Potassium nutrient balances of the farmland soils in 50 varieties of crops and 5 types of rotation and its impact to soil available K nutrient content were studied in 43 sitespecific locations over the past three years in Shanghai suburb.The result indicated that：(1)the potassium nutrient surplus tendency of different crops farmland was：the fewflower wildrice，the fruit>the vegetables≥the greensward>the crops; The potassium nutrient surplus of different rotation farmland was：the rotation of crops and crops > the rotation between vegetable and crops>the greensward only>the rotation between vegetable and vegetable>the fruit tree only;(2)Content of soil available potassium after harvest gradually increased with the depths of soil profile in the farmlands of different fields and different rotation fields.The more soil available potassium contents were，the more potassium nutrient surplus had been in different planting patterns fields;(3)Potassium nutrient surpluses of the farmland soil in different crops fields and different planting patterns were positive correlated with the content of available K content in the surface soil(0~30 cm)in harvesting，but not significantly.