Plant Population and Row-Spacing Effects on Maturity Group III Soybean

Soybean [Glycine max (L.) Merr.] production in the upper midsouthern United States is primarily nonirrigated. Reliance on rainfall to coincide with the soybean reproductive stages often results in low seed yields due to drought. Maturity Group (MG) III soybean cultivars have been introduced to this region to utilize early-season rains and avoid late-season drought. The objective of this research was to identify the relationship between seeding rate and final population on narrow (38 cm) and wide (76 cm) rows in nonirrigated MG III soybean grown in the upper midsouthern United States. Field experiments conducted during 2006 and 2007, using MG III cultivars ‘Asgrow 3906’ and ‘Pioneer 93M90’, were planted in mid-May in narrow and wide rows to determine seeding rates and final plant populations that optimize yield. Rainfall in 2006 necessitated seeding rates of 358,400 to 378,600 seed ha–1 and final plant populations of 288,900 to 326,500 plants ha–1 for optimum yield. Drought in 2007 resulted in soybean planted on 38- and 76-cm row spacing producing optimum yields from 192,800 and 92,100 plants ha–1, respectively. Narrow rows generally produced yields greater than or equal to those obtained from wide rows. These data suggest that MG III cultivars should be planted on narrow row spacing to a final population of 300,000 plants ha–1 to provide optimum yields when planted on nonirrigated sites in the upper midsouthern United States.