Effect of Long-term Application of K Fertilizer on Potassium Character of Soil-crop System under Continuous Maize Cultivation

Based on long-term application of K fertilizer on selected soils of three provinces in northeastern China for continuous 13 years,effect of K fertilizer on status of field maize and soil potassium system in the plough layer were studied.Results showed that K fertilizer could increase potassium content of different organs in plant distinctly,especially in straw.Application of K fertilizer could increase yield of grain but yield didn't increase with K fertilizer quantity's increasing and then K fertilizer's efficiency decreased.Soil potassium appeared apparent wane in the treatment of NP and NPK1,and potassium deficit rate ranged from 4.7 to 135.5 kg K2O hm2 annually,however there was a surplus in NPK2 treatment.Application of K fertilizer could increase content of available potassium and its content increased with K fertilizer quantity's increasing,K fertilizer application increased content of slowly available K and total K collectively compared to NP.Application of K fertilizer improved proportion of available K and slowly available K and reduced proportion of mineral K.Compared to 1993,content of available K in treatment of NP decreased,however others showed a rise,and content of slowly available K in each treatment increased a little,but content of total K decreased.It behaved consistent in three sites.In order to postpone soil potassium's decline,the application of maize straw's returning should be considered.