.2 to 0.4 times the volume of the planting hole for each Metasequoia glyptostroboides tree, with an irrigation interval of 7 to 15 days. For frequent small applications of water, the amount of water used each time is calculated as 0.1 to 0.2 times the volume of the planting hole for each Metasequoia glyptostroboides tree, with an irrigation interval of 3 to 7 days.

[0061] During the subsequent afforestation phase, soil electrical conductivity was measured in the buffer layer and the transition layer at a frequency of once a month to once every two months, at 25°C. The irrigation method, irrigation interval, and irrigation volume were adjusted based on the measured soil electrical conductivity values ​​to keep the soil electrical conductivity in the buffer layer and the transition layer within the allowable range of the target root zone.

[0062] In summary, the present invention has the following main beneficial effects:

[0063] This invention measures the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site by stratified sampling before afforestation, and determines the target root distribution depth range of Metasequoia glyptostroboides and the allowable soil electrical conductivity range in the target root zone. This achieves the purpose of setting seedling and planting parameters based on the soil salinity conditions of the plot, reducing the mismatch between the nursery substrate environment and the root zone environment of the afforestation site from the source, and avoiding the prolongation of the seedling recovery period and growth restriction caused by the root zone electrical conductivity exceeding the allowable range after planting.

[0064] This invention establishes a controllable conductivity gradient within the container during the nursery stage, dividing the substrate into three layers with increasing electrical conductivity from top to bottom. In the early stages of acclimatization, a low-conductivity irrigation solution is used to irrigate from above the container, while in the later stages, an irrigation solution with higher conductivity is used to replenish water from the bottom or side holes. Simultaneously, by sampling and adjusting the irrigation frequency and volume, the conductivity of the second substrate layer is stabilized within the allowable range of the target root zone. This achieves the goal of creating a controllable conductivity gradient within the container and guiding the roots downwards, ensuring that the root ball conductivity level of the seedlings leaving the nursery matches the conditions of the target root zone and provides a foundation for downward rooting.

[0065] This invention establishes a salt drainage layer by laying coarse-grained material at the bottom of planting holes in saline-alkali afforestation sites and setting up salt drainage channels connected to drainage ditches. Above the salt drainage layer, a buffer layer with an electrical conductivity roughly equivalent to and within the allowable range of the second matrix layer is backfilled, followed by a transition layer with an electrical conductivity between the buffer layer and the outer native saline-alkali soil. After planting, maintenance is carried out according to a system of frequent, light watering in the early stage of afforestation to drain salt, and frequent, moderate watering or light watering in the later stage of afforestation, combined with monitoring and adjusting the electrical conductivity of the buffer layer and the transition layer. This achieves the goal of maintaining the electrical conductivity of the root zone within the allowable range after planting and inhibiting salt migration, thereby improving the survival stability and subsequent growth consistency of Metasequoia glyptostroboides after planting in saline-alkali land conditions. Attached Figure Description

[0066] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] Example 1

[0069] refer to Figure 1 A gradient acclimatization and high survival rate cultivation method for salt-tolerant Metasequoia glyptostroboides includes the following steps:

[0070] S1: Based on the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site, determine the target distribution depth range of the Metasequoia glyptostroboides root system and the allowable soil electrical conductivity range in the target root zone;

[0071] S2: In the nursery, the container substrate is set up from top to bottom as a first substrate layer, a second substrate layer and a third substrate layer. The first substrate layer uses an improved substrate with an electrical conductivity lower than the lower limit of the soil electrical conductivity range allowed by the target root zone. The second substrate layer uses a substrate with an electrical conductivity within the range allowed by the soil electrical conductivity of the target root zone. The third substrate layer uses a substrate with an electrical conductivity higher than that of the second substrate layer, so as to form an increasing electrical conductivity gradient from top to bottom in the container.

[0072] S3: Plant the Metasequoia glyptostroboides seedlings in the container substrate. In the early stage of acclimatization, use a low conductivity irrigation solution to irrigate from the top of the container. In the middle and late stages of acclimatization, use an irrigation solution with a higher conductivity than the irrigation solution in the early stage of acclimatization to replenish water from the bottom of the container or the side hole. By adjusting the irrigation frequency and the amount of water per irrigation, the conductivity of the second substrate layer is stabilized within the soil conductivity range allowed by the target root zone, so as to obtain Metasequoia glyptostroboides container seedlings with roots penetrating into the second substrate layer and the third substrate layer.

[0073] S4: Excavate planting holes in the saline-alkali afforestation area, lay a coarse-grained material salt drainage layer at the bottom of the planting hole, and connect the salt drainage layer to the drainage ditch through the salt drainage channel. Backfill the salt drainage layer in sequence with a buffer layer, a transition layer and an outer layer of native saline-alkali soil. The buffer layer is made of improved soil with an electrical conductivity within the allowable range of soil electrical conductivity in the target root zone and basically equivalent to the electrical conductivity of the second matrix layer. The transition layer is a mixed soil with an electrical conductivity between that of the buffer layer and the outer layer of native saline-alkali soil.

[0074] S5: Place the container seedling of Metasequoia glyptostroboides along with its root ball into the planting hole, so that the root neck of Metasequoia glyptostroboides is located above the buffer layer and the lower part of the root ball enters the buffer layer and the transition layer. After covering with soil and compacting, a plant is formed.

[0075] S6: After planting, water and maintain the planted plants according to the preset irrigation system. In the early stage of afforestation, use large amounts of water for frequent irrigation, and work with the salt drainage layer and the salt drainage channel to allow the salt in the soil above the planting hole to migrate to the salt drainage layer and the soil layer below it. In the later stage of afforestation, use medium water for frequent irrigation or small amounts of water to maintain the electrical conductivity in the buffer layer and the transition layer of the planting hole not higher than the upper limit of the allowable electrical conductivity range of the target root zone.

[0076] Within the target saline-alkali afforestation area, sampling points are set up with each hectare as a sampling unit. Specifically, 3 to 5 sampling points are selected within each hectare, and the sampling points are arranged alternately to cover the differences in topography and salinity distribution within the plot. Sampling points should avoid obvious areas of soil accumulation, waterlogged areas, hardened road areas, and adjacent areas of drainage ditch edges to reduce the impact of outliers on the overall assessment.

[0077] Sampling was taken vertically at each sampling point, and the soil layer 0–80 cm below the surface was divided into four segments at 20 cm depth intervals:

[0078] First soil layer: 0-20cm;

[0079] Second soil layer: 20-40cm;

[0080] Third soil layer: 40-60cm;

[0081] Fourth soil layer: 60-80cm.

[0082] At least three soil samples were collected horizontally within each soil layer segment. The soil samples from each soil layer segment were then mixed evenly to form a mixed soil sample for that soil layer segment. A corresponding mixed soil sample was formed for each soil layer segment for subsequent soil conductivity determination.

[0083] To ensure the comparability of measurement results from different sites and soil layers, this embodiment uses uniform conditions for soil conductivity measurement:

[0084] The mixed soil sample was pretreated in a conventional manner (such as air drying, removing impurities, and sieving), and the extract was prepared according to a uniform extraction method. The soil sample and deionized water were mixed at a mass ratio of 1:5, stirred, and allowed to stand. The supernatant was then taken to measure the conductivity.

[0085] The conductivity of the extract was measured using a soil conductivity meter at 25 degrees Celsius, and the measured value was used as the soil conductivity value for the corresponding soil layer.

[0086] The same mixed soil sample can be measured at least twice, and the average result is taken as the soil electrical conductivity value of the mixed soil sample.

[0087] Within the same sampling unit, all sampling points are subjected to the same measurement conditions and recording format to ensure consistency in subsequent calculations.

[0088] To facilitate recording and subsequent generation of profile data, the measurement results were compiled according to the sample point number and soil layer number, forming Table 1.

[0089] Table 1. Record of Soil Conductivity Measurement at Different Soil Layers of Various Sampling Points

[0090] Sample number Soil electrical conductivity in the 0-20cm soil layer Soil electrical conductivity in the 20-40cm soil layer Soil electrical conductivity in the 40-60cm soil layer Soil electrical conductivity in the 60-80cm soil layer Sample 1 (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) Sample 2 (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) Sample 3 (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) …… …… …… …… …… Sample points n (n is the number of sample points) (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) (Fill in the measured value) Mean value of soil layer Average (1) Average (2) Average (3) Average (4)

[0091] The sample point numbers in Table 1 correspond to the 3 to 5 sample points selected within each hectare; the soil layer segments correspond to four soil layer segments: 0 to 20 cm, 20 to 40 cm, 40 to 60 cm, and 60 to 80 cm.

[0092] Each cell should contain the measured value, which is the soil electrical conductivity value of the mixed soil sample from the corresponding sample point and soil layer under uniform conditions.

[0093] The average values ​​(1) to (4) are representative soil electrical conductivity values ​​for the corresponding soil layer segments. Their calculation methods are determined by the soil layer segment mean calculation rules.

[0094] After obtaining the soil electrical conductivity measurements for each soil layer at each sampling point in Table 1, the arithmetic mean of the measurements for all sampling points within the same soil layer was calculated, and the result was taken as the representative soil electrical conductivity value for that soil layer.

[0095] For the 0-20cm soil layer, the soil conductivity measurements of all the sample points in the column of Table 1 are summed and then divided by the number of sample points to obtain the average value (1).

[0096] For the 20-40cm soil layer, the soil conductivity values ​​of all the samples in the column of Table 1 are added together and then divided by the number of samples to obtain the average value (2).

[0097] For the 40-60cm soil layer, the soil conductivity values ​​of all the sample points in the column of Table 1 are added together and then divided by the number of sample points to obtain the average value (3).

[0098] For the 60-80cm soil layer, the soil conductivity values ​​of all the samples in this column of Table 1 are added together and then divided by the number of samples to obtain the average value (4).

[0099] This forms the soil electrical conductivity distribution within the 0-80cm range of the target saline-alkali afforestation area. The profile data consists of average values ​​(1), (2), (3), and (4) in depth order. This profile data serves as the basis for subsequently determining the target distribution depth range of Metasequoia glyptostroboides roots and the allowable soil electrical conductivity range of the target root zone.

[0100] To avoid the unreasonable impact of abnormal measurement values ​​from individual sample points on the profile mean, the following processing rules can be adopted in this embodiment:

[0101] When the soil conductivity value measured at a certain point in the same soil layer deviates significantly from the soil conductivity values ​​of other points in the same soil layer, the mixed soil sample at that point in the same soil layer should be retested; if the retest result differs significantly from the initial test result, the retest result shall prevail.

[0102] When calculating the mean, the number and number of sample points used should be consistent with the records in Table 1 to ensure that the basis for the mean calculation is clear and traceable.

[0103] When performing gradient acclimatization seedling cultivation of Metasequoia glyptostroboides in the nursery, a containerized seedling cultivation method is adopted. A first, second, and third substrate layer are set from top to bottom within the seedling container to form a soil electrical conductivity gradient that increases from top to bottom. Specifically, the soil electrical conductivity of the first substrate layer is below the lower limit of the allowable soil electrical conductivity range for the target root zone; the soil electrical conductivity of the second substrate layer is within the allowable range for the target root zone; and the soil electrical conductivity of the third substrate layer is higher than that of the second substrate layer.

[0104] Selection of seedling containers and space reservation for filling:

[0105] The seedling container should be a rigid container with an open top. The container material can be polyethylene or polypropylene, and a drainage hole should be provided at the bottom of the container. The container can be cylindrical or square. The height of the container is preferably 25-40cm, and the diameter or side length is preferably 12-20cm to accommodate the three-layer substrate filling and subsequent irrigation.

[0106] Before filling with substrate, clean the inner wall of the container and the bottom drainage hole to ensure that the drainage hole is unobstructed. Then, leave a 2-5cm space from the bottom to the top of the container without substrate. This reserved space is used to buffer the liquid surface and prevent overflow during the subsequent watering process, avoiding uncontrollable changes in the electrical conductivity of each substrate layer caused by direct overflow of irrigation liquid.

[0107] Thickness setting and filling sequence of the three-layer matrix:

[0108] The first, second, and third substrate layers are filled into the seedling container from top to bottom in the following order: first the third substrate layer, then the second substrate layer, and finally the first substrate layer. After filling, the surface of each layer is gently pressed and leveled to avoid forming obvious voids.

[0109] The thickness of each layer is set as follows:

[0110] The thickness of the first matrix layer is 5–10 cm;

[0111] The thickness of the second matrix layer is 10–20 cm;

[0112] The thickness of the third matrix layer is 5–10 cm.

[0113] To ensure clear interlayer boundaries, in this embodiment, after the second matrix layer is filled, a layer of permeable nonwoven fabric or nylon mesh can be laid on the surface of the second matrix layer. The permeable nonwoven fabric or nylon mesh has a pore size of 0.3 to 1 mm and is used to suppress the mechanical mixing of different matrix particles during filling and transportation. The permeable nonwoven fabric or nylon mesh does not affect water infiltration and capillary conduction.

[0114] Formulation, mixing, and pretreatment of the three-layer matrix:

[0115] To ensure that the soil electrical conductivity of the three-layer matrix meets the requirements of the claims, this embodiment pre-treats the saline-alkali soil in stages and mixes them according to the mass ratio to form each layer of matrix.

[0116] Sources and classification of saline-alkali soil:

[0117] The saline-alkali soil was taken from the target afforestation site or a similar saline-alkali plot, with a preferred sampling depth of 0–40 cm. The saline-alkali soil was air-dried, impurities removed, and sieved through a 5 mm sieve to obtain the basic saline-alkali soil. Subsequently, three components were obtained as follows: saline-alkali soil treated with water leaching, partially improved saline-alkali soil, and unimproved saline-alkali soil.

[0118] Saline-alkali soil treated by rinsing with clean water: Place the basic saline-alkali soil in a perforated container and rinse it with clean water until the conductivity of the rinsing liquid stabilizes in a preset low range. Remove the soil, drain it naturally, and air dry it for later use. The preset low range is the range that is not higher than the lower limit of the soil conductivity range allowed in the target root zone.

[0119] Partially improved saline-alkali soil: Gypsum powder and humus materials are added to the basic saline-alkali soil for mixing and improvement. The amount of gypsum powder and humus materials added is determined according to the target conductivity range. After mixing evenly, the mixture is left to stand for 3 to 7 days for later use.

[0120] Unimproved saline-alkali soil: The basic saline-alkali soil is used directly as unimproved saline-alkali soil without leaching or improvement.

[0121] First matrix layer formulation:

[0122] The first matrix layer is formed by mixing peat, perlite, and saline-alkali soil treated by leaching with clean water in a mass ratio of 1:1:1 to 2:1:1. During mixing, the peat and perlite are first mixed evenly, and then the saline-alkali soil treated by leaching with clean water is added. After mixing evenly, it becomes the first matrix layer.

[0123] Second matrix layer formulation:

[0124] The second substrate layer is formed by mixing humus, garden soil, and partially improved saline-alkali soil in a mass ratio of 1:1:1 to 2:1:2. During mixing, the humus and garden soil are first mixed thoroughly, then the partially improved saline-alkali soil is added, and the mixture is thoroughly combined to form the second substrate layer.

[0125] Third matrix layer formulation:

[0126] The third matrix layer is formed by mixing coarse sand, garden soil, and unmodified saline-alkali soil in a mass ratio of 1:1:1 to 2:1:2. During mixing, the coarse sand and garden soil are first mixed thoroughly, then the unmodified saline-alkali soil is added, and the mixture is thoroughly combined to form the third matrix layer.

[0127] Consistency of moisture content:

[0128] To avoid inconsistencies in conductivity measurements due to differences in moisture content, the moisture content of each matrix layer should be adjusted to a similar level after mixing. Ideally, the mixed matrix should be in a state where it can be formed into a clump when squeezed but crumbles easily when released, to facilitate subsequent filling and measurement.

[0129] Methods and rules for determining the electrical conductivity of soil layers:

[0130] The soil electrical conductivity values ​​of each matrix layer were determined by sampling and measuring the matrix at 25℃. To ensure comparability, a measurement method consistent with that used for soil electrical conductivity measurements and profile data was adopted: samples were taken from each mixed matrix layer, an extract was prepared, and the electrical conductivity was measured at 25℃. The obtained values ​​were used as the soil electrical conductivity values ​​for that matrix layer.

[0131] For sampling locations and frequency, at least three samples should be taken from the same batch of substrate for testing. Sampling points should be taken from different locations in the mixed pile (upper, middle, and lower). The arithmetic mean of the measured results should be used as the representative value of the soil electrical conductivity of that layer of substrate. If a measurement result deviates significantly from the other measurement results, the sample should be retested, and the retest value should replace the outlier.

[0132] Judgment rules and necessary adjustments: After the matrix of each layer is measured, the following relationship should be satisfied:

[0133] The soil electrical conductivity value of the first matrix layer is less than the lower limit of the allowable soil electrical conductivity range for the target root zone;

[0134] The soil electrical conductivity value of the second matrix layer is within the allowable soil electrical conductivity range of the target root zone;

[0135] The soil electrical conductivity value of the third matrix layer is greater than that of the second matrix layer.

[0136] When the measurement results do not meet the above relationship, they can be corrected by adjusting the proportion of saline-alkali soil components in the corresponding layer or by adjusting the degree of saline-alkali soil pretreatment.

[0137] When the first matrix layer is too high, increase the leaching degree of the saline-alkali soil treated with clean water or reduce the mass ratio of saline-alkali soil in this layer.

[0138] When the second matrix layer is too low or too high, adjust the amount of amendment added to the partially improved saline-alkali soil or adjust the proportion of saline-alkali soil to bring it back to the allowable range of the target root zone.

[0139] When the third matrix layer is too low, the proportion of unimproved saline-alkali soil can be increased or the proportion of coarse sand can be decreased to improve the soil electrical conductivity of the third matrix layer.

[0140] Table 2. Record of Three-Layer Matrix Formulation and Soil Electrical Conductivity Measurement

[0141] Matrix layer Components and mass ratio range Number of samplings (≥3) Soil electrical conductivity measured at 25℃ (please fill in) Judgment conclusion (compliant / non-compliant) Adjustment measures (if any) First matrix layer Peat: Perlite: Leached saline-alkali soil = 1:1:1 to 2:1:1 ≥3 (fill in) (fill in) (fill in) Second matrix layer Humus : Garden soil : Partially improved saline-alkali soil = 1 : 1 : 1 to 2 : 1 : 2 ≥3 (fill in) (fill in) (fill in) Third matrix layer Coarse sand : garden soil : unimproved saline-alkali soil = 1 : 1 : 1 ~ 2 : 1 : 2 ≥3 (fill in) (fill in) (fill in)

[0142] The soil electrical conductivity values ​​measured at 25℃ in Table 2 are representative values ​​obtained by measuring the corresponding matrix layer using a uniform caliber.

[0143] The determination is based on whether the first layer is less than the lower limit of the allowable range, the second layer is within the allowable range, and the third layer is greater than the second layer.

[0144] When a non-compliance is determined, the specific adjustment method and the retest results after adjustment should be recorded in the adjustment measures column to form a traceable implementation path.

[0145] To reduce interlayer mixing during filling and handling, this embodiment performs light pressing and leveling after each layer is filled, and a permeable isolation layer is set between the second matrix layer and the first matrix layer, or between the third matrix layer and the second matrix layer. The isolation layer does not affect moisture conduction and the formation of electrical conductivity gradient, but can reduce the risk of electrical conductivity gradient disruption caused by particle migration.

[0146] Furthermore, the soil conductivity gradient of the three-layer matrix belongs to the spatial distribution relationship within the container. In this embodiment, the conductivity relationship of each layer is ensured to meet the requirements of the claims through formula differences, measurement and verification, and necessary adjustments, so that the irrigation method in the subsequent acclimatization stage can be implemented within the established matrix framework.

[0147] After the container was filled with three layers of substrate and the soil conductivity was measured to ensure that the first substrate layer was below the lower limit of the target root zone, the second substrate layer was within the target root zone's allowable range, and the third substrate layer was above the second substrate layer, the Metasequoia seedlings were planted in the container substrate. During the seedling stage, differentiated irrigation methods were implemented in the early and middle-to-late stages of acclimatization: in the early stage of acclimatization, low-conductivity irrigation solution was used to irrigate from the top of the container, while in the middle-to-late stage of acclimatization, irrigation solution with a higher conductivity than the irrigation solution in the early stage of acclimatization was used to replenish water from the bottom of the container or through the side holes. By monitoring and adjusting the irrigation frequency and the amount of water per irrigation, the soil conductivity of the second substrate layer was maintained within the allowable range of the target root zone.

[0148] Planting method and root collar positioning of Metasequoia glyptostroboides seedlings:

[0149] Seedling selection: Select seedlings of Metasequoia glyptostroboides with uniform growth, preferably robust seedlings with a height of 20-40cm and a ground diameter of 3-6mm; remove seedlings with obviously damaged roots, obvious pests and diseases, or weak growth to ensure batch consistency.

[0150] Planting holes are formed in advance in the middle of the first substrate layer. The depth of the planting holes is preferably 5-8 cm and the diameter is preferably 3-6 cm to avoid damaging the interface structure between the first substrate layer and the second substrate layer during planting.

[0151] Root system spreading and positioning: After the roots of the Metasequoia glyptostroboides seedlings are naturally spread out, they are placed into the planting hole, so that the root neck of the seedling is located near the junction of the first substrate layer and the second substrate layer, and the lower end of the seedling roots enters the second substrate layer; then the planting hole is backfilled with the first substrate layer and lightly pressed to fix it, ensuring that the seedling is upright and avoiding the formation of large pores.

[0152] To ensure consistent planting depth, this embodiment can set graduation lines on the inner wall of the container or mark the interface between the first and second substrate layers when filling the substrate, so that the root collar of each seedling falls near the interface.

[0153] Preparation and conductivity control of irrigation solution:

[0154] For irrigation water sources, clean water or low-salinity water sources are preferred; if surface water or groundwater is used, its conductivity should be measured and recorded first.

[0155] During the early acclimatization period, the irrigation solution should have a low electrical conductivity, meaning its conductivity is below the lower limit of the allowable soil electrical conductivity range for the target root zone. This can be achieved by: directly using clean water with sufficient conductivity; or by controlling the use of clean water without adding salt-enhancing components to maintain its conductivity below the aforementioned threshold.

[0156] The irrigation solution used during the later stages of acclimatization is one with a higher electrical conductivity than the irrigation solution used in the early stages of acclimatization, but within the allowable soil electrical conductivity range for the target root zone. This irrigation solution can be prepared by adding soluble salts to clean water, such as sodium chloride, sodium sulfate, or sodium bicarbonate. During preparation, the salts are added in small amounts multiple times with thorough stirring until the electrical conductivity of the irrigation solution reaches the target range. The conductivity is then checked and recorded using a conductivity meter at 25°C.

[0157] To ensure consistency in measurement, the conductivity of the irrigation solution and the conductivity of each substrate layer were measured using a unified temperature standard (25℃) and the same type of conductivity meter to guarantee the operability and consistency of threshold comparison.

[0158] Table 3 Record of Irrigation Fluid Conductivity Measurement and Preparation

[0159] stage Irrigation liquid type Water source conductivity (please fill in) Type and amount of salt added (if applicable) Measured conductivity of irrigation solution at 25℃ (fill in) Does it meet the threshold requirement (Yes / No)? Early domestication Low conductivity irrigation solution (fill in) No salt-enhancing components added / (fill in) (fill in) (fill in) Mid-to-late stages of domestication Water replenishment irrigation solution (fill in) (fill in) (fill in) (fill in)

[0160] The threshold requirements are as follows: the conductivity of the irrigation solution in the early stage of acclimatization is less than the lower limit of the soil conductivity range allowed in the target root zone; the conductivity of the irrigation solution in the middle and late stages of acclimatization is higher than that of the irrigation solution in the early stage of acclimatization but is within the range of soil conductivity allowed in the target root zone.

[0161] Irrigation methods and parameters during the early stages of acclimatization:

[0162] The early acclimatization period is defined as the period from the completion of planting the Metasequoia seedlings to 30-45 days after planting.

[0163] For irrigation, in the early stages of acclimatization, a low-conductivity irrigation solution is slowly poured from above the container. The preferred irrigation location is near the base of the seedling stem, allowing the irrigation solution to seep down to the first and second substrate layers under gravity. During irrigation, avoid forming obvious erosion trenches to reduce the risk of interlayer mixing.

[0164] For irrigation frequency and volume, irrigate once every 3 to 5 days during the early acclimatization period; the volume of irrigation solution for each irrigation should be 0.1 to 0.3 times the total volume of the seedling container. If there is continuous rain or the substrate moisture content is too high, the irrigation interval can be appropriately extended to avoid the substrate being too wet for a long time, which will affect root growth.

[0165] Since the conductivity of the irrigation solution used in the early stage of acclimatization is lower than the lower limit of the allowable range of the target root zone, and the irrigation mainly acts on the first substrate layer from top to bottom and gradually seeps down to the second substrate layer, the first substrate layer can be kept in a low conductivity state and the conductivity of the second substrate layer can be prevented from deviating from the allowable range of the target root zone by controlling the conductivity of the irrigation solution, the frequency of irrigation and the amount of water per irrigation in the early stage of acclimatization.

[0166] Table 4. Irrigation Implementation Record Sheet during Early Domestication

[0167] date stage Irrigation method (top irrigation) Irrigation liquid type Single water filling volume (multiple of container volume, please fill in). Irrigation interval (please fill in) Remark (fill in) Early domestication Top pouring Low conductivity irrigation solution (fill in) (fill in) (fill in) …… …… …… …… …… …… ……

[0168] Water supply methods and parameters for bottom or side holes during the later stages of acclimatization:

[0169] The mid-to-late stage of acclimatization refers to the seedling stage 30 to 45 days after planting.

[0170] The water supply channel structure allows water to be supplied through drainage holes at the bottom of the seedling container or side holes at the lower part of the container side wall.

[0171] The bottom drain hole is either an existing hole at the bottom of the container or a specially designed hole, with a preferred diameter of 5 to 10 millimeters.

[0172] The side hole is located on the lower part of the side wall of the container, with the center of the side hole 3-8 cm from the bottom of the container, and the hole diameter is preferably 5-10 mm.

[0173] Two to four side holes can be set and evenly distributed along the circumference to facilitate the formation of a relatively uniform water replenishment area near the third matrix layer.

[0174] During the later stages of acclimatization, irrigation solution is added to the third substrate layer through the bottom or side holes of the container. The methods include: placing the seedling container in the irrigation tray, allowing the irrigation solution to reach a certain level within the tray and be drawn in through the bottom drain hole; or using a flexible tube to inject the irrigation solution into the side holes. Overflow should be avoided during the irrigation process.

[0175] The frequency and amount of water replenishment should be adjusted as follows: irrigate once every 5 to 7 days during the middle and late stages of acclimatization; the volume of irrigation liquid for each irrigation should be 0.1 to 0.3 times the total volume of the seedling container.

[0176] Rules for monitoring and adjusting the electrical conductivity of the second matrix layer soil:

[0177] To ensure that the electrical conductivity of the second matrix layer remains stable within the allowable range for the target root zone, this embodiment employs a closed-loop control method involving periodic measurement and parameter adjustment during the later stages of acclimatization, as detailed below:

[0178] Sampling location and method: Soil electrical conductivity was measured by sampling from the middle of the second substrate layer. The sampling point was preferably located in the middle area between the inner wall of the container and the seedling roots, with the sampling depth at the middle of the second substrate layer thickness. A slender sampling tube or small shovel was used to sample from the side wall of the container, avoiding damage to the seedling taproot and the interlayer boundary. The sample volume for each measurement was sufficient for one electrical conductivity determination. After sampling, the holes were backfilled with the second substrate layer and gently pressed back into place.

[0179] The measurement frequency should be determined at least once during each irrigation interval in the middle and late stages of acclimatization. When continuous high temperature evaporation or heavy rainfall causes fluctuations in water content, the number of measurements can be increased to ensure sufficient basis for parameter adjustment.

[0180] Adjustment rules: When the measured soil electrical conductivity value of the second matrix layer deviates from the allowable range of the target root zone, adjust the irrigation frequency or the amount of water per irrigation according to the following rules:

[0181] When the electrical conductivity of the second matrix layer soil is higher than the upper limit of the allowable range of the target root zone, the irrigation interval is shortened or the amount of water per irrigation is increased in the next cycle to dilute the water with low electrical conductivity and promote salt migration. At the same time, the amount of soluble salt added to the irrigation solution can be reduced so that the electrical conductivity of the irrigation solution is close to the lower limit of the allowable range of the target root zone.

[0182] When the electrical conductivity of the second matrix layer soil is lower than the lower limit of the allowable range of the target root zone, the irrigation interval will be extended or the amount of water per irrigation will be reduced in the next cycle, and the electrical conductivity of the irrigation solution will be adjusted to a higher level within the allowable range of the target root zone, so that the electrical conductivity of the second matrix layer returns to the target range.

[0183] When the electrical conductivity of the second matrix layer soil is within the allowable range of the target root zone, maintain the current irrigation frequency and single irrigation volume unchanged, and continue to monitor and record according to the established cycle.

[0184] Before planting in saline-alkali afforestation areas, planting pits are first dug within the planting rows, and a coarse-grained material is laid at the bottom of the planting pits to form a salt drainage layer, which is connected to the drainage ditch through drainage channels. Then, a buffer layer, a transition layer, and an outer layer of native saline-alkali soil are backfilled sequentially above the salt drainage layer. The buffer layer uses improved soil with a soil conductivity within the allowable range for the target root zone and essentially equivalent to the conductivity of the second substrate layer in the container seedling stage. The transition layer is a mixed soil with a conductivity between that of the buffer layer and the outer layer of native saline-alkali soil. This layered structure creates a root zone environment within the planting pits that matches the allowable conductivity range for the target root zone and continuously connects with the conductivity level of the second substrate layer for container seedlings.

[0185] Planting location layout and planting hole excavation:

[0186] Planting locations are determined by spacing plants along the rows according to a predetermined spacing. The spacing can be determined based on the planting density and site conditions, preferably 2–4 meters. A separate planting hole is dug at each planting location.

[0187] Geometric parameters of the planting hole: the plane of the planting hole is approximately circular or approximately square.

[0188] When it is approximately circular, the diameter of the opening is 60–90 cm;

[0189] When it is approximately square, the side length of the opening is 60–90 cm;

[0190] The planting hole depth is 60-100cm. During the excavation process, the original saline-alkali soil stripped from the surface is piled up separately as the source of subsequent backfill for the outer layer of original saline-alkali soil, avoiding mixing with the improved soil.

[0191] Leveling and slope treatment of the planting hole: After the planting hole is dug to the designed depth, the bottom of the hole is leveled; a slight slope of 1 to 3% can be formed near the direction of the salt drainage channel to facilitate the flow of seepage water and dissolved salt water towards the salt drainage channel and avoid the formation of local water accumulation areas at the bottom of the hole.

[0192] Salt drainage layer laying and selection of coarse-grained materials:

[0193] The type and size of the coarse-grained material are determined by laying it along the entire bottom surface of the planting hole to form a salt-removing layer. The coarse-grained material is one or a mixture of several types of crushed stone, pebbles, or sintered ceramsite with a particle size of 5-20 mm. Preferably, the coarse-grained material is high-strength, water-resistant, and has a stable particle size distribution to prevent pulverization and pore blockage after long-term use.

[0194] Salt drainage layer thickness and laying method:

[0195] The thickness of the salt drainage layer is 10-20cm. When laying it, first spread the coarse material evenly to the designed thickness, and then perform light leveling; if necessary, a permeable isolation layer (such as non-woven fabric) can be laid on the upper surface of the salt drainage layer to prevent the fine soil from migrating into the pores of the salt drainage layer and causing blockage. The permeable isolation layer does not affect the downward flow of seepage water.

[0196] The salt drainage channel is connected to the drainage ditch:

[0197] The salt drainage channels should be laid out on one side of the salt drainage layer, extending along the direction of the planting rows or intersecting with them, and connecting with drainage ditches between rows or at the edge of the plot. The drainage ditches can be existing ditches on the plot or newly constructed ditches before afforestation, and should have a downstream outlet for drainage to the outside of the plot.

[0198] The structure and filling of the salt drainage channel can be either a trench structure or a buried perforated pipe structure.

[0199] Trench structure: A shallow trench is dug on the side of the planting hole and connected to the drainage ditch. The trench is filled with the same coarse-grained material as the salt drainage layer.

[0200] Perforated pipe structure: Permeable perforated pipes are laid on the side of the salt drainage layer and extend to the drainage ditch. The perforated pipes are wrapped with permeable geotextile and filled with coarse-grained material.

[0201] Regardless of the structure used, the salt drainage channels are filled with the same coarse-grained material as the salt drainage layer to form a connected, highly permeable path.

[0202] After the salt drainage channel is constructed, it should be checked whether the salt drainage channel is connected to the drainage ditch. It is preferable to observe whether the water flow can flow into the drainage ditch along the salt drainage channel by injecting a small amount of water, so as to avoid the failure of salt drainage due to the channel being broken.

[0203] Layered backfilling of buffer layer, transition layer and outer native saline-alkali soil:

[0204] For buffer layer backfilling, a buffer layer of 20-40cm thickness is first backfilled above the salt drainage layer. The buffer layer is composed of improved soil, a mixture of garden soil, organic fertilizer, and desalinated saline-alkali soil. During backfilling, the improved soil is filled in layers and lightly compacted to ensure the buffer layer reaches the set thickness and is level, preventing uneven stress on the root ball during subsequent planting.

[0205] The transition layer is backfilled on top of the buffer layer, with a thickness of 20-30cm. The transition layer is a mixture of the improved soil used in the buffer layer and the original saline-alkali soil removed during excavation, in a mass ratio of 1:1 to 1:2.

[0206] During mixing, the original saline-alkali soil is first air-dried, impurities removed, and crushed to make its particles uniform; then it is mixed evenly with the improved soil according to the mass ratio and backfilled to form a transitional environment between the buffer layer and the outer layer of original saline-alkali soil.

[0207] The outer layer of native saline-alkali soil is backfilled on top of the transition layer. This outer layer of native saline-alkali soil consists of saline-alkali soil that was stripped from the ground near the surface and piled up separately when the planting holes were dug. After backfilling, the outer layer of native saline-alkali soil forms a surface cover layer, which serves to maintain consistency with the surrounding native soil environment and reduce the exposure of the improved soil.

[0208] The soil conductivity of the buffer layer must be within the allowable range for the target root zone and be substantially equivalent to that of the second matrix layer. Simultaneously, the soil conductivity of the transition layer must be controlled to fall between that of the buffer layer and the outer primary saline-alkali soil. To achieve these constraints, the following measurement and adjustment process is implemented.

[0209] Sampling and measurement were conducted by taking several soil samples from each of the improved soil used to form the buffer layer, the mixed soil used to form the transition layer, and the outer layer of native saline-alkali soil, and mixing them thoroughly to form mixed soil samples. The soil conductivity of each mixed soil sample was measured using a soil conductivity meter at 25℃. The results were as follows:

[0210] The soil electrical conductivity value of the improved soil used in the buffer layer;

[0211] The soil electrical conductivity value of the mixed soil used in the transition layer;

[0212] The soil electrical conductivity value of the outer layer of native saline-alkali soil.

[0213] Sampling locations should ideally cover different areas of the soil pile, such as the top, middle, and bottom, to avoid local unevenness that could lead to distorted measurements. At least one mixed soil sample should be prepared for each type of soil and measured. If necessary, two to three mixed soil samples can be prepared and measured separately, and the average value should be taken.

[0214] To avoid ambiguity, the criteria for determining "basically equivalent" are explained as follows: the difference between the soil conductivity values ​​of the improved soil in the buffer layer and the second matrix layer does not exceed 20% of the soil conductivity value of the second matrix layer. In practice, this criterion can be met by adjusting the improved soil mix ratio or the degree of desalination treatment.

[0215] Adjustment method:

[0216] If the soil electrical conductivity value of the improved soil used in the buffer layer is higher than the upper limit of the allowable range of the target root zone, then increase the desalination degree of the desalinated saline-alkali soil or increase the proportion of garden soil and organic fertilizer, and retest until it enters the allowable range of the target root zone.

[0217] If the soil electrical conductivity value of the improved soil used in the buffer layer is lower than the lower limit of the allowable range of the target root zone, the proportion of desalinated saline-alkali soil added should be appropriately increased or the proportion of garden soil reduced, and the test should be repeated until it enters the allowable range of the target root zone.

[0218] The soil electrical conductivity of the transition layer mixed soil is controlled by adjusting its mixing ratio: when its electrical conductivity is biased towards the buffer layer, the proportion of native saline-alkali soil is increased; when its electrical conductivity is biased towards the outer native saline-alkali soil, the proportion of improved soil is increased; thus, the electrical conductivity of the transition layer is between that of the buffer layer and the outer native saline-alkali soil.

[0219] By measuring and adjusting the process, it can be ensured that the soil conductivity of the improved soil used in the buffer layer is within the allowable range of the target root zone and is basically equivalent to that of the soil conductivity of the second matrix layer. The soil conductivity of the mixed soil used in the transition layer is between that of the buffer layer and the outer native saline-alkali soil, thereby forming a root zone environment in the planting hole that is continuously connected with the conductivity level of the second matrix layer in the container seedling stage.

[0220] After completing the construction of the planting hole and forming a layered structure of salt drainage layer, buffer layer, transition layer and outer layer of native saline-alkali soil, the container seedlings of Metasequoia glyptostroboides, along with their root balls, are placed into the planting hole. The root neck of Metasequoia glyptostroboides is located above the buffer layer, and the lower part of the root ball enters the buffer layer and transition layer. This allows the initial growth environment of the root system to match the electrical conductivity level of the buffer layer, and the lower part of the root ball contacts the transition layer to form spatial continuity for downward rooting.

[0221] Preparation of container seedlings and root ball condition before transplanting:

[0222] The optimal conditions for transplanting container seedlings are when the acclimatization period is over and the electrical conductivity of the second substrate layer is stable within the allowable range for the target root zone. Stop heavy irrigation 1-2 days before transplanting to ensure the root ball is neither loose nor dripping wet, facilitating removal from the pot and handling.

[0223] When removing a containerized Metasequoia glyptostroboides seedling from its pot, it is best to gently tap along the outer wall of the container to separate the root ball from the inner wall, and then slide the root ball out as a whole. If the container has a detachable structure, the side wall can be opened before removing the seedling. During the removal process, maintain the overall shape of the root ball to avoid cracking and damaging the three-layer substrate structure.

[0224] Check the integrity of the root ball by inspecting the outer surface of the root ball for obvious cracks or loose areas. If loose areas are found, fill them with the second or first matrix layer and lightly press to fix them, so that the root ball surface is shaped and to ensure the consistency of subsequent planting hole matching and backfilling compaction.

[0225] Planting hole excavation and size matching:

[0226] The planting hole should be dug at the center of the upper surface of the buffer layer. The center of the planting hole should basically coincide with the center of the root ball, so that the root ball is located in the central area of ​​the buffer layer, reducing the risk of the root ball periphery directly contacting the outer native saline-alkali soil.

[0227] The planar shape and size of the planting hole should be the same as or similar to that of the root ball; the diameter or side length of the planting hole should be 2-5 cm larger than the diameter or side length of the root ball to form a uniform backfill gap, which facilitates backfilling and compaction of the improved soil.

[0228] The planting hole depth is related to the stratification. The planting hole depth should ensure that the bottom of the root ball is near the boundary between the buffer layer and the transition layer and enters the transition layer. Specifically, the depth at which the bottom of the root ball enters the transition layer is preferably 2 to 10 cm to ensure that the lower part of the root ball forms a contact interface with the transition layer, while avoiding the root ball from entering the transition layer too deeply, which would cause the root neck position to deviate from the upper part of the buffer layer.

[0229] Root ball placement and root collar position control:

[0230] Root ball placement involves placing the intact root ball into the planting hole, aligning the center of the root ball with the center of the planting hole; avoid rotation or compression during placement to prevent the root ball from disintegrating.

[0231] The root collar position should be such that it lies 5–10 cm below the upper surface of the buffer layer, and within the upper part of the buffer layer. After determining the root collar position, a small amount of improved soil can be temporarily used to support the root ball to prevent the root ball from sinking and causing the root collar position to be too deep.

[0232] Layer verification and post-planting inspection: The upper part of the root ball is mainly located in the buffer layer, and the lower part of the root ball enters the vicinity of the boundary between the buffer layer and the transition layer and enters the transition layer; if the bottom of the root ball does not enter the transition layer, the planting hole should be deepened; if the root neck depth exceeds 10cm, a small amount of buffer layer soil should be placed at the bottom of the root ball to raise it.

[0233] To facilitate consistent construction control and create traceable records, the following items can be documented in writing during implementation: planting hole number, root collar burial depth, the layer where the upper part of the root ball is located, whether the lower part of the root ball has entered the transition layer, and adjustment measures taken (such as deepening the planting hole or raising the soil level).

[0234] Backfilling and compaction methods:

[0235] The source and order of backfill soil, and the preferred backfill soil are consistent with the layering in step S4: the improved soil used to form a buffer layer is used to backfill around the root ball; the mixed soil used to form a transition layer is used to backfill the gaps between the root ball and the perimeter and the transition layer; the surface around the planting hole is finally covered with the outer layer of native saline-alkali soil.

[0236] The backfill thickness is determined by layering, with each layer being 10-15cm thick. Each layer is compacted before the next layer is applied, until the buffer layer above the planting hole is flush with the surface of the surrounding buffer layer.

[0237] Compaction methods and intensity control: Compaction can be carried out manually by light treading or with specialized compaction tools. The compaction intensity should be such that the backfill soil is compacted without significant settlement, avoiding over-compaction which can reduce permeability or compress the root ball. During compaction, avoid directly stepping on or impacting the main stem of the seedling. If necessary, set up temporary support poles around the seedling to help keep it upright.

[0238] After the surface is shaped and compacted, the outer layer of native saline-alkali soil is filled around the planting hole to form the surface, and a ring-shaped micro-concave water collection tray or micro-slope is formed around the plant to facilitate the collection of subsequent irrigation water to the root zone; the range of the water collection tray or micro-slope can be set according to the size of the planting hole opening.

[0239] After the Metasequoia glyptostroboides was planted, the plants were watered and maintained according to the pre-set salt-suppressing and salt-draining irrigation system. The irrigation system was divided into the initial stage of afforestation and the subsequent stage: In the initial stage, surface irrigation with large amounts of water was used infrequently, combined with the operation of salt drainage layers and channels, so that the salt in the soil above the planting hole would migrate to the salt drainage layer and the soil layer below it and be discharged through the salt drainage channels; In the subsequent stage, surface irrigation with medium amounts of water or frequent small amounts of water was used, combined with conductivity monitoring and parameter adjustment, so that the soil conductivity in the buffer layer and transition layer of the planting hole was maintained within the allowable soil conductivity range of the target root zone and not higher than its upper limit.

[0240] Delineation and irrigation implementation in the initial stage of afforestation:

[0241] The initial period of afforestation is defined as the first 2-3 months of the first growing season after the planting of seedlings. If the local climate results in high evaporation intensity or concentrated rainfall in the early stages after seedling emergence, the end time of the initial afforestation period can be determined within the above range, taking into account soil moisture content and electrical conductivity monitoring.

[0242] In the initial stage of afforestation, a surface irrigation method with large amounts of water applied infrequently is adopted: each irrigation involves injecting clean water from the surface into the planting hole, ensuring that the soil moisture content within the buffer and transition layers of the planting hole is close to saturation. Irrigation is preferably carried out in a water collection tray around the plant, allowing the irrigation water to concentrate and infiltrate into the root zone of the planting hole.

[0243] The irrigation volume is calculated by multiplying the volume of each planting hole by 0.4 to 0.8 times. The planting hole volume is based on the geometric volume determined by the diameter or side length of the planting hole opening and the depth of the planting hole; when the planting hole is approximately circular, it is calculated as a cylinder; when the planting hole is approximately square, it is calculated as a cuboid. In practice, an approximate volume can be taken based on the actual shape of the dug hole to ensure the irrigation volume is feasible.

[0244] Irrigation intervals should be 10–20 days during the initial stage of afforestation. Shorter intervals can be used under conditions of high temperature and strong winds with high evaporation; longer intervals can be used under conditions of frequent rainfall or high soil moisture content, but it should be ensured that each irrigation can achieve significant infiltration and promote salt migration.

[0245] The collaborative working mechanism between afforestation in the early stages and salt drainage layers and channels:

[0246] Maintain connectivity: During each irrigation period in the early stages of afforestation, keep the salt drainage channels connected to the drainage ditches to prevent blockage or artificial obstruction. If the drainage ditches are silted up, first clear the downstream outlet to ensure that the dissolved brine discharged from the channels can be smoothly drained.

[0247] The feasibility of the salt drainage mechanism is explained as follows: Under conditions of heavy irrigation and infrequent irrigation, irrigation water permeates downwards from the buffer layer and transition layer into the salt drainage layer, carrying dissolved salts to the salt drainage layer and drainage channels. Since the salt drainage layer and drainage channels are composed of coarse-grained materials, they have high permeability and can provide a low-resistance drainage path for dissolved salt water, thereby reducing the risk of salt accumulation in the root zone above the planting hole.

[0248] Definition of the post-afforestation stage and irrigation implementation:

[0249] The period from the end of the initial afforestation phase to the end of the second growing season is considered the subsequent afforestation phase.

[0250] For irrigation methods, in the subsequent stages of afforestation, surface irrigation with multiple applications of medium-grade water or frequent small applications of water should be used. The choice between the two methods can be made based on the monitoring results of seasonal evaporation intensity, rainfall, and electrical conductivity, or they can be implemented alternately.

[0251] Multiple irrigations: The amount of water used for each irrigation is calculated as 0.2 to 0.4 times the volume of the planting hole per plant, and the irrigation interval is 7 to 15 days.

[0252] Water frequently but in small amounts: the amount of water used each time should be calculated as 0.1 to 0.2 times the volume of the planting hole for each plant, and the irrigation interval should be 3 to 7 days.

[0253] The irrigation objectives for the subsequent stages are to maintain stable water content in the buffer and transition layers through the above irrigation methods, suppress the tendency of surface salt return caused by salt migration upward with evaporation, ensure that the soil electrical conductivity in the buffer and transition layers does not exceed the upper limit of the allowable soil electrical conductivity range in the target root zone, and keep it within the allowable range in the target root zone as much as possible.

[0254] Rules for monitoring and adjusting the conductivity of buffer and transition layers:

[0255] To ensure that the soil electrical conductivity in the buffer layer and transition layer does not exceed the upper limit of the allowable soil electrical conductivity range in the target root zone and remains within the allowable range in the target root zone, this embodiment implements regular sampling and measurement and system adjustment in the subsequent stages of afforestation.

[0256] Sampling location and depth: Buffer layer sampling: Within a 10-20cm ring around the plant, the sampling depth is located in the middle of the buffer layer thickness;

[0257] Sampling of the transition layer: The sampling depth is located in the middle of the thickness of the transition layer, in the vertical direction below the sampling point of the buffer layer.

[0258] When sampling, use a soil drill or sampling tube to take samples in layers to avoid mixing soil from different layers into the same sample; take at least 3 samples from each layer and mix them evenly to form a mixed soil sample.

[0259] The frequency of measurement should be once a month to once every two months during the later stages of afforestation. In the event of continuous high temperature evaporation, heavy rainfall, or switching of irrigation system, the measurement frequency can be temporarily increased to allow for timely correction of irrigation parameters.

[0260] Adjust the rules based on the measured soil electrical conductivity values ​​of the buffer and transition layers, and adjust the irrigation method, irrigation interval, and irrigation volume per cycle:

[0261] When the electrical conductivity of the buffer layer soil is close to or higher than the upper limit of the allowable range of the target root zone, priority should be given to frequent small irrigations or shortening the interval between multiple medium irrigations, and the amount of water for a single irrigation should be appropriately increased to the upper limit of the corresponding method, so as to reduce the upward movement of salt induced by evaporation and promote the infiltration of salt with water; if necessary, check the connectivity of the salt drainage channel to ensure that the infiltrated water can be discharged through the salt drainage layer.

[0262] When the electrical conductivity of the buffer layer soil remains within the allowable range of the target root zone and the water content is stable, the existing irrigation regime can be maintained.

[0263] When the electrical conductivity of the transition layer soil is higher than the expected transition level between the outer native saline-alkali soil and the buffer layer and shows an upward trend, priority should be given to increasing the irrigation frequency and shortening the irrigation interval so that the salt can migrate more easily towards the salt drainage layer with the infiltrated water.

[0264] When the electrical conductivity of the buffer or transition layer soil is significantly lower than the lower limit of the allowable range for the target root zone and the plants show signs of water shortage, the irrigation method can be switched from frequent small waterings to multiple medium waterings, and the amount of water for each irrigation should be adjusted to the median value of the corresponding range to balance water supply and salinity control.

[0265] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides, characterized in that, Includes the following steps: S1: Based on the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site, determine the target distribution depth range of Metasequoia glyptostroboides roots and the allowable soil electrical conductivity range in the target root zone; S2: In the nursery, the container substrate is set up from top to bottom as a first substrate layer, a second substrate layer and a third substrate layer. The first substrate layer uses an improved substrate with an electrical conductivity lower than the lower limit of the soil electrical conductivity range allowed by the target root zone. The second substrate layer uses a substrate with an electrical conductivity within the range allowed by the soil electrical conductivity of the target root zone. The third substrate layer uses a substrate with an electrical conductivity higher than that of the second substrate layer, so as to form an increasing electrical conductivity gradient from top to bottom in the container. S3: Plant the Metasequoia glyptostroboides seedlings in the container substrate. In the early stage of acclimatization, use a low conductivity irrigation solution to irrigate from the top of the container. In the middle and late stages of acclimatization, use an irrigation solution with a higher conductivity than the irrigation solution in the early stage of acclimatization to replenish water from the bottom of the container or the side hole. By adjusting the irrigation frequency and the amount of water per irrigation, the conductivity of the second substrate layer is stabilized within the soil conductivity range allowed by the target root zone, so as to obtain Metasequoia glyptostroboides container seedlings with roots penetrating into the second substrate layer and the third substrate layer. S4: Excavate planting holes in the saline-alkali afforestation area, lay a coarse-grained material salt drainage layer at the bottom of the planting hole, and connect the salt drainage layer to the drainage ditch through the salt drainage channel. Backfill the salt drainage layer in sequence with a buffer layer, a transition layer and an outer layer of native saline-alkali soil. The buffer layer is made of improved soil with an electrical conductivity within the allowable range of soil electrical conductivity in the target root zone and basically equivalent to the electrical conductivity of the second matrix layer. The transition layer is a mixed soil with an electrical conductivity between that of the buffer layer and the outer layer of native saline-alkali soil. S5: Place the container seedling of Metasequoia glyptostroboides along with its root ball into the planting hole, so that the root neck of Metasequoia glyptostroboides is located above the buffer layer and the lower part of the root ball enters the buffer layer and the transition layer. After covering with soil and compacting, a plant is formed. S6: After planting, water and maintain the planted plants according to the preset irrigation system. In the early stage of afforestation, use large amounts of water for frequent irrigation, and work with the salt drainage layer and the salt drainage channel to allow the salt in the soil above the planting hole to migrate to the salt drainage layer and the soil layer below it. In the later stage of afforestation, use medium water for frequent irrigation or small amounts of water to maintain the electrical conductivity in the buffer layer and the transition layer of the planting hole not higher than the upper limit of the allowable electrical conductivity range of the target root zone.

2. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 1, characterized in that, The steps of determining the target root distribution depth range of Metasequoia glyptostroboides and the allowable soil electrical conductivity range of the target root zone based on the electrical conductivity distribution of the 0-80cm soil layer in the target saline-alkali afforestation site include: Within each hectare of the saline-alkali afforestation land, select 3 to 5 sample points, and at each sample point, divide the soil layer 0 to 80 cm below the surface into 4 soil layer segments at a depth interval of 20 cm. At least three soil samples were collected horizontally within each soil layer segment. The soil samples were mixed evenly to form a mixed soil sample. The soil conductivity of each mixed soil sample was measured using a soil conductivity meter at 25 degrees Celsius to obtain the soil conductivity value of each soil layer segment in the 0-80cm soil layer. The determination of the target depth range of the root system of Metasequoia glyptostroboides includes: Based on the cultivation experiment results of Metasequoia glyptostroboides under different soil electrical conductivity conditions, a critical value for soil electrical conductivity is predetermined. The critical value for soil electrical conductivity is the upper limit of soil electrical conductivity that allows Metasequoia glyptostroboides to grow normally. In the 0-80CM soil layer, each soil layer segment with a soil conductivity value less than or equal to the critical soil conductivity value is selected. Adjacent soil layer segments with soil conductivity values ​​not greater than the critical soil conductivity value are merged to form a continuous depth interval, and the continuous depth interval is taken as the target distribution depth range of the Metasequoia glyptostroboides root system. The determination of the permissible soil electrical conductivity range for the target root zone includes: The soil electrical conductivity values ​​of each soil layer within the target distribution depth range of the Metasequoia root system are arithmetically averaged to obtain the average soil electrical conductivity value. 0.8 times the average soil electrical conductivity value is taken as the lower limit of the allowable soil electrical conductivity range of the target root zone, and 1.2 times the average soil electrical conductivity value is taken as the upper limit of the allowable soil electrical conductivity range of the target root zone.

3. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 2, characterized in that, The container substrate setting step includes: Select a seedling container with an open top, leave a 2-5cm space from the bottom to the top of the container without substrate, and fill the remaining space with the first substrate layer, the second substrate layer and the third substrate layer in sequence; The first substrate layer, the second substrate layer, and the third substrate layer are filled into the seedling container from top to bottom. The thickness of the first substrate layer is 5-10 cm, the thickness of the second substrate layer is 10-20 cm, and the thickness of the third substrate layer is 5-10 cm.

4. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 3, characterized in that, The first matrix layer is formed by mixing peat, perlite and saline-alkali soil treated by leaching with clean water in a mass ratio of 1:1:1 to 2:1:1; The second matrix layer is formed by mixing humus, garden soil and partially improved saline-alkali soil in a mass ratio of 1:1:1 to 2:1:2; The third matrix layer is formed by mixing coarse sand, garden soil and unmodified saline-alkali soil in a mass ratio of 1:1:1 to 2:1:

2. The soil electrical conductivity values ​​of the first matrix layer, the second matrix layer, and the third matrix layer were determined by sampling and measuring each matrix layer at 25°C. The soil electrical conductivity value of the first matrix layer was less than the lower limit of the allowable soil electrical conductivity range for the target root zone, the soil electrical conductivity value of the second matrix layer was within the allowable soil electrical conductivity range for the target root zone, and the soil electrical conductivity value of the third matrix layer was greater than that of the second matrix layer.

5. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 4, characterized in that, The step of planting Metasequoia glyptostroboides seedlings in the container substrate includes: Planting holes are pre-formed in the first substrate layer. After the roots of the Metasequoia glyptostroboides seedling are spread out, they are placed in the planting holes, so that the root neck of the Metasequoia glyptostroboides seedling is located near the junction of the first substrate layer and the second substrate layer. The lower end of the seedling roots enters the second substrate layer. The substrate from the first substrate layer is used to backfill the holes and the seedling is gently pressed to fix it. The step of irrigating the container from above with a low-conductivity irrigation solution during the early stages of acclimatization includes: The period from the completion of planting of Metasequoia glyptostroboides seedlings to 30-45 days after planting is considered the early acclimatization period. Irrigation solution with an electrical conductivity lower than the lower limit of the allowable soil electrical conductivity range of the target root zone is selected and slowly poured from above the container, so that the irrigation solution seeps down into the first substrate layer and the second substrate layer along the direction of gravity. Irrigation is carried out every 3 to 5 days during the early stage of acclimatization, with the volume of irrigation liquid each time being 0.1 to 0.3 times the total volume of the seedling container, so as to keep the first substrate layer in a low electrical conductivity state.

6. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 5, characterized in that, The step of using an irrigation solution with a higher electrical conductivity than the irrigation solution used in the early stages of acclimatization to replenish water from the bottom or side holes of the container, and stabilizing the electrical conductivity of the second substrate layer within the allowable soil electrical conductivity range of the target root zone by adjusting the irrigation frequency and the amount of water applied per irrigation includes: The seedling stage 30 to 45 days after planting is considered the mid-to-late stage of acclimatization. During this mid-to-late stage, irrigation solution with a conductivity greater than that of the irrigation solution in the early stage of acclimatization and within the allowable soil conductivity range of the target root zone is added to the third substrate layer through the drainage hole at the bottom of the container or the side hole located on the lower side wall of the container. Irrigation is carried out every 5 to 7 days during the middle and late stages of acclimatization. The volume of irrigation liquid for each irrigation is 0.1 to 0.3 times the total volume of the seedling container. During the irrigation interval, soil electrical conductivity is sampled and measured in the second substrate layer periodically. The irrigation frequency or the volume of single irrigation liquid is adjusted according to the measurement results to keep the soil electrical conductivity in the second substrate layer within the allowable range of the target root zone.

7. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 6, characterized in that, The steps of digging planting holes and laying a coarse-grained desalination layer in saline-alkali afforestation land include: Planting positions are arranged along the row direction according to the predetermined spacing between plants. Planting holes are dug at each planting position. The plane of the planting hole is approximately circular or approximately square. The diameter or side length of the opening of the planting hole is 60-90cm and the depth of the planting hole is 60-100cm. A coarse-grained material is laid along the entire bottom surface of the planting hole to form the salt drainage layer. The coarse-grained material is one or a mixture of several of the following: gravel, pebbles, or sintered ceramsite with a particle size of 5 to 20 mm. The thickness of the salt drainage layer is 10 to 20 cm. A salt drainage channel is provided on one side of the salt drainage layer. The salt drainage channel extends along the direction of the planting row or in a direction that intersects with the planting row and connects with the drainage ditch between the rows or at the edge of the plot. The salt drainage channel is filled with the same coarse-grained material as the salt drainage layer.

8. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 7, characterized in that, The step of backfilling a buffer layer, a transition layer, and an outer layer of native saline-alkali soil sequentially above the salt drainage layer includes: The buffer layer is backfilled above the salt drainage layer. The thickness of the buffer layer is 20-40cm. The buffer layer is formed by improved soil, which is soil obtained by mixing garden soil, organic fertilizer and desalinated saline-alkali soil. The transition layer is backfilled above the buffer layer. The thickness of the transition layer is 20-30cm. The transition layer is a mixed soil formed by mixing the improved soil used in the buffer layer with the original saline-alkali soil taken out during excavation at a mass ratio of 1:1 to 1:

2. The outer layer of native saline-alkali soil is backfilled above the transition layer. The outer layer of native saline-alkali soil is the saline-alkali soil that was stripped from the ground surface and piled up separately when the planting hole was dug. The soil electrical conductivity of the buffer layer and the transition layer was determined by sampling and measurement, which included: Several soil samples were taken from each of the improved soil used to form the buffer layer, the mixed soil used to form the transition layer, and the original saline-alkali soil of the outer layer, and mixed evenly to form a mixed soil sample. The soil conductivity of each mixed soil sample was measured using a soil conductivity meter at 25°C to obtain the soil conductivity values ​​of the improved soil for the buffer layer, the mixed soil for the transition layer, and the original saline-alkali soil of the outer layer. The soil conductivity value of the improved soil in the buffer layer is adjusted to be within the allowable soil conductivity range of the target root zone and is basically equivalent to the soil conductivity value of the second matrix layer. The soil conductivity value of the mixed soil in the transition layer is controlled to be between the soil conductivity value of the improved soil in the buffer layer and the soil conductivity value of the outer primary saline-alkali soil.

9. A method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 8, characterized in that, The step of placing the container seedling of Metasequoia glyptostroboides along with its root ball into the planting hole includes: A planting hole matching the size of the root ball of the Metasequoia glyptostroboides container seedling is dug at the center of the upper surface of the buffer layer. The planar shape of the planting hole is the same as or similar to that of the planting pit. The diameter or side length of the planting hole is 2-5 cm greater than the diameter or side length of the root ball. The depth of the planting hole is such that the bottom of the root ball is located near the junction of the buffer layer and the transition layer and enters the transition layer. Remove the completed Metasequoia glyptostroboides container seedlings from the seedling container, remove the outer shell of the container without damaging the root system and substrate, keeping the root ball intact, and place the root ball into the planting hole, so that the Metasequoia glyptostroboides root neck is 5-10 cm below the upper surface of the buffer layer. The soil compaction step includes: The improved soil used to form the buffer layer is used to backfill the voids around the root ball, and the mixed soil used to form the transition layer is used to backfill the voids below and around the root ball and between the transition layer and the root ball. The thickness of the backfilling layers is 10-15 cm. After each layer of improved soil or mixed soil is backfilled, the backfill soil is compacted by manual treading or by a special compaction tool until the buffer layer and transition layer above the planting hole are flush with the surface of the surrounding buffer layer and transition layer. After the backfill soil is compacted, the outer layer of original saline-alkali soil is filled around the planting hole to form the surface.

10. The method for gradient acclimatization and high survival rate cultivation of salt-tolerant Metasequoia glyptostroboides according to claim 9, characterized in that, The steps of using large amounts of water for infrequent irrigation in the early stages of afforestation, in conjunction with the salt drainage layer and the salt drainage channel, include: The first two to three months of the first growing season after the planting of Metasequoia glyptostroboides trees are considered the initial stage of afforestation. During each irrigation in the early stage of afforestation, clean water is injected from the ground surface into the planting hole so that the soil moisture content in the depth range corresponding to the buffer layer and transition layer in the planting hole is close to saturation. The amount of water for each irrigation is calculated as 0.4 to 0.8 times the volume of the planting hole for each Metasequoia glyptostroboides. The irrigation interval during the initial stage of afforestation is 10 to 20 days. During each irrigation, the salt drainage channel is kept connected to the drainage ditch so that the irrigation water seeps into the salt drainage layer from the buffer layer and the transition layer and then flows into the drainage ditch through the salt drainage channel. The steps of using multiple applications of medium-sized or small amounts of water to maintain the soil electrical conductivity in the buffer layer and transition layer of the planting hole at a level not exceeding the upper limit of the allowable soil electrical conductivity range for the target root zone in the subsequent stages of afforestation include: The period from the end of the initial afforestation phase to the end of the second growing season is considered the subsequent afforestation phase. During this phase, surface irrigation is carried out using either multiple applications of medium-grade water or frequent small applications of water. For multiple applications of medium-grade water, the amount of water used each time is calculated as 0.2 to 0.4 times the volume of the planting hole for each Metasequoia glyptostroboides tree, with an irrigation interval of 7 to 15 days. For frequent small applications of water, the amount of water used each time is calculated as 0.1 to 0.2 times the volume of the planting hole for each Metasequoia glyptostroboides tree, with an irrigation interval of 3 to 7 days. During the subsequent afforestation phase, soil electrical conductivity was measured in the buffer layer and the transition layer at a frequency of once a month to once every two months, at 25°C. The irrigation method, irrigation interval, and irrigation volume were adjusted based on the measured soil electrical conductivity values ​​to keep the soil electrical conductivity in the buffer layer and the transition layer within the allowable range of the target root zone.

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