Potassium deficiency and its management in a long-term rotation experimentin the south-western slopes New South Wales

Potassium (K) deficiency of wheat and pasture species was found at a site i n the south-western slopes of New South Wales. The soil was a subnatric yel low sodosol. Subterranean clover (Trifolium subterraneum) was found to be l ess competitive for K in the soil compared with its associated grasses. Hig her soil K concentrations were required to achieve the same subterranean cl over K concentration in the grass-legume mixtures than in a subterranean cl over monoculture. For wheat (Triticum aestivum) production, a soil exchange able K (K-ex) below 0.25 cmol(+)/kg appeared to be deficient for the limed treatments, but there was no obvious critical value for either limed or unl imed treatments. The critical K-ex values for the grass-legume mixtures cou ld not be simply specified because the values were affected by competition between species growing in swards of variable botanical composition. An ann ual rate of 20 kg K/ha for the pasture-crop rotations (50/50%) and 29 kg K/ ha for the permanent pastures was estimated to be sufficient to replenish t he K losses from product removal and animal excreta transferred to campsite s at this trial site.