Potassium deficiency, and molybdenum deficiency and aluminium toxicity due to soil acidification, have become problems for cropping sandy soils in south-western Australia

Nutrient omission experiments determined the cause of 'waves' of good and bad growth in wheat and barley crops following burning of swathed canola crop residues on acidified sandy soils in south-western Australia. Potassium deficiency, and molybdenum deficiency and aluminium toxicity induced by soil acidification, were identified as major problems. Burning canola swaths increased bicarbonate-extractable soil potassium by 20-100 mg/kg, and as measured in 0.01 mol/L CaCl2, increased soil pH by 0.3-0.8 of a pH unit and decreased aluminium extracted from soil by 1-6 mg/kg. These changes in soil chemistry were shown to be responsible for waves of better crop growth under the burnt swaths. Root lesion nematodes were shown not to be related to the problem.