Inconsistent Yield Responses Add Complexity to Identifying Optimum Soybean Seeding Depths

Abstract

Soybean [Glycine max (L.) Merr.] seeding depth from 2.54 to 3.81 cm is considered optimum in northern rainfed regions, despite limited recent field research. We evaluated four seeding depths (2.54, 3.81, 5.08, and 6.35 cm) in three separate field‐scale studies (2013 and 2014) in New York to identify optimum depth(s) on well‐drained silt loam, somewhat poorly drained silty clay/silt loam, and somewhat excessively drained gravelly loam sites. Quadratic regression equations predicted minimum yield (4.49 Mg ha−1) at 4.71 cm in 2013 but maximum yield (4.22 Mg ha−1) at 4.85 cm in 2014 on the silt loam. Soybean populations showed negative linear responses to seeding depth at the other two sites in both years, but yield did not respond to seeding depth on the silty clay/silt loam, and showed a positive quadratic response (maximum yield of 4.21 Mg ha−1 at 4.55 cm in 2013) on the gravelly loam. Yield component compensation (positive linear/quadratic responses of seeds plant−1 to seeding depth) probably limited negative yield effects of lower populations at deeper seeding depths on the silty clay/silt loam and gravelly loam sites. Inconsistent yield differences (4.4–5.8% on the silt loam and 6.8–9.7% on the gravelly loam), as indicated by year × seeding depth interactions at both sites and no response on the silt loam, underscore the complexity in identifying optimum soybean seeding depths. Furthermore, favorable emergence conditions (mostly > 80% plant establishment) prevailed so population and yield responses to seeding depth may differ under unfavorable conditions.Core Ideas Soybean seeding depth from 2.54 to 3.81 cm is considered optimum in northern rainfed regions. Soybean yield showed site‐specific yield responses to seeding depth. Site‐specific yield responses underscore the complexity in identifying an optimum soybean seeding depth.