| dc.description.abstract | Soybean [Glycine max (L.) Merr.] is normally planted between early April and early May using maturity groups (MG) III and IV, or from May through June using MG IV and V in Oklahoma. Planting date (PD) and MG can greatly impact yield components and consequently seed yield. Our objectives were to determine the effects of PD and MG on yield in an effort to assist Oklahoma soybean producers in making better decisions in choosing the correct MG for a specific planting period. Five MGs ranging between 3.8 and 5.6 were sown at five PDs between early April and July in Stillwater, OK, in 2009. Split Block Design was used as the experimental design, with 3 replications, having PD as the main plot and MG cultivar as the sub plot. Soybean yield components and canopy closure were assessed and correlated to seed yield. With early-season PDs (from April to late May) using early MGs, seed yield was greater compared to late-season PDs (from late May to late July) using later MGs. Early season MGs 4.4 and 4.8 produced higher yields compared to MG 3.8. No difference was found in seed yield among MGs IV and V planted in late-season, which was lower than in early plantings, and reduced significantly as planting dates were delayed. This reduction in yield was 160 kg ha-1 per week after 10-Jun. This reduction in yield was attributed to lower canopy closure and consequently a reduced light use efficiency that resulted in a lower number of pods m-2, followed by seeds m-2, and reproductive nodes m-2. For the 2010 growing season, five MGs were sown at all six PDs in Stillwater, OK, and four of these MGs were sown in the same PDs in Lahoma, OK. For the Stillwater location, late MG IV and MG V cultivars produced higher yields compared to MG 3.8 and early MG IV cultivars when planted from April to late May. For Lahoma, MGs 4.4, 4.8 and 5.6, presented an exponential increase in seed yield when planted until early June, and MG 5.2 did not change in yield for these early PDs. For both locations, no difference in yield was observed among MGs, in late planting and yield decreased significantly as planting dates were delayed after middle of June, losing an average of 235 kg ha-1 per week in Stillwater and 190 kg ha-1 in Lahoma. Number of reproductive nodes m-2, followed by number of pods and seeds m-2 were again the yield components which most affected seed yield. Selection of MG was less important when compared to PD. Planting before the middle of June was important to maintain yield potential. | |
