Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 25, 2001
Publication Date: N/A
Technical Abstract: Dryland soybean [Glycine max (L.) Merr.] production on the semiarid (<450 mm rain) southern High Plains adapts farm practices from either irrigated land or subhumid rain-fed regions. Low plant populations are recommended for dryland, but suggested planting dates vary from late April to late June with cultivar maturity varying from mid category III - late V. .Early planted soybeans would avoid heat and water stress before flowering/pod filling, but late planting limits vegetative growth and forces seed production while soil water is available. Our objectives were to test planting date, population, and maturity for optimum dryland soybean production. Using the crop simulator GLYCIM, known Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) properties, and long-term (1958-1999) weather records, we modeled soybean yield for all planting date (day = 116, 135, 155, 174), population (125,000-160,000 plants ha**-1), and dmaturity (early to late) combinations. Since dryland soybean data are unavailable, validation relied on irrigated tests. Modeled-yield was often higher than measured, because water stress was under estimated, but overall soybean response to treatment ranked similarly with measurements. Conventional mid-May to early-June planting resulted in better yield modeled across all maturities. Modeled yield was lowest and most variable for early planting. The higher yield of 1200 kg ha**-1 for early soybeans planted in early-late June suggests some water use was delayed for pod fill.