Simulation of Maize Phenology

In order to perform reliably, crop simulation models require an accurate treatment of crop phenology. A procedure for simulating maize (Zea mays L.) phenology was developed as a subroutine for a maize growth model which ran on an hourly time step. Maize development is simulated from hourly rates of leaf initiation and appearance during three phases of organ differentiation: juvenile, inductive, and reproductive. Leaf initiation occurs during the first two phases, and is terminated by tassel initiation, at which time final leaf number is established. The timing of tassel initiation during the inductive phase is determined by photoperiod and temperature effects on leaf number. The reproductive phase begins at tassel initiation and ends at silking shortly after the appearance of the last leaf before the tassel. Functions used to calculate leaf numbers and rates of leaf initiation and appearance are taken from published results of phytotron studies. Model estimates of leaf number, and of dates of tassel initiation and silking were compared with those observed from a maize phenology trial conducted at five sites in North America. Estimated dates of silking were also compared with those from other data sets. Estimated leaf numbers were usually within one of those observed at all but one site in the phenology trial, where leaf numbers were overestimated by as much as four leaves. Estimated dates of tassel initiation and silking were usually within 5 d of observed dates except at the warmer sites in Texas where estimated dates preceded observed dates by 5 to 15 d. The data suggest that high temperature acclimation may have resulted in slower rates of development than those predicted at some of the wanner sites. Chilling, acclimation, and other effects on phenology not present in phytotron studies will have to be considered further before the results of these studies may be widely used in models of maize phenology.