Shallow-water circular-groove water-saving rice and crab symbiotic three-dimensional agricultural ecological system and planting and breeding method

Abstract

The invention discloses a shallow-water circular-trench water-saving type rice and crab symbiotic three-dimensional agricultural ecological system and a planting and breeding method, and belongs to the technical field of ecological agriculture. Ridges are arranged on the periphery of a crab culture rice field, anti-escape crab membranes are constructed on the ridges, water-filled circular ditches are dug in the inner sides of the ridges, and water inlets and water outlets connected with water inlet channels and water outlet channels are formed in the opposite corners of the circular ditches respectively; soybeans and alternanthera philoxeroides are planted in ridges and circular ditches respectively, a dry-wet alternate irrigation mode is adopted in a rice planting area, water control is conducted after the tillering stage of rice, the lower limit threshold of water control is-10 kPa, and water is irrigated to the upper limit of the water level of the rice field when the lower limit of water control is reached. A three-dimensional planting and breeding system with two purposes in one land, two breeding in one water and three harvest in one season is realized; the land utilization efficiency is improved, and water-saving regulation and space optimization of the rice-crab symbiotic system are realized; water resource waste is reduced through an ecological cooperation mechanism, system stability is enhanced, it is ensured that rice and river crabs are in a proper growth environment, and planting and breeding comprehensive benefits are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ecological agriculture, and in particular relates to a shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem and a cultivation method. Background Art

[0002] Rice-crab symbiosis, a typical ecological agricultural model, leverages the mutually beneficial symbiotic relationship between rice and river crabs to achieve the production goal of "one water for two uses, one field for two harvests." With its multiple advantages, including resource recycling, improved ecological environment, and increased farmer income, this model has been widely adopted in agricultural production in my country, particularly in rice-growing areas in northern China. However, traditional rice-crab symbiosis systems present numerous challenges. For example, they cannot utilize water-saving irrigation techniques used in rice paddies. Furthermore, the intermittent and irregular water supply in traditional crab-rearing irrigation areas leads to a sharp drop in crab survival during droughts. Furthermore, compared to rice monoculture, irrigation water requirements in crab-rearing rice paddies are 30% to 50% higher. Alternating wet-dry irrigation is the most effective and widely used irrigation technique for water-saving rice field management. However, crabs are semi-aquatic crustaceans and rely on aquatic environments for survival, which limits their application in crab-rearing rice fields. Existing rice-crab symbiosis models often rely on empirical judgments about irrigation timing and lack a basis for irrigation regulation. Furthermore, the ecological functions of ridges are limited, and vertical space is underutilized. In order to break through the technical barriers of the application of dry-wet alternating irrigation technology in the rice-crab symbiosis model, the present invention proposes a shallow water ring ditch water-saving rice-crab symbiosis three-dimensional agricultural ecological model and breeding method. Through dry-wet alternating irrigation in the rice planting area, the ring ditch remains continuously flooded to provide a water environment for crabs to survive, and the dry-wet alternating irrigation technology is applied to the rice-crab symbiosis system. At the same time, soybeans are planted on the ridges and water peanuts are planted in the ring ditches, which not only promotes the diversified use of land resources, but also provides crabs with natural shelter and sufficient feeding space, optimizing their habitat. Based on an in-depth analysis of the technical bottlenecks of the application of dry-wet alternating irrigation technology in the rice-crab symbiosis model, the present invention optimizes the design from multiple dimensions such as farmland structure innovation and breeding technology upgrades, aiming to build a rice-crab symbiosis system with water-saving irrigation, efficient use of water resources, ecological stability and universal applicability. Summary of the Invention

[0003] In response to the above-mentioned water-saving irrigation technology problems, under the premise of ensuring the normal growth of crabs and applying dry-wet alternating irrigation technology to the rice-crab symbiosis system, the present invention provides a shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem and breeding method, which is suitable for the rice-crab symbiosis model with unstable water supply and insufficient water resources. While ensuring the stable production of rice and crabs, it reduces the irrigation cost of crab-raising rice fields.

[0004] The object of the present invention is achieved through the following technical solutions:

[0005] The present invention discloses a shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem. Ridges are arranged around crab-raising rice field units, crab escape-proof membranes are constructed on the ridges, and ring ditches are dug inside the ridges. A water inlet and a water outlet are respectively arranged at the diagonal points of the ring ditches. The inlet and outlet are respectively connected to the water inlet channel and the drainage channel located outside the two opposite ridges. Water is irrigated and drained through gates. Drought-resistant plants and aquatic plants are planted in the ridges and the ring ditches respectively. The water depth of the ring ditches is maintained at 0.8 to 1.5 meters for a long time, providing a stable living water environment for crabs. ; The rice-growing area adopts the dry-wet alternating irrigation method, and the water control standard is implemented according to the water level and water environment control standard of the rice-crab symbiosis model in the cold region of Northeast China in Table 1. From the rice greening period to the rice tillering period, the water level in the rice-growing area is maintained at 1-3 cm. After the rice tillering period, when the lower limit of water control is reached, the ring ditch drainage outlet is opened to drain water, and the drainage volume is 1 / 3-1 / 2 of the water volume in the ring ditch. Then the drainage outlet is closed and the water inlet is opened to irrigate to the upper limit of the rice field water level; the dry-wet alternating irrigation is stopped when the rice is yellow and ripe, and the water in the rice field is allowed to dry naturally.

[0006] Furthermore, the distance L1 between the ring ditch and the inner side of the ridge is 60 cm, the top width W1 of the ring ditch is 1 to 1.2 m, the bottom width W2 is 0.5 to 0.7 m, and the depth H1 is 1 to 1.2 m; the area of ​​the ring ditch is 10% or less of the unit area of ​​the crab-raising rice field.

[0007] Furthermore, the aquatic plants evenly planted along the ditch wall in the annular ditch are water peanuts, with a plant spacing of 0.3 to 0.5 m and 3 to 5 plants in each cluster, ensuring that 30% to 40% of the water surface of the annular ditch is covered.

[0008] Furthermore, the anti-escape crab membrane is made of plastic film, which is buried 10 to 15 cm in the soil of the field ridge, with a height H2 above the field ridge of 60 to 80 cm, and is fixed on bamboo poles arranged at intervals, and the plastic crab membrane is tightened and fixed.

[0009] Furthermore, a filter screen is installed at the water inlet, and the filter screen aperture is 20 to 40 meshes to prevent debris and wild fish from entering the annular ditch.

[0010] Furthermore, the top width W3 of the trapezoidal ridge is 0.5-0.6m, the bottom width W4 is 0.8-1m, and the height H3 is 0.6-0.8m; drought-tolerant plants are planted on both sides and side walls of the ridge, and the middle part of the top of the ridge is reserved as walking space. The drought-tolerant plants are drought-tolerant soybean varieties, with a row spacing of 0.4m and a plant spacing of 0.3m; the planting density is 5-6 plants per square meter.

[0011] Furthermore, an ultrasonic water level meter and a negative pressure gauge are provided in the rice field. The water level is observed by the ultrasonic water level meter, and the soil water potential is monitored by the negative pressure gauge to control water.

[0012] Furthermore, the placement depth H4 of the negative pressure gauge is 15 to 20 cm, which is consistent with the main distribution layer of the rice root system.

[0013] The cultivation method of the shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem of the present invention is specifically as follows:

[0014] S1. Preliminary preparation: 7 to 10 days before transplanting rice seedlings, apply decomposed organic fertilizer to the rice fields at a rate of 1000 to 1500 kg / 667 m 2 , inject clean water into the ditch to a depth of 0.8-1.5m, and release the disinfected river crab seedlings, with a specification of 100-120 crabs / kg, and a release rate of 300-500 crabs / 667m per mu. 2 ;

[0015] S2. Alternating wet-dry irrigation and ring ditch management: Alternating wet-dry irrigation is used in rice-growing areas. From the rice greening stage to the rice tillering stage, the water level is monitored using an ultrasonic water level gauge and maintained at 1-3 cm. After the rice tillering stage, the soil water potential is monitored using a negative pressure gauge. When the soil water potential reaches the lower limit, the ring ditch outlet is opened to drain water, with the discharge volume being 1 / 3-1 / 2 of the water volume in the ring ditch. The outlet is then closed and the water inlet is opened to irrigate the paddy field to the upper limit of the water level. Alternating wet-dry irrigation is stopped when the rice matures, and the paddy field is allowed to drain naturally. Based on the water layer depth and soil water potential control standards for rice-crab symbiotic systems in the cold regions of Northeast China in Table 1, the water depth in the ring ditch is always maintained at 0.8-1.5 m during non-irrigation periods.

[0016] Table 1: Water depth and soil water potential control standards for rice-growing areas in the rice-crab symbiotic system in the cold regions of Northeast China

[0017]

[0018] S3. Farming Management: No additional fertilizer is required during soybean growth. When soybean pods mature, harvest them promptly and crush the straw and return it to the field. Peanuts should be pruned monthly, removing any overcrowded areas to maintain the required coverage within the ditch. River crabs should be fed at multiple locations between the ditch and the crab's nest.

[0019] S4. Harvest: After the crabs reach sexual maturity in mid-September, they can be caught in concentrated quantities until the rice and soybean harvest. After the harvest, the remaining crabs in the fields and ditches should be caught every day until all the crabs are caught.

[0020] Furthermore, the daily feeding amount accounts for 5% to 10% of the total weight of river crabs. In the early stage of breeding, complete feed with a crude protein content of more than 30% is mainly fed; in the middle stage of breeding, plant bait is mainly fed, combined with complete granular feed and animal bait; in the later stage of breeding, it enters the rapid weight gain period of fattening, and more animal feed and high-quality granular feed are fed, and the proportion of animal feed is at least 50%.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention sets up circular ditches around the rice fields, and implements the "shallow water circular ditch" structure of rice field water-saving irrigation technologies such as dry-wet alternating irrigation in rice-growing areas. This solves the "bottleneck" problem that current rice water-saving irrigation technology cannot be applied to the rice-crab symbiosis system, enabling crab-raising rice fields to cope with water shortages caused by extreme weather. At the same time, it also solves the limitations of the intermittent and irregular water supply that are prevalent in irrigation areas on the rice-crab symbiosis industry.

[0023] 2. The present invention plants soybeans on the ridges and water peanuts in the ditch, fully activating the idle land space, achieving the dual value of "multiple harvests from one land" and ecological purification to ensure the survival stability of crabs.

[0024] 3. The "shallow water ring ditch" structure of the present invention combines rice planting and crab breeding with soybean planting on the ridge, realizing a three-dimensional breeding and farming system with rice in the water, crabs in the rice, fragrant beans on the ridge and fat crabs, and dual use of one land, two breeding in one water, and three harvests in one season, which increases the overall income by at least 60%.

[0025] 4. The present invention implements water-saving irrigation techniques such as dry-wet alternating irrigation in rice field planting areas, or when the irrigation area is short of water supply, especially when there is no water layer on the field surface, the ring ditch can provide a living water environment for crabs, and proposes specific breeding methods. This three-dimensional agricultural ecosystem can improve land use efficiency by planting plants on ridges and crab ditches, and achieve water-saving regulation and spatial optimization of the rice-crab symbiotic system; reduce water resource waste through ecological synergy mechanisms, enhance system stability, ensure that rice and river crabs are in a suitable growth environment, and improve the comprehensive benefits of breeding. This model reduces dependence on stable water sources, improves land resource utilization, and is suitable for rice-crab breeding scenarios of different scales. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Draw a map for field layout.

[0027] Figure 2 This is a schematic diagram of the rice-crab symbiotic three-dimensional agricultural ecological model of the present invention.

[0028] In the picture: 1. Rice field, 2. Circular ditch, 3. Ridge, 4. Inlet channel, 5. Inlet, 6. Drainage channel, 7. Drainage outlet, 8. Crab membrane, 9. Drought-resistant plants, 10. Aquatic plants, 11. Ultrasonic water level meter, 12. Vacuum gauge. DETAILED DESCRIPTION

[0029] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0030] Example 1: The present invention provides a shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecological model and breeding method. It takes water-saving irrigation of crab-raising rice fields as the starting point, adopts a "shallow water ring ditch" structure in which ring ditches are set around the rice fields and dry-wet alternating irrigation and other rice field water-saving irrigation technologies are normally implemented in the rice-growing areas. This can not only ensure the water environment for crab survival, but also reduce the irrigation water used in crab-raising rice fields.

[0031] The present invention discloses a shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem. Ridges 3 are arranged around crab-raising rice field units, and crab-proof membranes 8 are constructed on the ridges 3. A ring ditch 2 is dug inside the ridge 3. The ditch 2 maintains a water depth of 0.8 to 1.5 meters for a long time, providing a stable living water environment for crabs. A water inlet 5 and a water outlet 7 are respectively arranged at the diagonals of the ring ditch 2. The water inlet 5 and the water outlet 7 are respectively connected to an inlet channel 4 and a drainage channel 7 located outside two opposite ridges 3, and water is irrigated and drained through gates. Drought-resistant plants 9 and aquatic plants 10 are respectively planted in the ridge 3 and the ring ditch 2. In this example, soybeans and water peanuts are respectively planted.

[0032] In the rice-growing area, a dry-wet alternating irrigation method is adopted, and the water control standard is implemented according to the water layer depth and soil water potential control standards of the rice-growing area of ​​the rice-crab symbiosis system in the cold region of Northeast China in Table 1. From the rice greening period to the rice tillering period, the water level is observed by an ultrasonic water level meter and the water level is maintained at 1-3 cm. After the rice tillering period, the soil water potential is monitored by a negative pressure gauge. When the soil water potential reaches the lower limit (-10 kPa), the ring ditch drain is opened to drain water, and the drainage volume is 1 / 3-1 / 2 of the water volume in the ring ditch. Then the drain is closed and the water inlet is opened to irrigate the rice field to the upper limit of the water level, which is 10 cm in this case. The dry-wet alternating irrigation is stopped when the rice is yellow and ripe, and the water in the rice field is allowed to dry naturally.

[0033] The specific settings are as follows:

[0034] 1. System Construction

[0035] 1. Construction of shallow water ring ditch: crab farming rice fields with 6667m 2 ~13334m 2A crab farming unit is preferably constructed around the rice planting area, with ridges 3 (in this example, with a top width W3 of 0.5m, a bottom width W4 of 0.8m, and a height H3 of 0.6m) surrounding the rice field. A circular ditch 2 is dug 60cm inside the ridge 3. In this example, the top width W1 is 1m, the bottom width W2 is 0.5m, and the depth H1 is 1m. The area is less than 10% of the crab farming unit area. Crab-proof membranes 8 are constructed around the ridges 3. This plastic film is buried 10cm into the ridge soil, with the remaining portion protruding 60cm above the ridge 3 at a height H2. The membranes are secured to the tops of bamboo poles spaced 0.5m apart and held taut. A shallow water circular ditch 2, located diagonally around the rice field 1, has an inlet 5 and an outlet 7 connected to the inlet channel 4 and the outlet channel 6, respectively, for irrigation and drainage through gates. At the same time, a filter is installed at the water inlet 5, and the aperture of the filter is controlled at 20 to 40 meshes to prevent debris and wild fish from entering the ditch 2 and affecting the growth environment of rice crabs.

[0036] 2. Layout of soil water potential and water level monitoring devices: 1 negative pressure gauge 12 and 1 ultrasonic water level monitor 11 are evenly distributed in the rice field 1. The negative pressure gauge 12 is laid out at a depth H4 of 15 to 20 cm, which is consistent with the main distribution layer of the rice root system.

[0037] 3. Planting Layout. Plant soybeans (select drought-tolerant varieties, such as "Jidou 12") on both sides and along the sidewalls of ridge 3, with a row spacing of 0.4m and a plant spacing of 0.3m. Plant at a density of 5-6 plants per square meter, leaving space for walking in the middle of the ridge top. Plant water peanuts evenly along the walls of ditch 2, with a plant spacing of 0.5m and 3-5 plants per clump, ensuring that 30%-40% of the ditch water surface is covered (to provide shelter for river crabs and prevent over-breeding that affects water circulation).

[0038] 2. Cultivation and breeding method of shallow water ring ditch water-saving rice-crab symbiosis model of the present invention

[0039] 1. Early preparation: 7 to 10 days before transplanting rice seedlings, apply decomposed organic fertilizer (1000-1500kg / 667m 2 ), inject clean water into the annular ditch 2 to a depth of 0.8-1.5m, and release the disinfected river crab seedlings (specification: 100-120 per kg, 300-500 per 667m 2 ).

[0040] 2. Alternating dry-wet irrigation and ring ditch management: The rice planting area (paddy field 1) adopts the dry-wet alternating irrigation technology. From the rice greening period to the rice tillering period, the water level is observed by the ultrasonic water level meter 11 and the water level is maintained at 1-3 cm. After the rice tillering period, the soil water potential is monitored by the negative pressure meter 12. When the soil water potential reaches the lower limit (-10 kPa), the ring ditch drain port 7 is opened to drain water. The drainage volume is 1 / 3-1 / 2 of the water volume in the ring ditch 2. Then the drain port 7 is closed and the water inlet 5 is opened to irrigate until the water level in the rice field 1 is 10 cm; the dry-wet alternating irrigation is stopped when the rice is yellow and ripe, and the water in the rice field is allowed to dry naturally; based on the water level and water environment control standards of the rice-crab symbiosis model in the cold and cool areas of Northeast China, as shown in Table 1 below, during the non-irrigation period, the water depth in the ring ditch 2 is always maintained at 0.8-1.5 m.

[0041] Table 1: Water depth and soil water potential control standards in rice growing areas

[0042]

[0043] 3. Breeding management: No additional fertilizer is required during the growth period of soybeans (due to the nitrogen-fixing function of rhizobia). When the pods are mature, they are harvested in time and the straw is crushed and returned to the field. Water peanuts are trimmed once a month, and the overcrowded parts are removed (which can be used as supplementary feed for river crabs) to maintain a reasonable coverage in the ditch.

[0044] Feeding points for crabs are located between the ring ditch 2 and the crab membrane 8. Feeding is carried out at multiple locations, with a daily feed intake of 5% to 10% of the crab's total weight. Observational feeding is primarily employed. In the early stages of breeding, the crabs are generally fed a complete feed with a crude protein content of at least 30%, supplemented with plant-based feeds such as corn and soybeans. In the mid-stage, the crabs are primarily fed a plant-based feed such as corn, soybeans, soybean meal, and aquatic plants, supplemented with complete pelleted feed and appropriate animal feed. In the late stages of breeding, during the rapid fattening period, the crabs are fed an increased amount of animal feed and high-quality pelleted feed, with animal feed accounting for at least 50%, along with some corn and other grains. Daily management requires frequent observation and patrols. The crabs' activities should be monitored daily.

[0045] 4. Harvest

[0046] After river crabs reach sexual maturity in mid-September, they can be caught in concentrated quantities until the rice and soybean harvest. After the harvest, the remaining river crabs in the fields and ditches are caught every day until they are all caught.

[0047] 3. Applicable Scenarios

[0048] This implementation is suitable for plain or hilly areas with annual rainfall of 500-800 mm and unstable irrigation conditions. In large-scale irrigation areas, automated gates can be used to control ditch irrigation and drainage. Small-scale farmers can manually monitor the pressure gauge readings and perform manual operations. In both scenarios, water savings of over 10% can be achieved without compromising overall land returns.

[0049] The Shenyang Agricultural University Comprehensive Water Conservancy Experimental Base has been exploring this breeding model since 2022. The irrigation volume and irrigation water utilization efficiency from 2022 to 2024 are shown in Table 2.

[0050] Table 2 Irrigation water volume and irrigation water use efficiency

[0051]

[0052] Note: CF-RC: conventional rice-crab symbiosis system, AWD-RC: shallow water ring ditch water-saving rice-crab symbiosis system.

[0053] The rice and crab production from 2022 to 2024 is shown in Table 3.

[0054] Table 3 Rice and crab production

[0055]

[0056] Note: CF-RC: conventional rice-crab symbiosis system, AWD-RC: shallow water ring ditch water-saving rice-crab symbiosis system.

[0057] The economic benefits from 2022 to 2024 are shown in Table 4.

[0058] Table 4 Economic benefits

[0059]

[0060] Note: CF-RC: conventional rice-crab symbiosis system, AWD-RC: shallow water ring ditch water-saving rice-crab symbiosis system.

[0061] Soil carbon sequestration from 2022 to 2024 is shown in Table 5

[0062] Table 5 Soil carbon sequestration

[0063]

[0064] Note: CF-RC: conventional rice-crab symbiosis system, AWD-RC: shallow water ring ditch water-saving rice-crab symbiosis system.

[0065] According to Tables 1-6, it can be seen that compared with the conventional rice-crab symbiotic system, the shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem of the present invention significantly reduces irrigation water input by 12.34% to 13.48%, significantly improves irrigation water utilization efficiency by 12.83% to 20.51%, and ensures stable production of rice and crabs, and improves economic benefits and soil carbon sequestration.

[0066] Example 2: This example differs from Example 1 in that: in this example, the top width W1 of the ring ditch is 1.1m, the bottom width W2 is 0.6m, and the depth H1 is 1.1m; the spacing of the water peanuts in the ring ditch is 0.4m, with four plants per clump, ensuring that 30% to 40% of the ring ditch water surface is covered; the anti-escape crab membrane is buried 12cm in the soil of the ridge and the height H2 above the ridge is 70cm; the top width W3 of the ridge is 0.55m, the bottom width W4 is 0.9m, and the height H3 is 0.7m. The technical effects of water-saving regulation and space optimization of the rice-crab symbiotic system of this application can also be achieved.

[0067] Example 3: This example differs from Example 1 in that: in this example, the top width W1 of the ring ditch is 1.2m, the bottom width W2 is 0.7m, and the depth H1 is 1.2m; the spacing of the water peanuts in the ring ditch is 0.3m, with 3-5 plants per cluster, ensuring that 30%-40% of the ring ditch water surface is covered; the anti-escape crab membrane is buried 15cm in the soil of the ridge and the height H2 above the ridge is 80cm; the top width W3 of the ridge is 0.6m, the bottom width W4 is 1m, and the height H3 is 0.8m. The technical effects of water-saving regulation and space optimization of the rice-crab symbiotic system of this application can also be achieved.

[0068] The components not described in detail in this application are all existing conventional technologies and will not be described in detail here.

[0069] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the scope of protection of the present invention.

Claims

1. A shallow water ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem, characterized by: Ridges are set up around the crab-raising rice field unit, and crab-proof membranes are built on the ridges. Circular ditches are dug on the inner side of the ridges, with an inlet and an outlet set at the diagonal points of the ditch. The inlet and outlet are respectively connected to the inlet channel and drainage channel located on the outside of the two opposite ridges, and water is irrigated and drained through gates. Drought-resistant plants and aquatic plants are planted in the ridges and ditch respectively. The water depth of the ditch is maintained at 0.8 to 1.5 meters for a long time to provide a stable water environment for crabs to survive. Alternating dry and wet cycles are adopted in the rice planting area. Irrigation methods and water control standards are implemented in accordance with the water level and water environment control standards for the rice-crab symbiosis model in the cold regions of Northeast China in Table 1. From the rice greening period to the rice tillering period, the water level in the rice planting area is maintained at 1 to 3 cm. After the rice tillering period, when the lower limit of water control is reached, the ring ditch drainage outlet is opened to drain water, and the drainage volume is 1 / 3 to 1 / 2 of the water volume in the ring ditch. Then the drainage outlet is closed and the water inlet is opened to irrigate to the upper limit of the rice field water level; alternating dry and wet irrigation is stopped until the rice is yellow and ripe, and the water in the rice field is allowed to dry naturally.

2. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: The distance L1 between the annular ditch and the inner side of the ridge is 60 cm, the top width W1 of the annular ditch is 1 to 1.2 m, the bottom width W2 is 0.5 to 0.7 m, and the depth H1 is 1 to 1.2 m; the area of ​​the annular ditch is 10% or less of the unit area of ​​the crab-raising rice field.

3. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: The aquatic plants planted evenly along the ditch wall in the annular ditch are water peanuts, with a plant spacing of 0.3 to 0.5 m and 3 to 5 plants in each cluster, ensuring that 30% to 40% of the water surface of the annular ditch is covered.

4. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: The anti-escape crab membrane adopts a plastic film, which is buried in the soil of the field ridge by 10-15 cm, and is higher than the field ridge by a height H2 of 60-80 cm. The membrane is fixed on bamboo poles arranged at intervals, and the plastic crab membrane is tightened and fixed.

5. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: A filter screen is installed at the water inlet, and the filter screen aperture is 20 to 40 meshes to prevent debris and wild fish from entering the ring ditch.

6. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: The top width W3 of the trapezoidal ridge is 0.5-0.6m, the bottom width W4 is 0.8-1m, and the height H3 is 0.6-0.8m; drought-resistant plants are planted on both sides and side walls of the ridge, and the middle part of the top of the ridge is reserved as walking space. The drought-resistant plants are drought-resistant soybean varieties, with a row spacing of 0.4m and a plant spacing of 0.3m; the planting density is 5-6 plants per square meter.

7. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: An ultrasonic water level meter and a negative pressure gauge are also provided in the rice field. The water level is observed by the ultrasonic water level meter, and the soil water potential is monitored by the negative pressure gauge to control water.

8. The shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: The placement depth H4 of the negative pressure gauge is 15 to 20 cm, which is consistent with the main distribution layer of the rice root system.

9. The cultivation method of the shallow water ring ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem according to claim 1 is characterized by: Specifically: S1. Preliminary preparation: 7 to 10 days before transplanting rice seedlings, apply decomposed organic fertilizer to the rice fields at a rate of 1000 to 1500 kg / 667 m 2 , inject clean water into the ditch to a depth of 0.8-1.5m, and release the disinfected river crab seedlings, with a specification of 100-120 crabs / kg, and a release rate of 300-500 crabs / 667m per mu. 2 ; S2. Alternating wet-dry irrigation and ring ditch management: Alternating wet-dry irrigation is used in rice-growing areas. From the rice greening stage to the rice tillering stage, the water level is monitored using an ultrasonic water level gauge, maintaining a water level of 1-3 cm. After the rice tillering stage, the soil water potential is monitored using a negative pressure gauge. When the soil water potential reaches the lower limit, the ring ditch outlet is opened to drain water, with the amount of water discharged being 1 / 3-1 / 2 of the water volume in the ring ditch. The outlet is then closed and the water inlet is opened to fill the paddy field with water until the upper limit of the paddy field water level is reached. Alternating wet-dry irrigation is stopped when the rice matures, and the paddy field is allowed to drain naturally. Based on the water depth and soil water potential control standards of the rice-growing area of ​​the rice-crab symbiotic system in the cold regions of Northeast China in Table 1, the water depth in the ring ditch is always maintained at 0.8-1.5 m during the non-irrigation period; Table 1: Water depth and soil water potential control standards for rice-growing areas in the rice-crab symbiotic system in the cold regions of Northeast China S3. Farming Management: No additional fertilizer is required during soybean growth. When soybean pods mature, harvest them promptly and crush the straw and return it to the field. Peanuts should be pruned monthly, removing any overcrowded areas to maintain the required coverage within the ditch. River crabs should be fed at multiple locations between the ditch and the crab's nest. S4. Harvest: After the crabs reach sexual maturity in mid-September, they can be caught in concentrated quantities until the rice and soybean harvest. After the harvest, the remaining crabs in the fields and ditches should be caught every day until all the crabs are caught.

10. The shallow water annular ditch water-saving rice-crab symbiotic three-dimensional agricultural ecosystem cultivation method according to claim 9 is characterized by: The daily feeding amount accounts for 5% to 10% of the total weight of river crabs. In the early stage of breeding, complete feed with a crude protein content of more than 30% is mainly fed; in the middle stage of breeding, plant bait is mainly fed, combined with complete granular feed and animal bait; in the later stage of breeding, it enters the rapid weight gain period of fattening, and more animal feed and high-quality granular feed are fed, and the proportion of animal feed is at least 50%.

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