A rice planting method coupled with wet-dry alternation and biochar
By combining biochar with alternating wet and dry irrigation, the problems of high water consumption, serious greenhouse gas emissions, low nitrogen fertilizer utilization, and soil degradation in rice cultivation have been solved, achieving the effects of water conservation, emission reduction, increased yield, and improved quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI SHENGNONG AGRI GRP
- Filing Date
- 2026-03-30
- Publication Date
- 2026-05-29
AI Technical Summary
Existing rice cultivation methods suffer from problems such as high water consumption, serious greenhouse gas emissions, low nitrogen fertilizer utilization, unstable rice quality, and soil degradation. In particular, the effects of alternating wet and dry irrigation are unstable, and the effect on methane emission reduction is greatly affected by soil type and climate conditions.
A coupling method of biochar and alternating wet and dry irrigation was adopted. The porous structure of biochar adsorbs NH4⁺, which improves soil aeration and inhibits the activity of methanogenic bacteria. Combined with silicon-calcium fertilizer, it enhances rice quality. Combined with dynamic irrigation system and nitrogen fertilizer reduction basal application strategy, it improves nitrogen fertilizer utilization rate.
It achieves water conservation and emission reduction, increased production and improved quality. Biochar can maintain its effect for 3-5 seasons, increases soil organic carbon, improves nitrogen fertilizer utilization, improves rice quality, reduces the overall greenhouse effect by 35%-50%, and increases yield by 8%-12%.
Smart Images
Figure CN122095950A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of crop cultivation technology, specifically a rice cultivation method that couples wet and dry conditions with biochar. Background Technology
[0002] Rice is my country's largest grain crop, with a planting area of approximately 30 million hectares and a yield accounting for nearly 40% of the country's total grain output. Currently, the mainstream rice cultivation method still relies on traditional flood irrigation, maintaining a water layer of 3-10 cm throughout the entire growth period. While this method can suppress weeds and ensure water supply, it has the following shortcomings:
[0003] 1. Huge water consumption: Traditional flood irrigation consumes 8,000-12,000 m³ of water per hectare, while water resources in most rice-growing areas of my country are becoming increasingly scarce.
[0004] 2. Severe greenhouse gas emissions: Anaerobic decomposition of soil organic matter in flooded environments produces large amounts of methane (CH4), and rice cultivation contributes more than 40% of the country's agricultural methane emissions.
[0005] 3. Low nitrogen fertilizer utilization rate: Under flooded conditions, nitrogen denitrification, leaching and runoff losses are severe. The average nitrogen fertilizer utilization rate in paddy fields in my country is only 30%-35%, which is far lower than the level of developed countries.
[0006] 4. Rice quality is greatly affected by water management: long-term flooding leads to premature root aging, insufficient grain filling, high chalkiness, and a decrease in head rice rate, with the proportion of high-quality rice being less than 30%.
[0007] 5. Soil degradation problems are emerging: years of flooding and cultivation have led to soil compaction, secondary gleying, accelerated mineralization of organic matter, and a decline in soil health.
[0008] In recent years, alternating wet and dry irrigation (AWD) has been promoted as a water-saving irrigation technology. However, the use of AWD alone often leads to a decrease in soil organic matter and an increase in weeds, and its effect on methane emission reduction is greatly affected by soil type and climate conditions. Biochar, as a soil conditioner, has been proven to increase the soil carbon pool, adsorb ammonium nitrogen, and promote root growth, but its coupling effect with AWD and its regulatory mechanism on rice quality have not yet been systematically studied in planting methods.
[0009] Therefore, there is an urgent need in this field for a rice cultivation method that can achieve a balance between water conservation, emission reduction, increased yield, and improved quality. Summary of the Invention
[0010] The purpose of this invention is to provide a rice cultivation method that couples wet and dry conditions with biochar, which can solve the technical problems of existing rice cultivation methods in the background art, such as high water consumption, serious greenhouse gas emissions, low nitrogen fertilizer utilization, unstable rice quality, and soil degradation.
[0011] To achieve the above objectives, the present invention provides the following technical solution: a rice cultivation method coupled with alternating wet and dry conditions and biochar, comprising the following steps:
[0012] Step 1: Biochar Preparation and Base Application
[0013] (1) Biochar preparation: Rice husks or rice straw are collected, air-dried, and crushed to a particle size ≤2 cm. They are then placed in an oxygen-limited pyrolysis furnace and heated to 450-550℃ at a heating rate of 5-10℃ / min. The temperature is maintained for 2-3 hours, and after natural cooling, the biochar is passed through a 20-mesh sieve to obtain biochar. The biochar has a mesoporosity (2-50 nm pore size ratio) ≥40%, a specific surface area ≥150 m² / g, a cation exchange capacity ≥20 cmol / kg, a pH of 8.0-9.5, and an ammonium ion (NH₄⁺) adsorption capacity ≥0.8 mmol / g.
[0014] (2) Basal application: The above biochar is evenly spread on the surface of the cultivated layer at an application rate of 4500-6000 kg / hm². Then, a rotary tiller or moldboard plow is used to till the soil to a depth of 15-20 cm to ensure that the biochar is fully mixed with the cultivated soil.
[0015] Step Two: Application of Silicon-Calcium Fertilizer and Base Fertilizer
[0016] The silicon-calcium fertilizer is mixed with the nitrogen base fertilizer and then incorporated into the soil along with the biochar. The silicon-calcium fertilizer is industrial by-product silicon-calcium fertilizer or natural silicon-calcium mineral powder, containing SiO2 ≥ 25%, CaO ≥ 30%, and preferably also containing MgO ≥ 5% and Fe2O3 ≥ 1%; the application rate is 600-900 kg / hm². The nitrogen base fertilizer is urea (containing 46% N), ammonium bicarbonate, or ammonium sulfate, with the base nitrogen accounting for 40% of the total nitrogen application throughout the growing season. The total nitrogen application rate throughout the growing season is determined based on soil fertility, generally 150-195 kg N / hm². Preferably, the nitrogen base fertilizer is mixed with the nitrification inhibitor dicyandiamide (DCD), at a dosage of 1%-2% of the nitrogen content.
[0017] Step 3: Seedling raising and transplanting
[0018] Use either dry or wet seedling raising methods, with seedlings aged 25-30 days and having 3.5-4.5 leaves. Before transplanting, level the field and transplant at a density of 250,000-300,000 hills / hm² for conventional rice and 180,000-220,000 hills / hm² for hybrid rice, with 2-4 seedlings per hill.
[0019] Step 4: Water and fertilizer management during the tillering stage
[0020] (1) Greening period: After transplanting, keep a shallow water layer of 2-4 cm for 5-7 days to promote greening.
[0021] (2) Early tillering stage: After the seedlings turn green, use alternating wet and dry irrigation. Each time, irrigate to a water layer of 2-3 cm and let it dry naturally. Bury a soil tensiometer (vacuum gauge negative pressure gauge, buried at a depth of 15 cm) in the field. When the tensiometer reading reaches -10 kPa (i.e., soil water potential -10 kPa), irrigate again to a water layer of 2-3 cm, and repeat this cycle. Apply tillering fertilizer 10-12 days after transplanting, accounting for 20% of the total nitrogen application.
[0022] (3) Drying the field: When the number of tillers in the field reaches 80%-85% of the target number of ears, start drying the field. Drain the water in the field and let it dry naturally to a soil water potential of -25 kPa (reading of a tensiometer at a depth of 15 cm), and maintain this water potential for 7-10 days. Do not irrigate during the drying period, so that tiny cracks appear on the soil surface to promote root growth.
[0023] Step 5: Water and Fertilizer Management During the Heading Stage
[0024] (1) Re-watering: Re-water immediately after the field is dried, and maintain a shallow water layer of 2-3 cm until the heading stage.
[0025] (2) Panicle fertilizer: Panicle fertilizer accounts for 40% of the total nitrogen application. It should be applied in advance at the four-leaf stage (i.e., the second stage of young panicle differentiation, with a leaf age of 3.5-4.0). At this time, rice enters the young panicle differentiation stage, requires a large amount of fertilizer, and the field drying has ended, resulting in high fertilizer utilization.
[0026] (3) During the heading and flowering stage: Maintain a water layer of 2-3 cm and a soil water potential of no less than -10 kPa. If there is high temperature weather (daily average temperature ≥35℃), the water layer can be deepened to 5-8 cm to reduce the canopy temperature.
[0027] Step Six: Moisture Management During Grouting Maturation
[0028] (1) Grain-filling stage (15-20 days after heading): Light dry-wet alternating irrigation is adopted. The soil water potential at a depth of 15 cm is used as the control index: when the water potential drops to -15 kPa, irrigate to -5 kPa (i.e., a thin water layer appears in the field), and repeat the cycle. No long-term water layer is established during this stage, and the amount of water irrigated each time is about 300-450 m³ / hm².
[0029] (2) Leaf regulation during the heading stage: 2-3 days after heading, choose a cloudy day or evening to spray 0.2% potassium dihydrogen phosphate (KH2PO4) and 0.01% brassinolide (BR) with a backpack sprayer or drone. The dosage is 1500 g / hm² and 150 mL / hm², respectively, and diluted with 450 L / hm² of water.
[0030] (3) Drainage before harvest: Allow the grains to dry naturally 7-10 days before harvest to promote ripening and facilitate mechanical operations.
[0031] Step 7: Pest and Disease Control
[0032] Pest and disease control should be carried out using conventional methods. Since sun-drying the field reduces field humidity, the incidence of diseases and pests such as sheath blight and rice planthoppers is significantly reduced compared to traditional flooded planting, so the number of pesticide applications can be reduced by 1-2 as appropriate.
[0033] Technical Principle Explanation: This invention achieves multiple synergistic effects through the coupling of biochar and alternating wet and dry irrigation. The porous structure of biochar adsorbs NH4⁺, delaying nitrogen release and improving soil aeration. During the drying period of alternating wet and dry irrigation, it promotes soil oxidation, inhibits the activity of methanogenic bacteria (methanogenic archaea), and reduces CH4 production. As an electron shuttle, biochar promotes complete denitrification, reducing N2O intermediate emissions. Silicon from the calcium-silicon fertilizer is absorbed by rice and deposited in the epidermal cells of leaves and stems, forming silicified cells, enhancing lodging resistance and photosynthetic efficiency, while reducing chalkiness. During the grain-filling stage, alternating wet and dry irrigation stimulates root secretion of organic acids and cytokinins, delaying root senescence and increasing grain filling rate.
[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0035] 1. This invention achieves synergistic water conservation and emission reduction by coupling biochar with alternating wet and dry irrigation. The porous structure of biochar improves soil aeration, inhibits the activity of methanogenic bacteria under alternating wet and dry conditions, and its adsorption effect reduces nitrogen loss, thereby reducing methane emissions by 50%-65% and the overall greenhouse effect by 35%-50%.
[0036] 2. This invention alleviates the problem of micronutrient deficiency that may be caused by biochar by synergistic application of silicon-calcium fertilizer and biochar as a base fertilizer. At the same time, silicon-calcium fertilizer enhances cell wall silicification, reduces rice chalkiness by 25%-35%, and increases head rice yield by 4-8 percentage points.
[0037] 3. This invention, through a dynamic irrigation system based on soil water potential, especially the alternating wet and dry period during the grain-filling stage, increases root sap flow by more than 30%, prolongs the photosynthetic period of functional leaves, and achieves an increase in yield of 8%-12% and water saving of 35%-45%.
[0038] 4. This invention improves nitrogen fertilizer utilization to 45%-50% and reduces nitrogen fertilizer application by 15%-20% by using a strategy of reducing nitrogen fertilizer application as basal fertilizer and advancing the top dressing, combined with nitrification inhibitors.
[0039] 5. The present invention can maintain the effect for 3-5 seasons with a single application of biochar, increasing soil organic carbon by 10%-15% and reducing bulk density by 5%-8%, thus having a continuous soil improvement effect. Attached Figure Description
[0040] Figure 1 This is a schematic diagram of the rice cultivation method of the present invention, which combines alternating wet and dry conditions with biochar.
[0041] Figure 2 This is a schematic diagram illustrating the preparation and application of biochar according to the present invention.
[0042] Figure 3 This is a schematic diagram of the installation of the soil tensiometer and soil water potential monitoring according to the present invention. Detailed Implementation
[0043] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the methods used in the embodiments are conventional methods, and the reagents used are commercially available.
[0044] Example 1
[0045] This experiment was conducted in 2023 at the company's rice planting base. The tested variety was Xiangliangyou 900 (hybrid rice, with a full growth period of 135 days), and the previous crop was purple clover green manure. The soil type was a pooled paddy soil developed from river alluvium, with a texture of loam-clay. The basic physicochemical properties of the 0-20 cm topsoil were: organic matter 28.5 g / kg, total nitrogen 1.6 g / kg, available nitrogen 112 mg / kg, available phosphorus 18.5 mg / kg, available potassium 92 mg / kg, and pH 6.2. The experiment included a treatment using the method of this invention and a traditional flooding control treatment, with each treatment replicated three times. The plot area was 30 m², arranged in a randomized block design.
[0046] The method of this invention (implemented according to the above steps):
[0047] Step 1: Biochar Preparation and Base Application
[0048] Rice husks were used as raw material, air-dried, and pulverized to a particle size ≤1 cm. The pulverized material was then placed in an oxygen-limited pyrolysis furnace, heated to 500℃ at a rate of 8℃ / min, held at that temperature for 2.5 hours, and naturally cooled before passing through a 20-mesh sieve. The biochar was found to have a mesoporosity of 45%, a specific surface area of 168 m² / g, a cation exchange capacity of 23 cmol / kg, a pH of 8.8, and an NH₄⁺ adsorption capacity of 0.92 mmol / g. The application rate was 5200 kg / hm², evenly spread, and then rotary tilled to a depth of 18 cm.
[0049] Step Two: Application of Silicon-Calcium Fertilizer and Base Fertilizer
[0050] The application rate of silicon-calcium fertilizer (SiO2 28%, CaO 32%, MgO 6%, Fe2O3 1.5%) is 750 kg / hm². Urea (containing 46% N) is used as nitrogen fertilizer, with a total nitrogen content of 180 kg N / hm² throughout the growing season. The basal nitrogen content is 72 kg N / hm² (40%), and dicyandiamide (1.44 kg / hm², 2% of the total nitrogen content) is mixed into the basal fertilizer. The silicon-calcium fertilizer, urea, and dicyandiamide are mixed thoroughly and then incorporated into the biochar mixture through soil compaction.
[0051] Step 3: Seedling raising and transplanting
[0052] Dry seedling raising is adopted, with seedling trays having 434 cells, and 2-3 seeds sown per cell. Seedlings are 28 days old and have 4.0 leaves. Transplanting density is 200,000 seedlings per hectare, with 2 seedlings per seedling.
[0053] Step 4: Water and fertilizer management during the tillering stage
[0054] Maintain a 3 cm water layer for 6 days after transplanting. After the seedlings turn green again, use an alternating wet and dry method: irrigate to a depth of 2-3 cm, then allow the soil to dry naturally to a depth of 15 cm when the soil water potential is -10 kPa (tensimeter reading), and then re-irrigate. Apply tillering fertilizer (36 kg N / hm², urea) 11 days after transplanting. When the number of tillers reaches 82% of the target number of panicles (2.8 million panicles / hm²), begin drying the field, draining the water, and allowing it to dry naturally to a soil water potential of -25 kPa, maintaining this state for 8 days. During the drying period, 1-2 mm cracks will appear on the soil surface.
[0055] Step 5: Water and Fertilizer Management During the Heading Stage
[0056] Immediately after drying the field, re-flood it, maintaining a shallow water layer of 2-3 cm. Apply panicle fertilizer (72 kg N / hm², urea) at the four-leaf stage (58 days after transplanting, during the second stage of panicle differentiation). Maintain a water layer of 2-3 cm during the heading and flowering stage, deepening it to 6 cm when temperatures are high (≥35℃).
[0057] Step Six: Moisture Management During Grouting Maturation
[0058] After heading, a light alternating wet and dry approach is adopted: when the soil water potential at a depth of 15 cm drops to -15 kPa, irrigate to -5 kPa (approximately a 1 cm thin water layer), and repeat this cycle. Three days after heading, spray with 0.2% potassium dihydrogen phosphate + 0.01% brassinolide (1.5 L per plot). Allow the soil to dry naturally for 8 days before harvest.
[0059] Step 7: Pest and Disease Control
[0060] Thiamethoxam was sprayed 3 days before transplanting to control thrips; chlorantraniliprole was sprayed before drying the field during the tillering stage to control rice stem borers, based on forecasts; tricyclazole was sprayed during the heading stage to control rice blast; no additional control of sheath blight was needed during the grain-filling stage (drying the field inhibits it). This reduced the number of pesticide applications by one compared to the control.
[0061] Traditional flood control measures:
[0062] Maintain a water layer of 3-5 cm throughout the entire growth period, and drain the water 10 days before harvest. Apply a total nitrogen fertilizer of 180 kg N / hm², with a base fertilizer:tillering fertilizer:heading fertilizer ratio of 5:2:3. Do not apply biochar, silicon-calcium fertilizer, dicyandiamide, or foliar growth regulators. Other agricultural operations (seedling raising, transplanting density, and pest and disease control) are the same as those described in this invention.
[0063] Test items and methods:
[0064] Irrigation water volume: Water meters are installed in each community for measurement.
[0065] Methane emission flux: Gas samples were collected every 7 days using a static chamber-gas chromatography method to calculate the cumulative emissions over the entire growth period.
[0066] Yield: At maturity, all rice in each plot is harvested, threshed, dried, and weighed, and the actual yield is calculated based on a moisture content of 14%.
[0067] Rice quality: chalkiness and head rice yield were determined according to GB / T 17891-2017.
[0068] Nitrogen fertilizer utilization rate: The total nitrogen content of plants was measured by the difference method, and the apparent utilization rate of nitrogen fertilizer was calculated.
[0069] Root sap flow: 10 days after heading, select 5 plants from each plot, cut off the above-ground part in the evening, cover with a plastic bag containing absorbent cotton, and weigh the sap the next morning.
[0070] result: index This invention processes Control treatment rate of change Irrigation quota (m³ / hm²) 5600 9800 -42.9% <![CDATA[Cumulative CH4 emissions (kg / hm²)]]> 92.5 220.3 -58.0% <![CDATA[Integrated greenhouse gas emissions (CO2-eq kg / hm²)]]> 2850 5080 -43.9% Actual yield (t / hm²) 9.85 8.76 +12.4% chalkiness (%) 5.2 7.8 -33.3% Head rice yield (%) 68.5 62.1 +6.4 percentage points Apparent utilization rate of nitrogen fertilizer (%) 47.3 33.6 +13.7 percentage points Root damage flow rate (g / plant·night) 2.86 2.02 +41.6%
[0071] Analysis of variance showed that all the above indicators differed significantly among treatments (P<0.05). The results indicate that the method of this invention is significantly superior to the traditional flooded planting method.
[0072] Example 2
[0073] This example was conducted in 2023 at a rice planting base in Wuchang City, Heilongjiang Province. The tested variety was Wuyou Rice No. 4 (a conventional japonica rice with a full growth period of 142 days). The soil type was black soil. The physicochemical properties of the 0-20 cm topsoil layer were as follows: organic matter 42.0 g / kg, total nitrogen 2.1 g / kg, available nitrogen 145 mg / kg, available phosphorus 28.5 mg / kg, available potassium 115 mg / kg, and pH 6.8.
[0074] The method of this invention processes:
[0075] Biochar was prepared from rice straw (pyrolysis temperature 480℃, heating rate 7℃ / min, holding time 2 hours), applied at a rate of 4800 kg / hm², and rotary tilled to a depth of 20 cm. Calcium-silicon fertilizer (SiO₂ 26%, CaO 31%, MgO 5.5%) was applied at a rate of 600 kg / hm². The total nitrogen content throughout the growth period was 165 kg N / hm², with a basic nitrogen content of 66 kg N / hm² (40%), and 1.2 kg / hm² of dicyandiamide was added. Seedlings were raised in a moist environment for 30 days, with a transplanting density of 280,000 hills / hm². Water management was the same as in Example 1, except that during the tillering stage, the field was dried until the soil water potential was maintained at -25 kPa for 9 days, and during the grain-filling stage, the water potential was controlled between -15 kPa and -5 kPa. Other steps were the same as in Example 1.
[0076] Traditional flooding control treatment: Maintain a water layer of 3-5 cm throughout the entire growth period, apply a total nitrogen fertilizer of 165 kg N / hm², and use a base fertilizer: tillering fertilizer: heading fertilizer ratio of 5:2:3. Do not apply biochar, silicon-calcium fertilizer, etc.
[0077] result: index This invention processes Control treatment rate of change Irrigation quota (m³ / hm²) 4900 8600 -43.0% <![CDATA[CH4 cumulative emissions (kg / hm²)]]> 68.3 179.7 -62.0% <![CDATA[Integrated greenhouse gas emissions (CO2-eq kg / hm²)]]> 2100 4030 -47.9% Actual yield (t / hm²) 8.42 7.65 +10.1% chalkiness (%) 3.8 5.5 -30.9% Head rice yield (%) 71.2 65.8 +5.4 percentage points Apparent utilization rate of nitrogen fertilizer (%) 46.5 34.2 +12.3 percentage points Root damage flow rate (g / plant·night) 2.53 1.89 +33.9%
[0078] All differences were statistically significant (P<0.05).
[0079] Example 3 (Comparison of different biochar application rates)
[0080] Based on Example 1, a series of biochar application rates were added: 3000 kg / hm², 4500 kg / hm², 6000 kg / hm², and 7500 kg / hm², with other conditions remaining the same as in Example 1. The results showed that the yield, quality, and emission reduction effects were optimal within the range of 4500-6000 kg / hm²; the effect was not significant below 4500 kg / hm²; and above 6000 kg / hm², early tillering was inhibited, resulting in a slight decrease in yield. Therefore, the preferred range is 4500-6000 kg / hm².
[0081] Example 4 (Comparison of different water management methods)
[0082] Based on Example 1, a comparison of water management during the grouting period was added: (1) maintaining a shallow water layer (3 cm); (2) heavy wet-dry alternation (water potential dropped to -25 kPa for re-irrigation); (3) light wet-dry alternation of the present invention (-15 kPa to -5 kPa). Results: Treatment (1) had high chalkiness and premature root aging; Treatment (2) had decreased yield; Treatment (3) of the present invention had the best quality and yield.
[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A rice cultivation method coupled with alternating wet and dry conditions and biochar, characterized in that: Includes the following steps: Step 1: Biochar preparation and basal application. Rice husks or straw are decomposed under limited oxygen at 450-550℃ to obtain biochar. The application rate is 4500-6000 kg / hm², and the mixture is mixed by tilling to a depth of 15-20 cm. Step 2: Application of silicon-calcium fertilizer and base fertilizer. Mix 600-900 kg / hm² of silicon-calcium fertilizer with nitrogen base fertilizer and then bury it with biochar. The silicon-calcium fertilizer contains SiO2 ≥ 25% and CaO ≥ 30%. The base nitrogen content accounts for 40% of the total nitrogen application. Step 3: Seedling raising and transplanting; Step 4: Water and fertilizer management during the tillering stage. After the tillering stage, use alternating wet and dry irrigation, with the soil water potential at a depth of 15 cm being -10 kPa as the lower limit for irrigation. Tillering fertilizer accounts for 20% of the total nitrogen. When the number of tillers reaches 80%-85% of the target number of ears, dry the field until the soil water potential is -25 kPa and maintain this for 7-10 days. Step 5: Water and fertilizer management during the heading stage. After drying the field, re-irrigate to a depth of 2-3 cm; apply the heading fertilizer in advance at the four-leaf stage, accounting for 40% of the total nitrogen; the water potential should not be lower than -10 kPa during the heading and flowering stage. Step 6: Water management during the grain-filling and ripening stage, using alternating light dry and wet conditions, with a water potential lower limit of -15 kPa and an upper limit of -5 kPa; spraying with 0.2% potassium dihydrogen phosphate + 0.01% brassinolide at the heading stage; drying out 7-10 days before harvest; Step 7: Pest and disease control.
2. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: The biochar has a mesoporosity ≥40%, a specific surface area ≥150 m² / g, a cation exchange capacity ≥20 cmol / kg, a pH of 8.0-9.5, and an NH⁺ adsorption capacity ≥0.8 mmol / g.
3. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: The silicon-calcium fertilizer also contains MgO ≥ 5% and Fe2O3 ≥ 1%.
4. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: The nitrogen fertilizer base fertilizer contains dicyandiamide, a nitrification inhibitor, at a dosage of 1%-2% of the nitrogen content.
5. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: The soil water potential is monitored in real time using an embedded tensiometer and is linked to the automatic irrigation system for control.
6. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: For soils with high groundwater levels or heavy clay soils, the biochar application rate is 5500-6000 kg / hm², combined with ditch drainage.
7. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: In the alternating wet and dry irrigation, except for the tillering stage when the field is dried, the soil water potential during the drying stage should not be lower than -20 kPa, and the irrigation depth should not exceed 3 cm each time.
8. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: In step three, seedlings are raised using either dry or wet methods, with a seedling age of 25-30 days. The transplanting density is 250,000-300,000 hills / hm² for conventional rice and 180,000-220,000 hills / hm² for hybrid rice.
9. The rice cultivation method coupled with alternating wet and dry conditions and biochar as described in claim 1, characterized in that: The total nitrogen application rate for the entire growth period is 150-195 kg N / hm².