EFFECTS OF PLANTING DATE ON THE DEVELOPMENT AND YIELD OF SPRING WHEAT- SIMULATION OF FIELD DATA

Much of the work on planting-date effects has been carried out with ol d cultivars and over a relatively few years. This study was conducted to use data from a recent study to determine whether a simulation mode l (Cropsim-wheat) could be used to examine the response of modern cult ivars to planting date over an extended run of years. Field data for f our spring wheat (Triticum aestivum L.) cultivars seeded at 12 plantin g dates, ranging from 29 April to 12 June, at 4-d intervals at Crookst on, Minnesota, in 1992 were used. For all genotypes, crop duration was shortened as planting was delayed from 29 April to 23 May. Further de lay in planting lengthened this duration. Simulation outputs for devel opmental aspects closely matched the field data. The early plantings y ielded less than those established somewhat later, with the highest gr ain yields resulting from mid-May plantings. Cultivar Marshall planted on 7 May produced the highest yield (5.5 t ha(-1)) of any cultivar. L ate plantings decreased grain yield. Grain number appeared to be the m ajor component affecting grain yield. Simulation outputs from the basi c model, which computed grain number as a function of biomass shortly after anthesis, did not match well the field data for early and late p lantings. The inclusion of functions that related grain number to sola r radiation and maximum temperature around anthesis and to biomass imp roved the predictions for plantings early and later in the season. The inclusion of these functions in wheat simulation models may be necess ary for application to situations that result in differences in enviro nmental conditions around anthesis.