Reduced Soybean Seeding Rates: Changing Recommendations in Light of Environmentally Variable Data.

Research projects using soybean plant population as a factor but not necessarily as the primary objective of the research, were conducted in the late 1990's and early 2000’s in Virginia.  This research indicated that Virginia Cooperative Extension seeding rate recommendations for full-season production systems may be too high, and that recommendations for double-crop systems may not be accurate in all situations.  Further examination of these data revealed that response of soybean yield to plant population varied depending on planting date, maturity group, soil type, and rainfall.  This encouraged additional soybean plant population research to determine how those factors affected the plant population-yield response.  Simple plant population studies over numerous environments evolved into multi-factor planting date-maturity group experiments which evolved into experiments evaluating plant populations under the variable stand situations when using drills.  On-farm research and demonstrations comparing the producer’s normal seeding rate and 100,000 less seed per hectare (40,000 less seed per acre) were also implemented.   After five years of research, consistency seemed to decrease and variability increase.  Still, detailed analysis of the environmental factors affecting the data allowed for a reduction in full-season seeding rates by 30%.  These data also confirmed that double-crop seeding rates could not be reduced.  Surveys of grower’s current seeding rates indicated that significant savings in seed cost were possible.  Therefore, Virginia Cooperative Extension recommendations for soybean were revised in 2007.  Grower adaptation to these new recommendations will be confirmed with future surveys.