LAUSR

In light of China’s mineral potassium (K) deficit, it is imperative to improve K fertilizer use efficiency and conserve soil K. This study explored the effects of 15 years (1993–2007) of continuous potash application and wheat straw return on the K fixation capacity of cultivated soils in North China. Soil was collected from a number of long-term test sites, with different rates of potash application and wheat straw return and under different cropping systems. The results showed that long-term continuous potash application and straw return significantly reduced soil K fixation capacity. In addition, soil K fixation increased with the K concentration of the treatment solution. Soil K fixation levels were higher under double cropping systems than for single cropping systems. Soil K fixation capacity showed a clear zonal distribution pattern across North China; the soil K fixation capacity gradually increased from west to east. When the K concentration of the treatment solution was 1000 mg L−1, the average K fixation of soils fertilized only with N and P at experimental sites from Northwest, North-central and Northeast China were 359, 443, and 469 mg kg−1, respectively. The pattern of soil K fixation capacity across the different regions of North China matched the pattern of the timing of significant yield responses to K applications in the different regions. This research suggests that there should be a requirement for straw return as well as K fertilization to optimise K supply to crops during production.