The effect of soil acidity on potentially mobile phosphorus in a grassland soil

A - Papers appearing in refereed journals

Mcdowell, R. W., Brookes, P. C., Mahieu, N., Poulton, P. R., Johnston, A. E. and Sharpley, A. N. 2002. The effect of soil acidity on potentially mobile phosphorus in a grassland soil. The Journal of Agricultural Science. 139 (1), pp. 27-36.

AuthorsMcdowell, R. W., Brookes, P. C., Mahieu, N., Poulton, P. R., Johnston, A. E. and Sharpley, A. N.
Abstract

This study compared phosphorus (P) speciation and the relationship between bicarbonate extractable (Olsen) P and 0.01 M CaCl2 extractable P (a measure of potentially mobile P) in soils from plots of the Park Grass experiment started in 1856 at IACR-Rothamsted, UK and with and without nitrogen as (NH4)2SO4 and with and without calcium carbonate (CaCO3, lime). A point, termed the change point, was noted in Olsen P, above which 0.01 M CaCl2-P increased at a greater rate per unit increase in Olsen P than below this point. Previous findings have shown a change point for soils with a pH>5.8 at 56 mg Olsen P/kg and at 120 mg Olsen P/kg for soils below this pH. Soils given (NH4)2SO4 annually since 1856 and with lime periodically since 1903 mostly had a pH between 3.7 to 5.7, some of these (NH4)2SO4 treated soils were limed to pH 6.5 and above from 1965. Irrespective of their pH in 1991/92 all the soils had a similar change point (120 mg Olsen P/kg) to that found for other soils with pH<5.8 (112 mg Olsen P/kg). In a laboratory study lasting 30 days, the addition of CaCO3 to acid soils from the field experiment that had received (NH4)2SO4 had a similar change point to soils with pH<5.8 irrespective of pH, suggesting soil P chemistry was controlled by the long period of soil acidity and this was not reversed by a short period at a higher pH. The effect of pH was attributed to the creation of P sorptive surfaces on aluminium precipitates compared with less acidic soils (pH>5.8) where there was less exchangeable Al to be precipitated. This was confirmed with solid-state 31P nuclear magnetic resonance, which indicated that for soils of similar total P concentration and pH, there was twice as much amorphous Al-P in soils given (NH4)2SO4 compared with those without. Changes in pH as a result of applications of (NH4)2SO4 or lime can greatly change the concentration of potentially mobile P due to the effects on Al solubility. Although there was less potentially mobile P in soils with pH<5.8 than in soils above this pH, it is usually advised in temperate regions to maintain soils about pH 6.5 for arable crops.

Year of Publication2002
JournalThe Journal of Agricultural Science
Journal citation139 (1), pp. 27-36
Digital Object Identifier (DOI)doi:10.1017/S0021859602002307
Open accessPublished as non-open access
Funder project or code441
511
Publisher's version
Copyright license
Publisher copyright
Output statusPublished
Publication dates
Online01 Aug 2002
ISSN0021-8596
PublisherCambridge University Press (CUP)

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