Effect of Plant Population on Yield and Height Characteristics in Determinate Soybeans

Lodging resistance may be an important factor in determining how soybean [Glycine max (L.) Merr.] cultivars respond to high populations. Therefore, the effects of plant population on yield, lodging, pod number, height, internode number, and average internode length for the lower, center and upper main stem internode regions, in determinate soybean cultivars differing in lodging resistance were studied in a field experiment on a typic Arguidoll soil. Group V cultivars, ‘Essex’ (most lodging resistant); ‘Forrest’ (intermediate lodging resistant); ‘Mack’ (least lodging resistant); were evaluated in rows 97-cm wide over a 2-year period at populations of 23, 33, 43, and 53 plants/m of linear row (240,000; 340,000, 440,000; and 540,000 plants/ha). Lodging was moderate and increased as planting rate increased. Although yields were highest at the lowest plant density in all varieties, Essex did not respond to plant population as did the other two cultivars. Yield of Forrest at 23 plants/m was significantly greater than at 43 and 53 plants/m. Yield of Mack at 23 plants/m was higher than at the other populations. Pods per plant decreased as plant density increased. Forrest averaged significantly more pods per plant for all populations than Essex or Mack. Internode number in Essex was unaffected by population and was significantly less than in Forrest or Mack. Length of lower and central internodes increased and internode number declined as population increased in Forrest and Mack. Internode number and length offset each other resulting in similar heights across populations in Forrest and Mack while Essex was slightly taller with increasing populations. Essex which averaged 72 cm tall was significantly shorter than Forrest (93 cm tall) or Mack (90 cm tall) because of fewer and shorter internodes. However, yield of Essex was comparable to Forrest and better than Mack indicating that cultivars of short stature and improved lodging resistance can be grown without lowering yield. Yield stability across populations in lodging resistant Essex compared to significant yield reductions at the higher seeding rates in the more lodging susceptible cultivars, Forrest and Mack, indicates that lodging resistance is an important factor in determining how a soybean variety will respond to higher populations. Thus, lodging resistance is an important consideration in determining the optimum seeding rate of varieties best adapted to a particular area for maximizing yield, even in environments where lodging is only moderate.