Effect of long-term K application on corn yield and potassium forms in plough layer of black soil and meadow soil in northeast of China

Based on 13 year's continuous K fertilizer application on meadow soil and black soil delegating 3 provinces of northeast of China,effect of K fertilizer's application on corn yield and potassium forms in the plough layer were studied.Results showed that K application could increase corn yield distinctly,the treatment of NPK1 made an increase of 10.2% and 12.6% and 17.5% compared with NP alone in Liaoning and Jilin and Heilongjiang,but yield didn't increase along with K fertilizer quantity's increasing.K application could increase content and proportion of water-soluble potassium and non-specifically adsorbed K and specifically adsorbed K,and those two indexes increased with K quantity's increasing and treatments behaved as NPK2NPK1NP.NPK2 significantly increased those two indexes compared to NP,but no difference in those two indexes between upper two layers was observed for NPK2 and the difference became less pronounced in layer 2040 cm.K application increased content of non-exchangeable K,mineral K and total K collectively at the same time lowed proportion of mineral K.Content and proportion of different kind of K didn't vary unanimous in each regions.Total K showed fall,equal and increase separately in Heilongjiang,Jilin and Liaoning with soil depths.