Response of Irrigated Soybeans to Rate and Placement of Fertilizer Phosphorus1
- G. W. Rehm2
This study was conducted to measure the response of irrigated soybeans [Glycine max (L.) Merr.] to rate and placement of fertilizer P and to develop critical values for P in this crop. Five rates of P (0, 11, 22, 33, 44 kg ha−1) were either broadcast and incorporated before planting or applied to the side of and below the seed at planting (starter) at 10 irrigated sites over 3 yr. Tissue samples consisting of the most recently matured trifoliates (petiole excluded) were collected at early bloom and analyzed for P. Use of fertilizer P increased soybean yields at three of 10 sites and higher yields at these sites were recorded each year when the fertilizer P was broadcast and incorporated before planting. Fertilizer P increased yields when the soil test P level (0-20 cm) measured by the Bray and Kurtz no. 1 procedure was <3.1 mg kg−1. There was no response to fertilizer P when the P level measured by this method was 9.6 mg kg−1 or higher. Soil P measured by the Na HCO3 method was as satisfactory as the Bray and Kurtz no. 1 procedure for separating responsive from nonresponsive sites when subsoil P was considered. The P concentration of leaf tissue at responsive sites was increased with application of fertilizer P. At 95% of maximum yield, P concentration in leaf tissue was 3.35 g kg−1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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