Phosphorus fractions of a climosequence of soils in New zealand tussock grassland

Abstract

The different forms of phosphorus in alkaline extracts of eight New Zealand topsoils, which are members of a climosequence, were characterized by 31P-nuclear magnetic resonance (NMR). A further two topsoils were used in an experiment to demonstrate that the NMR technique detected all of the P in the extracts. This direct method of estimating organic P in soil extracts enabled the different types and the relative amounts of P compounds to be estimated. Inorganic orthophosphate and orthophosphate monoesters were the major P components of the extracts from all soils, while all but the two driest soils also contained orthophosphate diesters. Only the high country and alpine soils, developed in a moist cool environment, contained phosphonates, a recently-discovered form of soil P of probable microbial origin. Across the climosequence of soils, the amount of orthophosphate diesters in the extracts was strongly and positively correlated with annual precipitation. This organic P fraction, together with phosphonates, could provide through mineralization a ready supply of “available” P in these mainly undisturbed tussock grassland ecosystems.