A long-time study on the effect and balance of potassium

4-year experinlents on strip fields showed that the crop’s yield was improved by l7.0％～20.3％ after adding potassium fertilizer，and the effective time of potassium was delayed when the manure was applied．The results of 18-year rotating experiments show that the potassium applied in soils can satisfy the crop need of 2 rotation periods(3 years per rotation)and the increased yield up to 10.3％ ～30.7% appears from the third to six rotations．There is a positive correIation between the potassium effect and experimental process. Each year． the potassium in soils decreases by 135.0～335．5kg／hm² when the manure is applied，decreases by 97．4～335．7kg／hm² when the chemical potassium is added，and reduces by 76.5～268.0kg／hm² when both are applied mixedly The average available potassium in soils declines 2．6～17mg／kg per year when continuous plantation is done without potassium and decreases by 7.5mg／kg in strip-field but merely increased in rotated field The mixed application of chemical potassium and manure can improve the available effect of potassium in soils． The decreasing rate of slow effective K is 6．5～ 8．2 times of fast effective potassium ．