Plant Population and Row‐Spacing Effects on Early Soybean Production Systems in the Mid‐Atlantic USA

Limited information is available on early soybean Glycine max (L.) Merr. production systems (ESPS) in the Mid‐Atlantic USA. Furthermore, the effects of intermittent drought stress on the response of ESPS to plant population and row‐spacing alterations have not been fully explored. The objective of this research was to determine if increasing plant population and decreasing row spacing could increase yield of ESPS in the Mid‐Atlantic USA where intermittent drought is a major environmental limitation. Two maturity group (MG) III and two MG IV soybean cultivars were planted using row spacings of 23 and 46 cm and five populations ranging from 103 000 to 850 000 plants ha −1 at four locations that varied in levels of drought stress. With little drought stress, no response of soybean yield to plant population occurred. A population of 208 000 plants ha −1 was adequate for maximum yields at a site having only a brief period of stress; populations over 600 000 plants ha −1 were required to maximize yield where drought stress limited leaf area production. Narrowing row spacing increased mean leaf area index (LAI) by 0.15 and 0.30 units and yield by 100 and 290 kg ha −1 in low and moderate stress environments, respectively. Maturity group IV cultivars were better able to compensate for moisture stress periods because the stress occurred during earlier development stages compared with MG III cultivars. This research indicated that increasing LAI in ESPS via increased plant populations or narrow row spacing may increase ESPS yield, especially in environments of early season intermittent drought stress.