Soil phosphorus parameters affecting phosphorus availability to, and fertilizer requirements of, maize (Zea mays)

Abstract

The phosphorus status of each of 26 surface soils from Queensland was characterized by laboratory measurements and a glasshouse experiment. The glasshouse trial investigated the response between applied P in each soil and maize (Zea mays) dry matter yield. In the laboratory, the quantity of soil P was estimated by extraction with 0.5 M NaHCO3 (PB), and the intensity was estimated by soil solution P, 0.005 M CaCl2 extraction and equilibrium phosphorus concentration (EPC). Phosphorus-sorption curves were established for each soil and the data were used to derive the buffering index (BI) and equilibrium buffer capacity (EBC). Four single-point sorption indices were also determined. The desorption buffer capacity (dBC) of each soil was obtained in the laboratory by equilibrating soil samples with anion exchange resin for periods ranging from 0.1 to 18 h. This paper reports the relationships between the various P parameters and (i) the P uptake by maize (Zea mays) grown in untreated soil, and (ii) the amount of added P required for 90% maximum yield. Intensity, as estimated by EPC, was significantly (P < 0.001) correlated with P uptake. Any of the BI, EBC or the single-point sorption indices significantly improved the variation in P uptake accounted for by PB alone, but not to the same level as that obtained with EPC alone. When PB was combined with dBC, more variance was accounted for in P uptake than by using any of the adsorption buffer capacity measurements. The effects of quantity, intensity and buffer capacity on P availability are discussed in terms of their effects on P diffusion. For the suite of soils studied, it is concluded that intensity is the prime factor governing availability, and that the usefulness of adsorption buffer capacity measurements depends on their correlation with desorption buffer capacity. Variation in P requirement was best described by a combination of EPC and the Mitscherlich curvature coefficient, or EPC and one of the single-point sorption indices. As the single-point sorption indices were highly correlated with desorption buffer capacity, adsorption buffer capacity, and the curvature coefficient, they offer a convenient measure of the sorption properties of a soil.