SOYBEAN MATURITY GROUP, PLANTING DATE, AND DEVELOPMENT RELATED
Soybean varieties from maturity groups (MG) IV, V, and VI are planted in the midsouthern US. The majority is planted in April and May. Time of growth stage occurrence and the number of days between stages are components of development that may be affected by MG and date of planting..
Knowledge of soybean development and stage occurrence enhances the timing of inputs. For example, knowing the starting and ending stages for irrigation (such as R3 and R6) based on MG and planting date will allow allotment of enough time and water resources to maximize yield potential. For inputs that may be required at two reproductive stages (such as R3 and R5 fungicide applications), knowing the span of time between these stages will aid in the planning of timely re-application.
Prediction of maturity allows harvesting to be scheduled in relation to that of other crops such as corn and rice, and/or securing custom harvest resources. Maturity prediction is also important in the midsouth because a price bonus for August delivery is available some years.
Long-term research (1979-2003) with irrigated MG IV, V, and VI varieties at Stoneville, MS was summarized to provide guidance in predicting how varieties of different MGs will develop and when growth stages will occur in plantings made in April and May. Average days from planting to R1, between each reproductive stage, and from planting to R8 for each MG are given in the following table. Converting days to calendar dates can be done easily by using the table at http://www.vpcalendar.net/ .
In April plantings, MG V varieties averaged 17 days longer to beginning bloom or R1 than the 42 days for MG IV varieties. MG V varieties took 19 days longer to reach maturity or R8. Thus, the longer growing season of MG V varieties was mostly attributable to their longer time from planting to R1. Once bloom started, varieties from the two MGs had nearly equal lengths of time (94 and 96 days) from R1 to R8.
In May plantings using MG IV, V, and VI varieties, the same trend occurred; that is, MG V varieties matured an average 12 days later than MG IV varieties, and MG VI varieties matured an average 13 days later than MG V varieties. Most of the differences were attributable to the longer time from planting to R1 as MG number increased. As with MG IV and V varieties planted in April, MG IV, V, and VI varieties planted in May were nearly equal in time (81 to 86 days) from R1 to R8.
These results lead to an important conclusion. Yield of varieties from MGs IV, V, and VI should not be affected by differences in time between reproductive stages, but rather by the time they have for vegetative development and when reproductive stages occur during the growing season. Planting late-maturing rather than early-maturing varieties at any time results in a longer vegetative period with the resulting effect of reproductive development occurring later in the growing season.
Average number of days between stages for MG IV, V, and VI soybean varieties at Stoneville, MS.