A water and fertilizer synergistic management method for moderate coastal saline-alkali land based on brackish water irrigation

Abstract

The application discloses a kind of based on brackish water irrigation's moderate coastal saline-alkali soil rice water fertilizer synergic management method, belong to agricultural water and soil engineering technical field.It includes the following steps: according to the mineralization of target area's irrigation water source and soil salt distribution situation Dynamic selection suitable irrigation mode irrigation;Create differentiating irrigation and drainage strategy, synchronous execution corresponding irrigation water mineralization control standard;Based on moderate coastal saline-alkali soil soil fertility characteristics and rice salt-tolerant growth demand, determine the total amount of nitrogen, phosphorus and potassium and medium and micro-fertilizer application;Follow the principle of stable supply of base fertilizer, accurate stage nutrient management of topdressing;Optimize saline-alkali soil and brackish water irrigation fertilization type and suitable application method, realize water and fertilizer timing and amount synergic control.The application realizes salt inhibition and fertilizer preservation, nitrogen reduction and efficiency improvement by dynamically adapting irrigation mode, differentiating irrigation and drainage control, accurate nutrient management and fertilization control, improves the salt tolerance and yield of rice.

Description

Technical Field

[0001] This invention belongs to the field of agricultural water and soil engineering technology, specifically relating to a method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on slightly brackish water irrigation. Background Technology

[0002] Irrigation and drainage leaching is a core salt reduction measure for rice cultivation in saline-alkali land. Utilizing the aquatic growth characteristics of rice, scientific irrigation and drainage regulation during the rice's growth period promotes the leaching and infiltration of soil salts, creating a desalinated surface layer in the rhizosphere and ensuring normal rice growth and development. This technology has been widely applied in the saline-alkali areas of eastern coastal my country. Current mainstream irrigation and drainage leaching technologies include open ditch drainage, subsurface drainage, irrigation leaching, and a combination of subsurface and open ditch drainage.

[0003] Nitrogen fertilizer management is a key technology for increasing yield, mitigating salt damage, and improving fertilizer utilization in rice cultivation in coastal saline-alkali lands. Its core objective is to achieve efficient nitrogen utilization under salt stress. This is achieved by optimizing key parameters such as nitrogen application rate, fertilization timing, nitrogen ratio, fertilizer type, and application method, resulting in a synergistic effect of nitrogen loss reduction and efficiency enhancement. Existing technologies mainly focus on precise control of nitrogen fertilizer application, optimization of fertilization timing, optimization of nitrogen speciation, and the application of slow-release and controlled-release nitrogen fertilizers.

[0004] Coastal saline-alkali lands are mainly concentrated in coastal areas such as Jiangsu and Shandong. The groundwater in these areas is shallow and frequently affected by natural factors such as seawater intrusion and backwater effects, resulting in surface and groundwater that is predominantly brackish (mineralization 1-3 g / L). Under the core context of brackish water irrigation, existing irrigation and drainage desalination technologies and nitrogen fertilizer management technologies suffer from significant incompatibility. Specific shortcomings and their causes are as follows: I. Long-term irrigation poses a high risk of salt accumulation and exacerbates secondary soil salinization. On the one hand, the slightly brackish water in the coastal area , High levels of harmful ions directly inhibit the absorption and utilization of water and fertilizer by rice roots, interfering with normal physiological metabolism and ultimately leading to reduced crop yield. On the other hand, existing irrigation and drainage technologies largely replicate conventional paddy field models, failing to adequately consider the impact of brackish water irrigation on soil salt transport patterns, and neglecting to design preventative measures against the risk of long-term brackish water irrigation leading to topsoil salt accumulation. The core shortcoming lies in the lack of a coordinated "water-salt" regulation mechanism, making it impossible to achieve a dynamic balance between irrigation water supply and salt regulation.

[0005] II. The contradiction between salt control and fertilizer conservation is prominent, and nutrient leaching and loss are serious. First, there is a mismatch between the timing of irrigation and drainage and fertilization. Field irrigation and drainage measures to reduce salinity are concentrated 1-2 weeks after rice transplanting, a period that highly overlaps with the basal fertilizer application cycle. This disconnect between irrigation and fertilization operations leads to a significant loss of nitrogen from the basal fertilizer through leaching with the saline solution. Second, there is a lack of a synergistic salt-nitrogen regulation mechanism. The salt stress from brackish water irrigation, combined with the soil's inherent salinity, alters the transformation and migration patterns of nitrogen in the soil, significantly reducing nitrogen fertilizer use efficiency and further exacerbating the conflict between salt control and fertilizer conservation.

[0006] Third, the integration of management technologies is low, and a synergistic "water-salt-nitrogen" system has not been formed. Existing technologies are mostly geared towards a single regulatory objective. For example, irrigation and drainage technologies focus on salt leaching, and nitrogen fertilizer technologies focus on nutrient supply, failing to incorporate "safe utilization of brackish water, salt drainage and control, and efficient synergistic water and fertilizer management" into a unified regulatory framework. This fragmented approach results in rice being unable to effectively absorb and utilize water and fertilizer even when water and fertilizer supply is achieved, due to the dual stress of toxic ions from brackish water and soil salinity. Consequently, the technologies fail to achieve a synergistic effect of "1+1>2," instead exhibiting antagonistic effects due to conflicting regulatory objectives, ultimately leading to a decline in overall planting benefits. Summary of the Invention

[0007] To address the technical problems existing in the background art, this invention provides a method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on brackish water irrigation, which completely solves the problems of disconnection between irrigation and drainage and fertilization, separation of water, salt and nitrogen regulation, and low overall benefits in existing technologies.

[0008] This invention employs the following technical solution: a method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on brackish water irrigation, comprising the following steps: The following irrigation methods are pre-set based on brackish water irrigation: direct brackish water irrigation, brackish water-fresh water mixed irrigation, and brackish water-fresh water alternating irrigation; the appropriate irrigation method is dynamically selected based on the mineralization of the irrigation water source and the distribution of soil salinity in the target area. Create differentiated irrigation and drainage strategies, implement irrigation and drainage regulation in stages according to the rice growth period, and simultaneously implement the corresponding irrigation water mineralization control standards; Based on the soil fertility characteristics of moderately saline-alkali coastal land and the salt tolerance growth requirements of rice, the total amount of nitrogen, phosphorus, potassium and micronutrient fertilizers to be applied was determined; following the principle of stable supply of base fertilizer and precise topdressing in a phased nutrient management, the timing of fertilization was matched with the field irrigation and drainage salt leaching rhythm. Optimize the types of fertilizers and appropriate application methods for irrigation of saline-alkali land and brackish water to achieve coordinated regulation of water and fertilizer timing and dosage.

[0009] In a further embodiment, the process includes a combined step of straw burial and fertilization prior to irrigation: Straw mixed with soil and returned to the field: The straw of the previous season's crop is crushed and spread evenly, then mixed with soil in the topsoil through rotary tillage. Subsequently, water is added to regulate the soil moisture content and promote the decomposition of straw, forming a soil environment that inhibits salt, retains fertilizer, and improves soil structure. Coordinated application of base fertilizer: Base fertilizer is applied simultaneously after straw is mixed and buried to adjust the soil carbon-nitrogen ratio, avoid competition for nitrogen between straw decomposition and rice seedlings, and achieve matching of the timing of straw return to the field and nutrient release of base fertilizer, so as to provide synergistic fertilizer supply.

[0010] In a further embodiment, the dynamic selection method of the irrigation method is as follows: Obtain the average irrigation mineralization of the target area during the current time period. Simultaneously, the spatial distribution characteristics and temporal fluctuation characteristics of soil salinity in the root zone during the current period are collected to form the steady-state characteristics of soil salinity; If the soil salinity steady-state characteristics are unsteady, then brackish water-fresh water alternating irrigation should be used directly; conversely, if the soil salinity steady-state characteristics are stable, then irrigation should be based on the average value of irrigation mineralization. Analysis and selection: like In this case, slightly saline water should be used for direct irrigation. like Then, use a mixture of slightly saline and freshwater for irrigation until... ;in, , which are the first mineralization threshold and the second mineralization threshold, respectively.

[0011] In a further embodiment, the differentiated irrigation and drainage strategy includes: a seedling stage with enhanced salt removal and a mid-to-late stage with steady-state water supply; The seedling stage of enhanced salt removal is the initial stage after rice transplanting, which adopts an enhanced rinsing mode that alternates between periodic irrigation and drainage. The mid-to-late stage of steady-state water supply is from the late transplanting stage to before harvest. Based on the water requirements of rice during its growth period and soil moisture, a stable surface water layer is maintained, and the water layer depth is dynamically adjusted during key growth stages.

[0012] In a further embodiment, the irrigation water mineralization control standard is based on a first mineralization threshold. Second mineralization threshold To achieve this, the control method is as follows: During the enhanced salt removal stage in the seedling stage, a second mineralization threshold was used. Control measures were implemented: Real-time irrigation mineralization values ​​were obtained during the intensive salt removal phase in the seedling stage. The real-time irrigation mineralization value The following requirements must be met: ; During the mid-to-late stage of steady-state water supply, a first mineralization threshold is adopted. Control measures: Obtain real-time irrigation mineralization values ​​during the mid-to-late stage of steady-state water supply. The real-time irrigation mineralization value The following requirements must be met: .

[0013] In a further embodiment, the total amount of nitrogen, phosphorus, potassium, and micronutrient fertilizers applied is determined as follows: Based on the fertility characteristics of moderately saline-alkali coastal soils, such as low organic matter content and high risk of nutrient leaching, and combined with the salt tolerance requirements of rice, a calculation model for nitrogen application, phosphorus application, potassium application and micronutrient application was established by combining the target yield method with soil nutrient correction coefficient. Based on the nitrogen, phosphorus, potassium, and micronutrient application calculation models, the recommended nutrient application rates per unit area are calculated respectively. The final total application amount is then calculated by converting this amount to the target planting area. The conversion model is as follows: ; In the formula, For the first The final total amount of nutrients applied. For the first Recommended nutrient application rate per unit area for planting. The planting area is the target region.

[0014] In a further embodiment, the principle of phased nutrient management for stable supply of base fertilizer and precise topdressing is specifically as follows: nitrogen fertilizer is applied in stages, in proportion to base fertilizer, tillering fertilizer, and heading fertilizer, according to different growth stages; phosphorus fertilizer and potassium fertilizer are applied as a single base fertilizer application. Nitrogen fertilizer, basal fertilizer, phosphorus fertilizer, and potassium fertilizer should be applied to the field in a timely and simultaneous manner before rice transplanting, and thoroughly mixed with the topsoil to build a long-term and stable soil nutrient pool. Nitrogen fertilizer and tillering fertilizer should be applied at the appropriate time in the early stage of rice tillering, and panicle fertilizer should be applied at the appropriate time in the early stage of rice panicle differentiation.

[0015] In a further embodiment, the optimized fertilization type and suitable application method for saline-alkali land and brackish water irrigation include: Based on the soil environment of saline-alkali land and the water and salt transport characteristics of slightly saline water irrigation, appropriate types of nitrogen, phosphorus and potassium fertilizers are selected and matched with differentiated application methods. Nitrogen fertilizer is applied in stages, using a combination of slow-release and fast-acting nitrogen sources as basal fertilizer and a single fast-acting nitrogen source as top dressing. Phosphate fertilizer is applied using a highly soluble fertilizer suitable for alkaline soils and mixed with the soil. Potassium fertilizer is applied in concentrated strips to achieve coordinated control of water and fertilizer timing and dosage.

[0016] In a further embodiment, the method also includes a step of validating and dynamically optimizing the currently implemented water and fertilizer co-management scheme: During the implementation of current irrigation methods, irrigation and drainage strategies, nutrient management and fertilization methods, the soil water and salt content in the root zone of the target area, the mineralization of irrigation water, rice growth and nutrient absorption are collected in real time to verify the implementation effect of the current plan. If the verification results do not meet the preset soil desalination targets, rice growth indicators, and water and fertilizer use efficiency requirements, then targeted adjustments and optimizations will be made to the irrigation method selection parameters, mineralization control thresholds, irrigation and drainage sequence, nutrient application ratios, and fertilizer application methods in the current scheme until the preset targets are met, ensuring that the current water and fertilizer synergistic management scheme is suitable for moderately saline-alkali coastal land and slightly brackish water irrigation conditions.

[0017] This invention is tailored to the resource endowment of high-salt soil and predominantly brackish surface water in coastal saline-alkali areas. Addressing the core pain points of existing technologies—such as long-term brackish water irrigation leading to salt accumulation, difficulty in coordinating salt control and fertilizer conservation, and fragmented technologies—this invention proposes for the first time a three-pronged approach to water, fertilizer, and salt management for rice cultivation in moderately saline-alkali coastal areas, integrating brackish water irrigation, slow-release fertilizer, and straw return to the field. Its specific beneficial effects are as follows: This invention addresses the long-standing problem of salt accumulation from brackish water irrigation, achieving a win-win situation of safe utilization of brackish water resources and rapid salinity reduction. By using brackish water with a salinity below the safe mineralization threshold for irrigation and drainage, it efficiently utilizes the abundant brackish water resources in the region while specifically avoiding the shortcomings of existing technologies that simply copy ordinary paddy field irrigation and drainage parameters and lack "water-salt" synergistic regulation. This effectively inhibits salt accumulation in the topsoil, reduces the risk of secondary soil salinization, and simultaneously ensures a low-salt environment for rice root growth, solving the problem of toxic ions in brackish water inhibiting water and fertilizer absorption.

[0018] This approach resolves the core contradiction between salt control and fertilizer conservation, significantly improving nutrient utilization efficiency. By partially replacing urea with slow-release fertilizer, it precisely matches the nutrient requirements of rice, avoiding the overlap between the peak salt reduction period of irrigation and drainage in the early stages of rice planting and the basal fertilizer application cycle, thus reducing nitrogen loss through leaching with salt water. Simultaneously, it alleviates the interference of salt stress on nitrogen transformation and migration, fundamentally addressing the pain point of low nitrogen fertilizer utilization caused by the lack of synergistic salt-nitrogen regulation in existing technologies, achieving precise matching between nutrient supply and crop needs.

[0019] Breaking down the barriers of fragmented technologies, this invention constructs a synergistic system of "water-salt-fertilizer-soil." It is not a simple superposition of three technologies, but rather integrates the safe utilization of brackish water, salt drainage and control, and efficient synergistic water and fertilizer management into a unified regulatory framework. Combining straw with soil remediation can increase soil carbon and inhibit salt production, while reducing nutrient leaching, laying a soil foundation for salinization reduction through brackish water irrigation and efficient slow-release fertilizer supply. The three technologies mutually empower and synergistically enhance each other, completely solving the shortcomings of existing technologies that rely on single-control methods and are prone to antagonistic effects, truly achieving an integrated effect of "1+1+1>3."

[0020] In summary, this invention can simultaneously achieve multiple objectives in moderately saline-alkali coastal areas, namely, "safe and efficient utilization of slightly saline water resources, desalination and fertilization of topsoil, and reduction and enhancement of nitrogen nutrient loss," ultimately ensuring stable and increased rice production and significantly improving the overall benefits and sustainability of rice cultivation in the region. Attached Figure Description

[0021] Figure 1 This is a heatmap showing the correlation between single-plant yield and other variables in Example 3.

[0022] Figure 2 This is a variance decomposition analysis diagram of single-plant yield and other variables in Example 3.

[0023] Figure 3 The soil in Example 4 Content dynamic change graph.

[0024] Figure 4 The soil in Example 4 Dynamic changes in content Figure 5 It is the field surface water in Example 4 Concentration dynamic change graph.

[0025] Figure 6 It is the field surface water in Example 4 Concentration dynamic change graph. Detailed Implementation

[0026] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0027] Example 1 The goal of this embodiment is to achieve efficient and safe utilization of slightly saline water resources while ensuring the normal growth of rice, and at the same time to suppress soil salinity accumulation through scientific irrigation and drainage, so as to create a suitable environment for rice root growth and nutrient absorption.

[0028] Specifically, a method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on brackish water irrigation includes the following steps: The following irrigation methods are pre-set based on brackish water irrigation: direct brackish water irrigation, brackish water-fresh water mixed irrigation, and brackish water-fresh water alternating irrigation; the appropriate irrigation method is dynamically selected based on the mineralization of the irrigation water source and the distribution of soil salinity in the target area. Create differentiated irrigation and drainage strategies, implement irrigation and drainage regulation in stages according to the rice growth period, and simultaneously implement the corresponding irrigation water mineralization control standards; Based on the soil fertility characteristics of moderately saline-alkali coastal land and the salt tolerance growth requirements of rice, the total amount of nitrogen, phosphorus, potassium and micronutrient fertilizers to be applied was determined; following the principle of stable supply of base fertilizer and precise topdressing in a phased nutrient management, the timing of fertilization was matched with the field irrigation and drainage salt leaching rhythm. Optimize the types of fertilizers and appropriate application methods for irrigation of saline-alkali land and brackish water to achieve coordinated regulation of water and fertilizer timing and dosage.

[0029] In a further embodiment, the dynamic selection method of the irrigation method is as follows: Obtain the average irrigation mineralization of the target area during the current time period. Simultaneously, the spatial distribution characteristics and temporal fluctuation characteristics of soil salinity in the root zone during the current period are collected to form the steady-state characteristics of soil salinity; If the soil salinity steady-state characteristics are unsteady, then brackish water-fresh water alternating irrigation should be used directly; conversely, if the soil salinity steady-state characteristics are stable, then irrigation should be based on the average value of irrigation mineralization. Analysis and selection: like In this case, slightly saline water should be used for direct irrigation. like Then, use a mixture of slightly saline and freshwater for irrigation until... ;in, , which are the first mineralization threshold and the second mineralization threshold, respectively.

[0030] To illustrate further, with , For example, the dynamic selection method for irrigation is as follows: If the soil salinity steady-state characteristics are unsteady (i.e., significant spatiotemporal fluctuations in soil salinity in the root zone, uneven profile distribution, and a tendency for short-term salt accumulation or salt return), then brackish water-freshwater alternating irrigation should be directly selected. The specific form of brackish water-freshwater alternating irrigation described in this embodiment is as follows: during periods of continuous rainfall, brackish water is used for irrigation; during periods of prolonged drought, freshwater is used for irrigation, avoiding salt accumulation caused by long-term brackish water irrigation while ensuring water supply.

[0031] like If brackish water is used for irrigation, it simplifies irrigation operations and improves water resource utilization efficiency; if Then, brackish water and fresh water are mixed in a certain volume ratio to reduce the salinity of the irrigation water after mixing to a certain level. The following measures take into account both water conservation and salt control requirements.

[0032] In a further embodiment, the differentiated irrigation and drainage strategy includes: a seedling stage with enhanced salt removal and a mid-to-late stage with steady-state water supply; The enhanced salt removal stage during the seedling period refers to the initial post-transplanting phase of rice. This stage employs a periodic alternating irrigation and drainage leaching pattern to rapidly reduce soil salt concentration in the root zone through cyclical water-salt exchange, alleviating salt stress and improving root aeration. In this embodiment, the initial post-transplanting phase is preferably the first 10 days after transplanting, implementing a "daytime irrigation, nighttime drainage" enhanced irrigation and drainage pattern to quickly leach salt from the root zone and alleviate salt stress. Specific procedures include: irrigating at 8:00 AM daily until the water level reaches approximately 5 cm, maintaining this level until 6:00 PM; and completely draining the water at 6:00 PM to ensure the roots are in an aerobic environment and prevent high-salt waterlogging from inhibiting root growth.

[0033] The mid-to-late stage of steady-state water supply refers to the period from late transplanting to harvest. Based on the water requirements of rice during its growth cycle and soil moisture conditions, a stable surface water layer is maintained, and the water depth is dynamically adjusted during key growth stages to ensure water supply while promoting rice growth and grain development. Using the above example, the period from late transplanting to harvest in this embodiment refers to 10 days after transplanting to harvest. Specifically, daytime irrigation and nighttime drainage are stopped, and conventional stable irrigation is switched to. Depending on soil moisture conditions, irrigation is promptly carried out to a surface water depth of 5cm; after the grain-filling stage, the water layer can be appropriately lowered to 3cm to improve grain plumpness.

[0034] To strictly control the risk of salt stress caused by slightly saline irrigation and ensure the safety of the root environment of rice throughout its growth period, this embodiment introduces a graded control standard for irrigation water salinity. Based on the differences in salt tolerance and irrigation and drainage intensity at different growth stages of rice, dual salinity thresholds are set for the seedling stage with enhanced salt drainage and the mid-to-late stage with steady-state water supply. This achieves precise, safe, and dynamic control of irrigation water salinity, avoiding secondary soil salinization and inhibited rice growth due to excessive irrigation water salinity.

[0035] Specifically, through the first mineralization threshold Second mineralization threshold To achieve this, the control method is as follows: During the intensive salt-drainage stage in the seedling stage (the first 10 days after rice transplanting), the soil undergoes rapid desalination and exhibits strong salt buffering capacity due to the implementation of high-frequency leaching with "daytime irrigation and nighttime drainage," allowing for relatively high mineralization of the irrigation water. Therefore, a second mineralization threshold is adopted. Control measures were implemented: Real-time irrigation mineralization values ​​were obtained during the intensive salt removal phase in the seedling stage. The real-time irrigation mineralization value The following requirements must be met: The embodiments described herein Values .

[0036] During the mid-to-late stage of steady-state water supply (10 days after transplanting to before harvest), irrigation and drainage intensity decreases, soil salinity accumulates easily, and rice becomes more sensitive to salt stress. Therefore, the salinity content of irrigation water must be strictly controlled. Thus, the first mineralization threshold is used. Control measures: Obtain real-time irrigation mineralization values ​​during the mid-to-late stage of steady-state water supply. The real-time irrigation mineralization value The following requirements must be met: The embodiment described herein The value is 1 .

[0037] By controlling the mineralization of irrigation water in stages and at different thresholds, we can make full use of slightly saline water resources and maintain a low-salt environment in the root zone, thus ensuring the normal growth, nutrient absorption and yield formation of rice.

[0038] To adapt to slightly saline irrigation conditions and salt stress environments, and to achieve nitrogen fertilizer reduction and efficiency enhancement, ensure nutrient supply throughout the rice growth period, and improve rice salt resistance and yield, this embodiment of the fertilization technology addresses technical issues such as low nitrogen utilization, easy nutrient leaching, and prominent contradictions between salt control and fertilizer supply under salt stress. By optimizing fertilizer ratios, fertilizer types, and application methods, and synergistically matching irrigation rhythms with rice nutrient requirements, this technology achieves the dual goals of high rice yield and efficient nitrogen fertilizer utilization under saline conditions.

[0039] Specifically, the method for determining the total amount of nitrogen, phosphorus, potassium, and micronutrient fertilizers applied is as follows: Based on the fertility characteristics of moderately saline-alkali coastal soils, such as low organic matter content and high risk of nutrient leaching, and combined with the salt tolerance requirements of rice, a calculation model for nitrogen application, phosphorus application, potassium application and micronutrient application was established by combining the target yield method with soil nutrient correction coefficient. Based on the nitrogen, phosphorus, potassium, and micronutrient application calculation models, the recommended nutrient application rates per unit area are calculated respectively. The final total application amount is then calculated by converting this amount to the target planting area. The conversion model is as follows: ; In the formula, For the first The final total amount of nutrients applied. For the first Recommended nutrient application rate per unit area for planting. The planting area is the target region.

[0040] In this embodiment, the nitrogen application rate calculation model, phosphorus application rate calculation model, and potassium application rate calculation model can adopt a unified and general calculation model: ; In the formula, Target yield per unit area of ​​rice ( kg / mu), For the first Nutrient uptake coefficient per unit yield (kg nutrients / kg rice) For the first Soil-based available nutrient supply for planting ( kg / mu), For the first Fertilizer utilization rate of plant nutrients, This is a correction coefficient for fertility and salt stress in moderately saline-alkali coastal land.

[0041] This embodiment targets moderately saline-alkali coastal land (soil salinity 0.2%~0.4%) in eastern coastal Jiangsu Province. Based on the above model calculations and field verification, the recommended application rate of each nutrient per unit area is determined as follows: Nitrogen fertilizer: 22g pure nitrogen per mu (approximately 0.067 hectares). kg / mu (equivalent to 330) kg / ha Phosphate fertilizer applied per mu 6.7 kg / mu (equivalent to 100) kg / ha Potassium fertilizer applied per acre 6.7 kg / mu (equivalent to 100) kg / ha ).

[0042] In a further embodiment, the calculation model for the application rate of trace elements (such as silicon, zinc, etc.) is as follows: ,in, For the first Recommended application rate of micronutrients per unit area. For the first Recommended application rates of micronutrients in conventional farmland. This model establishes a correction coefficient for nutrient deficiencies in coastal saline-alkali soils and salt stress tolerance in rice. Values ​​are assigned based on the available silicon and zinc content of the soil and the degree of salt stress, and are used to improve the salt tolerance and nutrient absorption efficiency of rice roots. Based on this model, this embodiment determines the micronutrient supplementation plan as applying 15 kg of silicon fertilizer and 2 kg of zinc fertilizer per mu (approximately 0.067 hectares). By supplementing silicon and zinc, the stability of rice cell walls is enhanced, the toxic effects of salt ions on the roots are mitigated, and nutrient absorption efficiency is improved, synergistically enhancing rice salt tolerance and yield.

[0043] To address the technical challenges of fluctuating soil salinity, easy nutrient leaching during irrigation, significant differences in salt tolerance and nutrient requirements at different growth stages of rice, and the tendency for single-application fertilization to cause excessive vegetative growth in the early stages and nutrient deficiency in the later stages, this embodiment follows the principle of stable basal fertilizer supply and precise topdressing in a phased nutrient management approach. The specific configuration method is as follows: Nitrogen fertilizer is applied in multiple applications at different stages of growth, including as basal fertilizer, tillering fertilizer, and heading fertilizer. Phosphorus and potassium fertilizers are applied as a single basal fertilizer application.

[0044] Nitrogen base fertilizer, phosphorus fertilizer, and potassium fertilizer should be applied to the field in a timely and simultaneous manner before rice transplanting, and thoroughly mixed with the topsoil to build a long-term and stable soil nutrient pool, thereby alleviating the problems of insufficient nutrient supply and premature aging due to nutrient deficiency in the later stages under salt stress. Nitrogen fertilizer for tillering should be applied at the appropriate time in the early stage of rice tillering to meet the nutrient requirements during the peak tillering period and promote the vigorous growth of effective tillers. Nitrogen fertilizer for panicle should be applied at the appropriate time in the early stage of rice panicle differentiation to replenish nutrients during the critical period of reproductive growth, enhance the plant's salt resistance, and ensure panicle development and yield formation.

[0045] As a specific implementation example, nitrogen fertilizer is applied in multiple applications strictly according to the ratio of basal fertilizer: tillering fertilizer: panicle fertilizer = 4:3:3. Basal fertilizer is applied 3-5 days before rice transplanting; tillering fertilizer is applied 20 days after transplanting, i.e., at the early stage of tillering, when the rice's salt tolerance gradually increases and the intensity of salt leaching during irrigation and drainage in the field decreases, which can significantly reduce the risk of nutrient leaching loss; panicle fertilizer is applied 45 days after transplanting, i.e., at the early stage of panicle differentiation, to continuously supply nutrients for subsequent grain development.

[0046] Considering the characteristics of phosphorus and potassium nutrients being easily fixed by the soil and having a low risk of leaching loss in saline-alkali environments, phosphate and potash fertilizers are applied as a one-time basal application, fully mixed with the soil during land preparation to improve nutrient adsorption effectiveness and long-term supply capacity.

[0047] Furthermore, the optimization of fertilization types and appropriate application methods for saline-alkali land and brackish water irrigation includes: selecting appropriate nitrogen, phosphorus, and potassium fertilizer types according to the soil environment of saline-alkali land and the water and salt transport characteristics of brackish water irrigation, and matching them with differentiated application methods; among them, nitrogen fertilizer adopts a staged application method of basal fertilizer with slow-release nitrogen source and fast-acting nitrogen source mixed in proportion, and top dressing with a single fast-acting nitrogen source; phosphorus fertilizer adopts an application method of high-solubility fertilizer suitable for alkaline soil and mixed with soil; potassium fertilizer adopts a concentrated strip application method to achieve coordinated control of water and fertilizer timing and dosage.

[0048] In other words, nitrogen fertilizer is applied in two stages: basal fertilizer and topdressing. The basal fertilizer is a mixture of 50% polyurethane-coated urea and 50% ordinary urea to slow-release nitrogen and avoid nitrogen leaching loss caused by frequent irrigation and drainage in the early stage of transplanting, while ensuring the supply of fast-acting nitrogen in the early stage. Urea is applied entirely during the topdressing stage. The phosphate fertilizer selected is diammonium phosphate, which has high solubility in alkaline soil. It is applied by broadcasting and then rotary tillage to mix it with the soil. Potassium chloride was selected as the potassium fertilizer and applied in strips between rice rows to improve root absorption efficiency.

[0049] Example 2 This embodiment, based on Embodiment 1, also discloses a step prior to irrigation that involves burying straw in the field and applying fertilizer in conjunction with the straw application: Straw mixed with soil and returned to the field: The straw of the previous season's crop is crushed and spread evenly, then mixed with soil in the topsoil through rotary tillage. Subsequently, water is added to regulate the soil moisture content and promote the decomposition of straw, forming a soil environment that inhibits salt, retains fertilizer, and improves soil structure. Coordinated application of base fertilizer: Base fertilizer is applied simultaneously after straw is mixed and buried to adjust the soil carbon-nitrogen ratio, avoid competition for nitrogen between straw decomposition and rice seedlings, and achieve matching of the timing of straw return to the field and nutrient release of base fertilizer, so as to provide synergistic fertilizer supply.

[0050] Through the above technical solutions, straw can be used to improve soil structure, increase organic matter content, inhibit soil salt accumulation, reduce nutrient leaching, and simultaneously achieve the recycling of straw resources. It can also work in synergy with irrigation and fertilization technologies to improve soil fertility.

[0051] As an example, the straw is first mixed with soil and returned to the field: After the previous season's crop is harvested, the straw is chopped and pre-treated using a straw crusher. The length of the chopped straw is strictly controlled to be 5-10cm to ensure uniform crushing and prevent the straw from being too long and affecting subsequent field cultivation and rice transplanting. 7-10 days before rice transplanting, the crushed straw is evenly spread on the field surface, and then rotary tillage is carried out using a rotary tiller. The tillage depth is set to 15-20cm to ensure that the straw is fully mixed with the top 0-20cm of topsoil. After the straw is mixed with soil, fresh water is promptly irrigated to adjust the soil moisture content to 70%-80% of the field capacity, creating a suitable water and fertilizer environment for straw decomposition and accelerating the straw decomposition process.

[0052] It also includes steps for validating and dynamically optimizing the currently implemented water and fertilizer co-management program: During the implementation of current irrigation methods, irrigation and drainage strategies, nutrient management and fertilization methods, the soil water and salt content in the root zone of the target area, the mineralization of irrigation water, rice growth and nutrient absorption are collected in real time to verify the implementation effect of the current plan. If the verification results do not meet the preset soil desalination targets, rice growth indicators, and water and fertilizer use efficiency requirements, then targeted adjustments and optimizations will be made to the irrigation method selection parameters, mineralization control thresholds, irrigation and drainage sequence, nutrient application ratios, and fertilizer application methods in the current scheme until the preset targets are met, ensuring that the current water and fertilizer synergistic management scheme is suitable for moderately saline-alkali coastal land and slightly brackish water irrigation conditions.

[0053] In summary, this scheme, based on straw return to the field, aims to improve the soil structure of saline-alkali land, increase soil organic matter levels, inhibit the upward accumulation of soil salts, and reduce the deep leaching loss of nutrients. At the same time, it realizes the resource recycling of straw. By matching the timing and coupling the processes of irrigation, fertilization and straw return to the field, a technological synergy effect is formed, which improves the soil fertility and water and fertilizer utilization efficiency of coastal saline-alkali land as a whole.

[0054] First, irrigation and fertilization should be coordinated and matched. During the salt leaching window period of daytime irrigation and nighttime drainage 10 days before rice transplanting, no topdressing should be applied to prevent the loss of nitrogen due to frequent irrigation and drainage. Tillering fertilizer and panicle fertilizer should be applied one day before irrigation, so that nutrients can be steadily infiltrated and gathered in the crop root zone by relying on the subsequent irrigation, thereby improving the root system's efficiency in nutrient absorption and utilization.

[0055] Second, irrigation and straw return to the field should be coordinated in sequence. After straw is mixed and buried in the field, timely watering should be provided to create a suitable humidity environment and accelerate the straw decomposition process. The salt-controlled watering pattern of daytime irrigation and nighttime drainage for 10 days before transplanting can further promote the gradual release of straw decomposition products, continuously replenish soil nutrients, and steadily improve basic soil fertility.

[0056] Third, fertilization and straw return to the field should be coordinated to ensure nutrient supply. After the straw is mixed and buried in the field, base fertilizer should be applied in a timely manner to rationally regulate the soil carbon-nitrogen ratio and effectively avoid the problem of competition for nitrogen between microorganisms during straw decomposition and rice seedlings. At the same time, relying on the complementary rhythm of slow-release nutrients in base fertilizer and nitrogen supply from straw decomposition, a long-term and stable synergistic nitrogen supply system can be constructed to ensure a balanced supply of nutrients throughout the entire growth period of rice.

[0057] Example 3 To screen the appropriate saline water mineralization threshold and controlled-release fertilizer type for rice growth in moderately saline-alkali coastal areas, an in-situ soil column test was conducted in a field. Three irrigation treatment groups and three fertilization treatment groups were cross-tested: the irrigation treatment included direct freshwater irrigation (FW, mineralization: 0.15). Freshwater-slightly brackish water mixed irrigation (FBW, mineralization: 1-1.5) Direct irrigation with brackish water (BW, mineralization: 1.35-2.0) and brackish water (BW, mineralization: 1.35-2.0). The fertilization treatments included: basal application of urea (U), basal application of polyurethane-coated urea (PCU), and basal application of urea-formaldehyde (UF). This experimental system was used to investigate the effects of different irrigation-fertilization combinations on rice growth, root development, nitrogen uptake and utilization, and yield.

[0058] (I) Rice growth characteristics The effects of irrigation treatments on rice growth characteristics showed significant differences during the growth period: compared with freshwater irrigation (FW), the two brackish water irrigation treatments (FBW and BW) did not reduce the number of rice tillers, and had a significant promoting effect on rice tillering in the early and middle stages of rice growth: at the jointing and heading stages, the number of rice tillers in the FBW and BW treatments was significantly higher than that in the FW treatment. P It is a statistical indicator used to determine whether a difference truly exists. P <0.001, as shown in Table 1).

[0059] However, contrary to the promoting effect on tiller number, slightly saline irrigation showed a significant inhibitory effect on rice plant height elongation and leaf growth and development (Table 1): at and after the jointing stage, the rice plant height of FBW and BW treatments was significantly lower than that of FW treatment ( P <0.05); During and after the heading stage, the leaf area of ​​rice in both brackish water treatments was significantly lower than that in the FW treatment ( P <0.001).

[0060] Fertilizer treatments did not have a significant regulatory effect on rice growth characteristics: Compared with urea treatment (U), the two controlled-release fertilizer treatments (PCU, UF) had no significant effect on rice tillering, plant height elongation, and leaf growth; under the same irrigation conditions, there were no significant differences in tiller number, plant height, and leaf area among the different fertilization treatments. P >0.05 (Table 1).

[0061] The above results indicate that the effects of slightly saline irrigation on rice growth in moderately saline-alkali coastal areas exhibit a phased differentiation: it significantly promotes tillering during the early to mid-growth stages (jointing to heading stage), but significantly inhibits plant height elongation and leaf growth and development during the mid to late-growth stages (jointing stage and beyond). Different types of slow-release fertilizers did not show significant promoting effects on these rice growth indicators.

[0062] Table 1. Rice growth characteristics (II) Rice root morphology The results of the study on the effects of irrigation treatments on rice root growth showed that, compared with freshwater irrigation (FW), both brackish water irrigation treatments (FBW and BW) significantly inhibited rice root growth. Specifically, root biomass indicators (root dry weight, root length, root surface area, and root volume) and spatial configuration indicators (number of root tips, number of branches, and number of crossings) all decreased significantly. P <0.05, Table 2). However, brackish water irrigation had no significant effect on root diameter, and there was no significant difference in root diameter among different irrigation treatments ( P >0.05 (Table 2).

[0063] The results of the regulatory effects of fertilization treatments on rice root growth showed that, compared with urea treatment (U), the two controlled-release fertilizer treatments (PCU and UF) significantly promoted the morphological expansion and spatial distribution of rice roots, specifically manifested in a significant increase in root length, root tip number, and branch number. P <0.05, Table 2). However, slow-release fertilizers had no significant regulatory effect on root biomass-related indicators (root dry weight, root surface area, root volume, root diameter), and there were no significant differences in these indicators among different fertilization treatments. P >0.05 (Table 2).

[0064] The above results indicate that brackish water irrigation significantly inhibits the root growth and spatial distribution of rice in moderately saline-alkali coastal areas, resulting in a significant reduction in root biomass and spatial configuration indices. Under brackish water irrigation conditions, although the application of slow-release fertilizers failed to promote the increase of root biomass, it could effectively optimize the root morphology expansion and spatial distribution characteristics.

[0065] Table 2. Morphological characteristics of rice root system (III) Nitrogen absorption in rice The results of the study on the effects of irrigation treatments on nitrogen uptake in rice showed that brackish water irrigation significantly inhibited nitrogen uptake and utilization in all parts of rice, including roots, stems, leaves, and grains. Compared with freshwater irrigation (FW), the total nitrogen uptake of rice decreased significantly by 8-27% and the agronomic nitrogen use efficiency decreased significantly by 22-37% under both brackish water irrigation treatments (FBW and BW). P <0.001, Table 3).

[0066] The results of the regulatory effects of fertilization treatments on nitrogen uptake in rice showed that, compared with urea treatment (U), both controlled-release fertilizer treatments (PCU and UF) significantly promoted nitrogen uptake in rice. Under all three irrigation conditions, the application of polyurethane-coated urea (PCU) significantly increased the total nitrogen uptake and agronomic nitrogen use efficiency in rice. P <0.05, Table 3). Meanwhile, the application of slow-release fertilizer can effectively mitigate the negative impact of brackish water irrigation on nitrogen absorption and utilization in rice. Under the conditions of slow-release application, there were no significant differences in total nitrogen uptake and agronomic nitrogen use efficiency among different irrigation water treatments (…). P >0.05 (Table 3).

[0067] The above results indicate that brackish water irrigation significantly inhibits nitrogen absorption and utilization in rice grown in moderately saline-alkali coastal areas, reducing nitrogen agronomical use efficiency. Applying slow-release fertilizers can effectively alleviate the negative stress of brackish water irrigation on nitrogen absorption and utilization in rice, while significantly improving agronomical nitrogen use efficiency.

[0068] Table 3 Nitrogen uptake and yield in rice (iv) Rice yield The results of the study on the effects of irrigation treatments on rice yield showed that brackish water irrigation significantly reduced rice yield: compared with freshwater irrigation (FW), the yield reduction in rice under the two types of brackish water irrigation treatments (FBW and BW) was 17-35%. P <0.05, Table 3). However, there was no significant difference in rice yield between the FBW and BW treatments ( P >0.05 (Table 3).

[0069] The results of the fertilization treatment on rice yield regulation showed that the application of polyurethane film urea (PCU) could effectively alleviate the adverse effects of brackish water irrigation on rice yield. Under both FBW and BW brackish water irrigation treatments, the yield per rice plant in the PCU treatment was significantly higher than that in the urea (U) and urea-formaldehyde (UF) treatments. P <0.05, Table 3). It is noteworthy that even under saline irrigation conditions, the yield per rice plant treated with PCU was not significantly different from the three fertilization treatments under freshwater irrigation. P >0.05 (Table 3).

[0070] The above results indicate that brackish water irrigation significantly reduces rice yield in moderately saline-alkali coastal land, and the application of polyurethane film urea can effectively alleviate the yield reduction problem caused by brackish water irrigation. Under the condition of applying polyurethane film urea, using 2.0... The following slightly saline water irrigation will not cause a reduction in rice yield.

[0071] (V) The mechanism by which slow-release fertilizer alleviates growth stress in rice in moderately saline-alkali coastal land under brackish water irrigation Correlation analysis showed that nitrogen uptake in rice was significantly positively correlated with root surface area and root tip number. P <0.05, Figure 1 Agronomic nitrogen use efficiency was only significantly positively correlated with root tip number (P<0.05). Figure 1 Furthermore, rice yield showed a significant positive correlation with root dry weight, root surface area, number of root tips, number of root branches, number of root crossings, nitrogen uptake, and agronomic nitrogen use efficiency. P <0.05, such as Figure 1(As shown). To further clarify the main controlling factors of rice yield, the experimental monitoring variables were divided into three categories: rice growth characteristics (tiller number, plant height, leaf area), rice root morphology characteristics (root dry weight, root length, root surface area, root volume, average diameter, number of root tips, number of branches, number of crossings), and rice nitrogen absorption and utilization (nitrogen absorption and agronomical utilization efficiency in roots, stems, leaves, and grains). Analysis of variance (VPA) was used to quantify the relative contributions of each variable to the variation in rice yield. The results are shown in the figure. Figure 2 As shown: The variables monitored in this experiment can explain 85% of the variation in rice yield. Among them, three core effects are the main controlling factors of yield: the combined effect of rice nitrogen uptake and utilization and root morphology characteristics explains 23% of the yield variation, the individual effect of rice nitrogen uptake and utilization explains 21% of the yield variation, and the combined effect of rice nitrogen uptake and utilization and growth characteristics explains 20% of the yield variation.

[0072] The above results indicate that the inhibitory pathway of brackish water irrigation on rice yield in moderately saline-alkali coastal areas is as follows: brackish water irrigation inhibits rice root growth and spatial distribution, restricts nitrogen absorption and utilization, and thus affects plant height elongation and leaf development, ultimately leading to reduced rice yield.

[0073] The regulatory pathway for slow-release fertilizers to mitigate the negative effects of brackish water irrigation is as follows: the application of slow-release fertilizers (especially polyurethane film urea) can regulate nitrogen release, promote root space extension, and thus improve nitrogen absorption and utilization efficiency, ultimately achieving the dual goals of increasing rice yield and improving nitrogen fertilizer utilization.

[0074] In summary, the analysis shows that, under the background of brackish water irrigation, applying polyurethane film urea as a base fertilizer instead of pure urea can effectively alleviate the negative effects of brackish water irrigation on root growth, nitrogen absorption and utilization, and yield of rice in moderately saline-alkali coastal areas. Furthermore, considering both rice yield and nitrogen use efficiency as core indicators, 1.5 The salinity threshold for safe irrigation with slightly saline water is defined as the minimum salinity level for normal rice growth in moderately saline-alkali coastal areas. During production, irrigation with slightly saline water with a salinity below this threshold should be used whenever possible during the rice's growth period (especially after the jointing stage). When using water with a salinity below 1.5... Under the premise of slightly saline water irrigation, the application of polyurethane film urea as base fertilizer instead of urea can simultaneously achieve the triple goals of safe utilization of slightly saline water resources in coastal saline-alkali areas, improved nitrogen use efficiency, and stable rice yield, providing technical support for high-quality and high-yield water and fertilizer management of rice in moderately saline-alkali coastal areas.

[0075] Example 4 To characterize the nitrogen migration and transformation features of moderately saline-alkali coastal land under the influence of brackish water irrigation and to explore the regulatory effect of controlled-release fertilizer application, an in-situ soil column experiment was conducted in a field setting up a crossover experiment with three irrigation treatment groups and three fertilization treatment groups: the irrigation treatment included direct freshwater irrigation (FW, mineralization: 0.15) Freshwater-slightly brackish water mixed irrigation (FBW, mineralization: 1-1.5) Direct irrigation with brackish water (BW, mineralization: 1.35-2.0) and brackish water (BW, mineralization: 1.35-2.0). The fertilization treatments included: basal application of urea (U), basal application of polyurethane-coated urea (PCU), and basal application of urea-formaldehyde (UF). Based on continuous dynamic monitoring of inorganic nitrogen in soil and field surface water, the effects of different irrigation-fertilization combinations on nitrogen migration and transformation were systematically investigated.

[0076] (I) Dynamic Changes in Soil Inorganic Nitrogen Content soil Dynamic changes in content, such as Figure 3 As shown: After three applications of fertilizer—basal fertilizer, tillering fertilizer, and jointing / heading fertilizer—the soil... The content of all samples showed a dynamic change pattern of first rapidly increasing and then rapidly decreasing. Further analysis was conducted on the soil at each fertilization stage under different fertilization treatments. The difference in peak content indicates that under the U treatment, the soil after basal fertilizer application... The peak content was significantly greater than that after application of tillering fertilizer and jointing and booting fertilizer. P< 0.05); PCU and UF treatments showed opposite trends, with soil after jointing and heading fertilizer application... The peak content was significantly greater than the peak content after application of basal fertilizer and tillering fertilizer. P< 0.05).

[0077] Based on the irrigation and drainage schedule of this experiment, the rice growth period was divided into an irrigation / drainage period (the first 20 days after transplanting) and a non-irrigation / drainage period (20 days after transplanting). A linear mixture model was used to analyze the effects of different treatments on the soil. The effects of different irrigation treatments on soil composition were investigated, and the results showed that during the two irrigation and drainage periods, different irrigation treatments had varying effects on soil composition. The content was not significantly affected. P> 0.05). Different fertilization treatments had varying effects on soil quality during both irrigation / drainage periods and non-irrigation / drainage periods. The content had a significant impact, and the effect varied significantly with the irrigation and drainage period. Specifically, during the irrigation and drainage period, under FW and FBW irrigation conditions, the soil in treatment U... The content was significantly higher than that of PCU and UF treatments ( P< 0.001). During non-irrigation / drainage periods, the opposite trend was observed; under the three irrigation conditions, the soils treated with PCU and UF showed the highest values. The content was significantly higher in the U treatment than in the U treatment. P<0.001).

[0078] soil Dynamic changes in content, such as Figure 4 As shown: After the application of base fertilizer, the soil... The content gradually increases, reaching a peak 12-21 days after transplanting, and then shows a downward trend; after the application of fertilizer during the jointing and heading stages, the soil... The content rose again, then gradually decreased, until the soil... The content returned to the initial level of the experiment. Further analysis of the soil at each fertilization stage is needed. The difference in peak content indicates that under different fertilization treatments, the soil after application of basal fertilizer and tillering fertilizer... The peak content was significantly greater than the peak content after application of fertilizer at the jointing and booting stage. P< 0.05).

[0079] The results of the linear mixed model analysis show that different irrigation treatments have different effects on soil NO3 during the irrigation and drainage period and the non-irrigation and drainage period. - The content was not significantly affected. P> 0.05). The effects of different fertilization treatments on soil at two different time periods. The content produced different significant effects, and the pattern of influence was related to soil NH4. + The content was consistent. During the irrigation and drainage periods, under FW and FBW irrigation conditions, the soil in treatment U... The content was significantly higher than that of PCU and UF treatments ( P< (0.001). During the non-irrigation and drainage period, under the three irrigation conditions, compared with the U treatment, both the PCU and UF treatments significantly improved soil moisture content. content( P< 0.001).

[0080] (II) Dynamic Changes in Inorganic Nitrogen Concentration in Field Water Field water Dynamic changes in concentration, such as Figure 5 As shown: with soil The dynamic changes in content show significant differences, particularly in field surface water. The concentration only showed a significant increase after basal and tillering fertilizer application, followed by a rapid decline; no significant concentration fluctuation was observed after jointing and heading fertilizer application. Further comparison of field surface water at each fertilization stage was conducted. Differences in peak concentrations were observed: Under FW irrigation conditions, the surface water level after tillering fertilizer application was significantly lower. The peak concentration was significantly higher than the peak concentration after basal fertilizer application. P< 0.05); while under the two slightly saline irrigation conditions of FBW and BW, the surface water at different times There was no significant difference in peak concentration. P> 0.05).

[0081] The results of the linear mixed model analysis show that different irrigation treatments have different effects on field surface water during the irrigation and drainage period and the non-irrigation and drainage period. The concentration had no significant effect. P> 0.05). Furthermore, under the three irrigation conditions, the surface water content varied among different fertilization treatments. There was no significant difference in concentration. P> 0.05).

[0082] Field water Dynamic changes in concentration, such as Figure 6 As shown, its variation pattern is related to the soil. The content varies. After the application of base fertilizer, the surface water in the field... The concentration gradually increases, reaching a peak 6-10 days after transplanting, and then declines. This peak occurs earlier than the soil concentration. Content. It is also worth noting that, in relation to soil... The dynamic changes in content differ; after the application of fertilizer during the jointing and booting stages, the surface water content in the field... The concentration did not increase significantly.

[0083] The results of linear mixed model analysis showed that the two brackish water irrigation treatments (FBW and BW) significantly reduced surface water during the irrigation and drainage periods. concentration( P< 0.05), but for field surface water during non-irrigation and drainage periods The concentration did not have a significant effect. P> 0.05). During the irrigation and drainage periods, under three irrigation conditions, the surface water of the field was treated with two controlled-release fertilizers (PCU and UF). The concentrations were all significantly lower than those treated with urea (U). P< 0.001). During the non-irrigation and drainage period, under FW irrigation conditions, both slow-release fertilizer treatments significantly reduced surface water. concentration( P< 0.05); while under FBW and BW irrigation conditions, different fertilization treatments had different effects on field surface water. No significant effect on concentration ( P> 0.05).

[0084] The above results indicate that brackish water irrigation did not significantly affect the nitrogen migration and transformation characteristics of moderately saline-alkali coastal land. However, the application of controlled-release fertilizers (PCU and UF) as basal fertilizer significantly affected nitrogen migration and transformation. During periods of frequent irrigation and drainage (the first 20 days after transplanting and before the tillering stage), controlled-release fertilizers significantly reduced the inorganic nitrogen content in the soil and surface water, adapting to the high-intensity irrigation and drainage leaching characteristics of the field management during this stage. This effectively reduced the risk of nitrogen loss through leaching while ensuring the basic nutrient requirements for rice growth. During periods of infrequent irrigation and drainage (after 20 days after transplanting and after the tillering stage), controlled-release fertilizers significantly increased the inorganic nitrogen content in the soil, enhanced soil nitrogen availability, and ensured a continuous supply of nitrogen, thus supporting rice root growth, nitrogen absorption, and yield formation.

[0085] Example 5 Based on previous experiments, to screen suitable straw return methods and controlled-release fertilizer application ratios for rice growth in moderately saline-alkali coastal areas, an in-situ soil column experiment was conducted in a field. Three straw return treatment groups and three fertilization treatment groups were cross-tested: the straw return treatments included no straw return (S1), straw mixed with soil (S2, 20cm burial depth), and straw mixed with soil (S3, 20cm interlayer depth); the controlled-release fertilizer application ratios included: 100% urea as basal fertilizer (N1), 1:1 ratio of polyurethane-coated urea and urea as basal fertilizer (N2), and 100% polyurethane-coated urea as basal fertilizer (N3). This experimental system explored the effects of different straw return-fertilization combinations on rice growth, root development, and yield.

[0086] (I) Rice growth characteristics Multivariate analysis of variance showed that the interaction between straw return method and controlled-release fertilizer application ratio on growth characteristics such as rice plant height, SPAD value, and leaf area was not significant. P> The result was 0.05, meaning that the effects of the two factors on the growth characteristics of rice were independent and had no interaction effect.

[0087] The method of straw return to the field only had a significant effect on rice plant height during the rice maturity stage: compared with the no-return-to-field treatment (S1) and the straw mixed-landing-to-field treatment (S3), the straw mixed-landing-to-field treatment (S2) significantly promoted rice plant height growth. P <0.05, and there was no significant effect on rice plant height among different straw return treatments at other growth stages. P >0.05, as shown in Table 4). Fertilizer treatments only significantly affected rice plant height during the tillering stage. Compared to the urea treatment (N1), both polyurethane-coated urea treatments (N2 and N3) with different ratios significantly increased rice plant height. P <0.05, Table 4); at other times, fertilization treatments did not have a significant effect on rice plant height ( P >0.05 (Table 4).

[0088] Straw return treatment had a significant regulatory effect on the SPAD value of rice leaves, while fertilization treatment had no significant effect: At all four growth stages, compared with the no-return treatment (S1), the straw mixed-landing treatment (S2) and the straw mixed-landing treatment (S3) significantly increased the SPAD value of rice leaves. P <0.001), but there was no significant difference in SPAD values ​​between treatments S2 and S3 ( P >0.05, Table 4). Meanwhile, throughout the entire rice growth period, there were no significant differences in leaf SPAD values ​​among different fertilization treatments ( P >0.05 (Table 4).

[0089] During the heading and maturity stages, compared to the no-return-to-field treatment (S1) and the straw-mixed-landing-to-field treatment (S3), the straw-mixed-landing-to-field treatment (S2) significantly promoted the expansion of rice leaf area. P <0.05); however, at the jointing stage, different straw return methods had no significant effect on leaf area ( P >0.05, Table 4). Throughout the rice growth period, there was no significant difference in leaf area among different fertilization treatments (>0.05, Table 4). P >0.05 (Table 4).

[0090] In summary, the straw burial treatment (S2) is the most suitable method for rice cultivation in moderately saline-alkali coastal areas. Compared to the no-stubble treatment (S1) and the straw burial treatment (S3), it significantly increases the SPAD value of rice, promotes leaf area expansion, and promotes plant height development in the later stages of rice growth. In contrast, different proportions of polyurethane-coated urea treatments only have a temporary promoting effect on plant height during the tillering stage, and do not have a significant regulatory effect on the SPAD value, leaf area, or plant height at other stages throughout the entire growth period.

[0091] Table 4. Rice growth characteristics (II) Rice root morphology The results of multivariate analysis of variance showed that the interaction between straw return method and controlled-release fertilizer application ratio on rice root morphology characteristics was not significant. P> The coefficient of variation (0.05) indicates that the effects of the two factors on the root morphology of rice are independent and have no interaction effect.

[0092] The effects of straw return methods on rice root growth varied significantly (as shown in Table 5): The root biomass indices (root dry weight, total root length, root surface area, average root diameter, root volume) and spatial configuration indices (root tip number, branch number, and crossing number) of rice were significantly higher in the no-return-to-field treatment (S1) and the straw mixed-landing-to-field treatment (S2) than in the straw mixed-landing-to-field treatment (S3).P <0.05); while there were no significant differences in root morphology indices between treatments S1 and S2 ( P >0.05).

[0093] The application ratio of slow-release fertilizer has a significant regulatory effect on rice root growth (Table 5): Compared with urea treatment (N1), the two different ratios of polyurethane-coated urea treatments (N2, N3) can significantly increase root biomass indicators such as total root length and root surface area, as well as spatial configuration indicators such as root tip number, branch number, and crossing number. P <0.05, but had no significant effect on other rice root morphology indicators such as root dry weight, average root diameter, and root volume. P >0.05); and there were no significant differences in any root morphology index between the N2 and N3 treatments ( P >0.05 (Table 5).

[0094] In summary, the analysis shows that mixed burial of straw into the field has no significant regulatory effect on rice root growth in moderately saline-alkali coastal areas compared to non-composition. However, layered straw burial significantly inhibits root biomass accumulation and spatial configuration optimization. Meanwhile, the application of polyurethane-coated urea effectively promotes increased rice root biomass and optimizes root morphology and spatial distribution, but different application ratios show no significant difference in their regulatory effect on rice root growth.

[0095] Table 5 Morphological characteristics of rice root system (III) Rice yield The results of multivariate analysis of variance showed that the interaction between straw return method and controlled-release fertilizer application ratio on rice yield and its components was not significant. P> The coefficient of variation is 0.05, meaning that the effects of the two factors on rice yield and its components are independent and there is no interaction effect.

[0096] Further analysis showed that the method of returning straw to the field and the proportion of slow-release fertilizer application had no significant effect on the number of panicles and the thousand-grain weight of rice. P >0.05), but it has a significant regulatory effect on the number of grains per panicle and the yield per hill in rice ( P <0.001, Table 6). Specifically, compared with the no-return-to-field treatment (S1) and the straw mixed-landing-to-field treatment (S3), the straw mixed-landing-to-field treatment (S2) significantly increased the number of grains per panicle and the yield per hill (<0.001, Table 6). P <0.001); while compared with urea treatment (N1), the two different ratios of polyurethane-coated urea treatments (N2, N3) significantly increased the number of grains per panicle and the yield per hill in rice. P <0.001), and there was no significant difference in the promoting effects of N2 and N3 treatments on the number of grains per panicle and yield per hill in rice. P>0.05 (Table 6).

[0097] In summary, both straw burial and application of polyurethane-coated urea can significantly increase rice yield in moderately saline-alkali coastal land, but their effects on rice yield regulation are independent and have no interaction. At the same time, there is no significant difference in the promoting effect of different polyurethane-coated urea application ratios on rice yield.

[0098] Table 6 Rice Yield and its Components In summary, under the context of slightly saline irrigation, straw mixing and burying is a more suitable method for rice cultivation in moderately saline-alkali coastal areas. It not only significantly increases the SPAD value of rice leaves and promotes leaf area expansion, but also promotes plant height development in the later stages of growth, ultimately increasing rice yield by improving above-ground growth. Simultaneously, it has no negative impact on rice root growth, making it more valuable than layer-by-layer straw burial.

[0099] Meanwhile, applying polyurethane-coated urea as base fertilizer instead of conventional urea can effectively promote the accumulation of rice root biomass, optimize root morphology and spatial distribution characteristics, provide support for nitrogen absorption and aboveground growth, and thus significantly increase crop yield. Moreover, the experimental results show that different application ratios of polyurethane-coated urea have no significant difference in regulatory effect, providing room for optimizing production costs.

[0100] Taking into account both the effect of increasing rice yield and controlling production costs, the optimal management method for rice cultivation in moderately saline-alkali coastal areas is to adopt the straw mixed burial and return to the field model, and to replace conventional urea with 50% polyurethane-coated urea in the base fertilizer. This method balances high yield, economy and adaptability, and can provide technical reference for high-quality and efficient rice cultivation under slightly saline irrigation conditions in this region.

Claims

1. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation, characterized in that, Includes the following steps: The following irrigation methods are pre-set based on brackish water irrigation: direct brackish water irrigation, brackish water-fresh water mixed irrigation, and brackish water-fresh water alternating irrigation; the appropriate irrigation method is dynamically selected based on the mineralization of the irrigation water source and the distribution of soil salinity in the target area. Create differentiated irrigation and drainage strategies, implement irrigation and drainage regulation in stages according to the rice growth period, and simultaneously implement the corresponding irrigation water mineralization control standards; Based on the soil fertility characteristics of moderately saline-alkali coastal land and the salt tolerance growth requirements of rice, the total amount of nitrogen, phosphorus, potassium and micronutrient fertilizers to be applied was determined; following the principle of stable supply of base fertilizer and precise topdressing in a phased nutrient management, the timing of fertilization was matched with the field irrigation and drainage salt leaching rhythm. Optimize the types of fertilizers and appropriate application methods for irrigation of saline-alkali land and brackish water to achieve coordinated regulation of water and fertilizer timing and dosage.

2. The method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, Before irrigation, the process also includes straw burial and returning to the field, along with coordinated fertilization. Straw mixed with soil and returned to the field: The straw of the previous season's crop is crushed and spread evenly, then mixed with soil in the topsoil through rotary tillage. Subsequently, water is added to regulate the soil moisture content and promote the decomposition of straw, forming a soil environment that inhibits salt, retains fertilizer, and improves soil structure. Coordinated application of base fertilizer: Base fertilizer is applied simultaneously after straw is mixed and buried to adjust the soil carbon-nitrogen ratio, avoid competition for nitrogen between straw decomposition and rice seedlings, and achieve matching of the timing of straw return to the field and nutrient release of base fertilizer, so as to provide synergistic fertilizer supply.

3. The method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, The dynamic selection method for the irrigation method is as follows: Obtain the average irrigation mineralization of the target area during the current time period. Simultaneously, the spatial distribution characteristics and temporal fluctuation characteristics of soil salinity in the root zone during the current period are collected to form the steady-state characteristics of soil salinity; If the soil salinity steady-state characteristics are unsteady, then brackish water-fresh water alternating irrigation should be used directly; conversely, if the soil salinity steady-state characteristics are stable, then irrigation should be based on the average value of irrigation mineralization. Analysis and selection: like In this case, slightly saline water should be used for direct irrigation. like Then, use a mixture of slightly saline and freshwater for irrigation until... ;in, , which are the first mineralization threshold and the second mineralization threshold, respectively.

4. The method for coordinated water and fertilizer management of rice in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, The differentiated irrigation and drainage strategy includes: an enhanced salt removal stage during the seedling stage and a steady-state water supply stage in the middle and late stages; The seedling stage of enhanced salt removal is the initial stage after rice transplanting, which adopts an enhanced rinsing mode that alternates between periodic irrigation and drainage. The mid-to-late stage of steady-state water supply is from the late transplanting stage to before harvest. Based on the water requirements of rice during its growth period and soil moisture, a stable surface water layer is maintained, and the water layer depth is dynamically adjusted during key growth stages.

5. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation, as described in claim 4, is characterized in that... The irrigation water mineralization control standard uses a first mineralization threshold. Second mineralization threshold To achieve this, the control method is as follows: During the enhanced salt removal stage in the seedling stage, a second mineralization threshold was used. Control measures were implemented: Real-time irrigation mineralization values ​​were obtained during the intensive salt removal phase in the seedling stage. The real-time irrigation mineralization value The following requirements must be met: ; During the mid-to-late stage of steady-state water supply, a first mineralization threshold is adopted. Control measures: Obtain real-time irrigation mineralization values ​​during the mid-to-late stage of steady-state water supply. The real-time irrigation mineralization value The following requirements must be met: .

6. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, The method for determining the total amount of nitrogen, phosphorus, potassium, and micronutrient fertilizers applied is as follows: Based on the fertility characteristics of moderately saline-alkali coastal soils, such as low organic matter content and high risk of nutrient leaching, and combined with the salt tolerance requirements of rice, a calculation model for nitrogen application, phosphorus application, potassium application and micronutrient application was established by combining the target yield method with soil nutrient correction coefficient. Based on the nitrogen, phosphorus, potassium, and micronutrient application calculation models, the recommended nutrient application rates per unit area are calculated respectively. The final total application amount is then calculated by converting this amount to the target planting area. The conversion model is as follows: ； In the formula, For the first The final total amount of nutrients applied. For the first Recommended nutrient application rate per unit area for planting. The planting area is the target region.

7. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, The principle of phased nutrient management, which ensures a stable supply of base fertilizer and precise topdressing, is as follows: nitrogen fertilizer is applied in stages, in proportion to the base fertilizer, tillering fertilizer, and heading fertilizer, according to different growth stages; phosphorus fertilizer and potassium fertilizer are applied as a single base fertilizer application. Nitrogen fertilizer, basal fertilizer, phosphorus fertilizer, and potassium fertilizer should be applied to the field in a timely and simultaneous manner before rice transplanting, and thoroughly mixed with the topsoil to build a long-term and stable soil nutrient pool. Nitrogen fertilizer and tillering fertilizer should be applied at the appropriate time in the early stage of rice tillering, and panicle fertilizer should be applied at the appropriate time in the early stage of rice panicle differentiation.

8. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation, as described in claim 7, is characterized in that... The optimized fertilization types and suitable application methods for saline-alkali land and brackish water irrigation include: Based on the soil environment of saline-alkali land and the water and salt transport characteristics of slightly saline water irrigation, appropriate types of nitrogen, phosphorus and potassium fertilizers are selected and matched with differentiated application methods. Nitrogen fertilizer is applied in stages, using a combination of slow-release and fast-acting nitrogen sources as basal fertilizer and a single fast-acting nitrogen source as top dressing. Phosphate fertilizer is applied using a highly soluble fertilizer suitable for alkaline soils and mixed with the soil. Potassium fertilizer is applied in concentrated strips to achieve coordinated control of water and fertilizer timing and dosage.

9. A method for coordinated water and fertilizer management of rice paddies in moderately saline-alkali coastal land based on brackish water irrigation according to claim 1, characterized in that, It also includes steps for validating and dynamically optimizing the currently implemented water and fertilizer co-management program: During the implementation of current irrigation methods, irrigation and drainage strategies, nutrient management and fertilization methods, the soil water and salt content in the root zone of the target area, the mineralization of irrigation water, rice growth and nutrient absorption are collected in real time to verify the implementation effect of the current plan. If the verification results do not meet the preset soil desalination targets, rice growth indicators, and water and fertilizer use efficiency requirements, then targeted adjustments and optimizations will be made to the irrigation method selection parameters, mineralization control thresholds, irrigation and drainage sequence, nutrient application ratios, and fertilizer application methods in the current scheme until the preset targets are met, ensuring that the current water and fertilizer synergistic management scheme is suitable for moderately saline-alkali coastal land and slightly brackish water irrigation conditions.

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