The changes of nutrient balances driven by adjusting crop structure at county level during 25 years——A case study in Huimin County,Shandong Province

The impact of cropping structure on nutrient balance and soil nutrients were investigated in Huimin County in Shandong Province.Data analysis were based on the results of the household survey,the local statistical data,the national soil survey carried out in 1984 and in 2004.In last 25 years cropping systems in Huimin was changed from cereals-cotton to cotton-cereals-vegetables.The calculation of nutrient balance sheet in Huimin County showed that surplus of soil nitrogen and phosphorus were 6089-19405 t and 259-7001 t respectively,whereas deficiency of potassium was 2532-6712 t.Soil organic matter,total nitrogen and OlsenP were increased by 57%,22% and 303%,respectively,while NH4OAC-K was decreased by 6%.It was indicated that changes of the cropping systems had large impact on nutrient inputs in the soil,and further on the nutrient balance and soil nutrient content at regional level.Therefore,the optimization of the cropping systems and the fertilization technique is the key issue for the integrated nutrient management at regional scale in future.