Increasing yield of late-planted soybean through management practices in the Southern Great Plains

Increased soybean commodity prices and high-yielding cultivars have instigated producers to expand soybean production outside traditional regions. Introduction of soybean to relatively new areas such as the Southern Great Plains, has created the need for management practices unique to the region to exploit full yield potential in these environments. Oklahoma soybean production, for instance, frequently results in low yields due its adverse environmental conditions, along with common late-plantings, as a double crop following wheat harvest. Due to soybean photoperiod sensitivity, delayed planting leads to a shortened vegetative growth period, which potentially reduces seed yield. The influence of management practices, such as seeding rate, row spacing, maturity group selection, starter and foliar fertilization, irrigation, and the use of long juvenile soybean lines, on late-planted soybean yields has not yet been evaluated in the Southern Great Plains. The objectives of this study are to evaluate the effect of these specific management strategies on late-planted soybean yields and their potential adoption in the Southern Great Plains to minimize yield losses in these late production systems. Four different field studies were established on late plantings in Oklahoma as followed by numbers 1, 2, 3, and 4: 1) Four seeding rates ranging from 198,000 to 383,000 seeds ha-1, three row spacings (19, 38, and 76 cm) and two maturity groups (4.8 and 5.6) under rainfed conditions. Seed yield, plant population, canopy cover, and partial economic return were analyzed. Seed yield was not affected by seeding density, but yield results for 38 and 76 cm row spacings showed slight advantage to 19 cm rows. Partial economic return of 38 and 76 cm rows ranged from 13 to 25% greater than 19 cm row spacing, with the greatest returns at the lowest seeding densities. 2) Three soybean lines from maturity group (MG) 6, 7, and 8 carrying the long juvenile trait (LJ) were compared to three high-yielding varieties from MG 3, 4, and 5, in four planting dates from late-May to late-June. Vegetative growth period, canopy cover, seed yield, and seed quality were evaluated. Long juvenile soybean lines had greater growth but similar yields compared to non LJ varieties, due to the extended growth period overlapping early reproductive stages diminishing seed production potential. 3) Fertilization strategies including two starter and four foliar treatments were compared to a control treatment with no fertilizer applied. Starter or foliar treatments resulted in no seed yield differences compared to control treatment. 4) Soybean from MGs 4.8 and 5.6 were sown in 19 and 76 cm row spacings at three seeding rates (247,000, 346,000, and 445,000 seeds ha-1 were tested under irrigated conditions and seed yield evaluated. Seed yield of late-planted soybean under irrigation was affected only by MG. Seeding rate and row spacing had no effect on yield. Average yield of MG 4.8, across row spacings and years was 2620 kg ha-1, which was 25 % greater than MG 5.6 yield (1980 kg ha-1)