Ammonium phosphate fertilizers are a more effective phosphorus source than superphosphate for wheat grown on acidic gravelly soils

Abstract

Selecting the most effective phosphorus (P) fertilizer source is essential for maximizing crop yields. However, there is little information to guide the choice between the widely used soluble granular sources: ammonium phosphates and superphosphates. The aims of this study were to examine whether there are differences in wheat ( Triticum aestivum L.) grain yield response to ammonium phosphate and superphosphate fertilizers in field conditions, and if these differences relate to diffusion of P from fertilizer granules. Two field experiments were conducted on acidic gravelly soils in Western Australia where P deficiency occurs to compare wheat growth response to P applied as monoammonium phosphate (MAP), diammonium phosphate (DAP), single superphosphate (SSP) or double superphosphate (DSP). A diffusion study was conducted to quantify the effect of P source on P diffusion from the fertilizer granules. Grain yield with MAP was up to 18% higher than SSP at one field experiment, and 10% higher than DSP at the other. The extent of P diffusion around the granules in the diffusion study showed the same order as the wheat growth response in the field experiments. The difference among P sources is attributed to greater precipitation or adsorption of phosphate near the granule with superphosphates, likely due to the presence of calcium (Ca) in the fertilizer. Our results reinforce the continued use of MAP as a source of P for crops grown on the acidic, gravelly, P responsive soils in Western Australia.