Nitrogen and Boron Applications During Reproductive Stages for Soybean Yield Enhancement
The yield response of soybean [Glycine max (L.) Merr.] to reproductive stage applications of either nitrogen (N) or boron (B) has been inconsistent. This study evaluated soybean seed yield response to foliar applications of B and soil applications of N at two stages of plant development, at two row spacings, at four irrigation levels, and on three cultivars over three years. Planting dates were either mid-May or mid-June, except the year two of the irrigated soil moisture experiment which had a second planting date of early July. In an experiment to evaluate B rate and timing, B was applied at four rates from 0 to 0.56 kg ha-1 at the R3 or R5 development stage. In an experiment to evaluate N rate and timing, N was applied at seven rates from 0 to 168 kg ha-1 at either the R3 or R5 development stage. A third experiment to evaluate row spacing and cultivar effects on N and B had four treatments: 0 N and 0 B; 56 kg ha -1 N, and 0 B; 0 N and 0.28 kg ha-1 B; and finally 56 kg ha-1 N and 0.28 kg ha-1 B. Treatments were applied to three soybean cultivars planted in either 23 or 46 cm row spacings. The above experiments were irrigated to evaluate treatments at high yield levels. To further evaluate the effect of soil moisture, the same four N and B combinations were applied to soybeans irrigated via a sub-surface micro-drip irrigation system delivering four irrigation regimes: 0%, 33%, 66%, or 100% of plant required water. Gradients were established in year one of this experiment, but late season rains eliminated gradients, and high rainfall in the second year disallowed gradient establishment. Applications of N or B had no effect on seed yields in any experiment, or at any moisture level. In the row spacing and cultivar experiment, there were significant effects of varieties, and a significant interaction between row spacing and variety in two of the three years.