Calculation method of agricultural water and soil resource optimal allocation scheme based on'water-carbon-grain-economy-ecology 'coupling

Abstract

The invention discloses a calculation method of an agricultural water and soil resource optimal allocation scheme based on'water-carbon-grain-economy-ecology 'coupling, and relates to a calculation method of a regional agricultural water and soil resource optimal allocation scheme. The method aims at solving the problem that in an existing agricultural water and soil resource allocation method, water resources, economic benefits, carbon resources and ecological benefits are difficult to balance and coordinate. The method comprises the following steps: 1, analyzing supply and demand of agricultural water and soil resources; 2, constructing a regional agricultural water and soil resource multi-objective optimization configuration model by taking different land utilization types as decision variables, taking water resources, economic benefits, carbon resources and ecological benefits as optimization objectives and taking available water amount and total planting area as main constraint conditions; and 3, solving by adopting an optimization algorithm to obtain an agricultural water and soil resource optimization configuration scheme. According to the method, water resources, economic benefits, carbon sequestration benefits and ecological benefits are incorporated into the same optimization framework, target optimization is efficiently and accurately carried out, and the method can be applied to the field of agriculture.

Description

Technical Field

[0001] The present invention relates to a calculation method for an optimized allocation scheme of regional agricultural water and soil resources, and belongs to the field of agricultural resource management. Background Art

[0002] Under the background of unreasonable utilization and uneven matching of water and soil resources, how to achieve the efficient allocation of water and soil resources is an important issue in current agricultural resource management and agricultural sustainable development. As the basis of agricultural production, the reasonable utilization and optimized allocation of water and soil resources are directly related to the economic benefits, ecological benefits of agriculture and the sustainability of regional development. However, there are still deficiencies in the selection of multiple objectives and collaborative optimization in existing research, especially the attention and quantitative research on ecological benefits are relatively weak. At the same time, with the frequent occurrence of extreme climate events under the background of global climate change, energy conservation, emission reduction and ecological environment protection have become global issues that cannot be ignored. Traditional methods usually take economic benefits as the core objective, ignoring other key indicators such as ecological benefits, resulting in the optimization results being difficult to balance the interests and needs of all parties.

[0003] There is still a lack of research on the optimized allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology" in the detailed crop growth period, and there is an urgent need for a calculation method that can comprehensively consider multiple objectives and multiple constraints to achieve the efficient and reasonable allocation of water and soil resources. Summary of the Invention

[0004] The present invention aims to solve the problem that it is difficult to balance and coordinate water resources, economic benefits, carbon resources and ecological benefits in the existing agricultural water and soil resource allocation methods, and it is difficult to optimize the matching relationship between water resources and land resources in the region, and provides a calculation method for an optimized allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology".

[0005] The calculation method for the optimized allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology" of the present invention is carried out according to the following steps:

[0006] Step 1: Analysis of the supply and demand of agricultural water and soil resources; based on the main crop planting data, water volume data and meteorological data in the region, obtain the net irrigation water demand during the entire growth period of the crop and the total available water volume in the region to complete the analysis of the supply and demand of agricultural water and soil resources;

[0007] Step 2: Construct a multi-objective optimization model; determine decision variables, objective functions and constraint conditions. Taking different land use types as decision variables, water resources, economic benefits, carbon resources and ecological benefits as optimization objectives, and available water volume and total planting area as main constraint conditions, construct a multi-objective optimization allocation model for regional agricultural water and soil resources;

[0008] Step 3: Use an optimization algorithm to solve the model and obtain an optimized allocation plan for agricultural water and soil resources based on the coupling of "water - carbon - food - economy - ecology".

[0009] Furthermore, the specific steps of the supply - demand analysis of agricultural water and soil resources in Step 1 are as follows:

[0010] (1) Collect meteorological data, including precipitation, temperature, wind speed, relative humidity, and sunshine hours;

[0011] (2) Collect land - use type and crop - production data, including the land - use types in the region and their occupied areas, crop yields, planting costs, selling prices, water fees, carbon absorption rates, water content rates, and economic coefficient data; among them, the planting costs include labor, fertilizer, pesticide, and seed costs; the water fees include surface - water and groundwater subsidy costs;

[0012] (3) Calculate the net irrigation water demand during the entire growth period of the crop: According to the crop - planting data and meteorological data in the region, use the Penman formula recommended by the Food and Agriculture Organization of the United Nations to calculate the potential evapotranspiration of each crop at each growth stage, and multiply it by the crop coefficient to obtain the actual evapotranspiration; then calculate the effective precipitation at each growth stage according to the method recommended by the Soil Conservation Service of the United States Department of Agriculture; by subtracting the effective precipitation from the actual evapotranspiration, obtain the net irrigation water demand at each growth stage, and finally accumulate the net irrigation water demands at each stage to calculate the net irrigation water demand during the entire growth period of each crop;

[0013] (4) Collect available water - volume data. Based on the runoff, water - storage data of the main rivers, lakes, and reservoirs in the region and the monitoring - well data, determine the available water volumes of surface water and groundwater.

[0014] Furthermore, the multi - objective optimization model in Step 2 consists of three parts: decision variables, objective functions, and constraint conditions; among them, the areas of different land - use types are used as decision variables; the water - resource module, carbon - footprint module, economic - benefit module, and ecological - benefit module together constitute the objective function of the model; the available water volume and the occupied area of land - use types are used as constraint conditions.

[0015] The following are the specific details of the multi - objective optimization model:

[0016] (1) The decision variables are the areas of each land - use type, including the area of rice planting, the area of corn planting, the area of soybean planting, the area of forest land, the area of grassland, and the area of wetland;

[0017] (2) The objective functions are as follows:

[0018] ① Minimize the water shortage:

[0019]

[0020] In the formula, F 1 represents the water shortage; i is the crop type; n is the number of main crops; A i is the area of crop i, hm 2 ; W is the total available water volume in the region, m 3 ; W i is the total irrigation water requirement per unit area of crop i during the whole growth period, mm; ET c is the actual water requirement of the crop under standard conditions, mm / d; ET 0 is the reference crop water requirement, mm / d; Δ is the slope of the vapor pressure curve, kPa·°C; R n is the net radiation at the crop surface, MJ / (m 2 ·d); G is the soil heat flux, MJ / (m 2 ·d); γ is the psychrometric constant, kPa / °C; T is the daily average temperature, °C; u 2 is the wind speed at 2 m above the ground, m / s; e s -e a is the saturation vapor pressure deficit, kPa; e s is the saturation vapor pressure, kPa; e a is the actual vapor pressure, kPa; P e is the effective precipitation, mm; P is the daily precipitation, mm;

[0021] ② Maximum economic net value of crops:

[0022]

[0023] In the formula, F 2 represents the economic net value of crops, P i is the market price of crop i in the current year, yuan / kg; Y i is the crop yield per hectare, kg / hm 2 ; IC is the irrigation water use efficiency in the region; P w is the water supply cost per unit area, yuan / mu, L i is the planting cost of crop i, and the planting cost is the sum of labor costs, chemical fertilizers, pesticides and seed costs; M i is the subsidy amount for crop i;

[0024] ③ Maximum carbon sequestration:

[0025] max F 3 = E - E';

[0026]

[0027] E i = A i × e i ;

[0028]

[0029] In the formula, F 3 represents the carbon sequestration amount in the area; E is the total absorption equivalent of CO 2 in kg; E' is the total emission equivalent of CO 2 in kg; j is the land use type, divided into forest land, grassland, and wetland; m is the number of land use types; u j is the carbon absorption rate of land use type j; U j is the area of the land use type in hm 2 ; CEF is the conversion coefficient for converting carbon into CO 2 ; E i is the carbon absorption amount of crop i in kg; g i is the crop root-shoot ratio coefficient; wc i is the crop moisture content; H i is the economic coefficient of the crop; e i is the carbon absorption rate of the crop in kg / hm 2 ; is the three-layer carbon emission;

[0030] The specific formula for the first-layer carbon emission is as follows:

[0031]

[0032]

[0033] In the formula, is the conversion of carbon into CO 2 equivalent in kg;

[0034] is the CO 2 emission equivalent from the farmland ecosystem in kg;

[0035] is the CO 2 emission from straw burning in kg;

[0036] G g is the amount of chemical fertilizer used in kg; a is the carbon emission coefficient of the chemical fertilizer;

[0037] G p is the amount of pesticide used in kg; b is the carbon emission coefficient of the pesticide;

[0038] G m is the amount of agricultural film used in kg; c is the carbon emission coefficient of the agricultural film;

[0039] G i is the effective irrigation area of agriculture in hm 2 ; d is the carbon emission coefficient of irrigation;

[0040] A e is the total sown area of crops, hm 2 ; f is the carbon emission coefficient for sowing;

[0041] W e is the total power of agricultural machinery, kw; h is the carbon emission coefficient of agricultural machinery;

[0042] G s is the diesel consumption of agricultural machinery, kg; j is the carbon emission coefficient of agricultural machinery diesel;

[0043] S e is the ploughing area, hm 2 ; k is the carbon emission coefficient for ploughing;

[0044] s i is the straw-to-grain ratio of the crop;

[0045] o i is the open burning ratio of the straw of crop i;

[0046] l k is the combustion efficiency of crop i;

[0047] is the CO 2 emission coefficient for open burning of crop i, g / kg;

[0048] The specific formula for the carbon emissions in the second layer is as follows:

[0049]

[0050] In the formula, is the total N 2 O emission converted to CO 2 equivalent, kg; is the N 2 O emission converted to CO 2 equivalent for straw incorporation into the field, kg; is the N 2 O emission generated by straw burning and the direct N 2 O emission from chemical fertilizer application converted to CO 2 equivalent, kg; is the N 2 O conversion coefficient to CO 2 ; is the conversion coefficient of N to N 2 O; J is the straw incorporation rate; b i is the nitrogen content of the straw of crop i; r i is the dry weight ratio of the economic product part of crop i; N totalis the total input of nitrogen in chemical fertilizers, kg; l′ is the N 2 O direct emission coefficient; g i is the crop root-shoot ratio coefficient;

[0051] The specific formula for the carbon emissions of the third layer is as follows:

[0052]

[0053] is CH 4 emission converted to CO 2 equivalent, kg; is CH 4 converted to CO 2 conversion coefficient; A 水稻 rice sown area, hm 2 ; EF 水稻 is CH 4 emission factor; is the CH emission coefficient of open burning of crop i 4 g / kg;

[0054] ④ Maximum ecological benefit:

[0055]

[0056] In the formula, a i is the ecological benefit coefficient of each land use type;

[0057] (3) The constraint conditions are as follows:

[0058] ① Surface water volume constraint:

[0059]

[0060] In the formula, WS i is the surface water consumption of crop i; SW is the available surface water volume;

[0061] ② Groundwater volume constraint:

[0062]

[0063] In the formula, WG i is the groundwater consumption of crop i; GW is the available groundwater volume;

[0064] ③ Total water resource constraint:

[0065]

[0066] ④ Crop planting area constraint:

[0067]

[0068] Wherein, A is the total amount of land resources in the study area; A i ′ is the planting area of crop i in the current year;

[0069] ⑤ Area constraint of other land use types:

[0070] 0.95A′ 林 ≤ A 林 ≤ 1.05A′ 林 ;

[0071] 0.95A′ 草 ≤ A 草 ≤ 1.05A′ 草 ;

[0072] 0.95A′ 湿 ≤ A 湿 ≤ 1.05A′ 湿 ;

[0073] Wherein, A 林 is the forest land resource area in area q; A′ 林 is the forest land resource area in the region in the current year; A 草 is the grassland resource area in the region; A′ 草 is the grassland resource area in the region in the current year; A 湿 is the wetland resource area in the region; A′ 湿 is the wetland resource area in the region in the current year.

[0074] ⑥ Total land use area constraint:

[0075]

[0076] ⑦ Non - negative constraint:

[0077] WS i ≥ 0;

[0078] WG i ≥ 0;

[0079] A i ≥ 0.

[0080] Furthermore, the model solving algorithm described in step three is the third - generation non - dominated sorting genetic algorithm (non - dominated sorting genetic algorithm - Ⅲ, NSGA - Ⅲ). This algorithm has a more uniform and representative solution set distribution, and finally obtains a coordinated optimization plan for the mutual coupling of water and soil resources.

[0081] Compared with the calculation methods of existing agricultural water - soil resource optimization allocation plans, the present invention has the following advantages and beneficial effects:

[0082] (1) Incorporate water resources, economic benefits, carbon sequestration benefits, and ecological benefits into the same optimization framework to construct a "water-carbon-economy-ecology" coupling model. This model breaks through the limitations of single-objective optimization and innovatively incorporates ecological benefits into the multi-objective optimization model, achieving an effective balance between ecology and economic development within the region.

[0083] (2) Adopt the third-generation non-dominated sorting genetic algorithm (NSGA-Ⅲ) to achieve the uniformity and representativeness of the solution set distribution in the multi-objective trade-off solution, providing a more efficient and accurate solution for complex multi-objective optimization problems. Description of the Drawings

[0084] Figure 1 is the land use structure diagram before the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1;

[0085] Figure 2 is the land use structure diagram after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1;

[0086] Figure 3 is the comparison chart of crop water consumption changes before and after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1.

[0087] Figure 4 is the comparison chart of crop economic benefit changes before and after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1.

[0088] Figure 5 is the comparison chart of regional carbon sequestration changes before and after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1.

[0089] Figure 6 is the comparison chart of regional ecological benefit changes before and after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1.

[0090] Figure 7 is the comparison chart of the main crop yield changes before and after the implementation of the agricultural water and soil resources optimization allocation plan based on the "water-carbon-food-economy-ecology" coupling in Example 1. Detailed Implementation Manner

[0091] The invention will be further described below in conjunction with specific embodiments.

[0092] Example 1: Taking Nong'an County, Jilin Province as an example, this example calculates the optimal allocation plan of agricultural water and soil resources for the coupling of "water - carbon - food - economy - ecology". The specific method is carried out according to the following steps:

[0093] Step 1: Analysis of the supply and demand of agricultural water and soil resources:

[0094] (1) Collection of meteorological data: Collect precipitation, temperature, wind speed, relative humidity, and sunshine hours;

[0095] (2) Collection of land use type and crop production data: Collect the land use structure, floor area within the region, as well as crop yield, planting cost, selling price, water fee, carbon absorption rate, crop moisture content, and crop economic coefficient; among them, the planting cost is the cost of labor, chemical fertilizer, pesticide, and seeds; the water fee is the subsidy cost of surface water and groundwater;

[0096] (3) Calculation of the net irrigation water demand during the entire growth period of crops: According to the crop planting data and meteorological data within the region, use the Penman formula recommended by the Food and Agriculture Organization of the United Nations to calculate the potential evapotranspiration of each crop at each growth stage, and multiply it by the crop coefficient to obtain the actual evapotranspiration, where the crop coefficients are shown in Table 1; subsequently, calculate the effective rainfall at each growth stage according to the method recommended by the Soil Conservation Service of the United States Department of Agriculture; by subtracting the effective rainfall from the actual evapotranspiration, obtain the net irrigation water demand at each growth stage, and finally accumulate the net irrigation water demands at each stage to calculate the net irrigation water demand during the entire growth period of each crop, as shown in Table 2;

[0097] Table 1 Crop coefficients of various crops

[0098]

[0099]

[0100] Table 2 Net irrigation water demand during the entire growth period of crops in the study area

[0101]

[0102] (4) Collection of available water volume data: Collect the runoff volume, water storage data of rivers, lakes, and reservoirs within the region, as well as monitoring well data to determine the available water volume of surface water and groundwater.

[0103] Step 2: Select the floor area of different land use types as decision variables, and take the minimization of the regional irrigation water shortage, the maximization of economic net output value, the maximization of the total carbon fixation amount within the region, and the maximization of regional ecological benefits as the objective function of the optimization allocation model, and take the surface water volume, groundwater volume, and the floor area of land use types as the main constraint conditions to establish an agricultural water and soil resources optimization allocation model; the specific model is as follows:

[0104] (1) The decision variables are as follows: The decision variables are the rice planting area, corn planting area, soybean planting area, forest land area, grassland area, and wetland area; among them, the rice planting area is represented by x 1 ; the corn planting area is represented by x 2 ; the soybean planting area is represented by x 3 ; the forest land area is represented by x 4 ; the grassland area is represented by x 5 ; the wetland area is represented by x 6 ;

[0105] (2) The objective functions are as follows:

[0106] ① The minimum water shortage:

[0107]

[0108] In the formula, F 1 represents the water shortage; i is the crop type; n is the number of main crops; A i is the area of crop i, hm 2 ; W is the total available water volume in the region, m 3 ; W i is the total irrigation water requirement per unit area of crop i during the entire growth period, mm; ET c is the actual water requirement of the crop under standard conditions, mm / d; ET 0 is the reference crop water requirement, mm / d; Δ is the slope of the vapor pressure curve, kPa·°C; R n is the net radiation on the crop surface, MJ / (m 2 ·d); G is the soil heat flux, MJ / (m 2 ·d); γ is the psychrometric constant, kPa / °C; T is the daily average temperature, °C; u 2 is the wind speed at 2 m above the ground, m / s; e s -e a is the saturation vapor pressure deficit, kPa; e s is the saturation vapor pressure, kPa; e a is the actual vapor pressure, kPa; P e is the effective precipitation, mm; P is the daily precipitation, mm;

[0109] ② The maximum economic net output value of crops:

[0110]

[0111] In the formula, F 2 represents the economic net output value of crops, P i is the market price of crop i in that year, yuan / kg; Y i is the crop yield per hectare, kg / hm 2; IC is the irrigation water use efficiency in the region, taking 0.7; P w is the water supply cost per unit area, yuan / mu, L i is the planting cost of crop i, and the planting cost is the sum of labor cost, chemical fertilizer, pesticide and seed cost; M i is the subsidy amount for crop i;

[0112] ③ Maximum carbon sequestration:

[0113] max F 3 = E - E′

[0114]

[0115] E i = A i × e i

[0116]

[0117] In the formula, F 3 represents the carbon sequestration in the region; E is the total absorption equivalent of CO 2 , kg; E′ is the total emission equivalent of CO 2 , kg; j is the land use type (forest land, grassland, wetland); m is the number of land use types; u j is the carbon absorption rate of land use type j, taking 0.381 for forest land, 0.091 for grassland, and 0.00547 for wetland; U j is the area of land use type, hm 2 ; CEF is the conversion coefficient for converting carbon into CO 2 , taking 44 / 12; E i is the carbon absorption amount of crop i, kg; g i is the crop root-shoot ratio coefficient, taking 0.6 for rice, 0.16 for corn, and 0.13 for soybean; wc i is the crop moisture content, taking 12% for rice, 13% for corn, and 13% for soybean; H i is the economic coefficient of the crop, taking 0.45 for rice, 0.4 for corn, and 0.34 for soybean; e i is the carbon absorption rate of the crop, kg / hm 2 , taking 0.414 for rice, 0.417 for corn, and 0.45 for soybean; is the three-layer carbon emission;

[0118] The specific formula for the first-layer carbon emission is as follows:

[0119]

[0120] In the formula, is for converting carbon into CO2 Equivalent, kg;

[0121] CO emissions for the farmland ecosystem 2 Equivalent, kg;

[0122] CO emissions from straw burning 2 Emission, kg;

[0123] G g is the usage amount of chemical fertilizer, kg; a is the carbon emission coefficient of chemical fertilizer, taking 0.8956;

[0124] G p is the usage amount of pesticide, kg; b is the carbon emission coefficient of pesticide, taking 4.9341;

[0125] G m is the usage amount of agricultural film, kg; c is the carbon emission coefficient of agricultural film, taking 5.18;

[0126] G i is the effective irrigation area of agriculture, hm 2 ; d is the carbon emission coefficient of irrigation, taking 266.48;

[0127] A e is the total sown area of crops, hm 2 ; f is the carbon emission coefficient of sowing, taking 16.47;

[0128] W e is the total power of agricultural machinery, kw; h is the carbon emission coefficient of agricultural machinery, taking 0.18;

[0129] G s is the diesel consumption of agricultural machinery, kg; j is the carbon emission coefficient of agricultural machinery diesel, taking 0.5927;

[0130] S e is the ploughed area, hm 2 ; k is the carbon emission coefficient of ploughing, taking 312.6;

[0131] s i is the straw-to-grain ratio of crops, 0.9 for rice, 1.2 for corn, and 1.6 for soybeans;

[0132] o i is the open burning ratio of straw of crop i, 21.8% for rice, 11.9% for corn, and 23.6% for soybeans;

[0133] l k is the combustion efficiency of crop i, 0.89 for rice, 0.92 for corn, and 0.68 for soybeans;

[0134] CO emissions from open burning of crop i 2 Emission factor, g / kg, taking 1460 for rice, 1355 for corn, and 1445 for soybeans;

[0135] The specific formula for the carbon emissions in the second layer is as follows:

[0136]

[0137] In the formula, is the total N 2 O emissions converted to CO 2 equivalent, kg; is the N from straw incorporation into the soil 2 O emissions converted to CO 2 equivalent, kg; is the N 2 O emissions generated by straw burning and the direct emissions of N 2 O from chemical fertilizer application converted to CO 2 equivalent, kg; is the N 2 O conversion to CO 2 conversion factor, taking 298; is the conversion factor for N conversion to N 2 O, taking 44 / 28; J is the straw return rate; b i is the nitrogen content of the straw of crop i, taking 0.6 for rice, 0.4 for corn, and 1.3 for soybeans; r i is the dry weight ratio of the economic product part of crop i, taking 0.45 for rice, 0.37 for corn, and 0.28 for soybeans; N total is the total input of nitrogen element in chemical fertilizer, kg; l′ is the N 2 O direct emission factor, taking 0.0101; g i is the root-shoot ratio coefficient of crop i, taking 0.6 for rice, 0.16 for corn, and 0.13 for soybeans;

[0138] The specific formula for the carbon emissions in the third layer is as follows:

[0139]

[0140] is the CH 4 emissions converted to CO 2 equivalent, kg; is the CH 4 conversion to CO 2 conversion factor; A 水稻 Rice sown area, hm 2 ; EF 水稻 is the CH 4The emission factor is taken as 338; For the open burning of crop i, CH 4 The emission coefficient is g / kg, 3.2 for rice, 4.5 for corn, and 3.9 for soybeans;

[0141] ④ Maximum ecological benefit:

[0142]

[0143] In the formula, a i is the ecological benefit coefficient of each land use type, 16840 for cultivated land (rice, corn, and soybeans), 53250 for forest land, 17650 for grassland, and 112040 for wetland.

[0144] Step 3: Use the third-generation non-dominated sorting genetic algorithm (NSGA-Ⅲ) to solve the model in Step 2 to obtain the optimal allocation plan of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology".

[0145] The land use structure diagram of Nong'an County, Jilin Province in this embodiment before optimization is as Figure 1 shown, and the land use structure diagram after optimization is as Figure 2 shown.

[0146] The crop water consumption diagrams of agricultural water and soil resources in Nong'an County, Jilin Province in this embodiment before and after optimization are as Figure 3 shown, the crop economic benefit diagrams before and after optimization are as Figure 4 shown, the regional carbon sequestration amounts before and after optimization are as Figure 5 shown, the regional ecological benefits before and after optimization are as Figure 6 shown, and the main crop yields before and after optimization are as Figure 7 shown. The comparison data before and after optimization are shown in Table 3.

[0147] Table 3 Comparison of water and soil resources in the study area before and after optimization

[0148]

[0149] From Table 1, Figure 1 and Figure 2 it can be obtained the area and proportion of each land use before and after optimization. Before optimization, the planting areas of the three main crops of rice, corn, and soybeans are 1.52×10 8 m 2 , 3.47×10 9 m 2 0.5×10 8 m 2, the planting ratio is 4.1:94.4:1.3. After optimization, the planting areas of the three are 1.33×10 8 , 3.48×10 9 , 0.6×10 8 m 2 , and the adjusted planting ratio is 3.6:94.6:1.7, with adjustments of -12.6%, 0.19% and 24.5% respectively. The total amount of irrigation water required for the adjusted planting structure is 6.23×10 8 m 3 , which is 6.27×10 8 m 3 before optimization, saving 0.65% of water (see Figure 3 ), meeting the water-saving goal. The overall adjusted planting structure shows a tendency to reduce high-water-consuming crops and increase drought-tolerant and cash crops.

[0150] After the adjustment of water and soil resources, the economic benefits, carbon sequestration, and ecological benefits in the study area have all increased to a certain extent, and the yields of various crops have also been adjusted. From Figure 4 , it can be obtained that the economic benefit before optimization is 2.028×10 9 yuan, and after optimization, the economic benefit has increased to 2.0312×10 9 yuan. Although the planting area of rice with relatively high economic benefits has been reduced, by significantly increasing the planting area of soybeans and keeping the total planting amount of corn unchanged, the combined economic benefit growth of soybeans and the dominant position of corn have made up for the possible economic benefit losses caused by the reduction in the rice area, while optimizing the water resource utilization efficiency. In addition, due to the relatively large carbon sequestration per unit area of corn, the optimized planting structure has further improved the regional carbon sequestration capacity, increasing from 9.892×10 9 kg before optimization to 9.915×10 9 kg (see Figure 5 ). In terms of improving ecological benefits, the optimized adjustment of land use types such as forest land, grassland, and wetland is a key factor. Among them, wetlands occupy a relatively high weight due to their significant ecological service functions, and their strategic role has become increasingly prominent in recent years. On the basis of stabilizing the areas of forest land and grassland, the model moderately increases the wetland area to improve the regional ecological benefits. See Figure 6 , and the ecological benefit has increased from the original 8.829×10 10 yuan to 8.844×10 10 yuan. The adjusted land use structure has optimized the crop planting ratio, with the increased planting areas of corn and soybeans leading to increased yields and consolidating the stability of regional food production. Although the reduction in the planting area of rice with relatively high yield per unit has slightly reduced the total output, this adjustment effectively balances the utilization of water resources and better coordinates the development of each goal of the model described in step two.

[0151] As can be seen from this embodiment, this calculation method can effectively coordinate multiple objectives such as water resources, economic benefits, carbon sequestration amount, and ecological benefits, and realize the optimal allocation of agricultural water and soil resources. Under the condition of limited water resources, this method significantly improves the agricultural water use efficiency and optimizes the planting structure at the same time. By reducing the planting area of water-consuming rice and moderately increasing the planting proportions of corn and soybeans, the carbon sequestration capacity and ecological benefits of the region are further enhanced on the basis of balancing economic benefits. This calculation method has important practical significance and provides scientific support and a practical implementation path for the sustainable development of regional agriculture.

Claims

1. A calculation method for the optimal allocation of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology", characterized in that: The method proceeds as follows: Step 1: Analysis of supply and demand of agricultural water and soil resources: Based on the main crop planting data, water volume data and meteorological data in the region, the net irrigation water requirement of the crop during the whole growth period and the total available water volume in the region are obtained to complete the supply and demand analysis of agricultural water and soil resources; Step 2: Construct a multi-objective optimization model; Determine the decision variables, objective functions and constraints. Construct a multi-objective optimization model for regional agricultural water and soil resources, taking different land use types as decision variables, water resources, economic benefits, carbon resources and ecological benefits as optimization targets, and available water and total planting area as main constraints; Step 3: Use the optimization algorithm to solve the model and obtain the optimal allocation plan of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology".

2. According to claim 1, a calculation method for the optimal allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology" is characterized in that: The specific steps of the agricultural water and soil resources supply and demand analysis described in step 1 are: (1) Meteorological data collection: The collected data include precipitation, temperature, wind speed, relative humidity and sunshine hours; (2) Collection of land use type and crop production data: The collected data include the land use type and its area in the region, crop yield, planting cost, selling price, water fee, carbon absorption rate, water content and economic coefficient data; the planting cost includes labor, fertilizer, pesticide and seed costs; water fee includes surface water and groundwater subsidy costs; (3) Calculation of net irrigation water requirement for the entire growth period of crops: Based on the crop planting data and meteorological data in the region, calculate the potential evapotranspiration of each crop at each growth stage, and multiply it by the crop coefficient to obtain the actual evapotranspiration; then calculate the effective rainfall at each growth stage; subtract the effective rainfall from the actual evapotranspiration to obtain the net irrigation water requirement for each growth stage; finally, add up the net irrigation water requirements of each stage to calculate the net irrigation water requirement for each crop during its entire growth period; (4) Collection of available water data: Based on the runoff and storage data of major rivers, lakes and reservoirs in the region and the monitoring well data, the available water volume of surface water and groundwater is determined.

3. The calculation method of the optimal allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology" according to claim 1 or 2 is characterized in that: The multi-objective optimization model described in step 2 consists of three parts: decision variables, objective functions and constraints; the area of ​​different land use types is the decision variable; the water resource module, carbon footprint module, economic benefit module and ecological benefit module together constitute the objective function of the model; the available water volume and the area occupied by the land use type are the constraints.

4. The calculation method of the agricultural water and soil resources optimization allocation scheme based on the "water-carbon-food-economy-ecology" coupling according to claim 3 is characterized in that: The decision variables are rice planting area, corn planting area, soybean planting area, forest area, grassland area, and wetland area.

5. According to claim 3, a calculation method for the optimal allocation scheme of agricultural water and soil resources based on the coupling of "water-carbon-food-economy-ecology" is characterized in that: The objective function is as follows: ①Minimum water shortage: In the formula, F1 represents water shortage; i represents crop type; n represents the number of main crops; A i is the area of ​​crop i, hm 2 ; W is the total available water in the area, m 3 ; W i is the total irrigation water requirement per unit area of ​​crop i during the entire growth period, mm; ET c is the actual water requirement of crops under standard conditions, mm / d; ET0 refers to the water requirement of crops, mm / d; Δ is the slope of the vapor pressure curve, kPa·℃; R n Net radiation on crop surface, MJ / (m 2 ·d); G soil heat flux, MJ / (m 2 ·d); γ is the psychrometric constant, kPa / ℃; T is the daily average temperature, ℃; u2 is the wind speed at 2m above the ground, m / s; e s -e a Saturated vapor pressure difference, kPa; e s Saturated water vapor pressure, kPa; e a is the actual water vapor pressure, kPa; P e is the effective precipitation, mm; P is the daily precipitation, mm; ②The crop with the largest economic net output value: In the formula, F2 represents the net economic output value of crops, P i is the market price of crop i in that year, yuan / kg; Y i Crop yield per hectare, kg / hm 2 ; IC is the irrigation water utilization efficiency in the region; P w is the water supply cost per unit area, RMB / mu, L i is the cost of planting crop i, which is the sum of labor costs, fertilizers, pesticides and seeds; M i is the amount of subsidy for crop i; ③The largest amount of carbon fixation: maxF3=EE′; AND i =A i ×e i ; In the formula, F3 represents the amount of carbon sequestration in the region; E is the total CO2 absorption equivalent, kg; E′ is the total CO2 emission equivalent, kg; j is the land use type, which is divided into forest land, grassland, and wetland; m is the number of land use types; u j is the carbon absorption rate of land use type j; U j is the area of ​​land use type, hm 2 ; CEF is the conversion coefficient of carbon into CO2; E i is the carbon absorption of crop i, kg; g i wc is the crop root-crown ratio coefficient; i is the moisture content of the crop; H i is the economic coefficient of the crop; e i is the carbon absorption rate of crops, kg / hm 2 ; It is the three-layer carbon emission; The specific formula for the first level of carbon emissions is as follows: In the formula, is the carbon converted into CO2 equivalent, kg; is the CO2 equivalent emitted by the farmland ecosystem, kg; CO2 emission from straw burning, kg; G g is the amount of fertilizer used, kg; a is the carbon emission coefficient of fertilizer; G p is the amount of pesticide used, kg; b is the carbon emission coefficient of pesticide; G m is the amount of agricultural film used, kg; c is the carbon emission coefficient of agricultural film; G i is the effective agricultural irrigation area, hm 2 ; d is the carbon emission coefficient of irrigation; A e is the total area of ​​crops sown, hm 2 ; f is the carbon emission coefficient of sowing; W e is the total power of agricultural machinery, kw; h is the carbon emission coefficient of agricultural machinery; G s is the diesel consumption of agricultural machinery, kg; j is the carbon emission coefficient of diesel of agricultural machinery; S e is the tilled area, hm 2 ; k is the carbon emission coefficient of tillage; s i is the grass-to-grain ratio of the crop; i is the proportion of open burning of crop straw i; l k is the combustion efficiency of crop i; is the CO2 emission coefficient of open burning of crop i, g / kg; The specific formula for the second-tier carbon emissions is as follows: In the formula, is the total N2O emissions converted to CO2 equivalent, kg; N2O emissions from straw turning and returning to the field converted into CO2 equivalent, kg; N2O emissions from straw burning and direct N2O emissions from fertilizer application are converted into CO2 equivalent, kg; is the conversion factor from N2O to CO2; is the conversion coefficient of N to N2O; J is the straw return rate; b i is the nitrogen content of crop straw i; r i is the dry weight ratio of the economic product part of crop i; N total is the total nitrogen input in fertilizer, kg; l' is the direct emission coefficient of N2O; g i is the crop root-to-crown ratio coefficient; The specific formula for the third-tier carbon emissions is as follows: is the conversion of CH4 emissions into CO2 equivalent, kg; A is the conversion coefficient of CH4 to CO2; 水稻 Rice planting area, hm 2 ; EF 水稻 is the emission factor of CH4; is the CH4 emission coefficient for open burning of crop i, g / kg; ④The greatest ecological benefit: In the formula, a i is the ecological benefit coefficient of each land use type.

6. The calculation method of the agricultural water and soil resources optimization allocation scheme based on the "water-carbon-food-economy-ecology" coupling according to claim 3 is characterized in that: The constraints are as follows: ① Surface water constraints: Where WS i is the surface water consumption of crop i; SW is the available surface water; ② Groundwater Constraints: In the formula, WG i is the groundwater consumption of crop i; GW is the available groundwater; ③ Constraints on total water resources: ④ Constraints on crop planting area: Where A is the total land resources in the study area; i ′ is the current crop planting area in year i; ⑤Other land use type area constraints: 0.95A′ 林 ≤A 林 ≤1.05A′ 林 ; 0.95A′ 草 ≤A 草 ≤1.05A′ 草 ; 0.95A′ 湿 ≤A 湿 ≤1.05A′ 湿 ; In the formula, A 林 A′ is the forest resource area in region q; 林 A is the forest resource area in the current year; 草 is the grassland resource area in the region; A′ 草 A is the grassland resource area in the current year; 湿 is the wetland resource area in the region; A′ 湿 is the area of ​​wetland resources in the region in the current year; ⑥Total land use area constraints: ⑦Non-negative constraints: WS i ≥0; WG i ≥0; A i ≥0。 7. The calculation method of the agricultural water and soil resources optimization allocation scheme based on the "water-carbon-food-economy-ecology" coupling according to claim 1 or 2 is characterized in that: The model solving algorithm described in step three is the third generation non-dominated sorting genetic algorithm.

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