A leaching irrigation method for relieving secondary salinization and preventing and controlling early decline of drip irrigation cotton field

Abstract

This invention discloses a leaching method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields. It belongs to the field of agricultural irrigation technology. Addressing the shortcomings of existing drip irrigation-supported periodic leaching technologies, such as the lack of a quantitative indicator system for "activation threshold - leaching volume - leaching cycle" and poor synergy with cotton's water requirements, this invention innovatively constructs a dual-trigger mechanism of "salt threshold + growth period." Leaching is initiated when the soil conductivity in the root zone exceeds the salt tolerance threshold during the peak flowering to boll-forming stage. The leaching volume is precisely quantified using the leaching water requirement calculation model LR=θ×D×(1-LF), leaching the root zone salt to a safe depth of 40-60cm while simultaneously meeting the water requirements during the flowering and boll-forming stage. This invention achieves precise water and salt management, avoiding root hypoxia or excessive vegetative growth caused by blindly increasing water supply. It has significant effects in water conservation, yield increase, and delaying premature aging, and the technology has a high degree of standardization, making it easy to promote on a large scale.

Description

Technical Field

[0001] This invention relates to the field of agricultural irrigation technology, and more specifically to a method for irrigation that alleviates secondary salinization and prevents premature aging in drip-irrigated cotton fields. Background Technology

[0002] In arid cotton-growing areas of Northwest my country, such as Xinjiang and Gansu, drip irrigation under mulch film is widely used because it meets the core need for efficient water resource utilization. However, this technology has long employed a "small-volume, high-frequency, localized wetting" irrigation model, disrupting the dynamic balance of soil water and salt maintained by traditional flood irrigation. Drip irrigation water can only moisten the crop root zone, failing to generate sufficient infiltration to leach accumulated salts from the root zone into deeper soil layers. In arid regions, the combined effects of strong evaporation and crop transpiration cause deep soil salts to continuously migrate to the topsoil, eventually accumulating in the root zone and on the surface between the mulch film. This secondary soil salinization is particularly pronounced in extreme environments of drought and low rainfall, where evaporation far exceeds precipitation, and has become a key factor restricting sustainable cotton production in these regions.

[0003] Soil salinity stress often hinders cotton growth and development: Firstly, a high-salt environment increases the osmotic pressure of the soil solution, disrupting the water potential balance between the roots and the soil, thus hindering root water absorption and leading to physiological drought, interfering with the cotton plant's water metabolism and nutrient transport; secondly, excessive salt ions (such as Na+) can also cause problems. + Cl - The accumulation of reactive oxygen species (ROS) within the cotton plant leads to ion toxicity, disrupting the selective permeability and structural stability of cell membranes. Simultaneously, it accelerates the explosive accumulation of ROS in functional leaves, disrupting the balance of the body's antioxidant system and ultimately causing chlorophyll degradation and damage to photosynthetic organs. The external manifestations of these physiological processes are typical premature aging symptoms in cotton plants during the mid-to-late flowering and boll-forming stages, such as leaf chlorosis and yellowing, declining photosynthetic function, and boll shedding. This directly results in insufficient synthesis and transport of photosynthetic products, leading to increased boll shedding rates, ultimately causing reduced boll weight, decreased yield, and substandard fiber quality. Therefore, secondary soil salinization is the dominant environmental stressor inducing physiological premature aging in drip-irrigated cotton fields, and alleviating soil salinity accumulation in the root zone and improving the root zone microenvironment are prerequisites and breakthroughs for preventing premature aging in cotton.

[0004] To address the issue of salt accumulation and associated premature aging in drip-irrigated cotton fields, existing technical solutions mainly focus on three technical pathways for salt regulation. However, all of these have significant limitations and struggle to achieve efficient water conservation and delay aging, as detailed below:

[0005] 1. Traditional winter and spring large-water salt leaching technology: As the most widely used agronomic salt suppression measure, its core is to conduct 1-2 times of large-quantity flood irrigation on the ground in the non-growing season (freeze-thaw period before winter or spring sowing and soil preparation period), and leach the salt from the surface soil to the deep layer through gravity infiltration. However, this technology has the following three defects: ① Serious water waste: the single irrigation amount is usually above 1500 m³ per hectare, which contradicts the original intention of water-saving irrigation; ② Poor compatibility with drip irrigation systems: additional ditches or flood irrigation facilities are required, which increases construction costs and damages the laid drip irrigation pipe network system; ③ Uncontrollable salt leaching depth, with the risk of salt oscillation: if the irrigation amount is insufficient, the salt will flow back to the root zone with the upward movement of soil moisture in the growing season; if the irrigation amount is too large, it easily causes the rise of groundwater level, increasing the risk of secondary aggregation of deep salt on the surface.

[0006] 2. Saline water drip irrigation technology: Some studies have proposed to directly use low-salinity brackish water for drip irrigation, attempting to simplify salt management through "treating salt with salt". However, its application limitations are particularly prominent: ① Strict applicable scenarios: it is only suitable for areas with strong soil permeability, low groundwater level and complete drainage and desalination conditions; ② High long-term ecological risk: continuous irrigation will lead to net input of salt into the soil, aggravating salt accumulation in the root zone; ③ Combined stress induces premature senescence: the salt tolerance threshold of cotton decreases in the middle and late growth stages, and brackish water irrigation will further strengthen the salt stress effect, which becomes a direct inducing factor for premature senescence.

[0007] 3. Periodic salt leaching technology matched with drip irrigation: This solution advocates regularly increasing drip irrigation quota during the cotton growing season to achieve salt leaching in the root zone through enhanced infiltration. Its core defects are concentrated in "lack of precision" and "insufficient synergy": ① Contradicts the water requirement law of cotton: blindly increasing irrigation amount easily leads to local soil over-humidification, inhibits aerobic respiration of roots, and induces root rot diseases or excessive vegetative growth; ② Lacks scientific trigger and quantification mechanism: the quantitative index system of "leaching start threshold - appropriate leaching amount - leaching period" has not been established, and field operation mostly depends on experience judgment, making it difficult to achieve precise regulation of salt.

[0008] In summary, the existing technical paths all fail to break through the problems of poor system adaptability, low regulation accuracy, and unbalanced water-salt coordination, and there is a lack of a precise salt management method that can be efficiently coupled with drip irrigation systems, take into account water conservation and controllability, and dynamically coordinate with the cotton growth process and the water and fertilizer requirement law. Therefore, how to simultaneously achieve the dual goals of "salt leaching in root zone" and "precise regulation of cotton growth" and fundamentally solve the production problem of premature senescence induced by salinization is an urgent technical problem to be solved by those skilled in the art. Summary of the Invention

[0009] In view of this, the present invention provides a leaching method for alleviating secondary salinization and preventing premature senescence in drip-irrigated cotton fields.

[0010] To solve the above-mentioned technical problems, this application adopts the following technical solution: The primary objective of this application is to provide a method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields, comprising the following steps: S1. Real-time monitoring and early warning: During the cotton growth period, monitor the soil electrical conductivity (ECe) of the main root layer (0-40 cm) and the cotton growth process; when the soil electrical conductivity exceeds the salt tolerance threshold of cotton in the current growth period, and the cotton growth process enters the critical window period of full bloom to full boll formation, trigger the irrigation command. S2. Intelligent decision-making and rinsing water demand calculation: Based on the trigger command, the rinsing water demand is calculated according to the soil texture, target rinsing depth and preset rinsing fraction. S3. Precise Execution and Collaborative Process: Through the existing drip irrigation system, one or more irrigations are carried out according to the calculated leaching water requirement to leach the salt in the 0-40 cm soil layer of the root zone to a depth of 40-60 cm, while replenishing water for cotton during the flowering and boll-forming stage. Step S3 has the following beneficial effects: Physical process: Irrigation water moves downwards under the influence of gravity, separating dissolved salt molecules (Na+). + Cl - (etc.) Carry to a "safe depth" of 40-60 cm, where there are fewer roots and the impact of salt on crops is greatly reduced.

[0011] Physiological process: This irrigation simultaneously replenished the root zone soil water reservoir, alleviating the water demand pressure during the flowering and boll-forming stage.

[0012] The two processes work together to create a new root zone environment for cotton with significantly reduced salt stress and sufficient water supply within about a week after irrigation. This effect can last for several weeks, covering the critical period of boll enlargement and fiber development.

[0013] S4. The low-salt, water-suitable root zone microenvironment formed after irrigation delays the senescence of cotton functional leaves and increases boll weight and yield.

[0014] The optimized root zone environment brings the following effects: Root function recovery: Reduced resistance to water and nutrient absorption by roots, resulting in enhanced vitality. Leaf function extension: Suppressed reactive oxygen species blooms caused by salt damage, slowed chlorophyll degradation, and maintained a high net photosynthetic rate (Pn), effectively delaying premature senescence of functional leaves. Yield and quality enhancement: Sufficient photosynthetic products are transported to cotton bolls, reducing boll shedding, increasing single boll weight, ultimately leading to increased yield and improved quality indicators such as fiber strength.

[0015] As a preferred technical solution, the salt tolerance threshold for different growth stages during the flowering-boiling period described in S1 is 5.0 dS / m.

[0016] As a preferred technical solution, the criterion for determining that S1 enters the full blooming period is: when the flower buds on the 3rd to 4th fruit branches of a single cotton plant bloom, it is determined to enter the full blooming period.

[0017] As a preferred technical solution, the leaching water requirement described in S2 is: the total irrigation water amount required to leach the salt in the root zone to the target leaching depth, and simultaneously replenish the soil moisture within the target leaching depth to the field capacity; The calculation model of leaching water requirement is as follows: Leaching water requirement (LR) = θ × D × (1 - LF), wherein: θ is the soil field capacity, with the unit of %; D is the target leaching depth, which is the depth of the soil layer measured from the ground surface where salt is expected to move down to, with the unit of cm; LF is the leaching fraction, which represents the proportion of water used for dissolving and migrating salt in the total leaching water requirement, with a value range of 0.10-0.25.

[0018] As a preferred technical solution, the value of the leaching fraction LF is comprehensively determined according to the soil salt content, soil texture and water-saving target: (1) Determine the base value of LF based on the electrical conductivity (ECe) of the soil in the root zone: when ECe ≤ 3.5 dS / m, the base value of LF is 0.10-0.15; when 3.5 dS / m < ECe ≤ 4.0 dS / m, the base value of LF is 0.15-0.18; when 4.0 dS / m < ECe ≤ 5.0 dS / m, the base value of LF is 0.18-0.22; when ECe > 5.0 dS / m, the base value of LF is 0.22-0.25; (2) Correct the value of LF based on the base value of LF according to soil texture: for sandy loam, the value of LF is further corrected on the basis of the base value determined in step (1): when the base value of LF is 0.10-0.15, the corrected LF is 0.10~0.12; when the base value of LF is 0.15-0.18, the corrected LF is 0.15~0.165; when the base value of LF is 0.18-0.22, the corrected LF is 0.18~0.20; when the base value of LF is 0.22-0.25, the corrected LF is 0.22~0.23; for clay, the value of LF is further corrected on the basis of the base value determined in step (1): when the base value of LF is 0.10-0.15, the corrected LF is 0.13~0.15; when the base value of LF is 0.15-0.18, the corrected LF is 0.165-0.18; when the base value of LF is 0.18-0.22, the corrected LF is 0.20-0.22; when the base value of LF is 0.22-0.25, the corrected LF is 0.23~0.25; For loam, based on the baseline value determined in step (1), the LF value is further adjusted: when the baseline LF value is 0.10-0.15, the LF value is adjusted to 0.12-0.13; when the baseline LF value is 0.15-0.18, the LF value is adjusted to 0.16-0.17; when the baseline LF value is 0.18-0.22, the LF value is adjusted to 0.19-0.20; when the baseline LF value is 0.22-0.25, the LF value is adjusted to 0.23-0.24. (3) Adjustment based on water conservation target: If water conservation is prioritized, take (1) and (2) to determine the lower limit of the interval value; if rinsing effect is prioritized, take (1) and (2) to determine the upper limit of the interval value.

[0019] As a preferred technical solution, the irrigation described in S3 is either a one-time full irrigation or completed in two sessions within 48 hours.

[0020] As a preferred technical solution, after step S3 irrigation, regular water and fertilizer management can be resumed, and the amount of irrigation can be appropriately reduced or postponed for the next 1-2 irrigations.

[0021] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) For the first time, it was clearly defined that the environmental management measure of "salt leaching" was moved from the non-growing season to the critical reproductive growth period when cotton is most sensitive to salt and has the greatest water efficiency, so that "salt leaching" can also become a "yield-increasing water".

[0022] Innovation in decision-making models: The traditional experience of "observing the weather, the land, and the crops" is transformed into a quantitative decision-making model based on the dual triggers of salinity threshold and growth period, and a precise water volume calculation formula is provided, making the technology standardized and replicable.

[0023] Innovation through synergistic objectives: By combining the depth objective of "salt washing" with the distribution of cotton roots and the water requirements during the boll-forming stage, a clever unity was achieved between the downward movement of salt to the safe zone and the storage of water in the effective root zone, ultimately achieving the effect of "coordinated water and salt management" rather than "water and salt opposition".

[0024] (2) Significant water-saving advantages: This invention abandons the traditional extensive model of flood irrigation to suppress salt in winter and spring, and precisely positions the salt leaching operation during the critical period of cotton's water demand. The leaching water volume also serves as an effective water supply for the crop, avoiding the ineffective loss of a large amount of water resources during the non-growing season. Experimental data show that the optimal total irrigation volume of this invention is 259.67 cubic meters per mu, which is significantly lower than the traditional model of 340 cubic meters per mu, effectively saving water.

[0025] (3) Stable yield increase: This invention, through precise irrigation, effectively reduces salt stress in the root zone during the critical period of yield formation, from full bloom to full boll formation, creating a suitable microenvironment for boll development. Experimental results show that under the optimal treatment of this invention, the yield of seed cotton of early-maturing varieties increased by 11.4% compared with the traditional method, the yield of medium-maturing varieties increased by 11.1%, and the yield of lint cotton increased by 16.0% and 9.5% respectively, with significant and stable yield increase effects.

[0026] (4) Quantification of anti-premature aging effect: This invention effectively delays the aging process of cotton functional leaves by relieving salt stress. Experimental data show that under the treatment of this invention, the SPAD value of functional leaves 20 days after full bloom is more than 30% higher than that of the traditional model, and the lifespan of functional leaves is extended by 7-10 days, providing sufficient photosynthetic products for cotton boll development and ensuring yield and quality.

[0027] (5) The technology is simple to operate and highly compatible: This invention is based entirely on the existing drip irrigation system, without the need for additional engineering modifications. It is easy to operate, low in cost, highly accepted by farmers, and easy to promote and apply on a large scale.

[0028] (6) High degree of technical standardization: Addressing the core defects of existing drip irrigation-supported periodic rinsing technology—namely, the lack of a quantitative indicator system for "rinsing initiation threshold - appropriate rinsing amount - rinsing cycle," leading to reliance on experience-based judgment in field operations, which can easily result in blindly increasing water supply, conflicting with cotton's water requirements, and causing root hypoxia or excessive vegetative growth—this invention establishes a complete quantitative decision-making model. Specifically, this invention clarifies the scientific basis for rinsing initiation by setting a dual trigger mechanism of "salt threshold + growth period"; it achieves precise quantification of rinsing amount by constructing a rinsing water requirement calculation model LR = θ × D × (1 - LF); and it ensures dynamic coordination between rinsing operation and cotton's water requirements and yield formation period by locking the rinsing timing to the critical window period from full bloom to full boll formation. This quantitative indicator system transforms the technology from relying on experience-based judgment to standardized operations that can be calculated and replicated. It completely avoids the negative effects of blindly increasing water, such as root hypoxia, root rot, or excessive vegetative growth. It achieves precise management of water and salt synergy, with stable and controllable technical effects, making it easy to promote and apply on a large scale. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention was carried out in the Dunhuang saline-alkali cotton area. The basic soil physicochemical properties of the experimental field are as follows: total salt content 1.36%, organic matter 10.4 g / kg, available phosphorus 9.45 mg / kg, available potassium 187 mg / kg, available nitrogen 130 mg / kg, pH value (water:soil = 2.5:1) 8.88, sodium ion 0.90 g / kg, potassium ion 0.12 g / kg, magnesium ion 0.90 g / kg, calcium ion 0.85 g / kg, sulfate 6.95 g / kg, chloride 3.95 g / kg, bicarbonate 0.50 g / kg, which is a typical moderately saline-alkali cotton field.

[0031] The tested varieties were: Zhongmian 113, an early-maturing variety, and Longmian 16, a medium-maturing variety, both of which are the main varieties cultivated locally.

[0032] Example 1 A leaching method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields includes the following steps: S1. Real-time monitoring and early warning triggering: An experiment was conducted in the saline-alkali cotton region of Dunhuang. Soil electrical conductivity (ECe) in the 0-40 cm root zone was monitored at fixed points and regularly throughout the cotton's growth period. Specifically, monitoring was conducted every 10 days during the seedling stage and every 7 days after the budding stage. The cotton's growth progress was also recorded.

[0033] The experiment showed that the salt tolerance threshold for cotton seedlings (from emergence to budding) in the experimental area was 3.5 dS / m, the salt tolerance threshold for budding (from budding to flowering) was 4.2 dS / m, and the salt tolerance threshold for boll formation (from flowering to boll opening) was 5.0 dS / m.

[0034] Continuous monitoring revealed that on July 1st (peak flowering period), the average soil electrical conductivity in the 0-40 cm soil layer reached 5.8 dS / m, exceeding the cotton's salt tolerance threshold of 5.0 dS / m during the flowering and boll-forming stage. At this time, the cotton growth process was entering the critical window period between peak flowering and peak boll-forming, and soil salinity was already posing a stress on cotton growth, triggering the irrigation command.

[0035] S2. Intelligent decision-making and rinsing water demand calculation: Based on the trigger command, the required water for leaching was calculated. First, the field water holding capacity (θ) of the soil in the experimental area was determined to be 25% (volume water content) using the ring cutter method. Considering the need to leach soil salts from the 0-40 cm root layer to the 40-60 cm soil layer and avoid water wastage due to deep seepage, the target leaching depth (D) was set at 40 cm. This depth effectively removes salts from the main root layer while ensuring water use efficiency. Based on the local climate, soil texture (silty loam), and the salt tolerance of cotton, combined with previous research, ECe is 3.6 dS / m. Therefore, the leaching fraction (LF) was set at 15%, which effectively controls the total irrigation volume while ensuring salt leaching effect.

[0036] Finally, based on the soil volumetric moisture content, target leaching depth, and leaching fraction, the leaching water requirement (LR) was calculated. The formula is: LR = D × θ × (1 - LF). Substituting the values: LR = 40 × 25% × (1 - 15%) = 8.5 mm, which translates to a water consumption of 5.67 cubic meters per mu (8.5 × 0.667 ≈ 5.67). The final determined leaching water requirement is 5.67 cubic meters per mu.

[0037] The unit LR is mm. The conversion of water consumption per mu (a Chinese unit of area, approximately 0.001 m) is approximately 6.67 m³ (1 mu = 666.67 m³, 1 mm water depth = 0.001 m, 1 mm water volume per mu = 666.67 × 0.001 = 0.66667 m³). That is: 1mm ≈ 0.667 m³ / mu, 10mm ≈ 6.67 m³ / mu).

[0038] S3. Precise Execution and Collaboration Process: Based on the decision, sprinkler irrigation will commence on July 2nd (the day after the trigger command) using the existing drip irrigation system. During the cotton boll-forming stage (July 1st to August 15th), sprinkler irrigation will be combined with precision irrigation. The specific implementation method is as follows: The precision irrigation is as follows (a total of 254 cubic meters per mu): No watering is required before sowing. After sowing, drip water of 20 cubic meters per mu is applied until seedling emergence. Subsequent watering is precisely allocated according to the growth stage (budding stage: 47 cubic meters per mu; flowering and boll-forming stage: 140 cubic meters per mu; boll-opening stage: 47 cubic meters per mu).

[0039] The specific details of the irrigation are as follows (total irrigation volume: 5.67 cubic meters / acre): In addition to the normal irrigation during the flowering and boll-forming stage (140 cubic meters per mu), an extra irrigation operation was conducted (July 10th), increasing the water volume by 5.67 cubic meters per mu (total irrigation volume during the flowering and boll-forming stage: 145.67 cubic meters per mu), specifically for salt leaching. Through precise control of the drip irrigation system, the 5.67 cubic meters per mu of leaching water was evenly applied to the field, ensuring effective leaching of salt from the 0-40 cm soil layer in the root zone to a depth of 40-60 cm. This irrigation process not only achieved desalination in the root zone but also replenished crucial water for the cotton plants, which were at a critical water requirement stage, achieving coordinated water and salt regulation.

[0040] S4. Microenvironment Construction and Premature Aging Prevention: After irrigation, the rhizosphere environment was monitored. Results showed that 7 days after irrigation, the soil electrical conductivity in the 0-40 cm soil layer significantly decreased from 5.8 dS / m before irrigation to 4.2 dS / m, falling below the salt tolerance threshold for cotton flowering and boll formation, successfully establishing a low-salt, water-suitable rhizosphere microenvironment. This environment effectively alleviated the stress of salt on root function and leaf photosynthesis, and delayed the senescence process of functional cotton leaves.

[0041] Control treatment (traditional irrigation mode): 100 cubic meters / mu of water was flooded before sowing, and 60 cubic meters / mu of water was irrigated in 4 times during the growth period (budding stage, full bloom stage, full boll stage and initial fluffing stage), with a total irrigation volume of 340 cubic meters / mu.

[0042] Compared to traditional irrigation methods (total irrigation volume of 340 cubic meters per mu), the cotton leaves under the sprinkler irrigation method of this invention (precision irrigation + sprinkler irrigation, totaling 259.67 cubic meters per mu) maintained a high chlorophyll content and net photosynthetic rate in the later stages of flowering and boll formation, effectively controlling premature senescence. Ultimately, by optimizing the root zone environment, the cotton boll weight under the sprinkler irrigation method of this invention reached 6.2 grams, a 10.7% increase compared to 5.6 grams under the traditional irrigation method, resulting in a significant increase in yield and achieving multiple objectives of water conservation, salt control, senescence prevention, and yield increase.

[0043] Example 2 To clarify the technical effect of the core step of this invention (precise irrigation during the flowering and boll-forming stages), Example 2 was conducted in Suzhoumiao Town, Dunhuang City, Jiuquan City, with a total of 3 treatments: Control Group 1 (Traditional Winter-Spring Flood Irrigation for Salt Reduction, CK1): Before sowing (winter or spring irrigation), flood irrigation was carried out to reduce salt content, with an irrigation volume of 100 cubic meters per mu. During the growing season, conventional drip irrigation was used (40 cubic meters per mu during budding, full bloom, full boll formation, and boll opening). Example 1 and this example are both traditional irrigation control groups, but the experimental plots, soil salinity, climate, cotton varieties, experimental years, and irrigation system design objectives are different. Therefore, the single-period quotas for budding, full bloom, full boll formation, and boll opening are 60 cubic meters per mu and 40 cubic meters per mu, respectively), with a total irrigation volume of 260 cubic meters per mu.

[0044] Control group 2 (periodic rinsing technology with drip irrigation, CK2): No large-scale water suppression for salt was applied before sowing. During the growing season, a periodic rinsing strategy was adopted, that is, starting from the bud stage, 10 cubic meters / mu were irrigated every 15 days for a total of 3 times (bud stage, early flowering stage, and mid-flowering stage); the remaining irrigation during the growing season was the same as that of the EX group, with a total irrigation volume of 254 + 30 = 284 cubic meters / mu.

[0045] The treatment method of this invention (EX) is strictly implemented according to steps S1-S4 of claims of this invention. No large-scale water-salt suppression is performed before sowing. During the peak flowering-boll-setting period, irrigation commands are triggered through real-time monitoring, and the required irrigation water volume is accurately calculated based on soil texture, target leaching depth, and leaching fraction, resulting in one or more irrigation cycles.

[0046] The specific operation steps of the present invention (EX) are as follows: S1. Real-time monitoring and early warning triggering During the cotton growing season, soil moisture and salinity monitoring instruments were deployed at fixed points in the experimental area, and soil electrical conductivity (ECe) of the main root layer (0-40cm) was collected every 3 days. At the same time, the cotton growth process was recorded.

[0047] Based on previous measurements, the salt tolerance thresholds for key growth stages of cotton in this experimental area are: 4.2 dS / m during the budding stage and 5.0 dS / m during the flowering and boll-forming stage.

[0048] Continuous monitoring data shows that on July 5th (early flowering stage), the average ECe in the 0-40 cm soil layer rose to 4.8 dS / m; on July 10th (peak flowering stage), the average ECe reached 5.3 dS / m, exceeding the salt tolerance threshold of 5.0 dS / m for the flowering and boll-forming stage. At this time, the cotton growth process coincides with the critical window from peak flowering to peak boll-forming, and soil salinity already poses a potential stress on root water absorption and cotton growth. The system automatically triggers irrigation commands.

[0049] S2, Intelligent Decision Making and Rinse Water Demand Calculation The water demand calculation module for rinsing is activated upon receiving the trigger command.

[0050] (1) Determination of field water holding capacity: The average field water holding capacity (θ) of the 0-40 cm soil layer in the experimental area was measured to be 24.5% (volume water content) using the ring cutter method.

[0051] (2) Determine the target leaching depth (D): Based on the distribution depth of the main cotton root system (0-40 cm) and the salt leaching efficiency, the target leaching depth is set to 40 cm, which aims to leach the salt in the root zone to the 40-60 cm soil layer and avoid deep seepage.

[0052] (3) Determine the leaching fraction (LF): Based on local evaporation, soil texture (silty loam) and cotton salt tolerance, and with reference to the salt leaching experience value recommended by the Food and Agriculture Organization of the United Nations (FAO), the leaching fraction is set at 12%. This fraction can ensure effective desalination without wasting water resources.

[0053] (4) Calculate the rinsing water requirement (LR): Use the formula LR = D × θ × (1 - LF). Substituting the values: LR = 40 × 24.5% × (1 - 12%) = 8.62 mm, which is equivalent to approximately 5.75 cubic meters of water per mu. For ease of operation, round it to 5.8 cubic meters per mu. Based on the real-time monitoring of the salt content exceeding the standard, the water requirement for this rinsing is determined to be 5.8 cubic meters per mu.

[0054] S3, Precise Execution and Collaborative Process Based on the decision, irrigation will be carried out using the existing drip irrigation system on July 12 (within 2 days of triggering the command, provided the weather is sunny and windless).

[0055] The total quota for conventional precision irrigation of cotton throughout its entire growth period in the EX group of this invention is fixed at 254 cubic meters per mu (approximately 13.3 cubic meters per hectare). The breakdown of conventional water usage for each growth stage is as follows: no irrigation before sowing; drip irrigation of 20 cubic meters per mu during the sowing and seedling emergence stage; conventional irrigation of 47 cubic meters per mu during the budding stage; and a total conventional irrigation volume of 140 cubic meters per mu (divided into multiple irrigation batches during the flowering and boll-forming stage: 40 cubic meters per mu / 7 days for initial flowering, 40 cubic meters per mu / 7 days for full bloom, 30 cubic meters per mu / 7 days for full boll formation, and 30 cubic meters per mu / 7 days for the end of boll formation). The irrigation on July 12th was a single conventional irrigation batch during the early flowering and boll-forming stage, with a planned conventional irrigation quota of 40 cubic meters per mu (approximately 23.3 cubic meters per hectare); and conventional irrigation of 47 cubic meters per mu (approximately 23.3 cubic meters per hectare) during the boll-opening stage.

[0056] The specific operation is as follows: During the regular irrigation batch on July 12th, which is in the peak flowering and boll-forming stage, the original single-time 40 cubic meters / mu regular irrigation was adjusted to a combined drip irrigation and regular irrigation mode. That is, through the drip irrigation system head, the directional leaching command is prioritized and executed separately, with a leaching quota of 5.8 cubic meters / mu precisely applied to the field within 4 hours, leaching salt from the 0-40 cm root layer to the 40-60 cm soil layer; after the leaching process is completed, the original batch of 40 cubic meters / mu regular irrigation water supply is immediately and fully implemented to ensure the water needs of this batch of cotton growth are met.

[0057] This leaching quota of 5.8 cubic meters per mu is specifically for targeted desalination of the root zone, and does not occupy the total quota of 140 cubic meters per mu for regular crop growth irrigation during the entire flowering and boll-forming stage. The leaching operation is completed simultaneously with the regular water supply process in a single irrigation, ensuring no water shortage for crop growth and achieving "one irrigation, dual benefits." The entire process is precisely controlled through the solenoid valves and flow meters of the drip irrigation system.

[0058] S4. Microenvironment Construction and Premature Aging Prevention After irrigation is completed, continuous monitoring of changes in the root zone environment is conducted.

[0059] On the 3rd day after irrigation, the average ECe in the 0-40 cm soil layer decreased significantly from 5.3 dS / m before irrigation to 4.3 dS / m, which is below the salt tolerance threshold of 5.0 dS / m at the flowering and boll-forming stage. On the 7th day after irrigation, ECe stabilized between 4.1 and 4.4 dS / m, successfully establishing a low-salt and water-suitable root zone microenvironment.

[0060] The relative chlorophyll content of functional leaves (four leaves from the bottom of the main stem) of cotton was monitored using a chlorophyll meter (SPAD). The results showed that the SPAD value of the treatment (EX) remained at 52.3 in the late flowering and boll-forming stage (August 20), while the values ​​of control group 1 (CK1) and control group 2 (CK2) were 45.6 and 48.1, respectively. Simultaneously, superoxide dismutase (SOD) activity assays showed that the SOD activity of the EX-treated leaves was significantly higher than that of the two control groups, while the malondialdehyde (MDA) content was significantly lower than that of the control groups, indicating a lower degree of cell membrane lipid peroxidation and an effective delay in leaf senescence.

[0061] The results of this experiment show that: 1. Compared with the traditional winter and spring large-scale water suppression salt technology (CK1), the precision irrigation method of this invention saves 32.0%-36.0% of water and can more effectively control the salt content in the root zone during the peak flowering and boll-forming period below the salt tolerance threshold, significantly delaying leaf senescence and increasing boll weight and yield.

[0062] 2. Compared with the periodic rinsing technology (CK2) used in conjunction with drip irrigation, the method of this invention achieves better root zone desalination and anti-premature aging effects by "real-time monitoring - precise decision-making - on-demand irrigation" while reducing the total amount of irrigation water, demonstrating the precision and efficiency of on-demand decision-making.

[0063] 3. The method of this invention effectively coordinates water and salt regulation with crop physiological needs by constructing a low-salt and water-appropriate root zone microenvironment during the flowering and boll-forming stage. It is an effective technical approach to achieve water conservation, salt control, anti-senescence, and yield increase in saline-alkali drip irrigation cotton fields.

[0064] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0065] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields, characterized in that, comprising the following steps: S1, real-time monitoring and early warning triggering: during the growth period of cotton, monitoring soil electrical conductivity in the main root layer of 0-40 cm and the growth process of cotton; when the soil electrical conductivity exceeds the salt tolerance threshold of cotton in the current growth period, and the cotton growth process enters the critical window period from full bloom stage to peak boll-setting stage, triggering a leaching irrigation instruction; S2, intelligent decision-making and calculation of leaching water requirement: calculating the leaching water requirement based on soil texture, target leaching depth and preset leaching fraction according to the trigger instruction; S3, precise implementation and collaborative process: implementing one or more leaching irrigation according to the calculated leaching water requirement through an existing drip irrigation system, leaching the salt in the 0-40 cm soil layer of the root zone to the depth of 40-60 cm, and supplementing water for cotton at the flowering and boll-setting stage at the same time; S4, delaying the senescence of functional cotton leaves and increasing boll weight and yield through the micro-environment of the root zone with low salt and appropriate water formed after leaching irrigation.

2. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 1, characterized in that, The salt tolerance thresholds for different growth periods in the full bloom to peak boll-setting stage described in S1 are all 5.0 dS / m.

3. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 1, characterized in that, The criterion for determining entry into the full bloom stage in S1 is: when the flower buds on 3 to 4 fruit branches of a single cotton plant bloom, it is determined that cotton has entered the full bloom stage.

4. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 1, characterized in that, The leaching water requirement described in S2 is: the total irrigation amount required to leach the salt in the root zone to the target leaching depth and simultaneously replenish the soil moisture in the target leaching depth to the field water holding capacity; The calculation model of the leaching water requirement is as follows: Leaching water requirement (LR) = θ × D × (1 - LF), wherein: θ is the field water holding capacity of soil, with the unit of %; D is the target leaching depth, which is the soil depth counted from the ground surface that salt is expected to move downward to, with the unit of cm; LF is the leaching fraction, which represents the proportion of water used for dissolving and migrating salt in the leaching water requirement, with a value range of 0.10-0.

25.

5. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 4, characterized in that, The value of the leaching fraction LF is comprehensively determined according to soil salt content, soil texture and water saving target: (1) Determining the basic LF value according to the root zone soil electrical conductivity (ECe): when ECe ≤ 3.5 dS / m, the basic LF value is 0.10-0.15; when 3.5 dS / m < ECe ≤ 4.0 dS / m, the basic LF value is 0.15-0.18; when 4.0 dS / m < ECe ≤ 5.0 dS / m, the basic LF value is 0.18-0.22; when ECe > 5.0 dS / m, the basic LF value is 0.22-0.25; (2) Correcting the LF value based on the basic LF value according to soil texture: For sandy loam, further correcting the LF value on the basis of the basic value determined in step (1): when the basic LF value is 0.10-0.15, correcting LF to 0.10~0.12; when the basic LF value is 0.15-0.18, correcting LF to 0.15~0.165; when the basic LF value is 0.18-0.22, correcting LF to 0.18~0.20; when the basic LF value is 0.22-0.25, correcting LF to 0.22~0.23; For clay, based on the base value determined in step (1), the LF value is further modified: when the base value of LF is 0.10-0.15, the LF is modified to 0.13-0.15; when the base value of LF is 0.15-0.18, the LF is modified to 0.165-0.18; when the base value of LF is 0.18-0.22, the LF is modified to 0.20-0.22; when the base value of LF is 0.22-0.25, the LF is modified to 0.23-0.

25. For loam, based on the baseline value determined in step (1), the LF value is further adjusted: when the baseline LF value is 0.10-0.15, the LF value is adjusted to 0.12-0.13; when the baseline LF value is 0.15-0.18, the LF value is adjusted to 0.16-0.17; when the baseline LF value is 0.18-0.22, the LF value is adjusted to 0.19-0.20; when the baseline LF value is 0.22-0.25, the LF value is adjusted to 0.23-0.

24. (3) Adjustment based on water conservation target: If water conservation is prioritized, take (1) and (2) to determine the lower limit of the interval value; if rinsing effect is prioritized, take (1) and (2) to determine the upper limit of the interval value.

6. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 1, characterized in that, The irrigation described in S3 can be completed in one go, or in two separate applications within 48 hours.

7. The irrigation method for alleviating secondary salinization and preventing premature aging in drip-irrigated cotton fields according to claim 1, characterized in that, After irrigation, regular water and fertilizer management can be resumed, and the amount of irrigation can be reduced or postponed for the next 1-2 irrigations.