Abstract
Soyabean (Glycine max) optimizes yield over a broad range of plant populations, but mechanisms responsible for compensation have not been fully elucidated. Identification of these factors would help in selecting cultivars/genotypes having low optimal plant populations (minimal plant population required for best yield) and provide agronomists and farmers with indicators of optimal plant populations. Studies were conducted to determine the mechanism for plant yield compensation across a range of plant populations. Soyabean cultivar DeltaPine 415 (maturity group V) was planted at an optimal date at low (70 000 plants/ha), medium (164 000 plants/ha), medium-high (189 000 plants/ha) and high (234 000 plants/ha) plant populations on a Commerce silt loam near Baton Rouge. A 58% population decrease from 164 000 plants/ha resulted in a yield decrease of only 12%, while a 43% increase resulted in no significant yield change. Yield per plant was primarily regulated by changes in branch dry matter per plant, which averaged 14, 5.3 and 3.6 g per plant for the low, medium and high populations, respectively. Greater branch dry matter per plant created more branch nodes, branch reproductive nodes and branch pods. Pod per reproductive plant node also affected yield in some cases. High correlation between branch dry matter per plant and yield (r2 = 0.95) demonstrated the usefulness of this yield component for identifying cultivars or genotypes with low optimal plant populations.