Agronomic effectiveness of granular and fluid phosphorus fertilizers in andisols and oxisols

Abstract

Fluid phosphorus (P) fertilizers are more efficient than granular fertilizers in calcareous soils, but their potential to improve P use efficiency in strongly P-sorbing acidic soils is not known. We therefore evaluated P uptake by wheat (Triticum aestivum) from granular (calcium phosphate and ammonium phosphate) and fluid (ammonium phosphate) fertilizers in two Andisols from Chile and New Zealand, two Oxisols and a calcareous soil from Australia, by using an isotope (33P) dilution technique. All fertilizers were applied at a rate of 150 mg kg−1 soil. The availability of soil P was very low in the Oxisols and Andisols, and most P (>71%) was derived from the seed in the control treatment. Addition of P fertilizer increased dry matter yield up to sevenfold compared with the control, except with ammonium phosphates in the Chile soil, likely due to Ca deficiency limiting plant growth, and with triple superphosphate in the Oxisol with the highest pH, likely due to precipitation of fertilizer P. The percentage of P in the shoots derived from the fertilizer (%Pdff) in the P-amended Andisols and Oxisols ranged from 65 to 88%. No significant difference in %Pdff between granular and fluid sources was observed in these soils, except for the calcareous soil, in which significantly more P was derived from fertilizer with fluid than with granular MAP (as found previously). We conclude there is no agronomic benefit of fluid over granular P fertilizer sources in soils in which P availability is controlled by strong adsorption, that is, Andisols and Oxisols.