Evaluating methods for simulating soybean cultivar responses using cross validation

Crop simulation models are used in research worldwide, and efforts are now being made to incorporate them into decision-support systems fur farmers an d their advisors, However, their on-farm acceptance Kill be limited unless methods can be found to determine model coefficients for new cultivars that are released by public and private breeders. The availability of data to d etermine coefficients is usually limited; however, soybean breeders routine ly collect data far new cultivars from variety trials. Objectives of this r esearch were to (i) estimate soybean crop-model prediction errors for anthe sis, maturity, and yield using variety trial data; (ii) determine the effec tiveness of cross validation for estimating prediction errors of the soybea n model; and (iii) compare these errors with those based on regression equa tions relating specific cultivar yields to simulated maturity group (MG) yi elds, Root mean squared errors of prediction (RMSEP) were used for comparis ons, Georgia variety trial data from 1987 through 1996 for six MG VII culti vars were divided into sets for fitting model coefficients and independent validation. The RMSEP using cross validation were similar to fitting errors when all (n = 40) or only half of the data were used to fit cultivar coeff icients. These errors were similar to those computed using independent data The RMSEP for yield using linear regression were better than using generic MG coefficients but not as good as that found by fitting model coefficient s. We conclude that soybean yield tan be simulated for specific cultivars u sing either crop model or regression approaches, but the latter was not ade quate for predicting cultivar anthesis and maturity dates.