Method for combining straw returning to field, pond fish culture and rice, fish and soft-shelled turtle / shrimp comprehensive planting and breeding

Abstract

The invention discloses a method for combining straw returning to field, pond fish culture and rice, fish and soft-shelled turtle / shrimp comprehensive planting and breeding, and belongs to the technical field of rice, soft-shelled turtle, fish and shrimp comprehensive planting and breeding. After rice in the rice field is harvested, straw is smashed and returned to the field, a hidden survival place is provided for crayfish seedlings, rotten straw and derived zooplankter provide bait for crayfish and fish, and the straw decomposition rate is increased by eating; after water in the rice field module becomes serious along with straw rotting, the water is discharged into the culture pond through tail water treatment engineering treatment, and the water fertility of the pond is increased; meanwhile, after eutrophication of the water body in the culture pond, the water body is discharged into the rice field after being treated by a tail water treatment project and flows into the culture pond again after being further purified by the rice field. According to the constructed mode, the straw is converted into the organic fertilizer through the crayfish and the fish, and the paddy field is adopted for purifying pond culture tail water. No breeding wastewater is discharged in the mode. The investment of aquatic product baits and rice field fertilizers is reduced, and the income and quality of rice and fishes are increased.

Description

Technical Field

[0001] This invention belongs to the field of integrated rice-turtle-fish-shrimp farming technology, specifically involving a method that combines straw return to the field, pond fish farming, and integrated rice-fish-turtle / shrimp farming. Background Technology

[0002] Rice straw is the most direct agricultural waste generated during rice production. Statistics show that each ton of straw can produce over 5 kg of nitrogen fertilizer, 11.7 kg of potassium fertilizer, and 1.8 kg of phosphorus fertilizer. Returning straw to the field increases paddy field fertility and improves rice quality. Combining straw return with integrated rice-shrimp-turtle farming provides hiding places for crayfish and turtles, and the decomposition of straw produces organic debris and plankton, providing food for crayfish larvae. However, after April, rising temperatures accelerate straw decomposition, producing large amounts of organic acids, deteriorating water quality, and causing crayfish mortality. At this time, water exchange is the most common solution, but the discharged wastewater causes eutrophication of surrounding water bodies and contains a large number of pathogens.

[0003] Grass carp and silver carp are important domesticated fish species. Grass carp are herbivorous, while silver carp and bighead carp are filter feeders, primarily consuming plankton. They play a crucial role in water quality control. Currently, they are mainly cultured in high-density ponds. From March to May, well-rotted organic fertilizer needs to be added to the ponds to fertilize the water, thereby promoting the growth of plankton for the silver carp and bighead carp to feed on. However, during the high temperatures of summer, large amounts of uneaten feed and feces can lead to eutrophication of the water and bottom silt.

[0004] Based on the aforementioned problems in current integrated rice-crayfish-turtle farming, rice straw return to the field, and grass carp, silver carp, and bighead carp farming, this invention constructs a method combining straw return to the field, pond fish farming, and integrated rice-fish-turtle / crayfish farming. From October to November, after straw is returned to the field, water is added to the field. The straw provides hiding places for crayfish larvae, and the decaying straw and its derivative zooplankton provide food for the crayfish. The crayfish's feeding accelerates the straw decomposition rate. In April and May of the following year, the straw decomposition rate accelerates, and coupled with the feeding of crayfish, the water quality deteriorates significantly. By adding a tailwater treatment project, the water in the paddy field is sedimented, filtered, and disinfected before being discharged into the ponds where grass carp and silver carp are farmed. This effectively increases the fertility of the pond water and the quantity and diversity of plankton, providing food for the grass carp and silver carp. During the period from June to October, the amount of grass carp fed in the ponds was relatively large, which caused eutrophication of the pond water. After sedimentation, filtration and sterilization in the wastewater treatment project, the aquaculture wastewater was discharged into the paddy fields, and after further purification, it continued to flow into the ponds. Summary of the Invention

[0005] This invention, based on the natural decomposition patterns of straw and the feeding habits of different aquatic species, constructs an integrated rice-turtle-fish-shrimp farming model that combines straw return to the field with pond fish farming. This model achieves water conservation and emission reduction, as well as reduced fertilizer and pesticide use, resulting in cost savings and increased efficiency for rice and aquatic products. It offers significant social, economic, and ecological benefits.

[0006] To achieve the above objectives, the technical solution adopted in this invention is as follows: a method combining straw return to the field, pond fish farming, and integrated rice-fish-turtle / shrimp farming. This method constructs an integrated rice-turtle-fish-shrimp farming model consisting of rice paddy modules, wastewater treatment facilities, and aquaculture ponds. After rice harvesting, the straw in the rice paddies is crushed and returned to the fields, providing a sheltered habitat for crayfish larvae. The decaying straw and the resulting zooplankton provide food for the crayfish and fish, accelerating the straw decomposition rate. As the straw decomposes and the water in the rice paddy modules becomes increasingly eutrophic, it is treated through the wastewater treatment facility before being discharged into the aquaculture ponds, increasing the pond's fertility. Simultaneously, after the water in the aquaculture ponds becomes eutrophic, it is treated through the wastewater treatment facility before being discharged into the rice paddies, where it is further purified before flowing back into the aquaculture ponds.

[0007] As a preferred technical solution of the present invention, the method combining straw return to the field, pond fish farming, and integrated rice-fish-turtle / shrimp farming comprises the following steps:

[0008] (1) Construction of field engineering for paddy field modules:

[0009] Field engineering renovations are carried out in units of 20-30 mu (approximately 3.3-4 hectares). While ensuring that the paddy field area is no less than 90% of the total area, ring ditches are excavated. The ring ditches are excavated in an inverted trapezoidal shape using a "narrow, shallow ditch + wide, deep pit" pattern. Three sides of the ring ditches are narrow and shallow, 1-1.5 m deep, with a slope ratio of 1:2-3; one side is a wide, deep pit, 2-4 m deep, with a slope ratio of 1:2-1:3. The excavated soil is used to reinforce and raise the field ridges, making them 60-100 cm higher than the paddy field surface. Herbaceous plants such as Bermuda grass and tall fescue are used for slope protection.

[0010] Water inlets and outlets are set at the diagonal positions of the paddy fields, connecting to the tailwater treatment project and the aquaculture pond respectively; an escape prevention device is made of color steel tiles or stainless steel mesh, which is more than 40 cm above the ground, and an escape prevention eave is set on the top of the escape prevention device.

[0011] (2) Construction of tailwater treatment project:

[0012] The project adopts a three-pool, two-dam design, including a sedimentation pool, a filtration pool, and a disinfection pool;

[0013] (3) Construction of aquaculture ponds:

[0014] The ponds are divided into units of 10-20 mu, with a depth of 4-5 m, a water depth of 2-3 m, a flat bottom, and a silt thickness of no more than 20 cm. Each pond has one inlet and one outlet, with the outlet located at the bottom center of the pond or diagonally opposite the inlet. The inlet and outlet are connected to the wastewater treatment project and the aquaculture pond, respectively.

[0015] (4) Crayfish stocking, management and harvesting:

[0016] From late March to early April, release crayfish seedlings at a rate of 70 jin per mu (approximately 35 kg per hectare), with 60-70 crayfish per jin. From March to May, while the crayfish feed on decaying straw and zooplankton in the paddy fields, gradually increase the feed amount per 100 jin of crayfish from 2-3 jin to 6-7 jin. Crayfish are harvested and sold daily starting in May and continue until the end of May. As temperatures rise, the crayfish begin burrowing, ending the harvest.

[0017] (5) Release, management and harvesting of Chinese soft-shelled turtles:

[0018] From the end of May to mid-June, 20-30 Chinese soft-shelled turtles are stocked per mu in the paddy field modules and fed with extruded pellet feed at a rate of 1%-2% of the turtle's body weight. The Chinese soft-shelled turtles are harvested and sold after 3-4 years of breeding or when the market is favorable.

[0019] (6) Stocking, management and harvesting of aquatic products in ponds:

[0020] From January to March, fish fry are stocked in the following proportions: grass carp 30%, black carp 10%, crucian carp 20%, bream 10%, silver carp 15%, and bighead carp 15%; 800-1200 fry are stocked per mu (approximately 0.067 hectares); grass carp are fed using a feeder twice a day, morning and evening, with a feed amount of 2%-4% of the grass carp's weight; one 1KW aerator is provided for every 1-1.5 mu to ensure dissolved oxygen in the water is above 5 mg / L; pond fish are harvested and sold when market conditions are favorable.

[0021] (7) Rice planting, management and harvesting:

[0022] From late May to mid-June, rice is planted by machine transplanting or by direct seeding with drones, with 12,000-15,000 planting holes per mu (approximately 0.067 hectares) and 3-4 rice seedlings per hole. Ten days before harvest, the water level in the field is gradually lowered to allow Chinese soft-shelled turtles to move freely into deeper pits, thus reducing their population in the rice paddies. The rice is harvested and sold in October or November. After harvesting, half of the rice is crushed and returned to the field, while the straw from the lower half is left as stubble. 300-500 kg of well-rotted manure is applied per mu, and the field is exposed to the sun for 10-15 days. The water level is then increased by 10 cm each time, with the final water level maintained at 40-60 cm. Elodea is then planted in the rice paddies, and a fertilizer-water-oil-fertilizer mixture is applied.

[0023] (8) Water quality management

[0024] From March to May, quicklime and EM bacteria are used to regulate the water quality in the paddy field modules. When the water quality continues to deteriorate, the water is filtered through the tailwater treatment project, and after being disinfected and sterilized, it is discharged into the aquaculture pond for fertilization.

[0025] In April, the aquaculture ponds are sprayed with bactericides and insecticides to reduce the occurrence of diseases and pests later. From June to October, EM bacteria and quicklime are used to condition the water. Pay attention to the water quality and fish activity to ensure that dissolved oxygen is above 5.0 mg / L. When the water quality continues to deteriorate, the water is disinfected and sterilized through the tailwater treatment project before being discharged into the paddy field. After being purified by the paddy field, it is discharged back into the pond.

[0026] (9) Sludge treatment

[0027] After 3-4 years of farming and breeding, the silt at the bottom of the wide and deep pits in the paddy field modules and the silt in the breeding ponds are dredged into the paddy fields by excavators for use as fertilizer; Chinese soft-shelled turtles and fish are harvested and sold after pond clearing.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The technical principle of this invention is to utilize the feeding habits of different aquatic products to convert straw returned to the field into organic fertilizer for fertilizing the fields, while simultaneously using rice paddies to purify the wastewater from pond aquaculture. From April to May, crayfish in the rice paddies feed on crushed straw and humus, using the straw as cover. The water in the rice paddies is treated by a wastewater treatment project before being discharged into the ponds, where grass carp and silver carp feed on the decaying straw and the resulting plankton. From June to October, the wastewater from the ponds flows back into the rice paddies, is purified, and then continues to flow into the ponds. Additionally, soft-shelled turtles are introduced into the rice paddies to feed on the less vigorous crayfish. This invention utilizes crayfish and fish to convert straw into organic fertilizer and uses rice paddies to purify the wastewater from pond aquaculture. This model eliminates aquaculture wastewater discharge. It reduces the input of aquatic product feed and rice paddy fertilizer, while increasing the income and quality of rice and fish.

[0030] 2. The growth period of crayfish generally ends at the end of May, while the growth period of Chinese soft-shelled turtles is from May to September. Raising crayfish and Chinese soft-shelled turtles in rice paddies can effectively increase the utilization rate of rice paddies. On the one hand, the Chinese soft-shelled turtles eat the less vigorous crayfish, and on the other hand, it can effectively improve the economic benefits of the system.

[0031] 3. The integrated rice-turtle-fish-shrimp farming model constructed in this patent combines straw return to the field with pond fish farming. This model ensures efficient utilization of resources within the system, water circulation between planting and aquaculture, zero discharge of aquaculture wastewater, reduced fertilizer and pesticide use in rice cultivation, and decreased feed requirements for crayfish and grass carp. Therefore, this project's model offers good economic, social, and ecological benefits. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments.

[0033] Example 1

[0034] The integrated rice-turtle-fish-shrimp farming technology proposed in this invention, combining straw return to the field with pond fish farming, was implemented at Tongcheng Sushi Agricultural Co., Ltd., located in Anqing City, Anhui Province, covering an area of ​​300 mu of paddy fields and 300 mu of ponds. The main operation and process steps are as follows:

[0035] (1) Construction of field engineering for paddy field modules:

[0036] Field engineering was carried out in units of 25 mu (approximately 1.65 acres). While ensuring that the paddy field area was no less than 90% of the total area, ring ditches were excavated. These ditches were constructed in an inverted trapezoidal shape using a "narrow, shallow ditch + wide, deep pit" pattern. Three sides of the ring ditch were narrow and shallow, 1.5 m deep, with a slope ratio of 1:2. One side was a wide, deep pit, 2 m deep, with a slope ratio of 1:3. The excavated soil was used to reinforce and raise the paddy field embankments, making them 60 cm above the paddy field surface. Herbaceous plants such as bermudagrass and tall fescue were used for slope protection.

[0037] Water inlets and outlets are installed diagonally across the paddy field, connecting to the wastewater treatment plant and the aquaculture pond, respectively. An escape-prevention device, constructed using corrugated steel sheets or stainless steel mesh, is installed at least 40 cm above ground level, with an escape-prevention eave at the top.

[0038] (2) Construction of tailwater treatment project:

[0039] The project adopts a three-pool, two-dam design, including a sedimentation pool, a filtration pool, and a disinfection pool.

[0040] (3) Construction of aquaculture ponds:

[0041] The ponds are divided into units of 20 mu (approximately 3.3 hectares), with a depth of about 4.5 m and a controlled water depth of about 2.5 m. The bottom of the pond is flat, and the silt thickness does not exceed 20 cm. Each pond has one inlet and one outlet, with the outlet located at the bottom center of the pond or diagonally opposite the inlet. The inlet and outlet are connected to the wastewater treatment project and the aquaculture pond, respectively.

[0042] (4) Crayfish stocking, management and harvesting:

[0043] From late March to early April, crayfish seedlings are released at a rate of 70 jin per mu (approximately 35 catties per hectare), with 60-70 crayfish per jin. From March to May, while the crayfish feed on decaying straw and zooplankton in the rice paddies, the amount of feed given per 100 jin of crayfish gradually increases from 2 jin to 6 jin. Crayfish are harvested and sold daily starting in May, continuing until the end of May. As temperatures rise, the crayfish begin burrowing, ending the harvest.

[0044] (5) Release, management and harvesting of Chinese soft-shelled turtles:

[0045] From late May to mid-June, 30 Chinese soft-shelled turtles are stocked per mu (approximately 0.16 acres) of paddy field modules, fed with extruded pellet feed at a rate of 1% of the turtle's body weight. The turtles are harvested and sold after 3-4 years of rearing, or when market conditions are favorable.

[0046] (6) Stocking, management and harvesting of aquatic products in ponds:

[0047] Fish fry are stocked from January to March, with the following stocking ratios: grass carp 30%, black carp 10%, crucian carp 20%, bream 10%, silver carp 15%, and bighead carp 15%. 1000 fry are stocked per mu (approximately 0.16 acres). Grass carp are fed using a feeder twice daily, morning and evening, with a feed amount equal to 2% of the grass carp's weight. One 1KW aerator is provided per mu. Pond fish are harvested and sold when market conditions are favorable.

[0048] (7) Rice planting, management and harvesting:

[0049] From late May to mid-June, rice is planted by machine transplanting or by direct seeding using drones, with 12,000 planting holes per mu (approximately 0.16 acres) and 4 rice seedlings per hole. Ten days before harvest, the water level in the paddy field is gradually lowered to allow Chinese soft-shelled turtles to move to deeper pits, thus reducing their population in the paddy field. The rice is harvested and sold in October or November. After harvesting, half of the rice is crushed and returned to the field, while the straw from the lower half is left as stubble. 500 kg of well-rotted manure is applied per mu, and the field is exposed to the sun for 15 days. The water level is then increased by 10 cm each time, eventually maintaining a level of 50 cm. Elodea is then planted in the paddy field, and a fertilizer-water-oil mixture is applied.

[0050] (8) Water quality management

[0051] From March to May, quicklime and EM bacteria are used to regulate the water quality in the paddy field modules. If the water quality continues to deteriorate, the water will be filtered through the tailwater treatment system, disinfected, and then discharged into the aquaculture ponds for fertilization.

[0052] In April, bactericides and insecticides are applied to the aquaculture ponds to reduce the occurrence of diseases and pests later on. From June to October, EM bacteria and quicklime are used to condition the water. Water quality and fish activity are closely monitored to ensure dissolved oxygen levels are above 5.0 mg / L. If water quality continues to deteriorate, the water is treated and disinfected in a wastewater treatment plant before being discharged into the paddy fields. After purification in the paddy fields, the water is then discharged back into the ponds.

[0053] Ecological benefit analysis:

[0054] The constructed rice-shrimp-turtle-wastewater treatment-pond fish farming model solves the problems of rice straw decomposition in April and May, the need for fertilization in ponds during spring, and the discharge of pond aquaculture wastewater from June to October, while also increasing organic fertilizer in the rice paddies. This model eliminates aquaculture wastewater discharge, keeps both rice paddies and ponds within healthy aquaculture zones, and prevents the discharge of eutrophic water into surrounding areas.

[0055] Economic benefit analysis:

[0056] The integrated rice-turtle-fish-shrimp farming model of Tongcheng City Su's Agriculture Co., Ltd. yielded a per-mu output value of 5490 yuan and an economic benefit of 1438 yuan per mu. Details of income and expenditure are shown in Tables 1 and 2, respectively.

[0057] Table 1. Economic Benefit Analysis (per mu, expenditure / yuan)

[0058] expenditure Amount / Yuan Remark Land rent 700 Local prices Engineering renovation 116 The 300-mu integrated rice-fish farming model requires an investment of 700,000 yuan in infrastructure construction and renovation, and can be used for 20 years. Engineering maintenance 80 Mainly the maintenance of paddy field slope protection and escape prevention facilities. Equipment loss 80 Mainly crayfish sorting equipment, oxygenation facilities, smart IoT equipment, tricycles, crayfish traps, etc. feed 1000 artificial 860 Includes rotary tillage, rice transplanting, harvesting, and transportation costs. Hydropower 200 Used for water supply to rice paddies, as well as for oxygenation, etc. animal health 300 Mainly used for water quality control, and as a feed additive for crayfish, etc. labor protection 60 Mainly used for waders, etc. fertilizer 100 Fertilizer used in crayfish farming and fertilizer applied during rice cultivation. Fish fry, Chinese soft-shelled turtles, and rice seeds 556 Subtotal 4052

[0059] Table 2 Economic Benefit Analysis (per mu, revenue and expenses / yuan)

[0060] income Amount / Yuan Remark rice 1690 The yield per mu is 1300 jin, and the price is 1.3 yuan / jin. crayfish 2200 Yield 220 jin per mu, 10 yuan per jin Chinese soft-shelled turtle 600 Yield 5 jin per mu, 120 yuan / jin Fish and aquatic products 1000 Yield 100 jin per mu, 10 yuan / jin Subtotal 5490

Claims

1. A method combining straw return to the field, pond fish farming, and integrated rice-fish-turtle / shrimp farming, characterized in that, An integrated rice-turtle-fish-shrimp farming model is constructed, consisting of paddy field modules, wastewater treatment projects, and aquaculture ponds. After rice harvesting, the straw in the paddy fields is crushed and returned to the fields, providing a sheltered habitat for crayfish larvae. The decaying straw and the resulting zooplankton provide food for the crayfish and fish, accelerating the decomposition rate of the straw. As the straw decomposes and the water in the paddy field modules becomes more eutrophic, it is treated by the wastewater treatment project before being discharged into the aquaculture ponds, increasing the fertility of the pond water. At the same time, the water in the aquaculture ponds becomes eutrophic, and after being treated by the wastewater treatment project, it is discharged into the paddy fields, where it is further purified before flowing back into the aquaculture ponds.

2. The method for combining straw return to the field, pond fish farming, and integrated rice-fish-turtle / shrimp farming as described in claim 1, characterized in that, The steps are as follows: (1) Construction of field engineering for paddy field modules: Field engineering renovations are carried out in units of 20-30 mu (approximately 3.3-4 hectares) of paddy fields. Under the condition that the paddy field area is no less than 90% of the total area, ring ditches are excavated. The ring ditches are excavated in an inverted trapezoidal shape using a "narrow, shallow ditch + wide, deep pit" pattern. Three sides of the ring ditches are narrow and shallow, with a depth of 1-1.5 m and a slope ratio of 1:2-3. One side of the ring ditches is a wide, deep pit, with a depth of 2-4 m and a slope ratio of 1:2-1:

3. The soil excavated from the ring ditches is used to reinforce and raise the field ridges, making them 60-100 cm higher than the paddy field surface. Herbaceous plants such as Bermuda grass and tall fescue are used for slope protection. Water inlets and outlets are set at the diagonal positions of the paddy fields, connecting to the tailwater treatment project and the aquaculture pond respectively; an escape prevention device is made of color steel tiles or stainless steel mesh, which is more than 40 cm above the ground, and an escape prevention eave is set on the top of the escape prevention device. (2) Construction of tailwater treatment project: The project adopts a three-pool, two-dam design, including a sedimentation pool, a filtration pool, and a disinfection pool; (3) Construction of aquaculture ponds: The ponds are divided into units of 10-20 mu, with a depth of 4-5 m, a water depth of 2-3 m, a flat bottom, and a silt thickness of no more than 20 cm. Each pond has one inlet and one outlet, with the outlet located at the bottom center of the pond or diagonally opposite the inlet. The inlet and outlet are connected to the wastewater treatment project and the aquaculture pond, respectively. (4) Crayfish stocking, management and harvesting: From late March to early April, release crayfish seedlings at a rate of 70 jin per mu (approximately 35 kg per hectare), with 60-70 crayfish per jin. From March to May, while the crayfish feed on decaying straw and zooplankton in the paddy fields, gradually increase the feed amount per 100 jin of crayfish from 2-3 jin to 6-7 jin. Crayfish are harvested and sold daily starting in May and continue until the end of May. As temperatures rise, the crayfish begin burrowing, ending the harvest. (5) Release, management and harvesting of Chinese soft-shelled turtles: From the end of May to mid-June, 20-30 Chinese soft-shelled turtles are stocked per mu in the paddy field modules and fed with extruded pellet feed at a rate of 1%-2% of the turtle's body weight. The Chinese soft-shelled turtles are harvested and sold after 3-4 years of breeding or when the market is favorable. (6) Stocking, management and harvesting of aquatic products in ponds: From January to March, fish fry are stocked in the following proportions: grass carp 30%, black carp 10%, crucian carp 20%, bream 10%, silver carp 15%, and bighead carp 15%; 800-1200 fry are stocked per mu (approximately 0.067 hectares); grass carp are fed using a feeder twice a day, morning and evening, with a feed amount of 2%-4% of the grass carp's weight; one 1KW aerator is provided for every 1-1.5 mu to ensure dissolved oxygen in the water is above 5 mg / L; pond fish are harvested and sold when market conditions are favorable. (7) Rice planting, management and harvesting: From late May to mid-June, rice is planted by machine transplanting or by direct seeding by drone, with 12,000-15,000 holes per mu and 3-4 rice seedlings per hole. Ten days before harvest, the water level in the field is gradually lowered to allow the Chinese soft-shelled turtles to move to the deep pits on their own, thereby reducing the number of Chinese soft-shelled turtles in the rice field. Rice is harvested and sold in October and November; After the rice is harvested, the upper part of the straw is crushed and returned to the field, while the lower part is left as stubble. Apply 300-500 kg of well-rotted manure per mu (0.067 hectares), expose the rice to the sun for 10-15 days, and then add water 10 cm at a time, maintaining a final water level of 40-60 cm. Then plant Elodea in the paddy field and use a fertilizer-water-oil-fertilizer mixture. (8) Water quality management From March to May, quicklime and EM bacteria are used to regulate the water quality in the paddy field modules. When the water quality continues to deteriorate, the water is filtered through the tailwater treatment project, and after being disinfected and sterilized, it is discharged into the aquaculture pond for fertilization. In April, the aquaculture ponds are sprayed with bactericides and insecticides to reduce the occurrence of diseases and pests later. From June to October, EM bacteria and quicklime are used to condition the water. Pay attention to the water quality and fish activity to ensure that dissolved oxygen is above 5.0 mg / L. When the water quality continues to deteriorate, the water is disinfected and sterilized through the tailwater treatment project before being discharged into the paddy field. After being purified by the paddy field, it is discharged back into the pond. (9) Sludge treatment After 3-4 years of farming and breeding, the silt at the bottom of the wide and deep pits in the paddy field modules and the silt in the breeding ponds are dredged into the paddy fields by excavators for use as fertilizer; Chinese soft-shelled turtles and fish are cleared from the ponds and sold.