Potassium management effects on quantity/intensity relationship of soil potassium under rice-oilseed rape rotation system

Quantity-intensity curves were used to evaluate the dynamics of soil potassium (K) at different soil depths under different K management. The equilibrium concentration ratio of K (CR0) increased with increasing K concentration. K fertilization and straw return increased soil K supplying capacity by increasing CR0, non-specific available K (- increment K-0) and equilibrium K (CK0). The CR0 increase 107%, 392% and 577% at the 0-20 cm layer and 55%, 102% and 131% at the 20-40 cm layer, respectively, under K fertilization, straw return and the interaction of them. The CK0 and - increment K-0 at the 0-20 cm layer significantly increased after K fertilization and straw return. The labile K varied from 0.11 to 0.19 cmol kg(-1), contributed 85.3% to 107.6% of NH4OAc extracted K. Soil K potential buffering capacity showed significant differences in soil depths, while little difference was observed under different K management. Th e exchangeable K was meaningless for guiding K application when minimum exchangeable K took up 85.9% to 99.0% of equilibrium exchangeable K. Our results showed K fertilization and straw return was the optimal management to enhance soil K supplying capacity, especially at the 0-20 cm layer.