Impact of Phosphorus Fertilization Strategies on Efficiency of Nitrogen Use by Corn Rotated with Soybean

Application of P fertilizer before corn for a 2 year corn-soybean rotation significantly increased yields when soil tested Low to Medium. In areas testing High there was little to no benefit from P application. Soil chemical properties were related to landscape position within the field. Application of P fertilizer affected the overall yield and profitability of the trial area. There was no evidence that the optimum nitrogen rate varied between the P management strategies, and optimum N rates were near those recommended currently by the U of M. Phosphorus application increased soil P in low testing areas in spite of high soil pH in the short term, but low to no application of phosphorus generally decreased it in Medium and High testing areas. Removal based P rates in the BPM strategy on average resulted in soil test P increases. Net returns to P were the highest when soils tested Low to Medium. The SLAN strategy always resulted in a higher profit potential, but both strategies were profitable in Low and Medium testing soils if P fertilizer price was either $0.50 or $1.00 per lb. P2O5. Decisions on which strategy to use should be based on grower goals and land-tenure. Grid sampling can be used to vary fertilizer application rates to better utilize inputs in a varying landscape as long as the sampling scheme accurately represents the variability within the field.