New Zealand Journal of Agricultural Research abstracts
Soil acidification: a provisional model for New Zealand
pastoral systems
C. A. M. DE KLEIN
R. M. MONAGHAN
A. G. SINCLAIR*
AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand
Abstract Soil acidification is a major problem
internationally and occurs in pastoral systems as a result of nitrate leaching,
nutrient transfer/removal, and soil organic matter (SOM) accumulation. Existing
mechanistic models on soil acidification calculate acidification rates
retrospectively, based on quantitative information on these acidifying
processes. This paper presents an outline of a predictive soil acidification
model that includes sub-models for estimating the extent of nitrate leaching,
nutrient transfer/removal, and soil organic matter accumulation. The model was
used to predict acidification rates in a fertiliser trial on sheep-grazed
pastures, receiving superphosphate fertiliser for 35 years. The predicted rates
ranged from 1.46 to 3.83 kmolc/ha.year, which was in moderate agreement with
acid additions rates of 3.09 to 3.43 kmolc/ha.year as calculated from measured
changes in soil pH and the pH buffer capacity (pHBC). Further development of
the model is needed to include a SOM accumulation sub-model and to refine the
various relationships within the existing sub-models. In addition, accurate
information on the pHBC of soils is needed to convert soil pH change into acid
addition rate, which will be crucial for validating the model.
Keywords Acidification; dairy; grass/clover pasture; model;
New Zealand; sheep
New Zealand Journal of Agricultural Research, 1997, Vol. 40: 541-557
0028-8233/97/4004-0541 $7.00/0 (c) The Royal Society of New Zealand
1997
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