Effect of Fertilizer Phosphorus Particle Size on Phosphorus Fertilizer Efficiency

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. Appreciation is given to TVA and the Potash-Phosphate Institute for providing funds supporting in part this research. contribution of the Neb. Exp. Stn., Lincoln, NE as paper no. 8525.