Germination and Vegetative Growth Analysis of Early Planted Indeterminate Soybean

A majority (67%) of Indiana growers are planting soybeans earlier today than 10 years ago. Growers indicate a shift in weather patterns and increased yield as the two primary reasons for this change. Little research has been conducted to quantify the impact of early planted soybean on crop growth characteristics in the Eastern soybean belt. Therefore the objectives of this experiment were to characterize the effect of temperature on early season vegetative growth in soybean. The experimental design was a randomized complete block in a split-plot arrangement with four replications. The main-plot effect was soybean planting date (30 March, 13 April, 27 April, 10 May, 30 May and 7 June). Planting dates were spaced at 80 GDU intervals (base 10 °C). The subplot effect was soybean maturity group (2.6, 3.2, and 3.7). Soybean was planted no-till in 38-cm rows at 370,000 plants ha^-1. Soil temperature was recorded every half hour with StowAway TidbiT temperature loggers and gravimetric soil moisture content was calculated weekly. Vegetative growth was sampled weekly, from V1 to R1 soybean, to determine leaf area index (LAI), relative growth rate (RGR), net assimilation rate (NAR), crop growth rate (CGR), and total dry matter (TDM).

Percent soybean emergence differed among planting dates; however peak emergence occurred at the 27 April planting date. Though vegetative growth was more accurately described by GDU’s than calendar date the GDU model did not accurately describe early season growth of the early planted soybeans. This suggests that significant growth occurred below 10 °C and that a different base temperature is required to improve the accuracy of the GDU model.