Author
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Heatherly, Larry |
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Submitted to: Crop Management at www.cropmanagement.org
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/21/2004 Publication Date: 4/21/2005 Citation: Heatherly, L.G. 2005. Soybean development in the midsouthern usa related to date of planting and maturity classification. Crop Management at www.cropmanagement.org. doi:10.1094/CM-2005-0421-01-RS Interpretive Summary: Soybean is planted from late March through June in the midsouthern USA as a result of time, production, and environmental constraints. These plantings may utilize varieties from maturity groups (MG) IV through VI. Range in planting time of cultivars from the different MGs affects development. Results from 25 years of irrigated field studies at Stoneville, MS were used to determine developmental patterns of MG IV, V, and VI soybean cultivars as affected by these disparate planting times. Time from planting to beginning bloom (R1) increased as MG increased from IV to VI, time from R1 to full seed (R6) was seldom different among the MGs (differences were always less than or equal to 7 days), and there was a significant correlation between days to full maturity (R8) and length of the planting to R1 period. These results indicate that the major difference in the length of growing season among cultivars of different MGs occurs before reproductive development begins in the midsouthern USA. Thus, performance of cultivars of the disparate MGs should not be affected by differences in time between reproductive stages. Rather, the reproductive period of later-maturing cultivars will occur later in the season when stored soil moisture has been reduced, probability of rainfall is lower, and air temperatures are higher. Planting later-maturing cultivars results in later reproductive development and increases their exposure to late-season stresses such as drought, insects, and diseases. This knowledge improves: 1) allottment of time and resources for inputs such as irrigation; 2) the timing of pesticide applications that are geared toward a particular reproductive stage(s); and 3) the scheduling of soybean harvest in relation to harvest of other crops, and/or securing custom harvest resources. Knowledge of time of maturity as related to planting date is also important in the midsouthern USA because a price bonus for August delivery is available some years. Technical Abstract: Soybean [Glycine max (L.) Merr.] is planted from late March through June in the midsouthern USA. Different developmental patterns that result from this range in planting dates will affect management decisions. Irrigated field studies were conducted at Stoneville, MS (33 26'N) from 1979 through 2003 to determine effect of late March through June planting dates on developmental patterns of maturity (MG) IV through MG VI soybean. In all plantings, time from planting to beginning bloom (R1) increased as maturity group (MG) increased from IV to VI. Time from R1 to full seed (R6; pod cavity filled) was sometimes but not always different among the MGs, and differences were always 7 days. A significant correlation between days to maturity (R8) and length of the planting to R1 period indicates that the major difference in the length of growing season among cultivars of different MGs occurs before reproductive development begins in the midsouthern USA. Thus, performance of soybean cultivars of disparate MGs should not be affected by differences in time between stages of reproductive development, but rather by when the stages occur. |
