Low-carbon ecological rice-duckweed system and construction method thereof

Abstract

The invention discloses a low-carbon ecological rice-duckweed system and a construction method thereof. The system comprises a rice-duckweed symbiotic system, a duckweed coverage monitoring module and a rice field moisture monitoring and irrigation control module. The construction method comprises the following steps: duckweed putting; a water layer of 2-5 cm is kept in the period of seedling establishment; a wet-dry circulation mode is adopted from the tillering stage to the pustulation stage, in the wetting stage, a 5cm water layer is established through irrigation, the judgment index that the wetting stage is finished and the drying stage is started when the duckweed coverage degree reaches 100% is adopted, and in the wetting stage, a 1-5cm water layer is kept through irrigation; after the drying stage is started, taking the number of days of reaching the lower limit of the soil moisture content in each growth stage of the rice first or keeping the water-free layer as a discrimination index for ending the drying stage and starting the next wetting stage, and repeating the steps; drying the rice in the late tillering stage; monitoring rice field moisture information, and controlling irrigation; performing fertilization; monitoring the coverage degree of the duckweed; and returning duckweed to the field at the seasonal end. According to the method, greenhouse gas emission is greatly reduced, and the carbon sink function of the rice field is enhanced.

Description

Technical Field

[0001] The invention relates to a rice ecosystem and a construction method thereof, and in particular to a low-carbon ecological rice-duckweed system and a construction method thereof. Background Art

[0002] Rice fields are important ecosystems for agricultural production and are also one of the main sources of greenhouse gas emissions. The ecological regulation function of the duckweed system in rice fields not only helps to absorb and fix nitrogen and phosphorus nutrients and reduce pollution output, but also improves fertilizer utilization efficiency through the synergistic effect of duckweed and rice fields, reduces greenhouse gas emissions, enhances the carbon sink effect of farmland, and promotes the coordinated development of agriculture and the ecological environment. In addition, as an efficient aquatic plant resource, duckweed can significantly increase the content of soil organic matter and improve rice field production conditions through standardized management.

[0003] The problems currently faced by rice fields, such as low water resource utilization efficiency, excessive use of chemical fertilizers and declining ecological environmental carrying capacity, urgently need to be solved through technological innovation and system optimization.

[0004] Duckweed is a small aquatic phytoplankton that grows efficiently and is widely found in ditches, rivers and rice fields. It has certain ecological functions in rice planting systems, such as reducing evaporation, inhibiting weeds, and improving water fertility. However, the disordered reproduction of duckweed in rice field ecosystems still has the following obvious defects: (1) Over-reproduction competes with rice for fertilizer, affecting the surface environment of rice fields. Duckweed has an extremely high reproductive capacity and is prone to explosive growth under suitable conditions, leading to over-reproduction. This not only competes with rice for nutrients and space, but also may affect the light and ventilation conditions of rice fields, destroying the stability of rice field ecosystems. At present, there is a lack of technical means to effectively monitor and precisely regulate the growth process of duckweed, making it difficult to achieve a controlled and balanced symbiosis between duckweed and rice. (2) The ecological function is not fully utilized. Although duckweed can reduce greenhouse gas emissions from rice fields and improve soil fertility to a certain extent, its ecological function utilization is still in the extensive management stage. Existing technologies are insufficient in the comprehensive optimization of duckweed growth cycle, ecological benefits and the overall carbon footprint of rice fields, making it difficult to achieve the construction of a low-carbon and efficient ecosystem.

[0005] In summary, the existing technologies have great deficiencies in terms of growth regulation and ecological function optimization of duckweed, and cannot meet the needs of building a controllable, low-carbon, and efficient rice-duckweed ecosystem. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a low-carbon ecological rice-duckweed system that can achieve controllable growth of duckweed in rice fields and promote the sustainable development of rice field ecosystems;

[0007] The second object of the present invention is to provide a method for constructing the above-mentioned low-carbon ecological rice-duckweed system.

[0008] Technical solution: The low-carbon ecological rice-duckweed system described in the present invention includes a rice-duckweed symbiotic system, a duckweed coverage monitoring module, and a paddy field moisture monitoring and irrigation control module; the rice-duckweed symbiotic system includes rice, duckweed, and paddy field moisture and soil that maintain the coexistence of the two; the duckweed coverage monitoring module is used to collect the duckweed coverage area on the surface of the paddy field water layer during the entire rice growth period using a visible light image recognition method, and determine the duckweed coverage based on this; the paddy field moisture monitoring and irrigation control module is used to obtain paddy field moisture information during the entire rice growth period using water level and soil moisture content sensors, and perform irrigation based on preset rice irrigation indicators, combined with duckweed coverage and paddy field moisture data.

[0009] The method for constructing a low-carbon ecological rice-duckweed system of the present invention comprises the following steps:

[0010] (1) Duckweed is released some time after rice is transplanted;

[0011] (2) Irrigation management: During the greening period after rice transplanting, a 2-5 cm water layer is maintained; from the tillering period to the filling period, a wet-dry cycle water management method is adopted: the wet stage begins with irrigation to establish a 5 cm shallow water layer, and the duckweed coverage reaches 100% as the judgment indicator for the end of the wet stage and the beginning of the dry stage. During the wet stage, a 1-5 cm water layer is maintained by irregular irrigation; after the beginning of the dry stage, the lower limit of the soil moisture content of each rice growth stage or the number of days without a water layer is reached first as the judgment indicator for the end of the dry stage and the beginning of the next wet stage. When either of the two is reached, the next wet stage is started, and the cycle continues; at the end of the rice tillering period, the field is dried and sun-dried; the soil moisture content and the surface water level of the rice field are monitored, and irrigation is carried out;

[0012] (3) Fertilization;

[0013] (4) Monitor duckweed coverage on the water surface of rice fields;

[0014] (5) At the end of the season, duckweed returns to the fields.

[0015] Wherein, in step (1), duckweed is released 1-3 days after rice transplanting; the amount of duckweed released is 150kg-250kg / mu, and the amount of duckweed released refers to the fresh weight; and the water surface coverage rate reaches 60-80% in the initial stage.

[0016] Wherein, in step (2), the rice growth stages include tillering stage, jointing and booting stage, heading and flowering stage, and filling stage; the lower limits of soil moisture content in the dry-down stages of tillering stage, jointing and booting stage, heading and flowering stage, and filling stage are respectively: 65-75%θ s、65-75%θ s , 75-85%θ s 、60-70%θ s ; The number of days the water-free layer is maintained is 2-4 days, 2-4 days, 2-4 days, and 3-6 days, respectively; the drying stage starts when the water layer disappears, and the next wetting stage begins when the corresponding lower limit of soil moisture content or the number of days without water layer is reached first, and the cycle continues.

[0017] Furthermore, the lower limits of soil moisture content in the tillering stage, jointing and booting stage, heading and flowering stage, and grain filling stage are: 70%θ s 、70%θ s , 80%θ s 、65%θ s ; The number of days the waterless layer is maintained is 3 days, 3 days, 3 days, and 4 days, respectively.

[0018] Wherein, in step (2), the field is dried and exposed to the sun for about 5 days at the end of the rice tillering stage.

[0019] Among them, in step (2), water level and soil moisture content sensors are used to obtain rice field moisture information, and irrigation management is performed in combination with duckweed coverage and wet-dry cycle discrimination indicators.

[0020] Among them, in step (3), the amount of nitrogen and phosphorus applied is reduced by 10%-20% based on the total amount of fertilizer recommended for local rice fields; the application of base fertilizer or topdressing in the green period of rice fields should avoid the concentration of ammonia nitrogen in the surface water of the rice fields exceeding 20 mg / L after fertilization to avoid serious inhibition of duckweed growth. Among them, the total amount of fertilizer recommended for local rice fields is about 220 kg N hm in the Taihu Lake Basin in southern Jiangsu where the experiment is located. -2 In the main rice producing areas in the south, the nitrogen application rate ranges from about 150 to 250 kg N hm -2 .

[0021] Wherein, step (4) specifically comprises the following steps:

[0022] (4.1) Obtaining images of the water surface of the rice field regularly or in real time by installing a camera above the rice field;

[0023] (4.2) Processing the collected images to accurately identify the duckweed area;

[0024] (4.3) Extract the duckweed area in the image through image segmentation algorithm;

[0025] (4.4) According to the extracted duckweed area, the duckweed coverage is calculated. The specific calculation formula is:

[0026] K=A 浮萍 / A 总水面 ×100%

[0027] Where K is duckweed coverage; A 浮萍 is the area covered by the extracted duckweed; A 总水面 The monitoring area is the total area of ​​the water surface of the rice fields;

[0028] Pay attention to weather conditions and drying time to ensure that a small amount of duckweed floats to the surface and survives when the water is rehydrated, and reproduces quickly to reach a coverage of more than 60%.

[0029] Among them, in step (5), during the process of returning duckweed to the field at the end of the season, when harvesting rice, the rice harvesting machinery can be combined with a shallow rotary tillage machine to turn over the topsoil 10 cm above the ground, so that the duckweed on the surface is fully mixed with the soil and returned to the field, thereby reducing the carbon and nitrogen loss of duckweed due to natural decomposition on the surface, increasing the carbon and nitrogen content of the topsoil, and improving soil fertility.

[0030] Principle of the invention: The irrigation index is formulated so that the moisture condition of the paddy field can not only meet the needs of rice growth, but also control the reproduction of duckweed. In each wet-dry cycle, part of the duckweed dies and decomposes into the soil, increasing the carbon and nitrogen content of the surface soil. The wet-dry cycle breaks the anaerobic environment of the soil and significantly reduces the CH4 emission of the paddy field, but will lead to an increase in N2O emissions. Duckweed coverage significantly reduces the emission flux of CH4 and N2O. The combined effect of the wet-dry cycle and duckweed coverage balances the emission characteristics of CH4 and N2O, significantly reducing the global warming potential value composed of CH4 and N2O emissions from paddy fields. On the whole, wet-dry cycle irrigation and duckweed increase the surface organic carbon content of paddy fields at the end of the season, reduce the global warming potential value of greenhouse gas emissions from paddy fields throughout the growth period, and achieve a low-carbon ecological effect.

[0031] Beneficial effects: Compared with the prior art, the present invention has achieved the following significant effects: (1) A suitable rice-duckweed symbiotic system is constructed. The wet-dry cycle irrigation index mentioned in the present invention controls the suitable coverage of duckweed. The wet-dry cycle not only controls the excessive reproduction speed of duckweed to prevent its excessive reproduction from affecting rice growth, but also maintains the duckweed's coverage of the rice field surface to exert its ecological benefits; (2) The carbon sink function of rice field soil is increased, CH4 and N2O emissions are coordinated and regulated, and the comprehensive global warming potential of rice fields is reduced; part of the duckweed dies and decomposes during the drying stage, releasing carbon and nitrogen substances into the soil, promoting the increase of organic carbon content in the surface soil; duckweed coverage The cover is coordinated with the wet-dry cycle, the CH4 and N2O emissions are balanced, the global warming potential (GWP) of greenhouse gases in rice fields is reduced as a whole, and a low-carbon ecological sustainable effect is achieved; (3) The low-carbon ecological rice field-duckweed system constructed by the present invention, through duckweed placement management, water-saving irrigation, fertilization strategy and duckweed return to the field, can effectively control greenhouse gas emissions from rice fields, reduce nutrient losses, prevent and control non-point source pollution, and improve soil fertility on the basis of ensuring rice yield; (4) The implementation of this system can significantly improve the ecological and economic benefits of rice, and provide a feasible management model for ecological agriculture in rice production areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The global warming potential of the rice-algae system;

[0033] Figure 2 is the soil organic carbon content at the end of the season. DETAILED DESCRIPTION

[0034] The present invention is described in further detail below.

[0035] Implementation location: Kunshan Irrigation and Drainage Experiment Base, Kunshan City, Jiangsu Province

[0036] In the field plot at the implementation site, in order to clarify the effect of the present invention on increasing soil carbon content and reducing greenhouse gas emissions, the experiment involved in this embodiment set up 6 combinations of duckweed and irrigation methods: (1) flooding irrigation management + no duckweed, this condition is recorded as F; (2) flooding irrigation management + duckweed input, this condition is recorded as F+D; (3) dry-wet alternating irrigation management + no duckweed, this condition is recorded as A; (4) dry-wet alternating irrigation management mode 1 + duckweed input, this condition is recorded as A1+D; (5) dry-wet alternating irrigation management mode 2 + duckweed input, this condition is recorded as A2+D; (6) dry-wet alternating irrigation management mode 3 + duckweed input, this condition is recorded as A3+D.

[0037] Each treatment was repeated three times in a randomized block arrangement. 2In the field of treatment (4), a camera was installed 2 m above the field to take pictures of the field surface at a fixed angle. In order to eliminate the interference of rice on image acquisition, a camera was installed 1 m below the camera. 2 Rice is not grown in the space. Water level meters and soil moisture monitoring devices are installed in each field to obtain real-time field water level and soil moisture data.

[0038] The specific flooding management of treatment (1) and treatment (2) is as follows: maintain a water layer of 2-5 cm from the rice greening stage to the filling stage, except for 5 days of natural drying at the end of tillering; take 2 cm as the lower limit of irrigation, stop irrigation when water reaches 5 cm, and start irrigation again when water naturally drops to 2 cm, and repeat this cycle.

[0039] The dry-wet alternating irrigation management mode 1 of treatment (4) is as follows: a 2-5 cm water layer is maintained during the rice greening period, and optimized dry-wet alternating irrigation management is used from the tillering period to the filling period. The water layer is maintained at 1-5 cm during the wet stage of dry-wet alternating irrigation, specifically: watering starts with establishing a 5 cm shallow water layer, and 1 cm is used as the lower limit of irrigation, and irrigation begins after the lower limit is reached. The judgment indicator for the end of the wet stage is: the duckweed coverage reaches 100%. After reaching this indicator, the wet stage ends and the water layer naturally dries up. The drying stage begins when the water layer gradually disappears. The two limiting conditions of the lower limit of soil moisture content in the rice growth stage and the number of days without a water layer are used as the judgment criteria for irrigation rehydration, that is, the judgment indicators of mode 1 in Table 1. When any of the indicators is met, the next round of wet stage begins, and this cycle continues. The irrigation of treatment (3) is synchronized with treatment (4).

[0040] The second dry-wet alternating irrigation management mode of treatment (5) is specifically as follows: a 2-5 cm water layer is maintained during the rice greening period, and optimized dry-wet alternating irrigation management is used from the tillering period to the filling period. The water layer is maintained at a state of 1-5 cm during the wet stage of the dry-wet alternating irrigation. Specifically, it starts with the establishment of a 5 cm shallow water layer by irrigation, and 1 cm is used as the lower limit of irrigation. After reaching the lower limit, irrigation begins. The judgment indicator for the end of the wet stage is: the duckweed coverage reaches 100%. After reaching this indicator, the wet stage ends and the water layer naturally dries up. The drying stage begins when the water layer gradually disappears. The two limiting conditions of the lower limit of soil moisture content in the rice growth stage and the number of days without a water layer are used as the judgment criteria for irrigation rehydration, that is, the judgment indicators of mode 2 in Table 1. When any of the indicators is met, the next round of wet stage begins, and the cycle continues.

[0041] The three dry-wet alternating irrigation management modes of treatment (6) are as follows: a 2-5 cm water layer is maintained during the rice greening period, and optimized dry-wet alternating irrigation management is used from the tillering period to the filling period. The water layer is maintained at a state of 1-5 cm during the wet stage of the dry-wet alternating irrigation. Specifically, it starts with the establishment of a 5 cm shallow water layer by irrigation, and 1 cm is used as the lower limit of irrigation. After reaching the lower limit, irrigation begins. The judgment indicator for the end of the wet stage is: the duckweed coverage reaches 100%. After reaching this indicator, the wet stage ends and the water layer naturally dries up. The drying stage begins when the water layer gradually disappears. The two limiting conditions of the lower limit of soil moisture content in the rice growth stage and the number of days without a water layer are used as the judgment criteria for irrigation rehydration, that is, the judgment indicators of mode three in Table 1. When any of the indicators is met, the next round of wet stage begins, and the cycle continues.

[0042] On the second day after rice transplanting, treatments (2) and (4) were each provided with 200 kg / mu of duckweed, achieving duckweed coverage of about 70% of the rice field water surface; 200 kg / mu refers to the weight of fresh duckweed.

[0043] During the test period, the greenhouse gas methane (CH4) and nitrous oxide (N2O) emissions of the four rice fields were monitored using a static chamber-gas chromatography method. The sampling frequency was once every 3 days, and changed to once every 2 days within 10 days after each fertilization. Before rice transplanting and rice harvest, 5 cm of soil samples were collected from the surface to determine the organic matter content of each treatment. When collecting soil samples, 5 points were selected in a plot according to the S-shaped point method, and soil samples of the 0-5 cm soil layer were collected. The samples were mixed and used as soil samples for the plot.

[0044] A field experiment lasting one rice season was conducted for each of the above treatment groups. The increment of soil organic matter content ΔSOC and the comprehensive warming potential GWP of the surface soil at the end of the rice season were calculated based on the test results of the samples to evaluate the ecological effect of low-carbon emission reduction of each treatment.

[0045] like Figure 1 and Figure 2 As shown, Figure 1 and Figure 2 Different lowercase letters in the table indicate that the differences among treatments are significant at the p<0.05 level. The test results show that the treatment A1+D of the present invention has the lowest global warming potential and the largest surface soil organic carbon increment among the six treatments. Compared with the flooding + duckweed-free treatment F, the global warming potential GWP of the optimized dry-wet alternating irrigation + duckweed treatment A1+D during the observation period was reduced by 22.2%, and the surface soil organic carbon content increased by 43.5%. Compared with the higher irrigation lower limit A2+D and the lower irrigation lower limit A3+D treatments, the A1+D treatment had the lowest global warming potential value and the largest surface soil organic carbon increment during the experimental observation period.

[0046] Table 1 Irrigation lower limit judgment index values ​​for the main growth stages of rice

[0047]

[0048] Note: (1) During the green period, a thin water layer should be maintained in the field, and the depth of the water layer should be controlled, mm;

[0049] (2)θ s is the volume saturated moisture content of the soil.

Claims

1. A low-carbon ecological rice-duckweed system, characterized in that: It includes a rice-duckweed symbiotic system, a duckweed coverage monitoring module, and a paddy field moisture monitoring and irrigation control module; the rice-duckweed symbiotic system includes rice, duckweed, and paddy field moisture and soil that maintain the coexistence of the two; the duckweed coverage monitoring module is used to collect the duckweed coverage area on the surface of the paddy field water layer by using a visible light image recognition method during the entire rice growth period, and determine the duckweed coverage based on this; the paddy field moisture monitoring and irrigation control module is used to obtain paddy field moisture information by using water level and soil moisture content sensors during the entire rice growth period, and perform irrigation based on preset rice irrigation indicators combined with duckweed coverage and paddy field moisture data.

2. A method for constructing a low-carbon ecological rice-duckweed system according to claim 1, characterized in that: The following steps are involved: (1) Duckweed is released some time after rice is transplanted; (2) Irrigation management: During the greening period after rice transplanting, a 2-5 cm water layer is maintained; from the tillering period to the filling period, a wet-dry cycle water management method is adopted: the wet stage begins with irrigation to establish a 5 cm shallow water layer, and the duckweed coverage reaches 100% as the judgment indicator for the end of the wet stage and the beginning of the dry stage. During the wet stage, a 1-5 cm water layer is maintained by irregular irrigation; after the beginning of the dry stage, the lower limit of the soil moisture content of each rice growth stage or the number of days without a water layer is reached first as the judgment indicator for the end of the dry stage and the beginning of the next wet stage. When either of the two is reached, the next wet stage is started, and the cycle continues; at the end of the rice tillering period, the field is dried and sun-dried; the soil moisture content and the surface water level of the rice field are monitored, and irrigation is carried out; (3) Fertilization; (4) Monitor duckweed coverage on the water surface of rice fields; (5) At the end of the season, duckweed returns to the fields.

3. The method for constructing a low-carbon ecological rice-duckweed system according to claim 2, characterized in that: In step (2), the rice growth stages include tillering stage, jointing and booting stage, heading and flowering stage, and filling stage; the lower limits of soil moisture content in the dry-down stages of the tillering stage, jointing and booting stage, heading and flowering stage, and filling stage are respectively: 65-75%θ s 、65-75%θ s , 75-85%θ s 、60-70%θ s ; The number of days the water-free layer is maintained is 2-4 days, 2-4 days, 2-4 days, and 3-6 days, respectively; the drying stage starts when the water layer disappears, and the next wetting stage begins when the corresponding lower limit of soil moisture content or the number of days without water layer is reached first, and the cycle continues.

4. The method for constructing a low-carbon ecological rice-duckweed system according to claim 3, characterized in that: The lower limits of soil moisture content in the tillering stage, jointing and booting stage, heading and flowering stage, and grain filling stage are: 70%θ s 、70%θ s , 80%θ s 、65%θ s ; The number of days the waterless layer is maintained is 3 days, 3 days, 3 days, and 4 days, respectively.

5. The method for constructing a low-carbon ecological rice-duckweed system according to claim 2, characterized in that: In step (1), the amount of duckweed put in is 150kg-250kg / mu, and the water surface coverage rate reaches 60-80% in the initial stage.

6. The method for constructing a low-carbon ecological rice-duckweed system according to claim 2, characterized in that: Step (4) specifically includes the following steps: (4.1) Using a camera installed above the paddy field, collect images of the paddy field water surface regularly or in real time; (4.2) Processing the collected images to accurately identify the duckweed area; (4.3) Extract the duckweed coverage area in the image through image segmentation algorithm; (4.4) According to the extracted duckweed area, the duckweed coverage is calculated. The specific calculation formula is: K=A 浮萍 / A 总水面 ×100% Where K is duckweed coverage; A 浮萍 is the area covered by the extracted duckweed; A 总水面 The monitoring area is the total area of ​​the rice field water surface.

7. The method for constructing a low-carbon ecological rice-duckweed system according to claim 2, characterized in that: In step (3), the amount of nitrogen and phosphorus applied is reduced by 10%-20% based on the total amount of fertilizer recommended for local rice fields; the application of base fertilizer or topdressing in the green period of rice fields should avoid the ammonia nitrogen concentration in the surface water of the rice fields exceeding 20 mg / L after fertilization to avoid serious inhibition of duckweed growth.

8. The method for constructing a low-carbon ecological rice-duckweed system according to claim 2, characterized in that: In step (5), during the process of returning duckweed to the field at the end of the season, the topsoil is turned over to a depth of 5-10 cm so that the duckweed on the surface is fully mixed with the soil and returned to the field.

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