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This article in AJ

  1. Vol. 78 No. 1, p. 117-120
    Received: Apr 9, 1984

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Wheat and Forage Sorghum Response to Residual Phosphorus in Blackland Soils1

  1. Billy W. Hipp2



Phosphorus fertilizers are generally applied for crops grown on Blackland Prairie soils of Texas, but the crop yield response due to residual P from single applications of P is unknown. Studies were conducted over a 5-yr period (1977 to 1981) on Austin silty clay (fine-silty, carbonatic, thermic Entic Haplustolls) and Dalco clay (fine, montmorillonitic, thermic Udic Pellusterts) soils to evaluate the residual effects of P on subsequent crops. Fertilizer rates of 0, 25, and 50 kg P ha−1 were applied in 1977,1978, and 1979 at three sites with soil P levels of 6,10, and 13 mg kg−1 NaHCO3-extractable P (0 to 15 cm depth). Following the initial crop year, plots were split to include 25 kg P ha−1 with the seed. The other half received no fertilizer P other than the initial P application. The test crops were wheat (Triticum aestivum L.), forage sorghum (Sorghum bicolor L. Moench), and sweet clover (Melilotus albus Lam.). A significant yield increase due to initial P application was obtained at each site. Crop yield increases due to residual effects of the 50 kg P ha−1 rate ranged from 0 to 20%, while yield increases due to 25 kg P ha−1 at planting ranged from 19 to 43%. Percent yield increase from residual P was greater on soil with 6 mg kg−1 soluble P than on soil with 13 mg kg−1 soluble P. Phosphorus concentrations in wheat plants were increased by residual P, but were much higher in plants receiving P at planting. These data indicate that some yield increase can be expected from residual P from a single application of moderate amounts of P. For more efficient use of P and high yields, P should be applied to each crop if initial NaHCO3-extractable P levels are between 6 and 13 mg kg−1.

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