|Other Abstract||Moisture is one of the important factors restricting the sustainable management of rain-fed agricultural system, Loess Plateau as a typical rain-fed agricultural area, crop production and livestock production are systematically coupled in environmental gradients such as precipitation and heat, evolving diverse agricultural systems, and how to optimize the use of water still need to be studied. Therefore, in 2019-2020, on the north-south precipitation gradient of Qingyang, choose the northern region (Tianshui town, NR) , the central region (Quzi town, CR) and the southern region, (Shishi town, SR), were selected to conduct household surveys and field sampling analysis, and to study the water use of main crops of the agricultural system and the optimal coupling mode of crop-livestock system. The main results are as follows:
1. Soil moisture pattern of farmers'crop production
Inter-annual rainfall, geographical location, crop types, and soil depth have significant effects on soil moisture. The change in soil moisture content of crop land in 2020 is greater than that in 2019, which may be related to the spring drought in 2020. The 0-100cm soil moisture changes before and after the main crop growth period have obvious vertical distribution characteristics, the soil moisture changes sharply at the depth of 0-30 cm, and the soil moisture content at depths of 30-100 cm is relatively stable. In 2019, NR、CR、 SR crops soil moisture content had changes of 0-30cm before and after harvest at 4.22%, 3.64%, and 5.97%, at 30- 100 cm soil layer changes at 2.58%, 2.41% , and 3.73%. In 2020, NR、CR、 SR crops have changed soil moisture content of 0-30cm soil layers before and after harvest at4.71%, 5.18%, and 4.31%, at 30-100cm the change of soil layer are 3.62%, 3.63% , and 3.16%.
2. Crop water consumption in farmers'production systems
The water consumption of NR、CR、SR Farmers forcrops producion in specialized crop production system is 1718.49-2447.02 , 1662.13-3093.34, and 750.23-2253.51 t/households, respectively. The water consumption per unit area of crops is 176.45, 276.48, and 363.27 mm, respectively, is positively correlated with annual precipitation. In the integrated crop-livestock production system, they are 1880.65-2544.12, 1753.42-3038.25, and 920.75-2148.41 t/households, respectively. The water consumption per unit area of crops is 179.23, 274.78, and 364.86 mm, respectively, is positively correlated with annual precipitation. The relationship between maize biomass (y) and water consumption (x) is y = 0.047x + 13.049（R²= 0.46，P<0.001） in the specialized crop production system, y = 0.062x + 7.546 (R²= 0.76, P<0.001) in the integrated crop-livestock production system. The relationship between wheat biomass (y) and water consumption (x) is y = 0.022x + 2.739 (R²= 0.80, P<0.001) in the specialized crop production system, and y = 0.016x + 3.198 (R²= 0.77, P<0.001) in the integrated crop-livestock production system.
3. Water use efficiency of major crops
The water use efficiency (WUE) of maize is NR>CR>SR (P<0.001), The WUE of wheat is highest in NR, and there is no significant difference between CR and SR. And there is no significant difference between inter-annual of the two crops. In the same region, the difference in WUE of maize and wheat in specialized crop production system and the crop-livestock integrated production systemis not significant. After averaging the WUE of maize in two agricultural production systems of NR、CR and SR , is 39.28, 30.65, and 25.43 kg/(mm·ha), respectively in 2019, is 42.28, 31.16, and 26.40 kg/(mm·ha), respectively in 2020. After averaging the WUE of wheat in two agricultural production systems of NR、CR and SR, is 14.95 , 12.15, and 11.17 kg/(mm·ha) respectively in 2019, andis 14.53, 12.55, and 11.75 kg/(mm·ha), respectively in 2020.
4. Crop-livestock system optimization mode based on water use efficiency
There is a significant difference in the output value of the unit water consumed of crops (P<0.001), NR>CR>SR. In NR, CR, and SR, the output value of maize seeds transformed by farming and livestock coupling is 12.38, 9.23, and 7.81 yuan/mm, which gradually decreases with increasing precipitation. For every 1 mm increase in annual precipitation , the output value per unit of water consumption decreases by 0.025 yuan, and 60.15%, 63.65%, and 65.12% higher than selling wheat seeds. From 2016 to 2019, the coordinated development degree of the coupling of agricultural and livestock production in the three research regions showed an increasing trend. In 2019, the coordinated development of agricultural and livestock production coupling in the northern and central regions is in theintermediate coupling and coordinated development stage, and the southern part is in the primary coupling and coordinated development stage.
The farmer's production system is optimized to stable cultivated land area, promote the systematic coupling between crop production and livestock production, improve the efficiency of crop water use and increase farmers'income. NR, maize, buckwheat, sheep (average household planting area / household livestock breeding scale) increased, wheat, daylily, pigs and chickens decreased;CR, maize, lucerne and sheep increased, wheat, melons, pigs and chickens decreased;SR, maize and sheep increased, wheat, apples, peaches, pigs and chickens decreased. After optimization, NR、CR、SR average grass livestock were 31.6, 16.7, and 10.4 (sheep units/households), with per capita income of 9676, 8428, and 7695 yuan.
Keywords: Eastern Gansu Loess Plateau, Agricultural System, Water Use, Crop-Livestock production System, Coupling mode|