Selecting Soybean Planting Date and Maturity Group for Oklahoma.

Selecting Soybean Planting Date and Maturity Group for Oklahoma Alexandre S. Barreiro and Chad B. Godsey Soybean (Glycine max) is normally planted from early April to early May using maturity groups (MG) III and IV, or from May through June using MG IV and V in Oklahoma. Planting date and MG can greatly impact yield components and seed yield. Our objectives were to determine the effects of planting date and MG on yields in an effort to assist Oklahoma soybean producers in making better decisions in choosing the correct MG for a specific planting period. Five MG ranging between 3.8 and 5.6 were sown at 6 planting dates from early April through July in Stillwater, OK, in 2009. Experimental design was a split plot design, replicated 3 times, with planting date as the main plot and MG cultivar as the sub plot. Soybean yield components were determined and correlated to grain yield. Planting in April and early May, MG IV cultivars produced higher yields compared to the MG 3.8 cultivar, mainly due to a lower number of reproductive nodes per m2. When planting MG IV and V cultivars from late May through July, no difference in grain yield was found among these cultivars. However, when averaged across MG, yield decreased with later planting dates after late May, losing an average of 160 kg week-1. The decrease in yield can be attributed to a lower number of reproductive nodes per m2 and a lower number of pods per m2. A wide range of planting dates and MG can be used for soybean production in Oklahoma.