Jonathan W. McLachlan1,2, Richard J. Flavel1, Chris N. Guppy1, Richard J. Simpson2, Rebecca E. Haling2
1 University of New England, School of Environmental and Rural Science, Armidale, NSW, 2351, email@example.com
2 CSIRO Agriculture and Food, GPO Box 1700, Canberra, ACT, 2601
Phosphorus (P) is usually concentrated in the uppermost layers of the soil profile under pasture, hence topsoil root allocation is important for maximising P acquisition. However, total root length was recently found to be a marginally better predictor of variation in P uptake among twenty-six genotypes of subterranean clover (Trifolium subterraneum L.) when compared to topsoil root length alone. This result prompted a preliminary assessment of P acquisition by subsoil roots. Micro-swards of two cultivars were grown with a topsoil layer that was either P-deficient or amended with P for improved plant growth, overlying a low-P subsoil that contained 32P-labelled phosphate. Both cultivars produced less shoot dry mass under P constraint, and the cultivar that allocated more root length to the subsoil layer produced a larger shoot dry mass in the P-deficient soil. This cultivar also recovered more 32P-labelled phosphate from the subsoil layer in both P treatments. Therefore, variation exists for subsoil P acquisition and this trait may be important for determining shoot yield in P-deficient soil.