A rice seedling stage irrigation and drainage method for reducing greenhouse gas emission effect in rice field

Abstract

The application discloses a rice seedling stage irrigation method for reducing greenhouse gas emission effect in a rice field. In the method, a water layer in the field is emptied at a tillering middle stage of rice, dry-falling time is determined according to appearance forms or soil moisture indexes of different types of soil as diagnostic indexes, and then the water layer is re-watered and irrigated. The method can effectively reduce the greenhouse gas emission effect in the rice field, and can overcome problems of high technical requirement, limitation by types of varieties and soil, long technical regulation time in previous conventional water-saving and emission-reducing irrigation technologies. The method is simple in operation, and is suitable for indica rice, japonica rice and indica / japonica hybrid rice varieties, and is suitable for large-area popularization. The method can significantly reduce the greenhouse gas emission effect in the rice field and significantly increase economic benefits on the premise of guaranteeing the yield of the rice.

Description

Technical Field

[0001] This invention relates to a method for irrigation and drainage during the rice seedling stage to reduce greenhouse gas emissions from paddy fields, belonging to the field of agricultural technology. Background Technology

[0002] Global warming, caused by the increasing concentrations of greenhouse gases (GHGs) such as CO2, CH4, and N2O in the atmosphere, has become a global environmental problem. CH4 and N2O are significant greenhouse gases, with their global warming potentials (GWPs) being 25 and 298 times that of CO2, respectively, over a 100-year timeframe. Rice is my country's staple crop, with the world's largest total production, and its paddy field area accounts for 18% of the global rice-growing area. Paddy fields are a major source of CH4 and N2O emissions from crop systems. Statistics show that China's annual CH4 and N2O emissions from paddy fields are approximately 7.41 Tg and 32 Gg, respectively, accounting for 22% of agricultural greenhouse gas emissions. In its 2015 Nationally Determined Contribution to Climate Change submitted to the United Nations, China pledged to promote low-carbon agricultural development, strengthen the management of non-CO2 greenhouse gases, and control greenhouse gas emissions from paddy fields. Therefore, effectively controlling greenhouse gas emissions from paddy fields while ensuring food security has always been a research hotspot and challenge in rice breeding and cultivation. This is not only related to the transformation of low-carbon agricultural production but also involves fulfilling international climate negotiation obligations.

[0003] Greenhouse gas emissions from paddy fields are mainly influenced by soil properties, moisture status, fertilization, rice growth, and climate. Anaerobic soil conditions are a prerequisite for CH4 production and the promotion of methanogenic bacteria reproduction. Therefore, controlling irrigation water management can improve soil aeration and reduce CH4 emissions from paddy fields, but it also promotes N2O emissions. Jiang et al. found that controlled irrigation significantly reduced CH4 emissions from paddy fields by 51% while increasing N2O emissions by 105%. However, considering the greenhouse effects of CH4 and N2O, compared with continuous flooding, regardless of whether straw is returned to the field or nitrogen fertilizer is applied, the effect of irrigation regulation on reducing CH4 emissions from paddy fields is greater than its effect on promoting N2O emissions, thus reducing the overall greenhouse effect of carbon emissions from paddy fields. Therefore, reducing greenhouse gas emissions from paddy fields, especially CH4 emissions, through controlled irrigation is the most effective solution to reduce the greenhouse gas effect. However, existing paddy field water management measures have problems such as high technical requirements (requiring real-time monitoring of soil water potential) and long technical regulation time (regulation throughout the entire growth period or the entire grain-filling period), while also posing certain risks of yield loss. Therefore, there is an urgent need to develop a paddy field irrigation and drainage method that is easy to operate and suitable for large-scale promotion, to reduce the overall greenhouse effect of paddy field carbon emissions, and at the same time increase production and income.

[0004] Currently, commonly used irrigation management methods in production include controlled irrigation, intermittent irrigation, saturated soil irrigation, and alternating wet and dry irrigation. These irrigation patterns can effectively improve soil aeration, thereby altering extreme anaerobic reducing conditions, inhibiting the activity of methanogenic bacteria, and increasing the activity of methanogenic bacteria, significantly reducing CH4 emissions by 38%–59%. For example, alternating wet and dry irrigation has been widely used in China and Southeast Asian countries. During the rice growth process, a water layer is maintained for a period, allowing it to dry naturally until the soil is no longer severely cracked before re-irrigating, then allowing it to dry naturally again before re-irrigating. This cyclical water management method can significantly reduce CH4 emissions from paddy fields. However, all of the above irrigation methods have shortcomings. Controlled irrigation has poor operability, making it difficult to achieve uniform water distribution and ideal control indicators after irrigation; intermittent irrigation lacks quantitative water indicators and easily leads to excessive weed growth; saturated soil irrigation has an excessively high irrigation frequency, making it difficult to apply in production; and alternating wet and dry irrigation is difficult to control the degree of soil drying in practice, lacking simple and intuitive indicators, often relying on farmers' experience, and thus has certain limitations. The process is cumbersome, requiring farmers to have a certain level of technical expertise, and excessive drying can cause water deficit stress, posing a risk of yield reduction. Currently, there are no research reports on simple, cost-effective, and easily promoted irrigation technologies for reducing greenhouse gas emissions in paddy fields. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for irrigation and drainage during the rice seedling stage to reduce the greenhouse gas emission effects of paddy fields, in order to solve the problems of high greenhouse gas emissions and high environmental costs in rice production, as well as the high technical requirements, limitations due to variety and soil type, and long technical regulation time (regulation throughout the entire growth period or the entire grain-filling period) of current conventional water-saving and emission-reduction irrigation technologies.

[0006] Technical solution: The present invention provides a rice seedling irrigation and drainage method to reduce greenhouse gas emissions from paddy fields. In the middle of rice tillering, the water layer in the field is drained. The time of drying is determined based on the appearance and soil moisture index of different types of soil as diagnostic indicators. Re-irrigation is carried out, and after re-irrigation, the groundwater layer is maintained at 2-3 cm until one week before harvest.

[0007] Furthermore, the different types of soil are sandy soil, loam, or clay.

[0008] Furthermore, the soil moisture index is soil burial depth, relative soil moisture content, or soil water potential.

[0009] Furthermore, when the soil is sandy, irrigation should be carried out when the soil appearance begins to turn white at the edge of the field, or when the soil water depth is 8-12 cm, or when the relative soil moisture content is 92%-96%, or when the soil water potential is -7.5 to -5 kPa.

[0010] Furthermore, when the soil is loam, re-irrigation should be carried out when the soil appearance is compacted and does not sink underfoot, or when the soil water depth is 12-16cm, or when the relative soil moisture content is 88%-92%, or when the soil water potential is -10 to -7.5kPa.

[0011] Furthermore, when the soil is clay, re-irrigation should be carried out when the soil appearance is such that the topsoil can be squeezed into a ball by hand, or the soil water depth is 16-20cm, or the relative soil moisture content is 84%-88%, or the soil water potential is -12.5 to -10kPa.

[0012] The specific indicators mentioned above are shown in Table 1.

[0013] Table 1. Diagnostic Indicators for Soil Drying During Mid-Tillering Stage of Rice

[0014]

[0015]

[0016] Furthermore, when using soil water depth, relative soil moisture content, or soil water potential as diagnostic indicators for rehydration time, different indicators need to be selected according to different rice varieties.

[0017] Furthermore, when the rice variety is indica rice, hybrid indica rice (a hybrid of indica and indica), or hybrid indica-japonica rice (a hybrid of indica and japonica), the lower limit of soil relative moisture content, the upper limit of soil water depth, or the maximum value of soil water potential are taken as diagnostic indicators.

[0018] When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is sandy soil, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-irrigation time, re-irrigation should be carried out when the soil water depth is 12cm, the relative soil moisture content is 92%, or the soil water potential is -7.5kPa.

[0019] When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is loam, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-irrigation time, re-irrigation should be carried out when the soil water depth is 16cm, the relative soil moisture content is 88%, or the soil water potential is -10kPa.

[0020] When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is clay, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 20cm, the relative soil moisture content is 84%, or the soil water potential is -12.5kPa.

[0021] Furthermore, when the rice variety is japonica rice or hybrid japonica rice (a hybrid of japonica and japonica rice), the minimum value of the relative soil moisture content, the minimum value of the soil water depth, or the minimum value of the absolute soil water potential is taken as the diagnostic indicator.

[0022] When the rice variety is japonica rice or hybrid japonica rice, and the soil is sandy soil, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 8 cm, the relative soil moisture content is 96%, or the soil water potential is -5 kPa.

[0023] When the rice variety is japonica rice or hybrid japonica rice, and the soil is loam, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-irrigation time, re-irrigation should be carried out when the soil water depth is 12cm, the relative soil moisture content is 92%, or the soil water potential is -7.5kPa.

[0024] When the rice variety is japonica rice or hybrid japonica rice, and the soil is clay, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 16cm, the relative soil moisture content is 88%, or the soil water potential is -10kPa.

[0025] The soil desiccation index described in this invention varies depending on the type of rice. Specifically, when soil water depth, relative soil moisture content, and soil water potential are selected as diagnostic indicators, for indica rice (including hybrid indica rice) varieties, the lower limit value of relative soil moisture content is taken, and the higher limit value of absolute soil water depth or absolute soil water potential is taken; for japonica rice (including hybrid japonica rice) varieties, the higher limit value of relative soil moisture content is taken, and the lower limit value of absolute soil water depth or absolute soil water potential is taken.

[0026] Furthermore, from rice transplanting to the mid-tillering stage, maintain a 2-3 cm water layer in the field.

[0027] This invention achieves a significant reduction in greenhouse gas emissions from paddy fields and a significant increase in economic benefits by draining the water layer in the middle of rice tillering and determining the duration of drying based on soil appearance or soil moisture indicators of different soil types.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0029] (1) The method of this invention is simple to operate, has a short control cycle, and is easy to implement. Depending on the user's observation facilities and technical application preferences, one of four indicators—soil appearance morphology, soil water depth, relative soil moisture content, or soil water potential—can be selected to monitor the soil drying index. The method is simple. The soil drying index is monitored during the mid-tillering stage, with a drying time of 8-15 days. The monitoring cycle is short, and conventional irrigation methods are followed for the remaining growth stages of rice.

[0030] (2) The method of this invention has wide applicability and significant effects. The irrigation and drainage method for reducing greenhouse gas emissions from paddy fields proposed in this invention can be used on different types of soil (sandy, loam, clay) and has been verified by experiments on different types of rice varieties (indica, japonica, hybrid rice). All of them can significantly reduce the greenhouse gas emissions from paddy fields, and the global warming potential of greenhouse gases is reduced by 34.4%-48.1%.

[0031] (3) The method of this invention has no risk of yield reduction and yields high returns. The rice seedling irrigation and drainage method proposed in this invention to reduce greenhouse gas emissions from paddy fields has been verified through two years of field trials and has no risk of yield reduction. At the same time, it has the highest economic and environmental benefits and can reduce the potential for global warming of greenhouse gases while ensuring food security. It has important significance and broad prospects and plays a positive role in promoting sustainable agricultural development. Attached Figure Description

[0032] Figure 1 This is a global warming potential diagram for rice grown using the four irrigation methods described in Example 1;

[0033] Figure 2 The diagram shows the economic benefits of rice grown using the four irrigation methods in Example 1. Detailed Implementation

[0034] Example 1

[0035] 1. Overview of the experimental site and the tested varieties

[0036] The experiment was conducted in 2021 and 2022 in a rain-sheltered greenhouse field at the Jiangsu Provincial Key Laboratory of Crop Cultivation Physiology, Yangzhou University, to eliminate interference from external rainwater. The previous crop was wheat, and the soil texture was loam. The topsoil contained 24.4 g / kg of organic matter, 105.2 mg / kg of available nitrogen, 34.3 mg / kg of available phosphorus, and 68.2 mg / kg of available potassium. The tested varieties were Jinxiangyu No. 1 (japonica rice), Yangdao No. 6 (indica rice), and Yongyou 2640 (indica / japonica hybrid rice). Seeds of Jinxiangyu No. 1 and Yangdao No. 6 were purchased from Yangzhou Seed Company, Jiangsu Province, and seeds of Yongyou 2640 were purchased from Taizhou Seed Company, Zhejiang Province.

[0037] Seeds were soaked on May 18, sown on May 23, transplanted to seedbeds on May 25, and transplanted on June 13, 2021. In 2022, seeds were soaked on May 20, sown on May 25, transplanted to seedbeds on May 27, and transplanted on June 16. Two seedlings were planted per hill, with a spacing of 11.7cm x 30cm. Nitrogen, phosphorus, and potassium fertilizers were applied according to local high-yield cultivation practices, with a total nitrogen application rate of 240 kg / hm². 2 The fertilizer is applied in four applications: base fertilizer (applied 1 day before transplanting), tillering fertilizer (applied 7 days after transplanting), flowering fertilizer (applied when the remaining leaf age is 3.5), and flowering protection fertilizer (applied when the remaining leaf age is 1.5). The nitrogen content of each application accounts for 40%, 20%, 20%, and 20% of the total nitrogen application, respectively. One day before transplanting, 750 kg / hm² of superphosphate (P₂O₅ content 13.5%) is applied. 2 Potassium chloride (K2O content 59%) 300 kg / hm 2 The fertilizer was applied one day before transplanting and when the leaf age remained at 3.5, with a ratio of 7:3 between the two applications.

[0038] 2. Processing Settings

[0039] The experiment employed a split-plot design, with irrigation method (A) as the main plot and variety (B) as the split plot, with a plot area of ​​20m². 2 Randomized block design, repeated 3 times. Soil water potential was monitored using a soil tensiometer. The specific operation was as follows: during installation, a hole was drilled to a depth of 20cm from the ground using a drill bit with a diameter equivalent to the clay head of the soil tensiometer. The soil tensiometer was then vertically inserted, with the upper part of the clay head (5cm in length) 15cm and the lower part 20cm from the ground. Mud slurry was poured in to ensure close contact between the clay head and the tensiometer tube buried in the soil (refer to the product instruction manual for instructions). Four irrigation methods were set up:

[0040] (1) Conventional irrigation: Maintain a shallow water layer of 2-3 cm throughout the entire growth period until water is cut off one week before harvest.

[0041] (2) Irrigation and drainage during the rice seedling stage: On the 14th day after transplanting (mid-tillering stage, the optimal drainage date), drain the water layer in the field to maintain a waterless state. Re-irrigate according to the soil desiccation index (optimal desiccation period). In this example, when the soil water depth is observed to be 16cm, the relative soil moisture content is 88%, and the soil water potential is -10kPa, and the soil appearance shows that the soil is compacted and does not sink underfoot, re-irrigate. In this example, the desiccation period is 10 days, as detailed in Table 2; for the remaining periods, follow the conventional irrigation method for rice, that is, maintain a water level of 2-3cm from transplanting to the 14th day and from re-irrigation to one week before harvest, until water is stopped one week before harvest.

[0042] Table 2 Irrigation and drainage methods for reducing greenhouse gas emissions from paddy fields during the rice seedling stage.

[0043]

[0044] (3) Mild alternating wet and dry irrigation throughout the entire growth period:

[0045] From transplanting to 7 days after transplanting, maintain a shallow water layer of 2-3 cm in the field;

[0046] Seven days after transplanting until the critical leaf age for effective tillering (8–25 days after transplanting), allow the soil water level in the field to naturally dry from a shallow water layer of 2–3 cm to a depth of 15–20 cm below the surface. The soil water potential value is -10 kPa for japonica rice varieties, -12.5 kPa for indica rice varieties, and -15.0 kPa for indica / japonica hybrid rice varieties. Then, irrigate the field again with a shallow water layer of 2–3 cm, and allow it to dry naturally again. Repeat this cycle. If the soil water potential value is greater than the above soil water potential index values, do not irrigate the field.

[0047] From the critical leaf age for effective tillering to the beginning of jointing (26-45 days after transplanting), allow the soil water potential in the field to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. The values ​​are -15 kPa for japonica rice varieties, -17.5 kPa for indica rice varieties, and -20.0 kPa for indica / japonica hybrid rice varieties. Then, irrigate the field again with a shallow water layer of 2-3 cm, and allow it to dry naturally again. Repeat this cycle. If the soil water potential value is greater than the above soil water potential index values, do not irrigate the field.

[0048] From the jointing stage to the heading stage (46-80 days after transplanting), allow the soil water potential in the field to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. The values ​​are -5 kPa for japonica rice varieties, -7.5 kPa for indica rice varieties, and -10.0 kPa for indica / japonica hybrid rice varieties. Then, irrigate the field again with a shallow water layer of 2-3 cm, and allow it to dry naturally again. Repeat this cycle. If the soil water potential value is greater than the above soil water potential index values, do not irrigate the field.

[0049] One to 20 days after heading, the soil water level in the field is allowed to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. The soil water potential is -10 kPa for japonica rice varieties, -12.5 kPa for indica rice varieties, and -15 kPa for indica / japonica hybrid rice varieties. The field is then irrigated again with a shallow water layer of 2-3 cm, and allowed to dry naturally again. This cycle is repeated. If the soil water potential value is greater than the above soil water potential index values, the field is not irrigated. One day after heading, 50% of the rice panicles in the field should have emerged from the flag leaf sheath.

[0050] From 21 days after heading to maturity, the soil water potential in the field is allowed to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. For japonica rice varieties, this is -15.0 kPa; for indica rice varieties, it is -17.5 kPa; and for indica / japonica hybrid rice varieties, it is -20.0 kPa. Then, the field is irrigated again with a shallow water layer of 2-3 cm, and allowed to dry naturally again. This cycle is repeated. If the soil water potential value is greater than the above-mentioned soil water potential index values, the field is not irrigated.

[0051] (4) After flowering, irrigate alternately with dry and wet water:

[0052] From transplanting to the heading stage (80 days after transplanting), maintain a shallow water layer of 2-3 cm;

[0053] One to 20 days after heading, the soil water level in the field is allowed to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. The soil water potential is -10 kPa for japonica rice varieties, -12.5 kPa for indica rice varieties, and -15 kPa for indica / japonica hybrid rice varieties. The field is then irrigated again with a shallow water layer of 2-3 cm, and allowed to dry naturally again. This cycle is repeated. If the soil water potential value is greater than the above soil water potential index values, the field is not irrigated. One day after heading, 50% of the rice panicles in the field should have emerged from the flag leaf sheath.

[0054] From 21 days after heading to maturity, the soil water potential in the field is allowed to naturally dry from a shallow water layer of 2-3 cm to a depth of 15-20 cm below the surface. For japonica rice varieties, this is -15.0 kPa; for indica rice varieties, it is -17.5 kPa; and for indica / japonica hybrid rice varieties, it is -20.0 kPa. Then, the field is irrigated again with a shallow water layer of 2-3 cm, and allowed to dry naturally again. This cycle is repeated. If the soil water potential value is greater than the above-mentioned soil water potential index values, the field is not irrigated.

[0055] 3. Sampling and testing

[0056] Greenhouse gas (CH4 and N2O) emissions in the field were determined using a static dark chamber-gas chromatography method. The static chamber (PVC material, length × width = 0.5m × 0.5m, height 0.5m before panicle differentiation, 1m after panicle differentiation) was used. Measurements were taken every 7 days after transplanting, with additional measurements taken 2-3 days before and after fertilization. Gas collection was conducted from 9:00 AM to 11:00 AM, with five gradients collected at 10-minute intervals. At maturity (one day before harvest), 10 rice plants from each plot were sampled for determining yield components, with 5m² of actual harvested rice collected. 2 Production calculation.

[0057] 4. Data Measurement Methods

[0058] Greenhouse gases were collected and determined using a static chamber-gas chromatography method. Gas collection was conducted under stable weather conditions and without field management, with a 4-day interval between two sampling sessions, and three samples collected from each treatment. Additional measurements were taken after rain, before and after fertilization, and during field drying. The sampling chamber was a PVC cylinder with an inner diameter of 30 cm and a height of 100 cm, wrapped with insulation material to maintain a stable internal temperature. Before rice transplanting, a base with an inner diameter of 30 cm and a height of 15 cm was placed between the rice plants. Water was added to the groove of the base to seal it before each sampling, and the sampling chamber was then closed. Collection time was from 9:00 to 11:00, with gas samples collected using a syringe at 0, 10, 20, 30, and 40 minutes. The sampling chamber also had a round opening with a rubber stopper at the top, allowing for temperature measurement within the PVC cylinder during sampling. Gas samples were brought back to the laboratory within 24 hours for gas chromatography concentration measurement of greenhouse gases (CH4 and N2O). CH4 concentration was determined using an Agilent 7890A gas chromatograph with manual injection and an FID detector at a detection temperature of 350℃, a column temperature of 60℃, and a hydrogen flow rate of 40 mL / min. -1 Carrier gas is High-purity argon / CH4 Argon and CH4. The formula for calculating greenhouse gas emission flux is Equation (1):

[0059]

[0060] In the formula, F is the greenhouse gas emission flux, mg / m³. -2 h -1 H represents the measured height of the static dark chamber; M represents the molar mass fraction of the greenhouse gas, where CH4 is 16 g mol. -1 The amount of N2O is 44 g mol. -1 P is standard atmospheric pressure, 1.013 × 10⁻⁶. 5 Pa; R is the gas constant, 8.314 J mol -1 kg -1 T is the average temperature inside the static dark chamber for 30 minutes of sampling, in °C; dc / dt is the greenhouse gas emission rate, in mL / m³. -3 h -1 .

[0061] The formula for calculating total greenhouse gas emissions is Equation (2):

[0062]

[0063] In the formula, SUM represents the total greenhouse gas emissions, expressed in kg hm². -2 F represents greenhouse gas emission flux, in mg / m³. -2 h -1i represents the number of gas samplings; t i+1 -t i This represents the time interval between two adjacent measurement dates, where n is the total number of measurements taken during the observation period for cumulative greenhouse gas emissions.

[0064] Global warming potential (GWP) represents the cumulative radiation intensity of a unit mass of greenhouse gas over a certain time scale. Using CO2 as the reference gas, the warming potential values ​​for CH4 and N2O are 25 and 298 respectively over a 100-year time scale. When calculating the total CO2 equivalent, CO2 emissions from paddy fields are not included. The GWP calculation formula is Equation (3):

[0065] GWP=25×F(CH4)+298×F(N2O) (3)

[0066] In the formula: GWP is the global warming potential (kg CO2 - eq hm) -2 F(CH4) and F(N2O) represent the total CH4 and N2O emissions from paddy fields (kg / hm²), respectively. -2 ).

[0067] 5. Technical Effects

[0068] Table 3 shows the yield, total methane (CH4) and nitrous oxide (N2O) emissions, and global warming potential of the indica / japonica hybrid rice varieties under different irrigation treatments in this embodiment.

[0069] Table 3. Yield, total greenhouse gas emissions, and global warming potential of indica / japonica hybrid rice under different irrigation treatments. a

[0070]

[0071] Each rice variety is planted in fields equipped with rain shelters, which are covered when it rains during the drying period.

[0072] The output figures are the actual output received by each community.

[0073] Different letters a, b, and c indicate significant differences between different treatments within the same column (P < 0.05).

[0074] As shown in Table 3, compared with conventional irrigation treatment, the irrigation and drainage treatment during the seedling stage of rice according to the present invention had no significant effect on the yield of indica / japonica hybrid rice, but reduced the global warming potential of greenhouse gases by 43.5%-48.1%. Although the yield was increased under the alternating wet and dry irrigation treatment throughout the entire growth period, the global warming potential of greenhouse gases was reduced by 29.0%-31.6%, which was less effective than the irrigation and drainage treatment during the seedling stage. Although the alternating wet and dry irrigation treatment after flowering significantly increased the yield, the global warming potential of greenhouse gases was slightly increased.

[0075] Table 4 shows the yield, total methane (CH4) and nitrous oxide (N2O) emissions, and global warming potential of the japonica rice varieties under different irrigation treatments in this embodiment.

[0076] Table 4. Japonica rice yield, total greenhouse gas emissions, and global warming potential under different irrigation treatments. a

[0077]

[0078] Each rice variety is planted in fields equipped with rain shelters, which are covered when it rains during the drying period.

[0079] The output figures are the actual output received by each community.

[0080] Different letters a, b, and c indicate significant differences between different treatments within the same column (P < 0.05).

[0081] As shown in Table 4, compared with conventional irrigation treatment, the irrigation and drainage treatment during the rice seedling stage of the present invention had no significant impact on the yield of japonica rice, but reduced the global warming potential of greenhouse gases by 35.5%-39.0%. Although the yield was increased under the alternating wet and dry irrigation treatment throughout the entire growth period, the global warming potential of greenhouse gases was reduced by 17.6%-21.3%, which was less effective than the irrigation and drainage treatment during the rice seedling stage. Although the alternating wet and dry irrigation treatment after flowering significantly increased the yield, the global warming potential of greenhouse gases was slightly increased.

[0082] Table 5 shows the yield, total methane (CH4) and nitrous oxide (N2O) emissions, and global warming potential of the indica rice varieties under different irrigation treatments in this embodiment. Figure 1 .

[0083] Table 5. Rice yield, total greenhouse gas emissions, and global warming potential under different irrigation treatments. a

[0084]

[0085] Each rice variety is planted in fields equipped with rain shelters, which are covered when it rains during the drying period.

[0086] The output figures are the actual output received by each community.

[0087] Different letters a, b, and c indicate significant differences between different treatments within the same column (P < 0.05).

[0088] From Table 5 and Figure 1As can be seen, compared with conventional irrigation treatment, the method of the present invention for irrigation and drainage during the rice seedling stage has no significant impact on the yield of indica rice, but reduces the global warming potential of greenhouse gases by 34.4%-43.8%; although the yield is increased under the alternating wet and dry irrigation treatment throughout the entire growth period, the global warming potential of greenhouse gases is reduced by 18.4%-27.5%, which is less effective than the irrigation and drainage treatment during the rice seedling stage; although the alternating wet and dry irrigation treatment after flowering significantly increases the yield, the global warming potential of greenhouse gases is slightly increased.

[0089] The economic benefits of rice grown using the four irrigation methods mentioned above are shown in Table 6 and... Figure 2 As shown.

[0090] Table 6 Comparison of economic benefits of rice under different irrigation measures (10) 3 Yuan / hm 2 )

[0091]

[0092] By analyzing Table 6 and Figure 2 The economic benefits of rice under different irrigation measures show that although alternating wet and dry irrigation throughout the entire growth period and after flowering increased the yield of rice, their overall economic benefits were significantly lower than those of the rice seedling irrigation treatment due to the increased labor costs, the cost of using soil moisture tensiometers in the field, and the lower greenhouse gas emission reduction effect compared to the rice seedling irrigation treatment. In contrast, the rice seedling irrigation treatment of this invention does not require the installation of soil moisture tensiometers or frequent manual monitoring of soil water potential and timely irrigation, thus reducing material and labor costs. Furthermore, it significantly reduces greenhouse gas emissions and global warming potential from rice fields, increasing emission reduction benefits and ultimately significantly improving the overall economic benefits.

[0093] The field trials conducted over the two years demonstrated that an irrigation method involving draining the field water layer 14 days after rice transplanting (mid-tillering stage), followed by a 10-day drying period, and re-irrigating on the 11th day, significantly reduces greenhouse gas emissions and global warming potential from paddy fields, while improving overall economic benefits, compared to other irrigation methods, while ensuring yield. This method can be directly applied in the field and will yield even better results.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, or alterations made by those skilled in the art using the disclosed technical content shall fall within the protection scope of the present invention.

Claims

1. A method for irrigation and drainage during the rice seedling stage to reduce greenhouse gas emissions from paddy fields, characterized in that, During the mid-tillering stage of rice, the water layer in the field is drained, and the time for drying is determined based on the appearance or soil moisture index of different types of soil as diagnostic indicators, and then re-irrigation is carried out. When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is sandy soil, and soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 12 cm, the relative soil moisture content is 92%, or the soil water potential is -7.5 kPa. When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is loam, when soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 16 cm, the relative soil moisture content is 88%, or the soil water potential is -10 kPa. When the rice variety is indica rice, hybrid indica rice, or indica-japonica hybrid rice, and the soil is clay, when soil water depth, relative soil moisture content, or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 20 cm, the relative soil moisture content is 84%, or the soil water potential is -12.5 kPa. When the rice variety is japonica rice or hybrid japonica rice, and the soil is sandy soil, when soil water depth, relative soil moisture content or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 8 cm, the relative soil moisture content is 96%, or the soil water potential is -5 kPa. When the rice variety is japonica rice or hybrid japonica rice, and the soil is loam, when soil water depth, relative soil moisture content or soil water potential are selected as diagnostic indicators for re-irrigation time, re-irrigation should be carried out when the soil water depth is 12 cm, the relative soil moisture content is 92%, or the soil water potential is -7.5 kPa. When the rice variety is japonica rice or hybrid japonica rice, and the soil is clay, when soil water depth, relative soil moisture content or soil water potential are selected as diagnostic indicators for re-watering time, re-watering should be carried out when the soil water depth is 16 cm, the relative soil moisture content is 88%, or the soil water potential is -10 kPa. From the time rice is transplanted to the mid-tillering stage, maintain a water layer of 2-3 cm in the field.

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