Soybean yield response to reproductive stage soil-applied nitrogen and foliar-applied boron

Research on the effects of N and B applications on soybean [Glycine mar (L.) Merr.] yield is limited. Experiments were conducted to determine the effect of (i) application rate and reproductive stage timing of N or B on soybean seed yield and (ii) cultivar, row spacing, or planting date on the response of soybean to R3-stage N and B applications. Nitrogen was applied to the soil at 0, 14, 28, 56, 84, 112, or 168 kg ha(-1), or B was applied to the foliage at 0, 0.14, 0.28, or 0.56 kg ha(-1) to either R3- or R5-stage soybean in the rate and timing experiments. Treatments for the cultivar, row-spacing, and planting-date experiments included 0 + 0, 56 + 0, 0 + 0.28, and 56 + 0.28 kg hal N + B, respectively. In yield environments ranging from 2400 to 5300 kg ha(-1), application of N or B did not increase seed yield at any rate or application stage, nor did cultivar, row spacing, or planting date alter this lack of response. Analysis of leaf tissue taken at the R2 soybean development stage and before nutrient application indicated that N and B concentrations were above the minimum level required by soybean for maximum yields not limited by N or B. Lack of response to supplemental N or B suggested that N supplied via fixation and soil organic matter mineralization and native levels of B in soils are adequate for high yields in the Mid-Atlantic Coastal Plain soybean production region.