Numerical Study On The Water Dynamics In The Soil-crop System

The water circulation is a key process in the Soil-Plant-Atmosphere Continuum （SPAC） system. In this study, a systematic study on water dynamics in the soil-crop system was carried out based on the basic theory, model development and validation. Three models, named HYDRUS-1D model, SWMS₂D model, EU-Rotate_N model, were employed for investigating the characteristics of soil water movement. The findings from thus study were was helpful to make reasonable irrigation decisions and to optimize water use in crop production.Numerical simulations were performed for soil water content and soil wetting depth immediately after irrigation and 24 hours after irrigation under the conditions of different irrigation rate and time for a sandy loam soil using the HYDRUS-1D model. Results showed that immediately after irrigation the topsoil was almost saturated, indicating the irrigated water was mainly stored in the soil near the surface. Due to the redistribution of soil water induced by gravity over time, the irrigated water moved down and was stored in the deeper soil, resulting in a marked increase in soil wetting depth. Since soil wetting depth varied greatly after irrigation, it should be taken into consideration for irrigation planning.Based on the SWMS₂D model, a mesh generation module and a root distribution module which contained uniform, linear and exponential root distributions were developed and incorporated to enhance the pre-processing ability and to expand the use of the model for diverse crops. The numerical experiment was carried out for the scenarios of different root distribution in a clay loam soil and a sandy loam soil subject to different transpiration rate. Both soil water dynamics and cumulative transpiration were simulated by using the newly-developed model. It was found that in the case of the rooting depth being 30cm, soil water content in the root zone changed greatly, and the water below the 40cm largely could hardly be taken up by crop roots. The more uniform the root distribution, the more the water take up. Soil water content in the sandy loam soil changed more rapidly than that in the clay loam soil. Compared with that in the clay loam soil, the water near the maximum rooting depth in the sandy loam soil could be depleted more easily.An attempt was made to apply the EU-Rotate_N model, which was devised for vegetable crops, for cereal crops. The model predictions were rigorously and symmetrically compared with data collected from three experiments on winter wheat grown in different soils over 2 years in the Netherlands. Results showed that overall the model was satisfactory in re-producing the measurements, indicating that the model was correctly parameterized for the studied crop, and could therefore potentially be applied in wheat production for water dynamics.