Effect of Starter Fertilizer on Soybean Growth, Nodulation, and Yield.

Environmental conditions at the time of planting are a crucial determinant to soybean (Glycine max) yield potential. In recent years, it has become common in Ohio to begin planting earlier in the growing season, as soon as mid- or late-April in some cases. However, soil conditions are typically cooler and wetter at this time as opposed to later planting dates, and nutrient availability may be limited. When planting soybeans into cool and wet soil, the application of a starter fertilizer may be beneficial in providing nutrients to assist in root and shoot development until soils warm in the spring and nutrients become more available. The objectives of this study were to evaluate the effect of starter N and P fertilizer on (i) soybean growth (above and below ground biomass), (ii) nodulation,(iii) plant nutrient concentrations; and (iv) soybean yield. Objectives were evaluated at one location in 2013 (South Charleston, OH) and two locations in 2014 (South Charleston and Hoytville, OH). There were four soybean planting dates at South Charleston and three at Hoytville beginning the first week of May and every two to three weeks after. Five starter fertilizers were evaluated (urea, diammonium phosphate, urea + diammonium phosphate, triple superphosphate, and none). Nitrogen was applied at a rate of 33.6 kg N ha^-1 and phosphorus was applied at a rate of 44.8 kg P₂O₅ ha^-1. Fertilizer was applied in a band 5 cm beside and 5 cm below the row at planting. Results from 2013 indicated that nodulation at the R1 growth stage was reduced by both N and P starter fertilizer; however, root and shoot biomass were not affected. In 2013, there was a slight yield increase of 235 kg/ha in response to fertilizer-P.