NATIVE POTASSIUM FORMS AND PLANT AVAILABILITY IN SELECTED SOILS FROM NORTHERN CHINA

Twenty-five representative plower depth soil samples from 12 Provinces,Municipalities and Autonomous regions in major agricultural regions in northern Chinawere selected. Soil native potassium exists in 5 forms, namely water soluble K, non-specifically adsorbed K, specifically adsorbed K, non-exchangeable K and mineral K.Total potassium in the front 3 forms is less than 2. 0% of the total soil K. Non-exchangeable K accounts for 2. 7%~9. 4% of the total soil K, while mineral K accountsfor 89. 8%~96- 8% of the total soil K. According to the content of K in various forms,especially the content of soil non-exchangeable K, it is evident that potassium supplyingpower of the selected soils shows a general tendency of decrease from west to eastreglons (northwestern China -- northcentral Chlna -- northeasterri China j. Soilpotusslum deplet1on study was conducted in a pot experiment with successive plantingof corn seedling for 8~10 harvests. The 25 tested soils varied considerably in total netK absorption. wlth a range of 96. 3~793. 5mg/pot. In accordance with the amount oftotal net K uptake, potassium supplying power of the tested soils was divided into 5categories: very high, hlgh. medium. relatively low and low. In general, there was anotable tendency of decrease in soll K supplying power from west to east regions. Underdepletion condition and wlthout K application, the contrlbutions of various forms ofnative K to plant uptake varied significanUy in the order: water soluble K (with aaverage of 3. 1%) non-specifically adsorbed K (average 7- 7% specifically adsorbed K(average 10. 2%) non-exchangeable K (33. 3%) mineral K (45. 7%). In this research,contribution of mineral K was differenciated from non-exchangeable K, and the resultindicated that mineral K contributed significantly to K uptake by plants.