Temporal and spatial variation of soil available potassium in China(1990–2012)

Potassium (K) fertilizers are non-renewable resources and cannot be synthesized from other chemicals. Understanding soil K status in China is crucial for the efficient use of K resources, and the resulting food security and resource sustainability. We analyzed temporal and spatial changes in soil K from 58,559 soil samples, and yield responses from 2055 field experiments compiled from the International Plant Nutrition Institute (IPNI) China Program database from 1990 to 2012. The results indicated that on average soil available K increased from 79.8 mg /L in the 1990s, to 93.4 mg/L in the 2000s, with the increase for cash crops faster than that for grain crops. In fact the average increase in soil available K over time was attributed to increases in soil K for cash crop fields with high K fertilizer application (1.4 to 2.6 times more than for grain crops). The study found great variation in soil available K across different regions and over time in China. Soil available K varied over space with values of 76.8, 99.8, 118.0, 83.9 and 81.3 mg/L for northeast (NE), north central (NC), northwest (NW), southeast (SE) and southwest (SW), respectively. While no difference in soil available K over the time period of the study was observed in NE China, the values increased by 34.8%, 17.9% and 30.2% for NC, SE and SW, respectively, and decreased by 75.9% for NW China between the 1990s and 2000s. Great temporal and spatial variation existed for relative yield as well, which followed similar trends to soil available K. Potassium fertilizer application continued to be recommended for grain crops due to the low soil available K falling short of critical values, and cash crops where a larger yield response to K fertilizer has been recorded. This great variation observed in soil available K across the different regions in China demonstrated the urgent need for site-specific K nutrient management.