A mathematical model for simulating water balances in cropped sandy soil with conventional flood irrigation applied

In this paper, a model that integrates various complex model components for the purposes of water balance modeling throughout crop development in arid inland region under the conventional flood irrigation practiced is presented. These components are modules for calculating dynamic soil water content based Richard's equation, potential and actual evapotranspiration, and crop root water uptake. Soil water content in the active root zone and soil evaporation simulation obtained from the model were test using field data in 2003. The low values of MARE and high values of R² and PE in the active root zone of soil profile as well as daily soil evaporation indicated that the soil water balance simulation model presented in the paper can be used with reliable accuracy to simulate the components of water balance in cropped sandy soil under the conventional flood irrigation condition in arid inland regions. The model simulation on components of water balance using observed field data in 2004 indicated that large quantities – about 43% of irrigation water (amounting to 840 mm) – were consumed by deep percolation, only small (less than 41%) proportions of irrigation water used by the plants for transpiration. The current irrigation scheme is characterized by the unreasonable agricultural water management with the waste of water in the irrigational system in this region. The impact of irrigation scheduling on water balance presented in this paper showed that the reasonable irrigation scheme with more frequent irrigation and less amounts is more suitable for the irrigation of spring wheat in Heihe River basin, northwest China. Therefore, to establish a decision-making system for agricultural irrigation scheme and to utilize the limited water resources in this region have become an urgent problem that needs to be solved.