Prediction model of soil water and salt transport on yield of summer squash under mulch drip irrigation with brackish water

Abstract: Water resources are very scarce in northern China. In order to improve the utilization efficiency of brackish water and agricultural water resources, Mulch drip irrigation with brackish water has been widely studied. Mulch drip irrigation with brackish water is a highly efficient irrigation technology that combines brackish water and mulch drip irrigation, which not only saves water but also makes full use of brackish water resources. In order to quantitatively calculate the effects of mulch drip irrigation with brackish water on soil water salt and summer squash yield, the water salt transport model and water salt production function of mulch drip irrigation with brackish water were established according to the characteristics of soil water-salt transport under mulch drip irrigation with brackish and summer squash growth experiment. A prediction simulation model of soil water-salt transport and yield was established by combining the two models under mulch drip irrigation with brackish water. In order to verify the model, experiments with two groups of summer squash under mulch drip irrigation with brackish water were carried out. The first group was the growth experiment of summer squash under mulch drip irrigation with different salinity of brackish water (1.7, 3.5, 5.0 g/L). The second experiment was to study the effects of different irrigation levels and different salinity of brackish water on the growth of summer squash under mulch drip irrigation. Three irrigation levels were set at seedling stage, vine-pumping stage and flowering and fruiting stage, namely 70%-90% of field water holding capacity, 60%-80% of field water holding capacity, 50%-70% of field water holding capacity, respectively. The three levels of irrigation salinity were 1.7 g/L, 3.5 g/L and 5.0 g/L, respectively. A total of nine treatments were designed by orthogonal experiment. The results showed that the soil water content, soil salt content and yield of the summer squash calculated by the model was in agreement with the trend of the measured soil water content, soil salt content and yield of the summer squash under mulch drip irrigation with brackish water. The root mean square error of the soil water content, soil salt content and yield of the summer squash calculated by the model was 0.049 cm3/cm3, 0.065 g/kg and 3.83 t/hm2, respectively. The average relative error of the soil water content, soil salt content and yield of the summer squash calculated by the model was respectively 5.17%, 7.42% and 5.84%, and the average absolute error of the soil water content, soil salt content and yield of the summer squash calculated by the model was respectively 0.047 cm3/cm3, 0.062 g/kg and 3.95 t/hm2. Therefore, the model had higher simulation accuracy and can be used to simulate the distribution and dynamic changes of soil water-salt and yield of summer squash under mulch drip irrigation with brackish water. The optimum scheme of drip irrigation under film with brackish water for summer squash was obtained by range method. The soil water content at seedling stage was controlled at 70%-90% of field water holding capacity, at sprouting stage was controlled at 60% - 80% of field water holding capacity, at flowering and fruiting stage was controlled at 60% - 80% of field water holding capacity, and the salinity of brackish water was 1.7 g/L. However, brackish water with salinity of 3.5 g/L can also be used for irrigation in areas where freshwater resources are very scarce.