Effects of Planting Date for Soybean Growth, Development, and Yield in the Southern USA

As fluctuating commodity prices change the agriculture landscape on a yearly basis, soybean (Glycine max (L.) Merr.) has become the predominant crop in the southern USA, accounting for 65 percent of the total row crop production in the state. To accommodate increased soybean production, planting dates have expanded, spanning from late March through July. To determine the impact of this expanded planting window on soybean development and yield, field experiments were conducted at Starkville and Stoneville, MS, in 2013 and 2014. Treatments included seven planting dates ranging from 25 March to 15 July and two soybean cultivars (one Maturity Group IV and one Maturity Group V cultivar). These studies were conducted in irrigated high-yielding environments. Experimental units were sampled weekly for insect pests and insecticides were applied when populations exceeded the levels at which applications were recommended. Planting date had a significant impact on crop development, plant height, canopy closure, and yield. As planting date was delayed, the time required for crop development decreased from 122 total days for plantings on 25 March to 83 days for plantings on 15 July. For plantings after 2 June, plant height decreased by 1.1 cm per day. Canopy closure decreased by 1.01% per day after 27 May. Soybean yield decreased 26.7 kg/ha per day when soybean was planted after 20 April. This research demonstrates the importance of early planting dates for soybean producers in the southern US to ensure profitability by maximizing yield potential.