『Abstract
Phosphorus (P) loss from agricultural soils to water is a major
contributor to eutrophication. In an incubation experiment with
five contrasting soils, lime and gypsum showed potential as source
measures to decrease P loss risk, as assessed by water extractions.
Soils were incubated with lime to achieve a target pH of 6.5 and
with gypsum at equivalent Ca rates for 108 days. P was added (17
kg P ha-1) as KH2PO4
in solution. Gypsum appears to have greater potential as a source
measure, decreasing molybdate-reactive P (RP) solubility by 14-56%
and organic P (OP) by 10-53% across all soils. RP and Ca may have
precipitated or co-sorbed, and OP may have been stabilised in
organic matter complexes due to the bridging effect of Ca and
the flocculating effect of increased ionic strength. Greater effectiveness
of gypsum may be due to its higher solubility and the fact that
it increases Ca concentrations without increasing pH. Lime decreased
RP solubility in two soils (by 4% and 20%) but increased solubility
in two and had no effect in a third. The overall effect of lime
may depend on several competing effects of raised pH and Ca concentration
that may vary in importance depending on soil characteristics
such as base cation and P status. For the highest P status soil,
both lime and gypsum were effective, decreasing RP solubility
by 4% and 15%, respectively. Targeted treatment of high P soils
may be an effective and economical strategy to minimise P losses.
Keywords: Phosphorus; Lime; Gypsum; Phosphorus source measure;
Phosphorus loss; Organic phosphorus』
1. Introduction
2. Materials and methods
3. Results and discussion
3.1. pH
3.2. Reactive phosphorus
3.3. Organic phosphorus
4. Conclusions
Acknowledgements
References