Method for improving saline-alkali soil in tree hole based on using adapted dose of air-permeable anti-seepage sand

Abstract

The present application relates to the technical field of saline-alkali soil ecological restoration, in particular to a method for improving saline-alkali soil tree hole soil based on using adaptive dose of air-permeable anti-seepage sand, aiming at the problems of high cost, poor effect, single dose of air-permeable anti-seepage sand, unreasonable tree hole structure and the like in traditional improvement, the present application first determines the pH value of soil to determine the adaptive dose of air-permeable anti-seepage sand, excavates pot bottom-shaped tree hole and sets zeolite water collecting hole, compounds air-permeable anti-seepage sand, modified biochar and matured sheep manure into an improving agent, adopts layered gradient backfilling, and supports post-planting management such as precise irrigation and salt dynamic monitoring. The method can accurately adapt to different saline-alkalinity soils, optimizes water and gas and fertility in root zone, effectively separates salt and preserves water, significantly improves survival rate and growth of seedlings, saves water and reduces cost, and is suitable for afforestation and greening in arid and semiarid saline-alkali lands with pH 8.0-9.5.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali land ecological restoration technology, specifically a method for improving tree pit soil in saline-alkali land using an appropriate dose of breathable and impermeable sand. Background Technology

[0002] Linxia Hui Autonomous Prefecture is located in the transition zone from the Loess Plateau to the Qinghai-Tibet Plateau. Several rivers, including the Yellow River, Tao River, and Daxia River, flow through the prefecture, and saline-alkali soils are widely distributed along the river terraces and valleys. The soil pH in these areas is generally between 8.0 and 9.5, characterized by soil compaction, poor aeration, weak water and fertilizer retention capacity, and severe salt accumulation on the surface. This has led to long-term bottlenecks in afforestation and greening efforts, including low survival rates, weak growth, and high maintenance costs. In the Beishan Shazipo area, the soil particles are coarse and loose, with underlying mudstone softening upon contact with water and exhibiting poor permeability, resulting in insufficient water and fertilizer retention. In Shanggou, Lianhua Town, the soil is mainly red sandy loam. Although the field water holding capacity is relatively high, the surface of the tree pits easily dries and forms a crust due to intense evaporation, causing salt to rise with the moisture. The area where Youjiayuan Village is located has generally low nutrient levels, alkaline soil, and poor fertilizer retention capacity, which is already quite prominent in the topsoil.

[0003] Traditional methods for improving tree pits in saline-alkali land mainly include soil replacement, application of organic fertilizers, and chemical amendments. While soil replacement is effective quickly, it is costly and easily causes ecological damage to the soil extraction area, making large-scale implementation difficult. Applying organic fertilizers can improve soil nutrient status in the short term, but its effect on regulating soil pH and salinity is limited, and the rapid decomposition of organic matter results in short-lived improvement. Chemical amendments such as gypsum and sulfur can lower soil pH, but they easily cause soil structure damage and secondary pollution, and their effect on water regulation in arid and semi-arid regions is not significant.

[0004] In recent years, permeable and impermeable sand, as a novel inorganic mineral soil amendment material, has seen initial application in saline-alkali land improvement due to its combined air permeability and impermeability. Permeable and impermeable sand, with its porosity and specific particle size distribution, can form a stable water and air regulation layer in the root zone when applied to tree pit backfill, inhibiting excessive water infiltration, maintaining root aeration, and slowing salt accumulation. However, current technologies for applying permeable and impermeable sand often use a single fixed dosage, failing to precisely adapt to different degrees of salinity in soils. This results in excessive dosage and waste in mildly saline-alkali lands, while insufficient dosage leads to poor improvement in severely saline-alkali lands. Furthermore, using permeable and impermeable sand alone is insufficient to comprehensively improve the soil's physical and chemical properties and fertility; soil microbial activity is low, organic matter accumulation is slow, and the improvement effect is prone to rebound.

[0005] Furthermore, existing tree pit designs are simple, often featuring straight walls and flat bottoms, which hinders water collection and even distribution in the root zone. Irrigation water easily seeps rapidly down the pit walls, leading to water waste. Post-planting management also lacks targeted technical measures; irrigation frequency and fertilization amounts are not matched to the water and fertilizer retention characteristics of the breathable and impermeable sand, preventing the full realization of its technological advantages. Therefore, there is an urgent need to develop a comprehensive improvement method that can accurately determine the dosage of breathable and impermeable sand based on the degree of soil salinization, combined with composite improvement materials and optimized tree pit structure, along with scientific post-planting management, to improve the soil improvement effect of tree pits in saline-alkali land, increase seedling survival rates, and reduce maintenance costs. Summary of the Invention

[0006] To address the problems in existing technologies, this invention provides a method for improving tree pit soil in saline-alkali land using an appropriate dosage of breathable and impermeable sand. The appropriate dosage of breathable and impermeable sand is determined by accurately measuring the soil pH value. The "pot-shaped" tree pit shaping and water collection hole design optimize water distribution. The breathable and impermeable sand is combined with modified biochar and decomposed sheep manure to improve the soil's physical and chemical properties and fertility. A stable rhizosphere microenvironment is constructed through layered gradient backfilling. Combined with precision irrigation and dynamic salinity monitoring technology, this method achieves long-term improvement of tree pit soil in saline-alkali land and promotes the healthy growth of seedlings.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for improving saline-alkali soil tree pit soil by using an appropriate dosage of breathable and impermeable sand, comprising the following steps: (1) Soil baseline measurement: Soil samples were collected from a depth of 0 to 20 cm in the proposed planting area, and the initial pH value was measured. The appropriate dosage of permeable and impermeable sand was determined according to the pH range: when pH is 8.0 to 8.5, the appropriate dosage is 4% to 5% by volume; when pH is 8.5 to 9.0, the appropriate dosage is 5% to 6% by volume; when pH is 9.0 to 9.5, the appropriate dosage is 6% to 7% by volume. (2) Tree pit excavation and shaping: Excavate a tree pit with a length × width × depth of 50cm × 50cm × 50cm. Shape the bottom of the tree pit into a pot-shaped pit with the center lower than the surrounding area by 3~5cm. Excavate a water collection hole with a diameter of 10cm and a depth of 15cm in the center of the pot bottom. Fill the water collection hole with zeolite particles with a particle size of 2~5mm until it is level with the bottom of the pot. (3) Preparation of modified materials: The air-permeable and impermeable sand, modified biochar, and decomposed sheep manure were mixed evenly at a mass ratio of 10:2:3 to obtain a composite modifier; the modified biochar was corn straw biochar that had been soaked in 0.5 mol / L phosphoric acid solution for 24 h and then dried. (4) Layered backfilling: The excavated topsoil and subsoil are placed separately. First, a 5cm thick layer of subsoil is laid at the bottom of the tree pit and compacted. Then, the composite amendment and topsoil are thoroughly mixed according to the appropriate dosage determined in step (1). The mixture is backfilled into the tree pit in two layers, each layer being 20cm thick. After each layer is backfilled, it is compacted appropriately. The surface of the backfill soil is 5-8cm higher than the original ground surface. (5) Planting and planting of seedlings: Dig a planting pit in the center of the backfilled tree pit, put the seedling into the pit and straighten it so that the roots can spread out. Fill the soil in layers and tamp it down. The planting depth should be such that the root neck is level with the ground or slightly higher by 1-2 cm. Water thoroughly after planting. After the water has completely seeped in, cover the tree basin with a 5 cm thick straw covering layer.

[0008] Specifically, in step (1), at least 5 soil samples are collected from each proposed planting area, mixed evenly, and the pH value is measured. The measurement method is the potentiometric method specified in NY / T1121.

[0009] Specifically, in step (2), the porosity of the zeolite particles in the water collection hole is 40%~45%, and the zeolite particles are soaked in saturated calcium chloride solution for 12 hours and then dried.

[0010] Specifically, in step (3), the air permeability coefficient of the permeable impermeable sand is ≥1×10⁻⁶. -3 cm / s, seepage prevention coefficient ≤1×10 - 7 cm / s, with a particle size distribution of 0.1~0.5mm accounting for ≥85%.

[0011] Specifically, in step (3), the modified biochar has a particle size of 0.25~1mm and a specific surface area ≥300m². 2 / g, the organic matter content of well-rotted sheep manure is ≥45%, and the moisture content is ≤30%.

[0012] Specifically, in step (4), when backfilling in layers, the permeable and impermeable sand content of the lower layer of backfill soil is 0.5% to 1% higher by volume than that of the upper layer.

[0013] Specifically, it also includes post-planting management steps: In the first year after planting, water once each during the greening period, the rapid growth period, and before overwintering, using drip irrigation, with each irrigation amount being 15-20L / plant; Starting from the second year, apply well-rotted organic fertilizer once each in spring before sprouting and in autumn after leaf fall, with an application amount of 5-10kg / plant.

[0014] Specifically, post-planting management also includes dynamic monitoring of salt content: soil samples are collected from the tree pit at a depth of 0-20cm in June and September each year to measure pH value and soluble salt content. When the pH value rises by more than 0.3 units, 0.5% potassium dihydrogen phosphate solution is sprayed on the leaves 2-3 times, with an interval of 7-10 days between each application.

[0015] Specifically, the seedlings are any one of the following: Chinese pine, golden elm, Sichuan pepper, or pear.

[0016] Application of the method of improving tree pit soil in saline-alkali land with appropriate dosage of breathable and impermeable sand in afforestation and greening of arid and semi-arid saline-alkali land with pH value of 8.0-9.5.

[0017] The beneficial effects of this invention are: Precise dosage matching: The appropriate dosage of permeable and impermeable sand is determined according to the initial pH value of the soil, which realizes the precise improvement of soils with different degrees of salinization and improves the material utilization rate and improvement effect.

[0018] Optimized tree pit structure: The design of the pot-shaped tree pit and water collection holes optimizes the distribution of water in the root zone, improves water use efficiency, and enhances the ability to block salt.

[0019] Composite improvement formula: The combination of breathable and impermeable sand with modified biochar and decomposed sheep manure achieves a synergistic effect of soil pH regulation, water and air regulation and fertility enhancement, resulting in a more lasting improvement effect.

[0020] Layered gradient backfilling: A layered structure was constructed with a lower layer for seepage prevention and salt isolation and an upper layer for aeration and fertilizer retention, creating a stable rhizosphere microenvironment for root growth.

[0021] Post-planting management: The combination of precision irrigation and dynamic salinity monitoring technology fully leverages the technical advantages of breathable and impermeable sand, significantly improving seedling survival rate and growth while reducing maintenance costs. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Figure 1 The flowchart illustrates the method for improving saline-alkali soil in tree pits using an appropriate dose of breathable and impermeable sand, as provided in this invention. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0025] like Figure 1 As shown, the method for improving saline-alkali soil tree pit soil based on the use of appropriate dosage of breathable and impermeable sand according to the present invention includes soil baseline measurement, tree pit excavation and shaping, preparation of improvement materials, layered backfilling, seedling planting and transplanting, and post-planting management steps.

[0026] In the soil baseline determination step, this invention overcomes the limitation of existing technologies that use a single fixed dosage. It determines differentiated dosages of permeable and impermeable sand based on different initial pH ranges of the soil in the planting pit. Specifically, when the soil pH is 8.0–8.5 (slightly saline-alkali), the appropriate dosage is 4%–5% by volume; when the pH is 8.5–9.0 (moderately saline-alkali), the appropriate dosage is 5%–6% by volume; and when the pH is 9.0–9.5 (severely saline-alkali), the appropriate dosage is 6%–7% by volume. This dosage adjustment mechanism ensures that the permeable and impermeable sand achieves optimal improvement effects in soils with varying degrees of salinity, while avoiding material waste. To ensure the accuracy of the measurement results, at least five soil samples are collected from each proposed planting area, mixed thoroughly, and the pH value is determined using the potentiometric method specified in NY / T1121.

[0027] In the tree pit excavation and shaping steps, this invention optimizes the traditional straight-walled, flat-bottomed tree pit structure. First, a standard tree pit with dimensions of 50cm x 50cm x 50cm is excavated. Then, the bottom of the pit is shaped like a pot, with the center lower than the perimeter by 3-5cm. This structure allows irrigation water and natural rainfall to collect in the center of the root zone, prolonging the retention time of water in the root zone. More importantly, this invention excavates a 10cm diameter, 15cm deep water collection hole in the center of the pot bottom, and fills the water collection hole with zeolite particles treated with a saturated calcium chloride solution. Zeolite has excellent ion exchange properties and adsorption capacity, capable of adsorbing alkaline ions such as sodium ions in the soil while storing water and slowly releasing it during drought, providing a continuous water supply to the roots. The design of the water collection hole also promotes downward root growth, enhancing the seedling's resistance to adverse conditions.

[0028] In the improved material preparation process, this invention employs a composite formula of breathable and impermeable sand, modified biochar, and well-rotted sheep manure, instead of using breathable and impermeable sand alone. The breathable and impermeable sand provides basic breathability and impermeability, with a permeability coefficient ≥1×10⁻⁶. -3 cm / s, seepage prevention coefficient ≤1×10 -7 The particle size distribution is ≥85% (0.1~0.5mm), ensuring the formation of a stable water and air regulation layer in the soil. The modified biochar is corn straw biochar soaked in 0.5mol / L phosphoric acid solution for 24 hours and then dried, with a particle size of 0.25~1mm and a specific surface area ≥300m². 2 / g. Phosphoric acid modification increases the acidic functional groups on the surface of biochar, enhancing its adsorption capacity for alkaline ions and improving soil pore structure. Well-rotted sheep manure, with an organic matter content ≥45% and a moisture content ≤30%, provides abundant nutrients and promotes soil microbial activity. When the three are mixed evenly in a mass ratio of 10:2:3, a synergistic compound conditioner is formed, simultaneously achieving soil pH regulation, water and air balance, and fertility enhancement.

[0029] In the layered backfilling process, this invention employs a layered gradient backfilling technique instead of uniform mixing. First, the excavated topsoil and subsoil are placed separately, with priority given to using the more fertile topsoil for improvement. A 5cm thick layer of subsoil is laid at the bottom of the tree pit and compacted as an isolation layer to prevent the upward migration of lower-level salts. Then, the composite amendment is thoroughly mixed with the topsoil according to a predetermined dosage and backfilled into the tree pit in two layers, each 20cm thick, with each layer moderately compacted after completion. Specifically, the lower backfill layer has a 0.5%–1% higher volumetric content of permeable and impermeable sand than the upper layer. This gradient structure creates a stronger impermeable and salt-barrier layer in the lower root zone, effectively blocking the upward migration pathway of deep salts. The surface of the backfill soil is 5–8cm higher than the original ground level to prevent excessive settlement and water accumulation after watering.

[0030] In the seedling planting and transplanting process, this invention strictly controls the planting depth and transplanting quality. A suitable planting pit is dug in the center of the backfilled tree pit. The seedling is placed in the pit and straightened, allowing the roots to spread naturally and avoiding root constriction. Soil is filled in layers and compacted to ensure close contact between the roots and the soil. The planting depth should be such that the root collar is level with the ground or slightly higher (1-2 cm). Planting too deep can lead to root rot due to lack of oxygen, while planting too shallow can result in drought damage. Immediately after planting, the seedling is thoroughly watered. After the water has completely seeped in, a 5 cm thick layer of straw is placed around the base of the tree to reduce water evaporation, inhibit salt accumulation, and increase soil organic matter as the straw decomposes.

[0031] In post-planting management, this invention utilizes the water-retention properties of breathable and impermeable sand to develop precise irrigation and fertilization plans. The first year after planting is crucial for seedling survival. In addition to initial watering, watering is applied once each during the greening-up period, rapid growth period, and before winter, using drip irrigation with a volume of 15-20 L per plant each time. Compared to traditional irrigation methods, this reduces irrigation frequency by more than 30%, significantly saving water resources. From the second year onwards, well-rotted organic fertilizer is applied once each spring before bud break and in autumn after leaf fall, at a rate of 5-10 kg per plant, using a circular trench application method at a depth of 20-30 cm. Simultaneously, a dynamic salinity monitoring mechanism is established, with soil samples collected from a depth of 0-20 cm in the planting pit each June and September to determine pH value and soluble salt content. When the pH value rises by more than 0.3 units, spray the leaves with a 0.5% potassium dihydrogen phosphate solution 2-3 times, with an interval of 7-10 days between each application, to adjust the soil pH in a timely manner and prevent salt rebound.

[0032] Example 1: Improvement experiment of slightly saline-alkali land in Shazipo, Beishan, Linxia City: This experiment was conducted at the Shazipo experimental site in Beishan, Linxia City. The soil type in this area is thin-layered hillside soil with coarse particles, loose structure, high calcium carbonate content, and insufficient fertilizer and water retention capacity. Soil samples were collected from a depth of 0 to 20 cm before the experiment, and the initial pH value was measured to be 8.10 to 8.42, indicating slightly saline-alkali soil.

[0033] Experimental design: Four treatment groups were set up, with 10 Pinus tabuliformis seedlings in each group. The tree pits were all 50cm×50cm×50cm in size.

[0034] Treatment Group 1 (Method of the present invention): The method of the present invention is improved according to the technical solution of the present invention, and the appropriate dosage of the permeable and impermeable sand is determined to be 4.5% by volume based on the soil pH value.

[0035] Treatment Group 2 (single 5% permeable impermeable sand): Using existing technology, 5% permeable impermeable sand by volume is evenly mixed with topsoil and then backfilled. The tree pit has straight walls and a flat bottom, without water collection holes, and no modified biochar or decomposed sheep manure is added.

[0036] Treatment Group 3 (single 10% permeable impermeable sand): 10% permeable impermeable sand by volume is mixed evenly with topsoil and then backfilled. Other aspects are the same as in Treatment Group 2.

[0037] Control group (traditional method): No amendments were added, and the original soil was used for backfilling, with conventional irrigation and fertilization management. Specific implementation steps

[0038] Soil baseline determination: Five sampling points were randomly selected within the test area, and soil samples were collected from a depth of 0–20 cm. After thorough mixing, the pH value was determined using the potentiometric method, and the average pH value was 8.26. Based on the dosage matching standard of this invention, the suitable dosage of the permeable and impermeable sand was determined to be 4.5% by volume.

[0039] Tree pit excavation and shaping: Excavate tree pits to a size of 50cm × 50cm × 50cm, shaping the bottom of the pit into a pot-like shape with the center 4cm lower than the perimeter. In the center of the pot-like bottom, excavate a 10cm diameter, 15cm deep water collection hole. Fill the water collection hole with zeolite particles that have been soaked in a saturated calcium chloride solution for 12 hours and then dried until they are flush with the bottom of the pot. The zeolite particles have a particle size of 2-5mm and a porosity of 42%.

[0040] Preparation of the improved material: A composite improver was obtained by uniformly mixing breathable and impermeable sand, modified biochar, and well-rotted sheep manure at a mass ratio of 10:2:3. The breathable and impermeable sand had an air permeability coefficient of 1.2 × 10⁻⁶. -3 cm / s, seepage prevention coefficient is 8.5×10 -8The particle size distribution was 0.1-0.5 mm, with 88% of particles being 0.1-0.5 mm. The modified biochar was prepared by pyrolysis of corn stalks at 500℃, soaked in a 0.5 mol / L phosphoric acid solution for 24 hours, and then dried. The particle size was 0.25-1 mm, and the specific surface area was 320 m² / s. 2 / g; The organic matter content of well-rotted sheep manure is 48%, and the moisture content is 28%.

[0041] Layered backfilling: The excavated topsoil and subsoil are placed separately. First, a 5cm thick layer of subsoil is laid at the bottom of the tree pit and moderately compacted. Then, the composite soil conditioner is thoroughly mixed with the topsoil at a volume ratio of 4.5%, and backfilled into the tree pit in two layers. The lower layer of backfill soil has a permeable and impermeable sand content of 5% by volume and a thickness of 20cm, and is moderately compacted after backfilling. The upper layer of backfill soil has a permeable and impermeable sand content of 4.5% by volume and a thickness of 20cm, and is moderately compacted after backfilling. The final backfill surface is 6cm higher than the original ground level.

[0042] Planting and Transplanting: Select two-year-old Pinus tabuliformis seedlings of uniform height, with intact root systems and free from pests and diseases. Dig a suitable planting pit in the center of the backfilled planting hole, place the seedling in the pit, straighten it, ensuring the roots are naturally spread out, and fill the pit with soil in layers, tamping it down. The planting depth should be such that the root collar is level with the ground. Immediately after planting, water thoroughly, using 25L of water per seedling. After the water has completely seeped in, cover the tree basin with a 5cm thick layer of wheat straw.

[0043] Post-planting management: In the first year after planting, water once each in mid-May (greening-up period), early July (rapid growth period), and early November (before wintering), using drip irrigation, with each watering volume being 18L / plant. From the second year onwards, apply well-rotted sheep manure twice a year, in early April and late October, at a rate of 6kg / plant, using a circular trench application method at a depth of 25cm. Collect soil samples from the planting hole at a depth of 0-20cm twice a year, in June and September, to determine the pH value.

[0044] Experimental Results and Analysis: After 15 months of continuous monitoring, the soil pH, seedling survival rate, and growth of each treatment group are shown in the table below:

[0045] As can be seen from the table, the soil pH value of treatment group 1 decreased the most, reaching 0.41 units, which was significantly better than other treatment groups. The pH values ​​of treatment groups 2 and 3 also decreased, but the decrease was significantly smaller than that of treatment group 1, and the effect of the 10% dose was not as good as that of the 5% dose, which is consistent with the results of existing studies. The soil pH value of the control group not only did not decrease, but also increased slightly, which was due to salt accumulation on the surface.

[0046] Regarding seedling survival rate, treatment group 1 achieved 100%, while the other treatment groups all reached 90%. In terms of annual shoot growth, treatment group 1 had an average growth of 4.5 cm, which was 32.4% higher than the control group and significantly higher than treatment group 2 (11.8%) and treatment group 3 (5.9%). This indicates that the comprehensive improvement method of this invention can significantly improve the growth environment of *Pinus tabuliformis* and promote seedling growth.

[0047] Furthermore, in this invention, treatment group 1 was watered only 4 times during the entire experiment (including the initial watering), while the control group was watered 8 times, saving 50% of irrigation water. At the same time, the seedlings in treatment group 1 grew vigorously with dark green leaves and no obvious diseases or pests, while 2 seedlings in the control group showed early leaf drop.

[0048] Example 2: Improvement Experiment of Severely Saline-Alkali Land in Shanggou, Lianhua Town, Linxia County This experiment was conducted at the Shanggou test site in Lianhua Town, Linxia County. The soil type in this area is red sandy soil, which has relatively good water retention capacity but high alkalinity. The initial pH value of the soil was measured to be 9.25-9.38 before the experiment, indicating that it is a severely saline-alkali land.

[0049] Experimental design: Four treatment groups were set up, with 20 thornless Sichuan pepper seedlings in each group. The tree pits were all 50cm×50cm×50cm in size.

[0050] Treatment Group 1 (Method of the present invention): The method of the present invention is improved according to the technical solution of the present invention, and the appropriate dosage of the permeable and impermeable sand is determined to be 6.5% by volume based on the soil pH value.

[0051] Treatment Group 2 (single 5% permeable impermeable sand): Using existing technology, 5% permeable impermeable sand by volume is uniformly mixed with topsoil and then backfilled. Other aspects are the same as in Treatment Group 2 of Example 1.

[0052] Treatment Group 3 (single 10% permeable impermeable sand): 10% permeable impermeable sand by volume is mixed evenly with topsoil and then backfilled. Other aspects are the same as in Treatment Group 2 of Example 1.

[0053] Control group (traditional method): No amendments were added, and the original soil was used for backfilling, with conventional management. Specific implementation steps

[0054] Soil baseline determination: Five sampling points were randomly selected within the test area, and soil samples were collected from a depth of 0–20 cm. After thorough mixing, the pH value was measured, and the average pH value was 9.31. Based on the dosage matching standard of this invention, the suitable dosage of the permeable and impermeable sand was determined to be 6.5% by volume.

[0055] Tree pit excavation and shaping: Excavate tree pits according to the specifications of 50cm×50cm×50cm, and shape the bottom of the tree pit into a pot-shaped form with the center 5cm lower than the perimeter. In the center of the pot bottom, dig a water collection hole with a diameter of 10cm and a depth of 15cm, and fill it with zeolite particles that have been soaked in saturated calcium chloride solution until it is flush with the bottom of the pot.

[0056] Preparation of the modified material: Breathable and impermeable sand, modified biochar, and well-rotted sheep manure were mixed evenly at a mass ratio of 10:2:3 to obtain a composite modifier. The specifications of each material were the same as in Example 1.

[0057] Layered backfilling: First, lay a 5cm thick layer of subsoil at the bottom of the tree pit and compact it. Then, thoroughly mix the composite soil conditioner with the topsoil at a volume ratio of 6.5%, and backfill in two layers. The lower layer of backfill soil contains 7% permeable and impermeable sand by volume and is 20cm thick; the upper layer of backfill soil contains 6.5% permeable and impermeable sand by volume and is 20cm thick. The surface of the backfill soil is 7cm higher than the original ground level.

[0058] Seedling planting and transplanting: Select healthy, disease-free, one-year-old Sichuan pepper seedlings and plant them according to the method in Example 1. Immediately after planting, water thoroughly to settle the roots, using 30L of water per seedling. After the water has completely seeped in, cover the tree basin with a 5cm thick layer of corn stalks.

[0059] Post-planting management: In the first year after planting, water once each in early May, mid-July, and early November, with each watering volume being 20L / plant. From the second year onwards, apply well-rotted sheep manure once each in early April and late October, with an application rate of 8kg / plant. Measure the soil pH value in June and September each year. When the pH value rises by more than 0.3 units, spray the leaves with a 0.5% potassium dihydrogen phosphate solution.

[0060] Experimental Results and Analysis: After 15 months of continuous monitoring, the experimental results for each treatment group are shown in the table below:

[0061] As can be seen from the table, under severely saline-alkali soil conditions, treatment group 1 of this invention still showed good improvement effects. The soil pH value decreased by 0.21 units, which, although smaller than that of mildly saline-alkali soil, was significantly better than other treatment groups. The pH values ​​of treatment groups 2 and 3 decreased by a smaller amount, at 0.08 and 0.12 units respectively, while the pH value of the control group increased slightly.

[0062] Regarding seedling survival rate, treatment group 1 achieved 100%, while treatment group 2 reached 90%, and treatment group 3 and the control group both reached 85%. In terms of annual shoot growth, treatment group 1 had an average growth of 32.2 cm, which was 34.2% higher than the control group and significantly higher than treatment group 2 (10.4%) and treatment group 3 (7.5%). This indicates that the method of the present invention can still effectively improve the soil environment and increase the survival rate and growth of Sichuan pepper even under severely saline-alkali soil conditions.

[0063] Furthermore, the Sichuan pepper trees in treatment group 1 exhibited lush green leaves and numerous fruiting branches, while three seedlings in the control group showed yellowing leaves and premature leaf drop, with some plants exhibiting weakened growth. Treatment group 1 was watered four times throughout the experiment, while the control group was watered nine times, saving over 55% of irrigation water.

[0064] Example 3: Experiment on the improvement of moderately saline-alkali land in Youjiayuan Village, Xianyuan Town, Yongjing County This experiment was conducted at the Youjiayuan Village test site in Xianyuan Town, Yongjing County. The soil type in this area is loess soil, which is deep but has poor fertilizer retention capacity. Before the experiment, the initial pH value of the soil was measured to be 8.32~8.81, which is classified as moderately saline-alkali land.

[0065] Experimental design: Four treatment groups were set up, with 20 pear seedlings in each group. The tree pits were all 50cm×50cm×50cm in size.

[0066] Treatment Group 1 (Method of the present invention): The method of the present invention is improved according to the technical solution of the present invention, and the appropriate dosage of the permeable and impermeable sand is determined to be 5.5% by volume based on the soil pH value.

[0067] Treatment Group 2 (single 5% permeable impermeable sand): Using existing technology, 5% permeable impermeable sand by volume is uniformly mixed with topsoil and then backfilled. Other aspects are the same as in Treatment Group 2 of Example 1.

[0068] Treatment Group 3 (single 10% permeable impermeable sand): 10% permeable impermeable sand by volume is mixed evenly with topsoil and then backfilled. Other aspects are the same as in Treatment Group 2 of Example 1.

[0069] Control group (traditional method): No amendments were added, and the original soil was used for backfilling, with conventional management. Specific implementation steps

[0070] Soil baseline determination: Five sampling points were randomly selected within the test area, and soil samples were collected from a depth of 0–20 cm. After thorough mixing, the pH value was measured, and the average pH value was 8.56. Based on the dosage matching standard of this invention, the suitable dosage of the permeable and impermeable sand was determined to be 5.5% by volume.

[0071] Tree pit excavation and shaping: Excavate tree pits according to the specifications of 50cm×50cm×50cm, and shape the bottom of the tree pit into a pot-shaped form with the center 3cm lower than the perimeter. In the center of the pot bottom, dig a water collection hole with a diameter of 10cm and a depth of 15cm, and fill it with zeolite particles that have been soaked in saturated calcium chloride solution until it is flush with the bottom of the pot.

[0072] Preparation of the modified material: Breathable and impermeable sand, modified biochar, and well-rotted sheep manure were mixed evenly at a mass ratio of 10:2:3 to obtain a composite modifier. The specifications of each material were the same as in Example 1.

[0073] Layered backfilling: First, lay a 5cm thick layer of subsoil at the bottom of the tree pit and compact it. Then, thoroughly mix the composite soil conditioner with the topsoil at a volume ratio of 5.5%, and backfill in two layers. The lower layer of backfill soil has a permeable and impermeable sand content of 6% by volume and a thickness of 20cm; the upper layer of backfill soil has a permeable and impermeable sand content of 5.5% by volume and a thickness of 20cm. The surface of the backfill soil is 5cm higher than the original ground level.

[0074] Seedling planting and transplanting: Select healthy, three-year-old pear seedlings with intact root systems and plant them according to the method in Example 1. Immediately after planting, water thoroughly to settle the roots, using 30L of water per seedling. After the water has completely seeped in, cover the tree basin with a 5cm thick layer of wheat straw.

[0075] Post-planting management: In the first year after planting, water once each in mid-May, early July, and early November, with each watering volume being 20L / plant. From the second year onwards, apply well-rotted sheep manure once each in early April and late October, with an application rate of 10kg / plant. Measure the soil pH value in June and September each year, and adjust it with foliar fertilization if necessary.

[0076] Experimental Results and Analysis: After 15 months of continuous monitoring, the experimental results for each treatment group are shown in the table below:

[0077] As can be seen from the table, the soil pH value of treatment group 1 decreased by 0.49 units, which was the largest decrease among the three examples. This is related to the soil characteristics of Youjiayuan Village. The pH values ​​of treatment groups 2 and 3 decreased by 0.27 and 0.25 units, respectively, while the pH value of the control group increased slightly.

[0078] Regarding seedling survival rate, treatment group 1 achieved 100%, while treatment group 2 achieved 90%, and treatment group 3 and the control group both reached 85%. In terms of annual shoot growth, treatment group 1 had an average growth of 43.0 cm, which was 22.9% higher than the control group and significantly higher than the 10.0% of treatment group 2 and the 1.4% of treatment group 3. This indicates that the method of the present invention has a very significant effect on improving pear trees under moderately saline-alkali soil conditions.

[0079] Furthermore, the pear trees in treatment group 1 of this invention have a reasonable tree structure, robust branches, and good flower bud differentiation, and are expected to bear fruit in the second year. In contrast, the pear trees in the control group grow slowly, have thin and weak branches, and have fewer flower buds. Treatment group 1 was watered 4 times during the entire experiment, while the control group was watered 8 times, saving 50% of irrigation water.

[0080] The experimental results of the three embodiments above show that the method of improving tree pit soil in saline-alkali land based on the use of appropriately sized breathable and impermeable sand in this invention exhibits good improvement effects under mild, moderate, and severe saline-alkali land conditions. Compared with the prior art, this invention can more effectively reduce soil pH, improve seedling survival rate and growth, while significantly saving water resources and reducing maintenance costs.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving tree pit soil in saline-alkali land using appropriately sized, breathable, and impermeable sand, characterized in that... Includes the following steps: (1) Soil baseline measurement: Soil samples were collected from a depth of 0 to 20 cm in the proposed planting area, and the initial pH value was measured. The appropriate dosage of permeable and impermeable sand was determined according to the pH range: when pH is 8.0 to 8.5, the appropriate dosage is 4% to 5% by volume; when pH is 8.5 to 9.0, the appropriate dosage is 5% to 6% by volume; when pH is 9.0 to 9.5, the appropriate dosage is 6% to 7% by volume. (2) Tree pit excavation and shaping: Excavate a tree pit with a length × width × depth of 50cm × 50cm × 50cm. Shape the bottom of the tree pit into a pot-shaped pit with the center lower than the surrounding area by 3~5cm. Excavate a water collection hole with a diameter of 10cm and a depth of 15cm in the center of the pot bottom. Fill the water collection hole with zeolite particles with a particle size of 2~5mm until it is level with the bottom of the pot. (3) Preparation of modified materials: The air-permeable and impermeable sand, modified biochar, and decomposed sheep manure were mixed evenly at a mass ratio of 10:2:3 to obtain a composite modifier; the modified biochar was corn straw biochar that had been soaked in 0.5 mol / L phosphoric acid solution for 24 h and then dried. (4) Layered backfilling: The excavated topsoil and subsoil are placed separately. First, a 5cm thick layer of subsoil is laid at the bottom of the tree pit and compacted. Then, the composite amendment and topsoil are thoroughly mixed according to the appropriate dosage determined in step (1). The mixture is backfilled into the tree pit in two layers, each layer being 20cm thick. After each layer is backfilled, it is compacted appropriately. The surface of the backfill soil is 5-8cm higher than the original ground surface. (5) Planting and planting of seedlings: Dig a planting pit in the center of the backfilled tree pit, put the seedling into the pit and straighten it so that the roots can spread out. Fill the soil in layers and tamp it down. The planting depth should be such that the root neck is level with the ground or slightly higher by 1-2 cm. Water thoroughly after planting. After the water has completely seeped in, cover the tree basin with a 5 cm thick straw covering layer.

2. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: In step (1), at least 5 soil samples were collected from each proposed planting area, mixed evenly, and the pH value was measured. The measurement method was the potentiometric method specified in NY / T1121.

3. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: In step (2), the porosity of the zeolite particles in the water collection hole is 40%~45%. The zeolite particles are soaked in saturated calcium chloride solution for 12 hours and then dried.

4. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: In step (3), the air permeability coefficient of the permeable sand is ≥1×10⁻⁶. -3 cm / s, seepage prevention coefficient ≤1×10 -7 cm / s, with a particle size distribution of 0.1~0.5mm accounting for ≥85%.

5. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: In step (3), the modified biochar has a particle size of 0.25~1mm and a specific surface area ≥300m². 2 / g, the organic matter content of well-rotted sheep manure is ≥45%, and the moisture content is ≤30%.

6. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: In step (4), when backfilling in layers, the permeable and impermeable sand content of the lower layer of backfill soil is 0.5% to 1% higher by volume than that of the upper layer.

7. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: It also includes post-planting management steps: In the first year after planting, water once each during the greening period, the rapid growth period, and before overwintering, using drip irrigation, with each irrigation amount being 15-20L / plant; Starting from the second year, apply well-rotted organic fertilizer once each in spring before sprouting and in autumn after leaf fall, with a fertilizer amount of 5-10kg / plant.

8. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 7, characterized in that: Post-planting management also includes dynamic monitoring of salt content: soil samples are collected from the tree pit at a depth of 0-20cm in June and September each year to measure pH value and soluble salt content. When the pH value rises by more than 0.3 units, foliar spraying with 0.5% potassium dihydrogen phosphate solution is carried out 2-3 times, with an interval of 7-10 days between each application.

9. The method for improving saline-alkali soil for tree pits based on the use of appropriately sized breathable and impermeable sand according to claim 1, characterized in that: The seedlings are any one of the following: Chinese pine, golden elm, Sichuan pepper, or pear.

10. The method for improving tree pit soil in saline-alkali land based on the use of appropriate dosage of breathable and impermeable sand, as described in claim 1, is applied to afforestation and greening in arid and semi-arid saline-alkali land with a pH of 8.0 to 9.5.

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