THE PROPERTY OF POTASSIUM UPTAKE BY WINTER WHEAT AND THE UTILITY OF DIFFERENT POTASSIUM FRACTIONS OF SOILS AFTER DEPLETION

Pot experiment was carried out to sdudy the property of K uptake by winter wheat and the utillty of different K fractions after 5 cropping depletion on 11 main soils of China. The results showed that K uptake by wlnter wheat was obviously different at different growing stages. The peak of K uptake appeared at the Jointing full heading stage, while at the mature stage the wheat showed excretion of K. The exchangeable K of soils were low and stable at all growing stages, but the slowly availiable K increased after full heading of wheat. Most of the K absorbed by wheat was from the nonextractable K wlth 1mol/L HNO3, averaging 78. 5%, and only small proportion from the exchangeable K, averaging 21. 5%. This indicated that the contribution of nonextractable K with 1mol/L HNO3 to plant nutrlent has incresed after exhausted cropping. The date when the lowest value of exchangable K appeared and the lowest value was an important property of soil K supplying.