Coupled simulation of soil water-heat-carbon-nitrogen process and crop growth at soil-plant-atmosphere continuum system.

The quantitative description of soil water flow, carbon (C) and nitrogen (N) cycles, and crop growth processes at soil-plant-atmosphere continuum system is important for improving water and N use efficiencies and decision-making of crop production and environmental protection in the North China Plain (NCP). The objective of this study was to develop a water and N management model for intensive cropping systems and agricultural management practices in NCP. Based on the previous research findings, a coupled model (Soil Water Heat Carbon and Nitrogen Simulation, WHCNS) model was established. The model included 5 main modules: soil water, soil heat, soil C, soil N, and crop growth. The Penman-Montheith method from the Food and Agriculture Organization of the United Nation was used to calculate the reference crop evapotranspiration. The method for simulating soil water movement and heat transfer was directly introduced from the HYDRUS1D and RZWQM models. The PS123 model from the Netherlands was used to simulate crop growth. The simulation of C and N cycles was done by the Daisy model from Denmark. The model ran on a daily time step and was driven by the meteorological and crop biological variables, and agricultural management practices. The soil water infiltration and redistribution processes were described by Green-Ampt and Richard's equations, respectively. Soil N transport simulation was based on the modified convection-dispersion equation. The source-sink term of N transformation and transport included mineralization of soil organic N, immobilization in biomass, urea hydrolysis, ammonia volatilization, nitrification, denitrification, and crop uptake. The compensatory absorption mechanism was introduced in crop water and N uptake. The organic matter pools were divided into 3 active and 3 stabile C pools. The improved version of the PS123 model was applied to simulate crop development stage, dry matter production and allocation, and crop yield. The crop yield under water and N stress was calculated based on the simulation of potential and actual crop water and N uptake. Then the field applicability of the WHCNS model was tested using the two-year field observed data of winter wheat and summer maize system at Tai'an experimental site in Shandong province. The statistical indices (root mean square error, modeling efficiency, and agreement index) all indicated that the simulated values of crop yield, leaf area index, soil water content, and nitrate concentration in the soil profile all agreed reasonably well with the observed values, especially for crop yields with the root mean square error ranges from 205.5 to 318.8 kg/hm², the correlation coefficient of 0.90, and modeling efficiency values larger than 0.75 and concordance index larger than 0.9. We concluded that the WHCNS model could be used to simulate water movement and the fate of N as well as crop growth in high intensive cropping system in North China. [ABSTRACT FROM AUTHOR]