Description and evaluation of the rice growth model ORYZA2000 under nitrogen-limited conditions

Various crop growth simulation models exist for rice but thorough validation and evaluation reports are scarce. We present the model ORYZA2000, which simulates the growth and development of rice under conditions of potential production and water and nitrogen limitations. The model was evaluated against a data set of five field experiments with irrigated rice performed at IRRI between 1991 and 1993, with nitrogen levels varying from 0 to 400 kg ha−1 in different splits and timings of application. We compared simulated and measured leaf area index (LAI) and biomass of leaves, stems, panicles, and total aboveground biomass by graphics; by the slope, intercept, and adjusted coefficient of correlation; by Student’s t test of means; and by absolute and normalized root mean square errors (RMSE). On average, RMSE was 690–1280 kg ha−1 for total biomass, 350–380 kg ha−1 for leaf biomass, 460–790 kg ha−1 for stem biomass, and 380–580 kg ha−1 for panicle biomass. Yield was simulated with an RMSE of 840–850 kg ha−1 and a normalized RMSE of 11–13%. For these crop variables, normalized RMSE values were 65–84% higher than the typical coefficients of variation associated with their measurements. Simulated LAI generally exceeded measured values, especially at low levels of nitrogen application. We can use ORYZA2000 to support N field experiments and investigate optimum N application regimes with quantified errors of simulation. The developed database and quantitative goodness-of-fit parameters serve as references for future model improvements.