COMPARISON OF 2 PHENOLOGY MODELS FOR PREDICTING FLOWERING AND MATURITY DATE OF SOYBEAN

Unbiased prediction of plant growth stages is essential for accurate s imulation of stage-specific responses to environmental factors. The ph enology model in SOYGRO V5.42 was compared with the phenology model in CROPGRO V3.0 for prediction of flowering and maturity date. Data came from 17 sources in North America and covered a wide range of maturity groups. An additional large-scale data set from the U.S. Soybean Unif orm Tests was used to evaluate predictions of maturity date. Parameter s of the phenology models were estimated with an optimization procedur e in which the downhill simplex method determined the direction of the search. While the optimization procedure was valuable to estimate the parameters, additional criteria were required to obtain realistic val ues. Based on the root mean square error (RMSE) criterion between pred icted and observed dates, SOYGRO and CROPGRO predicted flowering equal ly well. Development rate after flowering was underpredicted by SOYGRO in cool environments so that in some years, maturity mas predicted ve ry late. CROPGRO has a separate temperature function after beginning s eedfill, which decreased the RMSE for prediction of maturity date comp ared with SOYGRO, especially for early maturity cultivars. Allowing th e critical short day length to increase after flowering date in the CR OPGRO model consistently decreased the RMSE for prediction of beginnin g seedfill and maturity. CROPGRO was superior to SOYGRO for prediction of maturity date.