The recovery of fertilizer phosphorus by wheat, its agronomic efficiency, and their relationship to soil phosphorus

Abstract

Phosphorus (P) uptake by wheat from both soil and fertilizer, the recovery of fertilizer P and its agronomic efficiency, and the fertilizer P required for maximum profit were measured in 55 wheat fertilizer experiments during 1986-89 in the northern and central wheat belts of New South Wales. Moisture conditions during crop growth had a dominant effect on all these parameters, whose values were generally highest in the wettest year (1988) and much lower in the driest year (1989). Lactate-extractable soil P was well correlated with each of these parameters, there being a different relationship for the 3 years of adequate rainfall (1986-88) from that for the very dry year: in general, the values of each parameter in the dry year were about half the values in the wetter years. Recovery of fertilizer P in the grain was very low and declined at increasing levels of soil P from about 13% at 1 mg/kg to 2% at 50 mg/kg in 1986-88. This indicates high potential levels of fertilizer P residues in this soil/climatic environment. Fertilizer P required for maximum profit was much better correlated (r2 = 0.50) with soil P than was the requirement for 90% of maximum yield (r2 = 0.30), and the latter did not differentiate between the moist and dry years.