Relationship between available K content and K input levels in fluvo-aquic soil under long term fertilization

Based on the long-term experiment of fertility and fertilizer effects in fluvo-aquic soil in Zhengzhou City of Henan Province, the dynamic patterns of soil available potassium (K) content were investigated in different fertilizer treatments and the relationship between soil available K content and K input level was examined. The results show that when no K is applied, soil available K contents gradually decline, then maintain at the level of around 60 mg/kg after 8 to 10 years. Soil available K contents increase with the combining application of K fertilizer and organic amendments, and a significant positive correlation between soil available K content and K input levels is observed. In treatment of pure chemical NPK fertilizers, 1 kg/ha of K input could lead to the soil available K content increase by 0.007 mg/kg. In the treatment of combination of NPK with manure or straw, the increase would be 0.025 mg/kg and 0.014 mg/kg, respectively. Inorganic fertilizers combined with farmyard manure or maize straw are the best management strategy for increasing soil K supply.