The effect of soil water status on fertiliser, topsoil and subsoil phosphorus utilisation by wheat
Background and aims
Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions.
An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm).
The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P.
Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.
KeywordsFertiliser efficiency Isotopic tracing Isotopic dilution Drought Crop nutrition
Funding for this work was from South Australian Grains Industry Trust and Australian Research Council (LP0882492). Thanks to Minnipa Agriculture Centre and the Hunt family for providing land and watering for EP sites and to the Loller, Obst and Schober families for providing land for Mallee sites. Thanks to Bill Davoren, Anthony Whitbread, Rick Llewllyn, Glenn McDonald and Bill Bovill for collaboration in the Mallee region. We gratefully acknowledge Colin Rivers and Caroline Johnston for technical support, Sean Mason for P analyses and Erik Smolders and Yibing Ma for discussions about the topsoil-subsoil experimental design. Thanks to Rob Bramley and Sean Mason for useful comments on the manuscript.
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