Crop Models

Most crop models, such as CROPGRO (Hoogenboom et al., 1994), which has evolved from the earlier soybean model SOYGRO, are process-oriented models that consider crop development, crop-soil carbon and nitrogen balances and soil-water balance. The hourly leaf-level photosynthesis formulation of CROPGRO allows for responses to changes in weather conditions that can be supplied by a regional climate model on subdaily time scales. Within the ensemble of CERES crop models, CERES-Maize is a model for corn developed originally by J.T. Ritchie and colleagues (see Jones and Kiniry, 1986), and is based on radiation-use efficiency as modified by nitrogen stress, water stress, plant population, and temperature. CROPGRO and CERES-Maize can be used in sequence to simulate multiyear crop production because they use the same balances for soil water and soil nitrogen, and recently have been coupled with the CENTURY soil organic matter model (Parton et al., 1987). The two crop models have been combined into a single model called the Cropping System Model (CSM) (Jones et al., 2003), representing the newest model development in crop modeling. We employed the CSM model for the study reported herein.

The climate model (whether dynamical or statistical) provides the crop model (CERES-Maize for our analysis) with daily totals of shortwave radiation and rainfall, as well as daily maximum and minimum temperatures. On the basis of these daily inputs, the crop model calculates daily updated values of plant biomass, evaporation, and transpiration, as well as the remaining water, carbon, and nitrogen in the soil profile. At the end of the growing season, the model supplies a total grain yield.

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