Optimizing soybean plant population for a short-season production system in the southern USA

Soybean [Glycine max (L.) Merr.] production systems that utilize short-season cultivars for double cropping and late sowing often have insufficient time to establish a complete canopy prior to reproductive development. Our objectives were to evaluate plant population as a tool to manage crop growth, maximum biomass (BM), the time required for canopy closure, and yield, Field tests were sown on 8 July 1997 and 26 June 1998 at Keiser, AR (35 degrees 67' N, 90 degrees 83' W) in 0.19-, 0.57-, and 0.95-m rows with maturity group IV soybean cultivars Asgrow 4922 (A4922) and Manokin. Yield from irrigated and nonirrigated treatments increased as population density increased from 7 to 134 plants m(-2), except when lodging occurred. Populations recommended for early-season sowing (25-35 plants m(-2)) resulted in many plots not achieving 90% light interception (LI), especially in 1998 when weather was hotter and drier than in 1997, The time required after emergence to begin linear crop growth (t(b)) was dependent on LI, and as density increased, tb decreased. The values of t(b) varied from 16 to 27 d in 1997 and 22 to 37 d in 1998, with up to 12 d difference in achieving >90% LI, In this short-season production system, yield, crop growth rate between R1 and R5, BM, and t(b) were dependent upon the early establishment of a high LI, Losses attributable to excessive delays in canopy establishment and slow crop growth could be minimized by using high populations in narrow rows, Our research indicates that higher populations than are traditionally recommended provide a way to optimize grain yields in time-constrained systems.