Water-salt-carbon-fertilizer coordinated regulation and control method for paddy-upland rotation soil in coastal water-rich saline-alkaline area

Abstract

The invention discloses a coastal wet-water saline-alkaline area paddy-upland rotation soil water-salt-carbon-fertilizer coordinated regulation and control method, which comprises the following steps: (1) constructing an open trench + concealed conduit + monitoring network three-dimensional drainage salt control system to realize zoned active salt control; (2) adopting an intermittent tillage system based on soil texture, and optimizing a plough layer structure through combination of periodic deep tillage and conventional rotary tillage; (3) performing straw zoned returning, constructing a deep salt-resistant layer in the deep tillage year, and quickly increasing organic matters in a plough layer in the rotary tillage year; (4) applying biologically active and stable carbon sources in a compatible manner, and determining the carbon input amount according to the salinity level, so as to realize directional fertilization and carbon library compatibilization; and (5) implementing a nitrogen-increasing fertilization strategy adaptive to salt stress, and realizing efficient utilization of nitrogen in combination with urease and a nitrification inhibitor. Through cooperation of multiple links, the productivity and sustainability of the coastal saline-alkali land paddy-upland rotation system are systematically improved.

Description

Technical Field

[0001] This invention relates to a method for the synergistic regulation of water, salt, carbon, and fertilizer in soil during crop rotation in coastal water-rich saline-alkali areas, belonging to the field of saline-alkali land improvement technology. Background Technology

[0002] Large areas of saline-alkali farmland are distributed in my country's coastal regions. These areas are generally affected by highly mineralized groundwater and strong evaporation, resulting in severe surface salt accumulation in the soil, which restricts sustainable agricultural development. Rice-wheat / rapeseed rotation (such as rice-wheat / rapeseed) is a typical planting pattern in these areas. Although it can achieve preliminary salt leaching through flooding during the rice season, it fails to fundamentally solve systemic problems such as incomplete salt removal, soil structure deterioration, organic matter deficiency, and low nutrient utilization.

[0003] Existing improvement technologies often suffer from limitations, offering only piecemeal solutions and lacking systematic integration. In terms of engineering-based salt control, open ditches and underground pipes are often used in isolation. Open ditches are prone to collapse and siltation, underground pipes are difficult to construct in heavy clay soils, and single engineering measures are insufficient for long-term, precise control of water and salt transport. Regarding soil structure, long-term rotary tillage thickens the plow pan, hindering water infiltration and root growth, while the frequency and depth of deep tillage lack scientific standards based on soil texture. Regarding soil fertility improvement, saline-alkali environments inhibit microbial activity, resulting in slow decomposition of traditional straw return to the field, and ordinary organic materials have limited targeted improvement effects on aggregate formation and salt adsorption. In terms of nutrient management, nitrogen under saline-alkali stress is easily lost through ammonia volatilization and nitrification leaching, which conventional fertilization strategies cannot effectively address.

[0004] Therefore, there is an urgent need in this field for a comprehensive solution that can synergistically regulate water, salt, carbon, and fertilizer. This solution needs to overcome the limitations of single technologies and achieve a systematic breakthrough from passive drainage to active salt control and from soil structure improvement to continuous soil fertility enhancement through a combination of engineering and agronomic measures, targeted matching of organic carbon sources, and intelligent nutrient management. This will provide reliable technical support for improving the productivity and sustainable utilization of coastal saline-alkali farmland. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the synergistic regulation of water, salt, carbon, and fertilizer in soil during crop rotation in coastal water-rich saline-alkali areas.

[0006] The technical solution adopted in this invention is as follows: A method for synergistic regulation of soil water, salt, carbon, and fertilizer in paddy-dryland rotation in coastal water-rich saline-alkali areas, characterized by comprising: (1) Drainage and salt removal project layout: A three-dimensional drainage and salt removal system is constructed by combining open ditches and underground pipes, and supplemented by a dynamic water and salt monitoring network to achieve accurate and zoned active salt control based on real-time data; (2) Intermittent tillage and straw return to the field: After rice harvest and before dry season crops are sown, intermittent tillage is carried out. Crop straw is crushed and scattered in the field. The cycle is 2 to 5 years. In each cycle, deep plowing with a depth of 25 to 30 cm is carried out in one year to turn the straw into the soil layer 25 to 30 cm deep to form a physical salt barrier layer. In other years, conventional rotary tillage with a depth of 15 to 18 cm is carried out to maintain the topsoil structure. (3) Multi-source organic material application: Bioactive carbon source and biostable carbon source are combined in a carbon ratio of 3:7 to 4:6. The total amount of exogenous organic carbon (bioactive carbon source + biostable carbon source) input should reach a level of not less than 3 g C / kg per mu of topsoil weight. The fertilization strategy is planned on a 3-year cycle. The biostable carbon source is applied once in the first year to quickly build a stable carbon pool. The bioactive carbon source is applied in equal amounts over three years to continuously supply microbial activity. (4) Coordinated management of nitrogen fertilizer nutrients: The total amount of nitrogen applied to crops is set to be 10% to 20% higher than the recommended amount of nitrogen applied to ordinary cultivated land in the same area, and flexible management is carried out based on the real-time soil salt stress level fed back by the water and salt monitoring network; when applying urea as a nitrogen source, 1% of the pure nitrogen weight of urease inhibitor NBPT and 2% of the pure nitrogen weight of nitrification inhibitor MHPP are applied together.

[0007] Preferably, the spacing of the underground pipes in feature (1) is set to 20~40 m and the burial depth is 1.6~1.8 m; the spacing of the open ditch is 50~60 m and the depth is 1.3~1.5 m; and the grid density of the water and salt dynamic monitoring network is not greater than 50 m×50 m.

[0008] Preferably, in fields where underground pipe construction is not feasible, drainage and salt removal using only open ditches is adopted.

[0009] Preferably, the water and salt dynamic monitoring network described in feature (1) refers to the pre-buried salt monitoring sensors in the ground. When the salt content is detected to exceed the crop's salt tolerance threshold, water is used to wash away the salt. Specifically, before crop planting, the salt content in the 0-20cm soil is controlled to not exceed 0.3% by irrigating to wash away the salt.

[0010] Preferably, in feature (2), a straw composting agent is sprayed simultaneously when scattering the straw, with a dosage of 2~3 kg / mu.

[0011] Preferably, the length of the cycle in feature (2) is negatively correlated with the soil clay content, that is, the higher the clay content, the shorter the cycle and the more frequent the deep plowing. If the soil clay content exceeds 30%, the interval of the deep plowing should not be greater than 2 years (that is, two years is a cycle, the first year is deep plowing and the second year is rotary tillage) to prevent excessive soil compaction.

[0012] Preferably, in feature (3), the bio-stable carbon source includes at least one of biochar and peat; the bio-active carbon source includes at least one of humic acid and bio-organic fertilizer. If the carbon source material used involves organic waste containing antibiotics, it must undergo thermal activation treatment at no less than 200°C to completely eliminate the risk of antibiotic residues to the soil ecological environment.

[0013] Preferably, the nitrogen application rate for ordinary cultivated land in feature (4) is 13~16 kg N / mu, that is, the amount of nitrogen fertilizer applied to saline-alkali land is 1.3~3.2 kg N / mu more than that to ordinary cultivated land. Flexible management means that when the soil salinity is <0.2%, the total nitrogen application rate of crops is set to be 5%~10% higher than the recommended nitrogen application rate of ordinary cultivated land in the same area; when the soil salinity is 0.2~0.4%, the total nitrogen application rate of crops is set to be 10%~15% higher than the recommended nitrogen application rate of ordinary cultivated land in the same area; when the soil salinity is >0.4%, the total nitrogen application rate of crops is set to be 15%~20% higher than the recommended nitrogen application rate of ordinary cultivated land in the same area. The soil salinity refers to the soil salinity before drainage and salt removal. Because the higher the salt content, the lower the overall soil organic matter and nitrogen and phosphorus nutrient content, in order to meet the needs of crop growth, after salt leaching and salt removal, it is also necessary to apply different amounts of nitrogen fertilizer according to the original soil salinity.

[0014] The beneficial effects of this invention are as follows: 1. Three-dimensional salt control, long-term stability: Through the engineering system of "open ditch + underground pipe + monitoring", three-dimensional drainage from the surface to the ground and data-based precise salt control are achieved, which effectively inhibits salt accumulation on the surface.

[0015] 2. Optimized tillage layer and coordinated water and salt: Intermittent deep plowing breaks up the plow pan, enhancing the vertical infiltration of water and the ability to leach salt; combined with straw return to the field, it forms a salt-blocking layer in the deep layer and improves the structure on the surface, thus synergistically regulating water and salt transport.

[0016] 3. Carbon pool construction, capacity expansion and quality improvement: Through a multi-source combination and phased application strategy of "stable carbon source as the foundation and active carbon source as the follow-up", the rapid increase and long-term storage of soil organic carbon are taken into account, effectively reversing the trend of carbon pool degradation in saline-alkali land.

[0017] 4. Enhanced nutrient efficiency, reduced loss and prevented salinization: Through the management strategy of "increased nitrogen application + inhibitors + carbon-nitrogen synergy", the utilization rate of nitrogen fertilizer has been significantly improved, the economic and environmental costs caused by nitrogen loss have been reduced, and secondary salinization caused by improper fertilization has been avoided.

[0018] 5. Systematic Improvement: This invention organically links multiple aspects such as water conservancy projects, soil cultivation, carbon management and nutrient regulation, and constructs a linkage mechanism of "water and salt regulation - carbon source matching - nutrient synergy" to achieve multi-element synergistic management of saline-alkali soil in coastal water-rich areas. Attached Figure Description

[0019] Figure 1 Comparison of soil salinity after the completion of the example and comparative experiments.

[0020] Figure 2 Comparison of soil bulk density after the completion of the example and comparative experiments.

[0021] Figure 3 Comparison of total soil organic matter content after the completion of the example and comparative experiments.

[0022] Figure 4 Comparison of soil oxidizable organic carbon content after the completion of the example and comparative experiments.

[0023] Figure 5 Comparison of total nitrogen content in soil after the completion of the example and comparative experiments.

[0024] Figure 6 Comparison of soil available nitrogen content after the completion of the example and comparative experiments.

[0025] Figure 7 Comparison of crop yields after the completion of the example and comparative experiments.

[0026] Figure 8 Comparison of nitrogen fertilizer partial productivity after the completion of the example and comparative experiments. Detailed Implementation

[0027] The following examples further illustrate the content of the present invention, but should not be construed as limiting the invention. Modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are all within the scope of the invention. Specific instruments or reagents used in the embodiments of the present invention are provided below. However, it should be understood that these are merely exemplary and not intended to limit the invention. Materials of the same or similar type, model, quality, properties, or functions as the reagents and instruments described below can be used to implement the present invention. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the soil agricultural chemical analysis methods involved are all performed in accordance with "Soil Agricultural Chemical Analysis Methods" (edited by Lu Rukun et al., China Agricultural Science and Technology Press, 1999).

[0028] Technical application verification was conducted in the coastal saline-alkali area of ​​Dongtai City, Jiangsu Province, from 2022 to 2025. This area has a humid subtropical monsoon climate with an average annual precipitation of 1059 mm, 70% of which is concentrated between June and September. It has a high groundwater level and high mineralization, making it a typical coastal water-rich saline-alkali area. The tested soil was alluvial saline soil. Before application, the physicochemical properties of the 0–20 cm topsoil layer were: total salt content 3.01 g / kg, bulk density 1.42 g / cm³. 3 The organic matter content was 6.36 g / kg, easily oxidizable organic carbon was 0.65 g / kg, total nitrogen was 0.45 g / kg, alkaline available nitrogen was 23.77 mg / kg, and clay content was 12.5%. A rice-rapeseed double-cropping rotation system was adopted. The locally recommended fertilizer application rates were 15 kg N / mu and 9 kg P2O5 / mu for the rice season and 15 kg N / mu and 9 kg P2O5 / mu for the rapeseed season. The conventional tillage system was rotary tillage to a depth of approximately 15 cm.

[0029] The specific implementation steps are as follows: (1) Construction of drainage and salt control system: A submerged drainage system with a spacing of 30 m and a burial depth of 1.7 m was laid in the field, which was combined with open ditches with a spacing of 55 m and a depth of 1.4 m to form a three-dimensional drainage network of "open drainage and submerged water control". The open ditches and submerged pipes were set up in parallel. At the same time, water and salt dynamic monitoring points with a density of 40 m × 40 m were set up to monitor the soil salinity and moisture status in real time and guide the zoned irrigation and drainage.

[0030] (2) Intermittent tillage combined with targeted straw return to the field: Based on the soil clay content and structure, a tillage layer regulation plan with a 3-year cycle is formulated. After the first year's crop harvest, the straw is crushed to 3-5 cm and evenly spread, and 2.5 kg / mu of composting agent is sprayed. A 28 cm deep plowing is carried out to compact the straw to a depth of 28 cm to build a physical salt barrier layer. Deep plowing can break the plow pan and enhance water infiltration. In the second and third years, combined with rotary tillage, the straw is crushed and mixed into the 0-16 cm tillage layer to maintain the looseness of the tillage layer and promote rapid decomposition and carbon return.

[0031] (3) Multi-source carbon allocation and fertilization: Planned according to a 3-year fertilization cycle, based on the initial soil bulk density (1.42 g / cm³). 3 Furthermore, the total input of exogenous organic carbon (biologically active carbon source + biologically stable carbon source) should reach a level of not less than 3 g C / kg per mu of topsoil (i.e., the total input of exogenous organic carbon should be not less than 568 kg C / mu), and the total input of exogenous organic carbon should be determined to be not less than 580 kg C / mu. The carbon source ratio is 3:7 for activated carbon (fulvic acid) and stable carbon (biochar). Biochar is applied once during the first year of rapeseed season land preparation, while fulvic acid is divided into three portions and applied before rapeseed sowing each year.

[0032] (4) Co-management of nitrogen fertilizer: Based on the soil salinity stress, the total amount of nitrogen applied to rice and rapeseed during the season was set to be 10% higher than the local conventional recommended amount. All urea was applied with 1% of the pure nitrogen weight of urease inhibitor NBPT and 2% of the nitrification inhibitor MHPP.

[0033] Comparative Example 1 (Single Project Salt Control) Only step (1) in Example 1 is used, namely the “open ditch + underground pipe + monitoring” three-dimensional drainage and salt removal system. The farming method is conventional rotary tillage every year, straw is not returned to the field, and the fertilizer is applied according to the local conventional recommended amount and method (no nitrogen increase, no inhibitors are applied), and no exogenous organic carbon materials are applied.

[0034] Comparative Example 2 (Engineering + Intermittent Tillage + Straw Return to Field) The steps (1)–(2) of Example 1 were adopted, namely, three-dimensional drainage and salt removal, intermittent tillage (deep plowing in the first year and rotary tillage in the following two years) and straw return to the field. Fertilizer management was the same as that of Comparative Example 1, namely, the conventional recommended nitrogen application rate, no inhibitors were applied, and no exogenous organic carbon was added.

[0035] Comparative Example 3 (Engineering + Carbon Source Allocation) The steps (1) and (3) in Example 1 are adopted. That is, a drainage and salt removal system is constructed, and a 3-year carbon source application plan is implemented (biochar is applied as a base fertilizer in the first year, and humic acid is applied in subsequent years). However, the tillage method is changed to conventional rotary tillage every year, straw is not returned to the field, and nitrogen fertilizer is not combined with inhibitors.

[0036] Comparative Example 4 (Engineering + Nitrogen Fertilizer Co-management) Steps (1) and (4) in Example 1 were adopted. That is, a drainage and desalination system was constructed, and a nitrogen fertilizer management strategy of increasing nitrogen and applying inhibitors was implemented. However, the tillage method was conventional rotary tillage, straw was not returned to the field, and no exogenous organic carbon materials were added.

[0037] Figures 1 to 8 The test results show that the present invention has a significant systemic improvement effect on water and salt regulation, fertility enhancement, and crop productivity in the 0-20 cm topsoil layer of coastal water-rich saline-alkali areas, as detailed below: (1) Soil salt control and salt suppression effect ( Figure 1 Compared to the initial state, the "open ditch + underground pipe + monitoring" engineering system alone can achieve a salt reduction of 11.8% in the topsoil. On this basis, combined with intermittent tillage and straw return to the field, multi-source organic material application or nitrogen fertilizer synergistic management, the salt reduction rate is increased to 37.9%, 29.6% and 18.0% respectively. The system integration technology used in the example has the best overall effect, with a salt reduction rate of 39.8%, which significantly enhances the salt stability of the root zone.

[0038] (2) Improvement of soil structure Figure 2Drainage projects and nitrogen fertilizer management have no significant impact on soil bulk density, but intermittent deep plowing combined with straw return to the field and multi-source organic material application can reduce bulk density by 8.3% and 5.5%, respectively; system integration technology reduces bulk density by 11.2%, significantly optimizing soil pore structure and aeration and permeability.

[0039] (3) Improve the storage capacity of organic matter ( Figure 3 , Figure 4 The engineering drainage system increased the total organic matter content by 8.9%; combined with intermittent tillage and straw return to the field, multi-source organic material application, or nitrogen fertilizer synergistic management, the increases were 22.7%, 52.3%, and 12.8%, respectively; system integration technology increased the total organic matter content by 64.9%. The content of easily oxidizable organic carbon increased by 8.7% and 20.1% under multi-source organic material application and system integration technology, respectively, indicating that the soil carbon pool was simultaneously enhanced in terms of both storage and activity.

[0040] (4) Changes in nitrogen levels ( Figure 5 , Figure 6 The effects of engineering-based salt control, deep plowing and straw return to the field, and the application of organic materials on total nitrogen content are limited. However, nitrogen fertilizer synergistic management and system integration technologies increased total nitrogen content by 11.8% and 7.6%, respectively. Regarding nitrogen availability, all technologies improved nitrogen content, with nitrogen fertilizer synergistic management and system integration technologies showing the most significant improvement.

[0041] (5) Crop yield and nitrogen fertilizer use efficiency ( Figure 7 , Figure 8 As soil salinity decreases and fertility improves, crop yields increase significantly. Based on engineering-based salt control, combined with intermittent tillage and straw return to the field, multi-source organic material application, and nitrogen fertilizer synergistic management or system integration technologies, rice yields increased by 2.2%, 7.8%, 9.0%, and 15.7%, respectively, while rapeseed yields increased by 3.0%, 13.6%, 8.3%, and 17.8%, respectively. The nitrogen fertilizer partial productivity under system integration technology was the highest, reaching 16.3 kg / kg for rice and 10.1 kg / kg for rapeseed.

[0042] (6) Technological synergy effect: The system integration technology is significantly better than any single technology in all indicators, reflecting the comprehensive advantages of multi-path synergistic regulation of "water-salt-carbon-fertilizer", and verifying the overall benefits of the invention in the systematic improvement of saline-alkali land.

Claims

1. A method for synergistic regulation of soil water, salt, carbon, and fertilizer in paddy-dryland rotation in coastal water-rich saline-alkali areas, characterized in that... Comprise: (1) Drainage and salt removal engineering arrangement: adopt the mode of combining open ditch with buried pipe to construct the three-dimensional drainage and salt removal system, and add water and salt dynamic monitoring network to realize accurate and partitioned active salt control based on real-time data; (2) Intermittent tillage and straw returning treatment: after rice harvesting and before dry season crop sowing, implement intermittent tillage, crush and scatter crop straw in the field, and every 2-5 years, one year is deep ploughing with a depth of 25-30 cm, and the straw is pressed into the soil layer of 25-30 cm to form a physical salt blocking layer; the rest of the years are regular rotary tillage with a depth of 15-18 cm to maintain the surface soil structure; (3) Multi-source organic material application: bioactive carbon source and biological stability carbon source are matched in a carbon amount ratio of 3:7 to 4:6, and the total amount of exogenous organic carbon input reaches not less than 3 g C / kg of the weight standard of the cultivated layer soil; the fertilization strategy is planned every 3 years, wherein the biological stability carbon source is applied once in the first year to quickly build a stable carbon pool foundation; the bioactive carbon source is applied equally in three years to continuously supply microbial activity; (4) Nitrogen nutrient collaborative management: the total nitrogen application amount of crops is set to be 10%-20% higher than the recommended nitrogen application amount of ordinary farmland in the same region, and elastic operation is carried out based on the real-time salt stress level of soil fed back by the water and salt monitoring network; when urea is used as the nitrogen source, 1% of pure nitrogen weight of urease inhibitor NBPT and 2% of pure nitrogen weight of nitrification inhibitor MHPP are applied.

2. The method of coordinated regulation of claim 1, wherein: In feature (1), the buried pipe spacing is set to 20-40 m, and the buried depth is 1.6-1.8 m; the open ditch spacing is 50-60 m, and the depth is 1.3-1.5 m; the grid density of the water and salt dynamic monitoring network is not more than 50 m x 50 m; in the field without buried pipe construction conditions, only the open ditch mode is used for drainage and salt removal.

3. The method of coordinated regulation of claim 2, wherein: In feature (1), the water and salt dynamic monitoring network refers to pre-buried salt content monitoring sensors in the field, and when the salt content detected exceeds the crop salt tolerance threshold, salt washing and removal are carried out by irrigation.

4. The method of coordinated regulation according to any one of claims 1-3, wherein: In feature (2), straw is scattered while spraying straw composting agent, and the amount is 2-3 kg / mu.

5. The method of coordinated regulation according to any one of claims 1-3, wherein: In feature (2), the length of the cycle is negatively correlated with the soil clay content, that is, the higher the clay content, the shorter the cycle, and the more frequent the deep ploughing, specifically: when the soil clay content is <15%, the cycle length is not more than 5 years; when the soil clay content is 15%-25%, the cycle length is not more than 3 years; when the soil clay content is >25%, the cycle length is not more than 2 years.

6. The method of coordinated regulation of claim 5, wherein: In feature (3), the biological stability carbon source includes at least one of biochar and peat; the bioactive carbon source includes at least one of fulvic acid and bio-organic fertilizer.

7. The method of coordinated regulation of claim 6, wherein: The nitrogen application amount of the ordinary farmland in the feature (4) is 13-16 kg N / mu, and the elastic operation is that when the soil salt content is less than 0.2%, the total nitrogen application amount of crops is set to be 5%-10% higher than the recommended nitrogen application amount of the ordinary farmland in the same region; when the soil salt content is 0.2%-0.4%, the total nitrogen application amount of crops is set to be 10%-15% higher than the recommended nitrogen application amount of the ordinary farmland in the same region; when the soil salt content is more than 0.4%, the total nitrogen application amount of crops is set to be 15%-20% higher than the recommended nitrogen application amount of the ordinary farmland in the same region, wherein the soil salt content refers to the soil salt content before drainage and salt removal.

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