Effects of initial phosphate intensity and sorption or buffering capacity of soil on fertilizer requirements of different crops grown in pots or in the field

Abstract

Rates of added P required for maximum yields of ryegrass grown in pots and of field tobacco and maize were related to functions of P intensity (I) and capacity (AQ/AI, or C) in soils. It was found that log I alone was negatively correlated with optimum fertilizer for ryegrass and tobacco, but not for maize. Capacity alone had little relationship with P requirements of tobacco but was significantly correlated, although having opposite effects, with those of ryegrass (positive) and maize (negative). Optimum fertilizer rates for all crops were best accounted for by multiple regressions including intensity and a capacity term together, using log C when P requirements were increased (ryegrass in pots, R² = 0.94) or √C when they were decreased by increasing capacity (field tobacco, R²= 0.96; and maize, R² = 0.98). Inclusion of both capacity terms with log I in regression was of no advantage with ryegrass and tobacco, but with maize all three terms contributed significantly to the correlation, log C tending to increase and √C to decrease fertilizer needs.