Experiments and simulation of soil moisture, temperature and salinity dynamics and oil sunflower growth in saline border irrigated farmland

Abstract: Shiyang River Basin is located in northwest China, with a total area of 41 600 km2. Due to the lack of precipitation and large evaporation, the contradiction of water use in this basin is prominent, and the ecological environment problem is serious. Local industrial, domestic and agricultural water use is highly dependent on groundwater resources. The shallow subsurface salt water resources are abundant, and the rational use of salt water for irrigation can greatly alleviate the current water shortage in this basin. In order to explore the dynamics of water, heat and salt transport in farmland soil and its influence on the growth of oil sunflower under saline border irrigation, a field experiment was conducted in the Shiyanghe Experimental Station in northwest China in 2020. The experimental settings include two irrigation levels (100% and 50% of the water demand for border irrigation of oil sunflower, respectively) and three salinity of irrigation water (0.7, 4.0, and 8.0 g/L, respectively). The soil moisture content, soil salt content, temperature in the depth of 100 cm (20 cm as a layer), leaf area, and yield of oil sunflower were measured regularly during the whole crop growth period. With a combination of experiment and model simulation, the distribution characteristics of soil moisture and salt, the law of temperature changes during the growth and development of oil sunflowers, and their effects on the growth and yield of oil sunflowers under different experimental treatments were studied. The results showed that the variation range of water, salt and heat distribution in the root zone (0-40 cm) was larger than that in the deep layer (40-100 cm). The more irrigation water, the greater the variation range of water and salt. With the increase of irrigation times, the soil profile showed desalination at 0.7 g/L salinity, and salt accumulation at 4.0 g/L and 8.0 g/L salinity. The higher the irrigation amount, the higher the corresponding salt removal and accumulation rate. The variation range of ground temperature in each layer in the early stage of the experiment was larger than that in the later stage, and the variation range of temperature decreased with the increase of soil depth. The Leaf Area Index (LAI) and yield of oil sunflower were the highest at 0.7 g/L and 100% water requirement of crop and the lowest at 8 g/L and 50% water requirement. The LAI of two treatments were 8.41 and 3.80 cm2/cm2, and the yield was 5.49 and 3.08 t/hm2, respectively, with significant difference (P<0.05). The simulation results showed that WASH-C model can well simulate the distribution characteristics of water content in root zone and deep layer of soil in different periods, the change rule of average salt content in soil within 0-100 cm, the change trend of temperature, the LAI and yield of crops, and the R2 of all simulation results is higher than 0.53. In addition, in the set scenario simulation, salt water with salinity of 3 g/L or less will not produce obvious salt accumulation in the root zone of crops. A reasonable border irrigation system of salt water is beneficial to make full use of salt water resources and improve water use efficiency and yield of oil sunflower.