Study On The Soil Hydrodynamics Model For The Soil-Plant-Atmosphere Continuum (SPAC) System

The study of soil hydrodynamics and the model-based decision support systems for optimizing resource use is of great importance.Optimum use of resource can enhance the use efficiency of water,pesticide and fertilizer in agriculture,reduce the crop production cost,and minimize the environmental consequences.In this study,a systematic method was employed to develop such models for optimizing water and nitrogen fertilizer use in crop production.The main findings of the study are summarized as follows.1.A growth reduction coefficient was introduced in the EU-Rotate_N model to consider the negative osmotic effect caused by excessive application of nitrogen fertilizer on crop growth.Results show that the newly-developed module works well. It gives overall good descriptions of crop dry weight(excluding fibrous roots) reduction by mineral N in the soil over a range of crops.2.By incorporating a recently developed root growth module,and an approach of estimating evapotranspiration into a two-dimensional finite element method model SWMS₂D for soil water movement,we developed a new model for water dynamics in the soil-plant-atmosphere continuum system.The model was validated against the measurements from field experiments.It was found that the root module was able to reproduce the root distribution patterns measured at intervals;the effect of rainfall on soil water content down the profile decreased with the depth,and the simulated soil evaporation and crop transpiration were reasonable.3.We further developed an Integrated-Richards-Equation(IRE) based hydrodynamic model for bare soils by extending the conditions imposed on the top and lower boundaries.The application of the model to a case of rainfall infiltration revealed that the simulated results were between those by the FEM and by Green Ampt method.The model was also validated data from an evaporation experiment. Good agreement was obtained between simulation and measurement.The robustness of the model was also domenstrated in reproducing data from a field evaporation experiment.Good agreement was obtained in the amounts of cumulative infiltration, cumulative evaporation and cumulative drainage at the lower boundary between the simulated results by the model and the FEM model.The differences,mainly limited to the top 6 cm soil column,might be due to the diffusivity used in IRE model and the conductivity used in the FEM model.4.The responses of soil to different external conditions cannot easily be quantified because of the complexity in external conditions and the soil.In this study, simulations were carried out for 5 different European soils near saturation subject to a high evaporation and free drainage for 100 days.Comparisons including water content distribution and evaporation amount were made.The results could be used for the practical purposes.5.To improve the accuracy of hydrological simulations by the cascade type of algorithm in the EU-ROTATE_N model,the newly developed IRE model,which is able to consider water transfer in various processes in the SPAC system,was incorporated into the EU-ROTATE_N decision support system.The improved model was tested in the wheat-soil system.Good agreement was obtained for water content down the soil profile at different time internals between simulation and measurement. Simulated results of soil evaporation,crop transpiration and the mineral nitrogen content in the soil were reasonable.This suggests that generally the model gives good predictions of water and nitrogen transfers in the crop-soil system,and thus has the potential to be used in practice.