When is short-season soybean most susceptible to water stress?

Fourteen soybean (Glycine max L. Merr.) cultivars were grown at Ottawa from 1993 to 2004 in a replicated design. Phenology, yield and seed quality data were collected. Climate data were merged into the data set. Seven key phenological growth stages were identified and the total precipitation (ppt) between stages was calculated per cultivar for all possible durations. Mean cumulative ppt among the growth stage durations was correlated with mean seed yield, 1000-seed weight (tsw) seed protein and oil content. Variation in ppt prior to flowering did not influence yield. Yield and tsw were found to be most susceptible to water stress from flowering to the end of seed development. The most sensitive stage occurred during a period from the beginning to the end of pod development (R4 to mid R5). Seed protein was correlated with ppt from the beginning of flowering to the beginning of seed development. Seed oil content was reduced by late season precipitation. The identification of the most sensitive stage of deve...