Potential of early-maturing soybean cultivars in late plantings

Late planting reduces soybean [Glycine max (L.) Merr.] yields in soybean-winter wheat (Triticum aestivum L.) double-cropping systems. We evaluated the hypothesis that the use of early-maturing soybean cultivars to shift reproductive growth into a more favorable environment would avoid some or all of this yield penalty. Soybean cultivars Hardin and Kasota [maturity group (MG) I], Burlison and Elgin 87 (MG II), Pioneer 9392 and Probst (MG III), and Stressland and Penny-rile (MG IV) planted in 38-cm rows were used in a 3-yr irrigated experiment with two planting dates (early, mid-May; late, late June) at Lexington, KY (38 degrees N lat). Delayed planting reduced yield (7-36%) of all cultivars as a result of fewer seeds m(-2). Cultivars from MG I and II did not produce higher yields in the late plantings. A combination of narrow rows (19 cm) and high seeding rates (105 seeds m(-2)) had no effect on yield of cultivars from MGs I and II in either planting date. However, early maturity did provide an earlier harvest date without significant yield loss. Seed number was significantly related to crop growth rate (CGR) during flowering and pod set (r(2) = 0.36) and to length of flowering and pod set (r(2) = 0.56). Radiation use efficiency (g dry matter MJ(-1) intercepted photosynthetically active radiation) was generally reduced in the late plantings for MG III and TV cultivars but not for MG I and II. Early-maturing cultivars in an irrigated environment did not reduce the yield penalty associated with late plantings.