Study on the characteristics of potassium cycling in different soil-crop systems in northern China

As the potassium contents in soils of northern China are relatively high, it is of significance to strengthen the potassium cycling in the agricultural production systems and apply potash fertilizer rationally based on the potassium cycling characteristics in soil-plant systems and the soil potassium balance under different cropping system. Soil analysis revealed that the soil total K contents in northern China soil showed small variation but the soil readily available K and slowly available K contents were significantly higher in soils of northwestern China. The soil readily available K contents were much higher in soils of northeastern China than in north?central China, and for the soil slowly available K contents the reverse was true. The fixed site field trials on the representative soils under the main cropping systems in northern 12 provinces revealed that crop K uptakes under various cropping systems varied significantly. The crop K uptakes in northwestern China were general higher and the double cropping under north-central China showed much higher annual crop K uptakes than the single crop in northeastern China. Returning the wheat straw back into the soil and applying potash fertilizer improved the crop K uptake, with the applying potash fertilizer combined to wheat straw returning showing most prominent effect. The soils were under the depleting status of K when no potash fertilizer was used, the soil readily available K content declined gradually. Potash application and its combination to straw returning would reduce the soil K depletion by crop uptake and slow down the decline of soil K content to some extent.