Foliar Fertilization of Soybeans. II. Effect of Biuret and Application Time of Day1

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Abstract
Negative yield results from the foliar application of NPKS solutions to soybeans [Glycine max (L.) Merr.] at the podfilling stage have been reported recently. Many of these studies have cited phytotoxicity and leaf burn as a causal factor. The purpose of this study was to investigate two factors which may contribute to these yield decreases: (1) biuret in the urea and (2) time of day of application. Biuret, a contaminant in fertilizer‐grade urea, was added to a base NPKS solution containing biuret‐free urea at the rates of 0, 0.25, 0.50, 1.0, 2.0, and 4.0% of the weight of the urea in the fertilizer material. Application of the biuret containing fertilizer solutions either one or three times did not reduce soybean yield and seed weights at three sites in the 2 study years. To determine the effect of application time of day, an NPKS solution containing 24 + 2.4 + 7.2 + 1.2 kg N + P + K + S/ha was applied to soybeans at 0300, 0600, 0900, 1200, 1500, 1800, 2100, and 2400 hours four times at 7 to 10 day intervals during podfilling. Under the climatic conditions encountered in the 2 years of this study, soybean yields were not significantly (P=O.lO level) affected by the time of application. However, consistent trends toward lower yields with midday applications allow us to suggest that the application of foliar fertilizer before 0800 or after 1700 hours will minimize chances of foliar injury and may improve chances of a positive response.