The effects of P and K fertilization on soybean [Glycine max (L.) Merr.] seed quality are unclear. Fertilization rates can have a positive effect on yield and composition in some growing locations and years but not in others. As the cost of soybean seed production increases, seed companies are interested in improving seed quality of soybeans possibly through increased soil fertilization. The objectives of this study were to determine the effect of different levels of P and K fertilization on soybean seed quality defined as seed viability, vigor, and seed composition. Seed samples were obtained from a long-term P and K fertilization trial. Phosphorus and K treatments were 0, 28, or 56 kg P ha−1 yr−1 and 0, 66, or 132 kg K ha−1 yr−1. Results indicated that excessive levels of P and K fertility decreased seed quality. Seed composition changed across sites and treatments, but changes were generally inconsistent. Total seed protein and oil were not significantly affected by P and K fertilization in most locations. However, linolenic acid concentrations increased with excessively high P and K fertilization while linoleic acid concentrations decreased only with P. These results indicate that excessively high levels of soil fertility may have a negatively impacted on seed quality.
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