Estimation of soil available potassium in Chinese agricultural fields using a modified sodium tetraphenyl boron method

Abstract China has a long history and has made a substantial contribution to global crop production, but lacking in potassium (K) mineral resource, have led to numerous studies of K availability in Chinese agricultural soils. In this study, we collected 2,428 surface soil samples from nine important agricultural regions to investigate available K reserves in Chinese agricultural soils. Soil highly available K (HAK) and maximally available K (MAK) were estimated using a modified sodium tetraphenyl boron (NaTPB) method. With HAK and MAK distribution maps constructed, the characteristics of available K contents distribution were visibly observed as higher in Western and Northern China, and lower in the East and South. We then used the Kriging method to estimate the HAK reserve and its potential utilization. The soil HAK reserve was predicted to maintain only crops producing >70% of the relative biomass yield for approximately 10 years in the absence of external K application. With straw returning, this utilization period was predicted to increase to about 40 years. Soil MAK content was generally less than 1,000 mg kg –1 , and reached as low as <500 mg kg –1 throughout most of central and Eastern China. The results of this study graphically demonstrate the shortage of K storage in Chinese agricultural soil and its looming sustainability crisis. These findings provide a scientific basis support the improved use and protection of agricultural resources in China.