土壤水氮动态及作物生长耦合EPIC-Nitrogen2D模型

为计算农业区不同作物生长条件下土壤水氮迁移转化过程,该文基于Erosion/Productivity Impact Calculator(EPIC)作物模型建立了作物根系生长子模块,将其进行有限元数值离散,与土壤氮素迁移转化模型Nitrogen2D耦合,使模型能计算作物生长条件下土壤水氮迁移转化过程。该作物生长模块可计算多种胁迫下作物根系对土壤水分和氮素的动态吸收速率,及作物收获时的生物量和吸氮量。采用武汉大学灌溉排水试验场冬小麦生长条件下土壤水氮试验数据对模型进行了率定,并用于土壤水氮分布和作物生物量预测,土壤含水率、氮素的模拟值与实测值的一致性系数分别为0.86~0.97、0.52~0.98,Nash效率系数为0.59~0.90(含水率)、0.44~0.93(土壤氮素),说明模拟结果与实测值吻合度较高。同时,分别采用该文的作物生长模块和简单根系吸收模块计算根系吸氮过程,结果显示,简单根系吸收模型会显著高估作物吸氮量,而作物生长模型则由于考虑了根系生长和各环境因子的胁迫作用,计算结果更符合作物实际吸氮过程,计算的根系吸氮量相对均方根误差为3.4%~46%。

Coupling model of EPIC-Nitrogen2D and crop growth, soil water, nitrogen dynamics in winter wheat

Abstract: Quantitative estimation of soil moisture, nitrogen transformation and transport, and crop growth is important for improving nitrogen use efficiency and decreasing nitrogen pollution in agricultural areas. The objective of this study was to develop a transient soil water and nitrogen dynamics model with the consideration of crop growth. A crop growth module was developed based on Erosion/Productivity Impact Calculator (EPIC) model. It was then discretized by Galerkin finite element method to be integrated with the unsaturated-saturated soil water and nitrogen transformation and transport model Nitrogen2D. The integrated model was multi-functional in simulating soil water movements, soil nitrate and ammonium transformation and transport processes, and crop growth of specified type of crop. The crop growth module could calculate the root growing dynamics and its distribution in the soil, as well as the biomass in real time. And the module could also simulate the root uptake of water and nitrogen according to the real time root distribution. The yield of crop and nitrogen uptake mass would be output at the end of the crop growth period duration. The model was adopted to simulate the soil water and nitrogen distribution dynamics and winter wheat crop growth progresses in the irrigation and drainage experimental sites in Wuhan University, China. The experiments were implemented in 3 lysimeters, each with a size of 2 m × 2 m × 3 m. Winter wheat was planted and irrigated 3 times by the treated sewage water during the growing season. The nitrate and ammonium concentrations in the irrigation water were measured. The information on climatic factors such as temperature, precipitation was adopted. The reference evapotranspiration was calculated by Penman-Monteith equation. The temporal soil moisture content, soil temperature, ammonium and nitrate concentrations at different depths were measured, as well as the soil moisture, nitrate and ammonium concentration profiles before planting and after harvesting. The biomass and nitrogen uptake mass were measured after harvesting. The soil moisture and pressure head in the soil profile were measured simultaneously to obtain the soil water parameters of van Genutchen model. The model parameters including nitrogen transformation and transport parameters, and crop growth parameters were calibrated and validated by comparing the simulations with the measurements in test pit 8, 10 and 18. The Nash-Sutcliffe efficiency coefficient and agreement index of the simulated soil moisture content were 0.59-0.90, and 0.86-0.97 and these 2 statistical indexes for the simulated nitrogen concentration were 0.44-0.93, and 0.52-0.98. The simulation results showed good agreements with the measurements and indicated the model reliability for water and nitrogen simulation with crop growth. This study further compared the nitrogen root uptake results simulated by the proposed crop growth module and by a simple root uptake module. The results showed that the results from the crop growth module were in much agreement with the measurements with the relative root mean square error (RRMSE) 3.4%-46%, while the larger deviations between the simple model and the measurements were observed with the RRMSE 25%-176%, due to ignoring the root growing dynamics in real time and the effects of soil environments. Thus the integrated crop growth module and Nitrogen2D can be used for simulating soil water movements, the fate of nitrogen and crop growth in agricultural areas.