New Zealand Journal of Agricultural Research abstracts

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Estimating phosphorus loss from New Zealand grassland soils

R. W. McDowell

AgResearch Limited
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand

L. M. Condron

Soil, Plant & Ecological Sciences Division
P.O. Box 84
Lincoln University
Canterbury 8150, New Zealand

Abstract  The potential for phosphorus (P) loss from New Zealand grassland soils was assessed using a combination of measured soil chemical properties and concentrations of dissolved reactive P (DRP) determined in drainage and overland flow from simulated rainfall experiments. Soil analyses included Olsen P, calcium chloride (0.01M CaCl₂) and water extractable DRP, P sorption index (PSI), and % P retention. Results confirmed that DRP concentrations in drainage and overland flow were closely related to CaCl₂- and water-extractable DRP in soil, respectively. The preliminary data indicated that the potential concentration of DRP in subsurface and overland flow from pasture soils that have not been recently grazed and at a small scale (e.g., overland flow from 1-m lengths) could be estimated from Olsen P and PSI (or P retention) data according to the following equations:
DRP (subsurface flow) = 1.480 (Olsen P/PSI) = 0.069 (Olsen P/P retention) + 0.007
DRP (overland flow) = 0.495 (Olsen P/PSI) = 0.024 (Olsen P/P retention) + 0.024.

Keywords  phosphorus; pasture; nutrient loss

A03038; Received 23 June 2003; accepted 7 January 2004; Online publication date 27 May 2004
New Zealand Journal of Agricultural Research, 2004, Vol. 47: 137-145
0028-8233/04/4702-0137 © The Royal Society of New Zealand 2004

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