Double-Crop Soybean Response to Maturity Group and Plant Population in the Ohio River Valley Region
Maturity group (MG) and plant population are two important agronomic factors for successful double-crop soybean [Glycine max (L.) Merr.] production. The first objective of this research was to determine the agronomic and economic optimum plant populations (AOPP; EOPP) of soybean varieties representing early-, medium-, or full-season MG for double-crop soybean production following winter wheat across the Ohio River Valley Region. Eleven small-plot field research trials were conducted during the 2016 and 2017 growing seasons in Missouri, Illinois, Kentucky, Indiana, and Ohio. Trials were designed in a two-way factorial (5 seed rates x 3 MG). Seeding rates ranged from 123,600 to 617,800 ha-1 with each variety classified as an early, medium, or full season MG. Stand establishment and grain yield were collected to calculate partial net returns (PNR). Seed rate, MG, and seed rate x MG were analyzed within individual environments for their effects on stand establishment, grain yield and PNR. Interactions between MG and seed rate occurred at four growing environments for grain yield and PNR. In the absence of a MG x seed rate interaction, the medium or full MG produced greatest grain yield, pooled over seed rates. Based on the actual early-season plant populations, the AOPP was no greater than 351,000 plants ha-1 in 27 of 31 environments. Grain yields at the AOPP ranged from ~2250 to 4960 kg ha-1. When economic returns were influenced by plant population, the EOPP was no greater than 306,000 plants ha-1 at 23 of 26 environments. Early MG tended to have higher AOPP and EOPP, and lower grain yield-which resulted in lower partial net returns-relative to medium and full MG. A secondary objective of this research was to determine the response of double-crop soybean yield components to MG and plant population in southern Indiana. Prior to harvest, plant populations of 100,000; 200,000; 300,000 and 400,000 plants ha-1 (2017 only) for each MG were sampled. Three replicates were measured in 2016 while four replicates were used in 2017. Pods were counted with respect to main-stem and branch node position. Grain yield and stover biomass were also measured and each variable was calculated on a per-plant and an area basis. In 2016, excellent grain yields were achieved (~500 g m -2), and neither MG nor population affected grain yield or the other yield components sampled on an area basis. In 2017, lower grain yield (~300 g m-2) occurred, which was due to lower grain yield on a plant basis (mean = 19.3 g plant-1), a result of exceptionally low precipitation. Pods plant-1 increased 2.4x (2016) and 2.8x (2017) when population decreased from 300K to 100K, which was due to increased branch pods at 100K. Grain yield was lower for the early MG in 2017, which occurred due to ~11% smaller seed mass. Overall, these results support using medium and full season MG varieties to maximize double-crop soybean grain yield in the Ohio River Valley Region. Further studies including more varieties of the same maturity rating and increased number of locations will help validate these results and provide growers with reliable information for their agronomic inputs in a double-crop soybean system.
Casteel, Purdue University.
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