Effect of Fertilizer Phosphorus Particle Size on Phosphorus Fertilizer Efficiency

Abstract Five field experiments were conducted over 3 yr (1983–1985) to evaluate the effect of P fertilizer particle size on winter wheat ( Triticum aestivum L.) yield and P uptake. In 1983, an introductory experiment indicated that the P fertilizer particle size could greatly affect fertilizer P effectiveness. Studies in 1984 and 1985 confirmed these observations. In these studies ammonium polyphosphate (11‐24‐0, N‐P‐K), at particle weights of 0.00019, 0.0009, 0.025, 0.93, and 22 mg were applied at P rates of 8.4, 16.8, and 25.2 kg P ha −1 on four different soils. Wheat grain yields were increased significantly by applied P on all four soils. Grain yields were affected by P fertilizer particle size only, however, on the Ascalon and Holdrege soils (Aridic and Typic Argiustoll, respectively) where yield increases from applied P were greatest. Maximum grain yield occurred at approximately the intermediate particle size studied (0.025 mg), although optimum particle size was dependent on P rate. As the P rate increased, particle size became less of a factor influencing fertilizer effectiveness. Wheat grain yield at the 8.4‐kg ha −1 P rate was 0.31 Mg ha −1 less for the 22‐mg particle compared to the 0.025 mg particle. Calculations indicated that the 22‐mg fertilizer particles had an average distance of 2.8 cm from one another in the band area, compared to 0.003 cm or a continuous band for the 0.025‐mg particles. Phosphorus uptake and other yield components generally paralleled the results with grain yield. Fertilizer P efficiency in terms of fertilizer P uptake, reached a maximum of 47% with a particle size of 0.15 mg and an application rate of 8.4 kg P ha −1 on the Holdrege soil. This was a 20% increase in efficiency over a normal farm fertilizer size of 20‐mg particle 1 . While optimum fertilizer size probably ranges from 0.025 to 1 mg per particle, the optimum size in these experiments in terms of both yield and fertilizer efficiency was generally less than the 20‐mg particle size reported for farm fertilizers. Results indicate that greater root proliferation in continuous P bands may be responsible for an increase in fertilizer P uptake and efficiency compared to discontinuous P bands.