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Planting Date and Maturity Group to Maximize Yield and IWUE

During the past several years, the MSPB funded the RISER project (click here for project final report) that was conducted under the leadership of Dr. Jason Krutz, now the Director of the Miss. Water Resources Research Institute. This project investigated various technologies or best management practices (BMP’s) that potentially can be used to increase irrigation efficiency and thus minimize or stop the decline in the water level of the Mississippi River Valley Alluvial Aquifer (MRVAA), which is the primary water source for Delta-wide crop irrigation.

Midsouth soybean producers can plant soybeans over a wide range of calendar dates–e.g. from early April to late May/early June. They also have a range of maturity groups (MG)–e.g. MG 3, 4, and 5–from which to choose varieties for these plantings. For producers who irrigate their soybean crop, the primary considerations when making these decisions are seed yield and water use, or amount of irrigation water needed to maximize seed yield.

In a published article by Wood et al. (CFTM Mar. 2019), results from a three-year study that investigated planting date and MG effects in furrow-irrigated soybean systems are presented. A summary of that research and its results follows.

•   The objective of the research was to determine the interactions of soybean planting date (DOP) and MG on seed yield, net returns above irrigation costs, and irrigation water use efficiency (IWUE).

•   The research was conducted from 2015-2017 near Stoneville, Miss. on a Dundee silty clay loam soil.

•   Early planting dates were Apr. 25-27 (EARLY), Mid planting dates were May 13-18 (MID), and late planting dates were June 1-5 (LATE) across the three years.

•   Varieties in MG III (3.8-3.9), MG IV (4.5-4.7), and MG V (5.2-5.3) were included in each year’s study.

•   Sites were furrow-irrigated through lay-flat polyethylene tubing each year when average soil water potential in the 0-24 in. soil zone reached -75 centibars. Computerized hole selection (PHAUCET) was used each year.

•   DOP and MG interacted to affect soybean seed yield. In the EARLY planting, MG IV and MG V varieties produced similar yields, and both yielded at least 16% more than the MG III variety. In the MID planting, MG IV yield was at least 30% greater than yields from MG III and MG V varieties. In the LATE planting, yield from all MG’s were not statistically different, but the yield from the MG IV variety was numerically greater than yields from the MG III and MG V varieties. Yield of varieties in each MG were greatest in the EARLY plantings.

•   DOP and MG interacted to affect IWUE. However, IWUE of MG III varieties was always the greatest regardless of DOP. IWUE of varieties in all three MG’s generally declined as DOP became later.

•   The DOP x MG interaction did not affect net returns above total specified costs. Net returns from the EARLY planting were greatest, as were net returns from the MG III variety. However, as stated above, yields from the MG III variety in all three DOP’s were the lowest.

•   These results indicate that maximum yield of soybeans planted across the range of DOP’s used in this study will be achieved if MG IV varieties are planted. Also, the maximum IWUE that can be achieved without sacrificing yield and net returns is to plant MG IV soybean varieties across these planting dates. These results confirm the yield results obtained from a 3-year regional study conducted from 2012-2014 in four Midsouth states (click here for those results).

•   If water for irrigation becomes limited beyond the amount needed to maximize yields from MG IV varieties, then these results indicate that MG III varieties should be planted early to ensure the greatest yield, IWUE, and net returns from their use.

•   Thus, the preponderance of evidence obtained from numerous studies in the Midsouthern US indicate the same thing, and that is, mid- and late-MG IV varieties should be considered the best choice for planting in the region regardless of planting date unless irrigation water becomes limited to or allocated in an amount that will not allow their maximum yield.

Composed by Larry G. Heatherly, Apr. 2020, larryheatherly@bellsouth.net