Effect of Soybean Planting Date and Relative Maturity on Grain Yield.

            In-season variations in Ohio weather patterns have greatly impacted soybean (Glycine max) yields with high temperatures during the month of July, causing the largest reduction in grain yield. Over the past twenty years, for every degree Fahrenheit increase in temperature, soybean grain yield decreased by one bu/acre. To reduce this effect, planting dates and maturity groups may need to be adjusted so the sensitive reproductive developmental stages occur when temperatures are lower. Planting soybeans early extends the growing season and allows for earlier canopy closure. Earlier canopy closure reduces soil temperature and minimizes in-season water loss due to evaporation. A trial was established in Wood County, Wayne County, and Clark County, Ohio in 2016 with the objective of evaluating planting date and relative maturity combinations to reduce soil and canopy temperature, promote early canopy closure, and maximize yield. The trial was a split-plot randomized complete block design with four replications of treatments. The main plot factor was soybean planting date (early May and early June) and subplot factor was relative maturity (ranging from 2.2 to 4.4). At the V2 growth stage (two fully developed trifoliates) through August, canopy closure and soil and canopy temperature were recorded every two weeks. Date of soybean maturity (95% of pods mature color) was also noted. Data were analyzed using analysis of variance and Fisher’s least significant difference. Soybean yield was 1.4 bu/acre and 6.4 bu/acre greater for earlier planted soybeans compared to later planted soybeans in Clark and Wayne County, respectively. Relative maturity was significant in all three counties. Yield was statistically the same with the 3.1-3.6 relative maturity varieties in Wood and Clark County and 2.2 and 2.8-3.8 relative maturity varieties in Wayne County.