Growth Dynamic Factors Controlling Soybean Yield Stability across Plant Populations

Abstract

Soybean [Glycine max (L.) Merr.] optimizes yield over a broad range of plant populations because of its ability to increase yield per plant at sparse plant populations. Greater understanding of this response would aid research efforts aimed at achieving optimal plant population (minimal plant population required for best yield). The objective of this study was to determine the growth dynamic factors responsible for yield compensation across a range of plant populations. Soybean cultivar Delta Pine 415 (Maturity Group V) was planted an optimal date during 1994 and 1995 at low (70 000 plants ha−1), medium (164 000 plants ha−l), medium/high (189 000 plants ha−1), and high (234 000 plants ha−1) plant populations on a Commerce silt loam soil (fine‐silty, mixed, nonacid, thermic Aeric, Fluvaquents) near Baton Rouge, LA. Increasing plant population by 234% from low to high treatments resulted in only a 9% yield increase. This yield stability resulted from equilibration of crop growth rate and total dry matter pers quare meter across populations by R1 and significantly greater (P < 0.05) dry matter partitioning into branch dry matter per square meter (14.8% in the low population and 9.9% in the high population). Consequently, similar branch dry matter per square meter and pod number per square meter occurred across populations. Equilibration of crop growth rate and total dry matter per square meter by R1 across populations was aided by greater light interception efficiency and net assimilation rate in the low vs. higher populations during the vegetative and early reproductive periods. In conclusion, similar yields may result as plant population declines through maintenance of crop growth rate during the early reproductive period and greater dry matter partitioning into branch dry matter per square meter.