Soil moisture distribution characteristics simulation of maize-tomato intercropping field with drip-irrigated under plastic mulch

Abstract: Intercropping and drip irrigation with plastic film is widely applied in North China and appears to be an important technique for gaining high crop yield. Further understanding the soil water distribution is important to increase the water use efficiency (WUE) and crop yield under drip-irrigated intercropping field. A 2-year experiment (2014 and 2015) was conducted including high (T1), middle (T2) and low (T3) irrigation quota, and the soil water difference for different locations, horizontal soil water exchange and 2-D soil water distribution were simulated by HYDRUS2D model in an drip-irrigated intercropping field. The results showed that hydraulic model for drip-irrigated intercropping field base on HYDRUS2D software had good accuracy, and the mean relative error (MRE) and root mean error (RMSE) and high value of determination coefficient (R2) were in range of 5.72%-8.14%, 0.017-0.023 cm3/cm3, and 0.85-0.90, respectively. There was significant difference among different locations under drip-irrigated intercropping field in 0-40 cm soil layer, especially for 0-20 cm. The average soil water content (SWC) in tomato and corn sides being about 20.17% and 17.83% higher than at the between 2 crops respectively in 2014, and being about 16.02% and 12.99% in 2015. The soil water flux moved horizontally from crop sides to between 2 crops during crop growth period. The soil water amount form tomato side to bare area was 1.3 times of that of corn side, was about 60 mm/a, and the soil water exchange in 0-40 cm layer was 2.5 times of that in 40-100 cm layer. Compared with the treatment of low irrigation quota, high irrigation quota and middle irrigation quota increased by 2 times and 1.5 times respectively, while the amount of water flowing into bare area in 0-40 cm layer increased by 1.75 times and 1.3 times respectively, based on the direct proportion relationship. The 2-D soil water distributions for different irrigation treatments showed drip soil wetting pattern was well agreement with crop root distribution. The saturated zone mainly concentered in 0-30 cm layer in irrigation after 1 day, and the areas for high, middle and low irrigation quota treatments were 559.14, 288.61 and 109.78 cm2, respectively. The water stress zone was found in 30-40 cm soil layer in irrigation after 2 days. When the amount of irrigation water was reduced in treatments middle and low irrigation quota treatments, the water stress zone increased in size. The size of the water stress zone was about 129.86 cm2 for treatment of high irrigation quota that resulted in negligible stress on root water uptake. The water stress zone was about 1 663.29 cm2 for treatment of middle irrigation quota that caused a slight restriction of the crop growth. On the other hand, the water stress zone was about 3 883.94 cm2 for treatment of low irrigation quota, which created a significant influence to crop growth. There was obvious water stress for low irrigation quota treatment after 2 days, and the area for soil water deficit in treatment of low irrigation quota was 30 times than high irrigation quota. The researches provide the information for making irrigation scheduling under drip-irrigated intercropping field.