Planting Date, Row Spacing, and Seeding Rate Effects on Soybean Yield.

Input costs for soybean production continue to rise, causing farmers to consider lowering seeding rate and making other changes to improve production efficiency. In 2010 our study compared the effects of different planting date, row spacing, and seeding rate combinations on soybean yield across six locations in Illinois. At four locations with productive soils in northern Illinois, four planting dates from mid-April to early June, two row widths (38 and 76 cm), and three seeding rates (173, 297, and 420 thousand seeds per hectare) were evaluated. At the southernmost location, Dixon Springs, the soybeans were planted 1 to 2 weeks later than the northern sites. Our other southern location, Brownstown, was limited to three planting dates that were about seven weeks later. Also, at the two southern Illinois locations, seeding rates were 25,000 seeds per hectare higher. There was a planting date effect for the six locations; the latest planting date yielding 1463 kilograms per hectare less than the earliest planting date (34.8% decrease). Across the four northern sites, the prediction equation was: y=-0.246x^2+43.09x+2,957 where y is the yield in kilograms per hectare and x is the Julian date the soybeans were planted, which ranged from 13 to 71 days after April 1st. Later soybean planting improved emergence, but better emergence did not impact yields. When comparing row spacing and seeding rates, yield difference varied by location. Overall, 38-cm and 76-cm rows yielded 3620 and 3516 kilograms per hectare respectively (2.87% decrease). The highest seeding rate yielded 3611 kilograms per hectare while lowest seeding rate yielded 3504 kilograms per hectare (3.01% decrease). Similar studies have not shown soybeans to be as responsive to planting date; however, with ideal planting conditions early in the season the soybean yields were positively influenced.