Comparison of Crop Model Validation Methods

In this paper, the many indices used in validation of crop models, such as RMSE (root mean square errors), S-d (standard error of absolute difference), d(a) (mean absolute difference), d(ap) (ratio of d(a) to the mean observation), r (correlation), and R-2 (determination coefficient), are compared for the same rice architectural parameter model, and their advantages and disadvantages are analyzed. A new index for validation of crop models, d(ap) between the observed and the simulated values, is proposed, with d(ap)<5% as the suggested standard for precision of crop models. The different kinds of validation methods in crop models should be combined in the following aspects: (1) calculating d(a) and d(ap); (2) calculating the RMSE or S-d; (3) calculating r and R-2, at the same time, plotting 1:1 diagram.