Method for improving farmland soil by deep burying and returning decomposed straw to field to prevent salinization

Abstract

This invention relates to a method for improving arable soil by deep burying decomposed straw to prevent salinity and alkalinity. The method includes: 1) deep loosening of the soil, including deep loosening of the arable land to form trenches with a depth of not less than 45 cm; 2) straw filling, including evenly filling the trenches with pre-decomposed straw (approximately 6 days old) to form a biobarrier layer with a bulk density of 0.4-0.6 g / cm³; and 3) topsoil backfilling, including covering with topsoil to construct an improved arable soil with a low-salt, fertile upper layer and a salt-intercepting lower layer. This invention thoroughly breaks down the plow pan through deep burial (45-70 cm), constructing a long-lasting salt-blocking barrier, optimizing the thickness and compaction of the barrier layer, and achieving spatial separation of salt interception at depth and nutrient enrichment at the surface.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali land management and resource utilization technology, specifically to a saline-alkali land salt-blocking process achieved through straw pretreatment control, deep burial physical configuration optimization and microbial niche engineering, that is, a method for decomposing straw, burying it deep and returning it to the field to block salinity and improve arable soil. Background Technology

[0002] Currently, salt-blocking technologies for improving saline-alkali land mainly focus on constructing artificial isolation layers to cut off the capillary channels through which deep salt rises with groundwater. For example, physical materials such as plastic films and gravel are used to cut these capillaries, but these materials are difficult to degrade and do not improve soil quality. Some studies have also explored chemical control methods, such as applying gypsum or polymers. While these methods can regulate ion balance, they cannot provide a long-term physical barrier and pose a risk of secondary pollution. Traditional biological isolation methods involve pulverizing crop straw and returning it to the field. Current methods typically control the straw's return depth to 30-40 cm, using its porous structure to block salt. Although biological isolation methods (straw return) have ecological advantages, they face the following serious technical bottlenecks in practical applications:

[0003] (1) Material acquisition and sustainability issues: The existing technology has a shallow burial depth (≤40 cm), which cannot completely break the hard "sticky layer" or "plow pan". This not only allows deep salt to rise through capillary tubes, but also restricts the extension of crop roots to deeper layers, causing the phenomenon of "soil layer caving", which is harmful to the growth of subsequent crops.

[0004] (2) If untreated dry straw is buried directly, it will undergo intense anaerobic or semi-anaerobic fermentation in the soil. The heat and organic acids generated in this process can easily lead to "root and seedling burn", and the slow decomposition of straw will consume a large amount of nitrogen, competing with crops for fertilizer.

[0005] (3) Traditional methods lack precise control over the degree of straw decomposition. Excessive decomposition will cause the straw to lose its fiber skeleton, causing the physical barrier layer to collapse and lose its ability to intercept water migration; while insufficient decomposition will not effectively improve the soil's microbial ecology. Summary of the Invention

[0006] Research has found that the core problem with traditional biological isolation methods lies in the lack of balance between "maintaining physical configuration" and "eliminating fermentation heat damage" in the pre-decomposition of straw. There is also a lack of systematic research on the bulk density and compaction of salt-blocking layers at great depths (≥45 cm), which makes it impossible to form a stable "biological interception barrier" in severely saline-alkali environments.

[0007] The purpose of this invention is to provide a synergistic technology of "mild decomposition + deep burial + precise parameter control," aiming to solve the problems of insufficient traditional straw return depth, straw burning of seedlings, and asynchronous salt inhibition and soil improvement. It utilizes readily available straw resources, providing organic matter and microbial diversity through pre-decomposition treatment. Deep burial (45-70cm) thoroughly breaks up the plow pan, constructing a long-lasting salt barrier, optimizing the thickness and compaction of the barrier layer, and achieving spatial separation of salt interception at depth and nutrient enrichment at the surface.

[0008] More specifically, the present invention provides a method for deep burial of decomposed straw to prevent salinity and improve arable soil, comprising:

[0009] 1) Deep loosening and soil breaking, including deep loosening of cultivated land to form deep trenches with a depth of not less than 45cm;

[0010] 2) Straw filling, including evenly filling pre-composted straw (approximately 6 days old) into excavated deep trenches to form a biobarrier layer with a bulk density of 0.4-0.6 g / cm³, for example, 0.5 g / cm³; and

[0011] 3) Topsoil backfilling, including topsoil covering, to create an improved arable soil with a low-salt, fertile upper layer and a salt-intercepting lower layer.

[0012] According to an embodiment of the present invention, the depth of the deep trench is 45-70 cm, for example, 45-55 cm.

[0013] According to an embodiment of the present invention, the straw is corn straw; of course, other straws, such as sorghum, wheat, etc., can also be used; these straws can be crushed to a particle size of 10-20 mm.

[0014] According to an embodiment of the present invention, the pre-composting includes inoculating with a cellulose-degrading microbial agent at a weight ratio of 4-7%, adjusting the moisture content to 60%-65%, and composting at room temperature. Cellulose-degrading microorganisms may be, for example, *Pseudomonas sp.*, etc.

[0015] According to an embodiment of the present invention, the thickness of the bio-barrier layer is 5-10 cm, for example, 5-8 cm.

[0016] According to an embodiment of the present invention, in step 2), the filled straw is mechanically layered and compacted to form the biobarrier layer.

[0017] Compared with existing technologies, this invention provides a method for decomposing straw, deeply burying it in the field, and returning it to the soil to prevent salinity and improve arable land, which can achieve beneficial effects:

[0018] Strong salt-blocking and anti-salt-returning capabilities: By controlling the burial depth of 45-70cm and the bulk density of 0.5 g / cm³, it effectively blocks the migration of salt with water, reducing the surface conductivity by more than 30%.

[0019] Continuously improve soil quality: Decomposed straw can continuously release organic matter, promote the formation of soil aggregates, reduce soil pH by 0.5-1.2, and increase microbial biomass carbon by ≥50%;

[0020] Crop growth environment safety: Through 6 days of targeted decomposition pretreatment, the fermentation heat damage caused by uncomposted straw burial is completely eliminated, ensuring the survival rate of plants (≥95%).

[0021] Highly efficient resource utilization: By using readily available straw from the fields as soil improvement material, treatment costs are reduced, and the resource utilization of agricultural waste is realized. Attached Figure Description

[0022] Figure 1 A flowchart of a method for deep burial of decomposed straw to prevent salinity and improve arable soil;

[0023] Figure 2 The graph shows the change in electrical conductivity EC during the straw decomposition process in Example 1.

[0024] Figure 3 The effect of straw interlayers with different decomposition degrees on soil electrical conductivity EC in Example 2: (a) upper interlayer; (b) lower interlayer.

[0025] Figure 4 The effect of the straw decomposition interlayer on the longitudinal variation of soil electrical conductivity EC in Example 2: (a) Day 20; (b) Day 50.

[0026] Figure 5 The effect of the straw decomposition interlayer on soil ammonia nitrogen content in Example 2: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0027] Figure 6 The effect of the straw decomposition interlayer on soil nitrate nitrogen content in Example 2: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0028] Figure 7 The effect of the straw decomposition interlayer on the available phosphorus content of the soil in Example 2: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0029] Figure 8 The effect of the straw decomposition interlayer on the available potassium content in the soil in Example 2: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0030] Figure 9The effect of the straw decomposition interlayer on soil organic matter content in Example 2: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0031] Figure 10 The effect of different interlayer thicknesses and compaction on soil electrical conductivity EC in Example 3: (a) upper interlayer; (b) lower interlayer.

[0032] Figure 11 The effects of interlayer thickness and compaction on the longitudinal variation of soil electrical conductivity EC in Example 3: (a) Day 20; (b) Day 50.

[0033] Figure 12 The effects of the thickness and compaction of the interlayer on the ammonia nitrogen content in soil in Example 3: (a) upper layer of the interlayer; (b) lower layer of the interlayer.

[0034] Figure 13 The effect of the thickness and compaction of the partition layer on the nitrate nitrogen content of the soil in Example 3: (a) upper partition layer; (b) lower partition layer.

[0035] Figure 14 The effect of the thickness and compaction of the interlayer on the available phosphorus content of the soil in Example 3: (a) upper layer of interlayer; (b) lower layer of interlayer.

[0036] Figure 15 The effect of the thickness and compaction of the interlayer on the available potassium content in the soil in Example 3: (a) upper layer of interlayer; (b) lower layer of interlayer.

[0037] Figure 16 The effects of the thickness and compaction of the partition layer on the soil organic matter content in Example 3: (a) upper partition layer; (b) lower partition layer. Detailed Implementation

[0038] 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.

[0039] like Figure 1 As shown in the figure, the principle and steps of the method for deep burial of decomposed straw to prevent salinity and improve arable soil according to the embodiment of the present invention are as follows:

[0040] 1. Pretreatment process for salt-barrier materials (control of mild corrosion)

[0041] Inoculation with microbial agents: Select corn stalks, crush them to 10-20mm, and inoculate them with cellulose-degrading microbial agents (such as Pseudomonas sp., etc.) at a weight ratio of 5%; Decomposition cycle setting: Use highly efficient microbial groups for on-site pre-decomposition, and precisely control the time to 6 days (light decomposition).

[0042] Key advantages: Mild decomposition solves the problem of seedling burn caused by uncomposted straw, while preserving the complete fiber skeleton and porous structure of the straw. It can effectively block capillary flow and release organic acids to drive sodium-calcium replacement in the soil.

[0043] 2. Development of physical configuration parameters for the interlayer

[0044] Landfill depth: The depth is set at 45-70cm (preferably 45-55cm) to completely break up the hard, sticky layer and cut off the upward path of deep salt; Intermediate layer thickness: The core salt-blocking layer thickness is set at 5-10cm (preferably 8cm) to provide sufficient salt interception capacity; Compaction degree (bulk density): Mechanical compaction is used to achieve a bulk density of 0.4-0.6g / cm³, preferably 0.5g / cm³. Under these conditions, the pores formed by the straw fibers are mainly micropores and closed pores, resulting in the highest physical salt-blocking efficiency.

[0045] 3. Technical Implementation Steps

[0046] Deep tillage: Deep tillage operations with a depth of ≥45cm are carried out using specialized equipment.

[0047] Straw filling: Evenly fill the dug trenches with pre-composted straw that has been decomposed for 6 days, ensuring a filling uniformity of ≥90%.

[0048] Layered compaction: The compaction process ensures the tightness of the interlayer, forming a stable biobarrier layer.

[0049] Topsoil backfilling: Covering the topsoil to create a spatial pattern of "low-salt and fertile upper layer and salt-intercepting lower layer".

[0050] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0051] Example 1: Preparation of straw pre-decomposition and inhibition-removing salt materials

[0052] I. Experimental Materials

[0053] 1. Straw raw material: Select corn stalks and crush them to a particle size of 10-20mm.

[0054] 2. Microbial agent: Cellulose-degrading microbial agent (Pseudomonas sp., etc.), inoculated at 5% of the straw weight.

[0055] 3. Saline-alkali soil: Soil samples were collected from the surface (0-20cm) and deep (40-60cm) layers of severely saline-alkali land at an experimental station in North China.

[0056] II. Experimental Methods and Results

[0057] 1. Straw pre-composting treatment

[0058] Crushed corn stalks were inoculated with a cellulose-degrading microbial agent at a weight ratio of 5%, and the moisture content was adjusted to 60%-65%. The stalks were then composted at room temperature. Two treatment groups were established: one with 6 days of composting (light composting) and the other with 12 days of composting (moderate composting). A control group of uninoculated stalks was also included. The temperature and electrical conductivity of the compost pile were monitored daily during the composting process.

[0059] The measuring instruments and methods are as follows:

[0060] (1) Soil electrical conductivity

[0061] Soil samples were air-dried naturally, passed through a 2 mm sieve, mixed with water at a ratio of 5:1, and shaken at 25℃ for 1 hour. The supernatant was collected and the soil conductivity was measured using a DDS-307A conductivity meter (Shanghai Leici).

[0062] The results are as follows Figure 2 As shown, the electrical conductivity (EC) of straw during decomposition initially increased and then decreased with increasing decomposition time. On day 0, the straw conductivity reached 3.5 mS / cm, due to mechanical damage caused by pretreatment, increased cell membrane permeability, and rapid dissolution of intracellular potassium, chloride, nitrate, and organic acid ions. On day 6, the straw retained its complete fibrous skeleton and porous structure, with a moderate electrical conductivity. The conductivity of groups T1 and T2, inoculated with the microbial agent, dropped below 2.0 mS / cm, while the CK group was at 2.6 mS / cm. The significantly lower EC during the high-temperature period was due to the rapid assimilation of soluble salts by functional microorganisms for cell synthesis and salt transfer to the solid phase, while the high-temperature alkaline environment promoted the loss of ammonium salts in the form of ammonia. On day 12, the EC of group T2 slightly increased but did not exceed 2.5 mS / cm, indicating that its microbial succession was faster than the control group. The straw structure underwent significant degradation, with partial collapse of the fibrous skeleton. Slightly decomposed (6 days) straw eliminates the risk of "burning seedlings" that may be caused by directly burying undecomposed straw, while retaining an effective physical barrier structure.

[0063] Example 2: The effect of straw interlayers with different degrees of decomposition on soil salinity migration

[0064] I. Soil Column Simulation Experiment

[0065] A soil column was used to simulate a saline-alkali soil environment to study the regulatory effect of straw interlayers with different degrees of decomposition on soil water and salt transport. The experimental setup consisted of a transparent acrylic soil column (10 cm inner diameter, 60 cm high), with a straw interlayer placed in the middle (30-35 cm) of the soil column. The thickness of the interlayer was uniformly 5 cm, and the bulk density was 0.2 g / cm³.

[0066] The following experimental treatment groups were set up (see Table 1):

[0067] Table 1: Experimental Groups of Straw Decomposition

[0068]

[0069] Each group had three replicates. Salt water was continuously supplied to the bottom of the soil column (simulating groundwater rise) to simulate a 50-day salt migration process. Soil samples were taken from the upper and lower layers of the interlayer every 5-10 days. The contents of ammonia nitrogen, nitrate nitrogen, available phosphorus, available potassium, and organic matter were determined using a YT-TR01 high-intelligence soil nutrient analyzer. Soil electrical conductivity (EC) and pH were measured using a DDS-307A conductivity meter (Shanghai Leici).

[0070] The specific measurement method is as follows:

[0071] (1) Ammonia nitrogen determination

[0072] Nessler's reagent colorimetric method. Take 2.00 g of air-dried soil sample and place it in a 50 mL centrifuge tube. Add 10 mL of 2 mol / L KCl extraction solution and a level spoonful of decolorizing agent. Extract by shaking at 200 rpm for 60 min in a 25 ℃ constant-temperature shaker. After centrifuging the extract at 5000 rpm for 10 min, pass the supernatant through a 0.45 μm mixed cellulose filter membrane and collect the filtrate. Accurately transfer 2.00 mL of the filtrate to a 50 mL colorimetric tube and dilute to the mark with ultrapure water. Add 0.5 mL of potassium sodium tartrate solution and 0.75 mL of Nessler's reagent sequentially, mix thoroughly, and let stand in the dark for 10 min. Using the same batch of ultrapure water as a blank control, measure the absorbance at 420 nm using a 1 cm cuvette.

[0073] (2) Nitrate determination

[0074] Accurately transfer 1.00 mL of the supernatant after centrifugation (which can be pre-diluted if necessary) into a 25 mL colorimetric tube, and bring the volume to 10 mL with ultrapure water. Equilibrate the tube in a 20 °C water bath for 20 min. Add 1 mL of 1 mol / L hydrochloric acid solution and 0.1 mL of sulfamic acid solution sequentially to remove nitrite interference, mix thoroughly, and then bring the volume to 25 mL. Using ultrapure water as a blank, measure the absorbance at 220 nm and 275 nm wavelengths, calculate the corresponding values ​​using the calibration formula, and plot a standard curve.

[0075] (3) Determination of available phosphorus and available potassium

[0076] Weigh a soil sample and place it in a container. Add soil extractant at a soil-to-water ratio of 1:20 and an appropriate amount of decolorizing agent. Place the mixture in a 25℃ water bath shaker and shake for 3 minutes. After settling for 5 minutes, filter through 11 cm diameter medium-speed qualitative filter paper and collect the supernatant. Add appropriate reagents to the supernatant and perform analysis using a high-intelligence soil nutrient analyzer (YT-TR01, Shandong Yuntang).

[0077] (4) Determination of organic matter

[0078] Soil samples were mixed with extractant at a soil-to-water ratio of 1:5. The mixture was then shaken in a 25°C water bath for 5 minutes, allowed to settle for 5 minutes, and then filtered through 11 cm diameter medium-speed qualitative filter paper. The supernatant was collected. The supernatant was then mixed with appropriate reagents and analyzed using a high-intelligence soil nutrient analyzer (YT-TR01, Shandong Yuntang).

[0079] (5) Measurement of soil pH

[0080] Soil pH value determination requires air-drying the soil sample naturally and then passing it through a 2 mm sieve. Deionized water is added at a water-to-soil ratio of 5:1, and the sample is kept at 25℃ and shaken for 1 hour. The supernatant is then collected and measured using a DDS-307A conductivity meter (Shanghai Leici).

[0081] II. Stacking effect testing

[0082] 1. The effect of straw interlayer on soil electrical conductivity (EC)

[0083] Whether the electrical conductivity profile shows a "cliff-like" drop at the interlayer interface is the core indicator for judging whether straw still has the ability to physically block salt.

[0084] The results are as follows Figure 3 and 4 As shown in the figure, soil column experiments with straw interlayers at different degrees of decomposition revealed that the changes in soil electrical conductivity over 50 days clearly reflected the salt-blocking effect. As indicated, the EC of the upper layer CK group increased significantly from 1137 μS / cm to 3750 μS / cm, a 2.3-fold increase, exhibiting typical surface salt accumulation. In contrast, the EC of the other experimental groups remained relatively stable, with almost no change in the CB1-12 group, and the lowest at 50 days in the CB1-6 group at only 975 μS / cm. At the 25–35 cm interlayer depth, the EC of the CK group first increased and then decreased, while the changes in the experimental groups were gradual, forming a profile of low salt in the upper layer and high salt in the lower layer. The higher EC in the lower layer of the C-6, C-12, and CB2-12 groups after 50 days indicates that the straw interlayer effectively blocked the upward movement of salt, keeping the upper layer EC stable, and demonstrating a significantly better salt-blocking effect than the control group.

[0085] Whether a significant gradient is formed in the electrical conductivity profile at the interlayer interface directly determines whether the straw still possesses complete physical barrier capabilities at this stage of decomposition. The results are as follows: Figure 4 As shown in the longitudinal changes, based on the changes in electrical conductivity profiles of the soil column over 20 and 50 days, EC first increases and then decreases with depth, reaching a peak near the 30–40 cm interlayer. Groundwater brine migrates upwards under transpiration and is intercepted and retained by the straw interlayer, forming a distinct salt-enriched zone. The EC in the 10–20 cm soil layer decreases significantly, indicating that the interlayer effectively cuts off the upward flow of salt, preventing continuous salt replenishment to the upper layer and resulting in a significant decrease in salt concentration. Over time, the difference between the control (CK) group and the treatment group widens dramatically: at 20 days, the EC of the CK group is 1.3 times the average of the experimental groups, rising to 3.38 times at 50 days. In the CK group without an interlayer, salt continues to accumulate on the surface, while in the treatment group, a sharp drop in EC occurs at the interlayer interface, indicating that salt is stably locked in the lower layer. The results show that decomposed straw can effectively disrupt capillaries, achieving deep salt retention and significantly inhibiting surface salt return.

[0086] 2. The impact of straw interlayers on soil ammonia nitrogen content

[0087] The results are as follows Figure 5 As shown, the straw interlayer significantly affected the ammonia nitrogen content in both the upper and lower soil layers within 50 days. On day 5, the surface ammonia nitrogen content was low, as the saline solution did not reach the surface, resulting in no significant effect. From days 5 to 20, the straw rapidly mineralized, releasing ammonium nitrogen, leading to a substantial increase in upper-layer ammonia nitrogen. All experimental groups showed significantly higher levels than the control group, with the mildly decomposed straw group showing the most pronounced effect. From days 30 to 50, ammonia nitrogen tended to stabilize, with some groups showing a decrease due to enhanced nitrification, converting ammonium nitrogen to nitrate nitrogen. Overall, ammonia nitrogen in the lower layer continuously increased, with the control group consistently lower than the experimental groups. The straw interlayer hindered the upward movement of ammonia nitrogen with water, and coupled with the ease with which ammonia nitrogen was adsorbed by soil colloids, significant enrichment occurred in the lower layer, with the decomposed straw treatment group exhibiting the highest peak ammonia nitrogen accumulation.

[0088] 3. The impact of straw interlayers on soil nitrate nitrogen content

[0089] The results are as follows Figure 6 As shown in the 50-day soil column experiment, there were significant differences in the changes of nitrate nitrogen in the soil layers above and below the straw interlayer. The nitrate nitrogen in the upper layer remained stable at around 40 mg / kg for the first 15 days. After 15 days, the control group showed slight fluctuations, while the experimental group with added microbial agents showed a significant increase, stabilizing after 30 days. The initial slow increase in nitrate nitrogen was due to the slow activation of nitrifying bacteria as nitrogen was initially released in the form of ammonia nitrogen. Later, with improved environment and enhanced nitrification, ammonia nitrogen was converted to nitrate nitrogen, leading to an increase in content and a tendency to reach equilibrium. In the lower layer, the control group showed only a slight increase in nitrate nitrogen, while the experimental group saw an increase of 123.95%. Nitrate nitrogen carries a negative charge and is not easily adsorbed, making it easily transported with water. The straw interlayer blocked its upward migration path, causing it to accumulate in the lower layer. Due to the good barrier effect, the decomposed straw treatment resulted in the most significant accumulation of nitrate nitrogen in the lower layer.

[0090] 4. The impact of straw interlayer on soil available phosphorus content

[0091] The results are as follows Figure 7 As shown, the changes in available phosphorus in the upper and lower layers of the straw layer in the soil column experiment were clearly observed. Available phosphorus in the upper layer increased significantly in the first 15 days, with an increase of 138.75% in the control group and 65.10% in the experimental group (CB1-6). This was due to improved aeration and the low-salt microenvironment created by the straw, which promoted microbial proliferation and phosphate mineralization. Available phosphorus decreased significantly from days 15 to 20, as microorganisms entered their vigorous growth phase, fixing a large amount of available phosphorus for cell synthesis, leading to a sharp decrease in available phosphorus in the liquid phase. Available phosphorus in the lower layer generally showed a downward trend, mainly because its phosphorus content was already low, and the available phosphorus released from the upper layer was fixed near the straw layer, making it difficult to migrate downwards for replenishment.

[0092] 5. The effect of straw interlayer on soil available potassium content

[0093] The results are as follows Figure 8 As shown, potassium is an essential nutrient for crops, crucial for growth, development, and quality formation, with soil potassium being its direct source. As illustrated in the figure, the degree of straw decomposition significantly affected the distribution of available potassium in the upper and lower layers during the soil column experiment. Available potassium in the upper layer fluctuated less over the first 30 days, peaking mostly between 15 and 20 days. On day 50, the available potassium in the 6-day decomposition group was significantly higher than that in the 12-day decomposition group, because the longer the decomposition time, the greater the loss of soluble potassium; short-decomposition straw can provide a continuous supply of potassium. Available potassium in the lower layer accumulated continuously in a stepwise manner, with the highest content in the CB2-6 group at 50 days. As potassium ions moved upwards with the water, they were intercepted by the straw layer, while sodium ions largely replaced colloidal adsorbed potassium in the liquid phase, accumulating synchronously with sodium, resulting in a significant increase in available potassium in the lower layer.

[0094] 6. The impact of straw interlayers on soil organic matter content

[0095] The results are as follows Figure 9 As shown, the straw interlayer significantly affected the distribution of soil organic matter in the soil column experiment. The organic matter content in the upper experimental group generally showed an upward trend, increasing slowly in the early stages and accumulating rapidly in the later stages. Straw is rich in organic carbon components, with an intact structure in the early stages, and organic matter is mainly in particulate form, with only a small amount of water-soluble matter and metabolic products diffusing. In the later stages, microbial decomposition is sufficient, forming humus which mixes with the soil, leading to rapid enrichment of organic matter. The organic matter content in the lower layer remained relatively stable at around 2 g / kg, slightly higher in the experimental group than the control group, with a smaller variation. This was mainly due to the interlayer retaining water, which slightly promoted microbial mineralization. Ultimately, a profile distribution of high organic matter in the upper layer and high salinity in the lower layer was formed, achieving the separation of salt damage downwards and fertilization in the upper layer, creating a low-salt, high-organic-matter growth environment for crop roots.

[0096] Example 3: The effect of interlayer thickness and compactness on salt barrier effect

[0097] I. Experimental Design

[0098] To optimize the physical configuration parameters of the straw barrier layer, a soil column simulation experiment was conducted to study the effects of different barrier layer thicknesses and compaction levels (bulk density) on water and salt transport in saline-alkali land. The experimental setup was the same as in Example 2. Straw that had been decomposed for 6 days and inoculated with microbial agents was used as the barrier material, and the barrier layer was placed in the middle of the soil column.

[0099] The following experimental treatment groups were set up (see Table 2):

[0100] Table 2. Soil column simulation experiment groups based on thickness and compaction.

[0101]

[0102] Each group had 3 replicates. Salt water was continuously supplied to the bottom of the soil column to simulate the salt migration process over 50 days, and soil samples were taken periodically to measure various indicators.

[0103] 1. Effects of interlayer thickness and compaction on soil electrical conductivity (EC)

[0104] The results are as follows Figure 10 and 11 As shown in the figure, the 50-day soil column experiment indicates that the thickness and compaction of the straw directly determine the salt-blocking effect. The electrical conductivity of the upper straw layer (CK group) surged from 2185 μS / cm to 6800 μS / cm, an increase of 3.1 times, reflecting strong surface salt accumulation without intervention. The EC of the straw treatment groups remained relatively stable, with the TS8 group (8cm thickness, 0.5g / cm³ compaction) showing the best salt-blocking effect. By disrupting capillaries and forming a dense barrier, it essentially achieved "zero salt penetration." The EC of the lower layer remained relatively stable overall, with all treatment groups showing higher EC values ​​than CK, indicating that salt was effectively trapped near the interlayer. At 50 days, the lower layer electrical conductivity of the TS5, TS8, and LS8 groups was high and tended to stabilize, which is related to salt retention and water-salt redistribution.

[0105] refer to Figure 11 From the longitudinal profile of electrical conductivity, both on days 20 and 50 showed a slight decrease with depth, while the surface layer had higher salt concentration due to evaporation. Some treatment groups exhibited EC peaks near the 20–30 cm straw interlayer, likely due to the interlayer disrupting capillary continuity, causing significant retention and accumulation of rising salt. In the control group (CK), the electrical conductivity of the 10–20 cm soil layer increased significantly over time because the capillary channels remained intact, allowing for continuous upward salt accumulation; however, the straw treatment group blocked the upward movement of brine, resulting in a relatively stable EC in this layer, a significant difference from the CK.

[0106] Studies have shown that capillary action is the main driving force for salt accumulation on the surface. Straw interlayers effectively inhibit the upward movement of salt by severing capillary connections and form a salt-enriched zone below the interlayer, confining salt to the middle and lower soil layers. This provides a reliable physical method for salt inhibition in saline soil improvement, and its effect is consistent with the distribution pattern of sodium ion transport in soil.

[0107] 2. Effects of interlayer thickness and compaction on soil ammonia nitrogen content

[0108] The results are as follows Figure 12 As shown, the thickness and compactness of the straw interlayer significantly affected the distribution of ammonium nitrogen in the upper and lower layers within 50 days. Ammonia nitrogen in the upper layer accumulated slowly overall, with a concentration far lower than that of sodium ions. The increase in the CK group was smaller. In the experimental groups, ammonium nitrogen was released due to the mineralization of organic nitrogen in the straw, with the LS2 group accumulating the most. The TS8 group, with its greater thickness and more adsorption sites, had stronger ammonia nitrogen retention. Ammonia nitrogen in the lower layer rose rapidly from 0 to 20 days and then stabilized, with the TS group generally higher than the LS group. The TS group had dense pores and thorough interception, while the TS8 group, due to its greater thickness, had a higher adsorption capacity, resulting in significant ammonia nitrogen retention. In the early stages, ammonia nitrogen moved upwards with the water and was intercepted by the interlayer. Combined with the "sodium-ammonium replacement" caused by high-concentration sodium ions, this led to a rapid increase in ammonium nitrogen in the lower layer. In the later stages, the colloidal adsorption became saturated, and the anaerobic environment in the lower layer inhibited nitrification, causing ammonia nitrogen to exist in a stable form, and the concentration plateaued.

[0109] 3. The effect of interlayer thickness and compaction on soil nitrate nitrogen content

[0110] The results are as follows Figure 13 As shown, the thickness and compaction of the straw interlayer significantly affected the distribution of nitrate nitrogen in the upper and lower layers within 50 days. Nitrate nitrogen in the upper layer continuously increased, with the lowest concentration in group TS8 and the highest in groups LS2 and LS5, with an accumulation rate far greater than that of ammonia nitrogen. The upper layer nitrate nitrogen mainly originates from ammonia nitrogen nitrification, and good aeration facilitates this conversion; the interlayer prevents nitrate nitrogen from migrating vertically and causes it to remain trapped. Group TS8 exhibits strong barrier properties, weakening the upward diffusion of ammonia nitrogen and reducing nitrification substrate, thus resulting in a lower nitrate nitrogen content. Nitrate nitrogen in the lower layer increased rapidly from 0 to 20 days, gradually decreasing after 20 days, mostly reaching its peak around 20 days, with group TS8 showing the highest peak. In the early stages, nitrate nitrogen accumulated due to interception by the interlayer as water flowed upwards; in the later stages, high humidity and anaerobic conditions in the lower layer triggered denitrification, leading to significant nitrate nitrogen loss. A thicker interlayer intercepts more nitrate nitrogen in the lower layer, resulting in a more abundant substrate pool; even with denitrification consumption, the final residual concentration remains higher.

[0111] 4. The effect of interlayer thickness and compaction on soil available phosphorus content

[0112] The results are as follows Figure 14As shown, in the 50-day soil column experiment, available phosphorus exhibited a completely different variation pattern from nitrogen and salinity due to its poor mobility. The available phosphorus in the upper layer remained generally stable, with each treatment group consistently higher than the control group, reaching its highest level in the TS8 group at 50 days. Organic phosphorus contained in straw mineralized and released available phosphorus under the action of phosphatases, and this phosphorus mainly migrated via diffusion, making it difficult to be lost with water, thus remaining stable in the closed upper layer environment. The available phosphorus in the lower layer showed a continuous and slow decreasing trend, with the CK group showing the lowest and most gradual decrease. Phosphorus mobility was extremely poor, unable to be transported with water or diffused from the upper layer for replenishment, making the lower layer an isolated phosphorus layer. The continuous metabolic proliferation of indigenous microorganisms consumed the available phosphorus in the soil, and without external replenishment, the content continued to decrease.

[0113] 5. Effects of interlayer thickness and compaction on soil available potassium content

[0114] The results are as follows Figure 15 As shown in the 50-day soil column experiment, the changes in available potassium (KP) are similar to those of sodium ions but also have their own characteristics. The overall available potassium in the upper layer continuously increased, with the TS8 group showing the largest increase, reaching 304.5487 mg / kg after 50 days. Potassium in straw exists in ionic form and can be directly dissolved upon contact with water, continuously supplying potassium to the upper layer; the TS8 group, with its large straw content, had the highest total potassium supply. Available potassium in the lower layer accumulated in a stepwise manner, with the TS8 and TS5 groups both exceeding 569 mg / kg after 50 days. As potassium ions moved upwards with the water, they were intercepted by the straw layer, while a large amount of sodium ions, through ion exchange, converted colloidal adsorbed potassium into liquid potassium, accumulating simultaneously with sodium ions. The ranking of available potassium in the upper layer for each treatment was: TS8 > LS8 > TS5 > LS5 > TS2 > LS2 > CK.

[0115] 6. The effect of interlayer thickness and compaction on soil organic matter content

[0116] The results are as follows Figure 16 As shown in the soil column experiment, the straw interlayer significantly affected the distribution of organic matter between the upper and lower soil layers. The organic matter content in the upper layer showed a slow upward trend over 50 days, with the experimental group (TS8) having a significantly higher content than the control group (CK). On day 50, the TS8 group reached 2.731 g / kg, while the CK group only reached 1.594 g / kg. Continuous straw decomposition provided exogenous organic carbon to the upper layer, while simultaneously promoting microbial proliferation and metabolism. The newly added biomass carbon and extracellular polymers jointly drove the accumulation of organic matter. The organic matter content in the lower layer generally increased slightly, but the pattern was not obvious. Particulate organic matter had difficulty penetrating the interlayer, mainly relying on the weak diffusion and downward movement of soluble organic carbon released from the straw, which then accumulated in small amounts after adsorption or microbial transformation.

[0117] Based on the results of the above embodiments, it can be seen that the straw interlayer scheme of "light decomposition (6 days) + high bulk density (0.5 g / cm³) + large thickness (8cm)" provided by the present invention, when buried at a depth of 45-70cm, can effectively block the deep salt in saline-alkali land from rising to the topsoil with capillary water, while significantly improving the nutrient status of the upper soil (ammonia nitrogen, nitrate nitrogen, available phosphorus, available potassium and organic matter content are all significantly increased). It has a good dual effect of salt inhibition and soil improvement, and has broad application prospects.

[0118] 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 decomposing straw and deeply burying it in the field to prevent salinity and improve arable soil, characterized in that, include: 1) Deep loosening and soil breaking, including deep loosening of cultivated land to form deep trenches with a depth of not less than 45cm; 2) Straw filling, including evenly filling the deep trench with pre-composted straw for about 6 days to form a bio-barrier layer with a bulk density of 0.4-0.6 g / cm³; as well as 3) Topsoil backfilling, including topsoil covering, to create an improved arable soil with a low-salt, fertile upper layer and a salt-intercepting lower layer.

2. The method for deep burial and returning decomposed straw to the field to prevent salinity and improve arable soil according to claim 1, characterized in that: The depth of the trench is 45-70cm.

3. The method for deep burial and returning decomposed straw to the field to prevent salinity and improve arable soil according to claim 1, characterized in that: The straw is corn straw, crushed to a particle size of 10-20mm.

4. The method for deep burial and returning decomposed straw to the field to prevent salinity and improve arable soil according to claim 1, characterized in that: The pre-composting process involves inoculating the bacteria with cellulose-degrading microbial agents at a weight ratio of 4-7%, adjusting the moisture content to 60%-65%, and then composting the bacteria at room temperature.

5. The method for deep burial and returning decomposed straw to the field to prevent salinity and improve arable soil according to claim 1, characterized in that: The thickness of the bio-barrier layer is 5-10 cm.

6. The method for deep burial and returning decomposed straw to the field to prevent salinity and improve arable soil according to claim 1, characterized in that: In step 2), the straw filling is mechanically layered and compacted to form the biobarrier layer.

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