Comparative effects of crop residue incorporation and inorganic potassium fertilisation on apparent potassium balance and soil potassium pools under a wheat–cotton system
The objective of this study was to evaluate the effects of consecutive crop residue incorporation and potassium (K) fertilisation on plant–soil K balance, K forms, K release and K fixation capacity under wheat–cotton rotation at Nanjing and Dafeng in China. Six treatments were evaluated: control (without K input), wheat straw at 0.9tha–1, cotton residue at 0.7tha–1, wheat straw and cotton residue at the aforementioned rates, and 150 and 300kg ha–1 fertiliser K. Treatments in each rotation year had an identical rate of nitrogen and phosphate fertiliser application. The initial soil K content was higher in Dafeng than Nanjing. In the low K content soil of Nanjing, crop K uptake with double crop straw was significantly higher than that under single crop straw return or inorganic fertiliser, and K uptake increased with increasing K inputs. Only double crop straw or 300kg ha–1 fertiliser K treatments reached apparent K balance in Nanjing, but not in Dafeng. The high negative K balance resulted from the elevated K removal by crops in Dafeng. Incorporation of double crop residues favoured accumulation of different forms of K. Application of K fertiliser tended to increase soil water-soluble K, and crop residue incorporation greatly improved non-exchangeable K at a depth of 0–20cm. Similar to K fertiliser, crop residue incorporation significantly increased soil K release and decreased K fixation at both sites. In summary, in a 3-year field experiment, crop residue incorporation and inorganic K fertilisation had similar effects on soil K pools and balance depending on initial soil K level and actual K input.