Abstract: 1. The mean values of potassium contents from mediumlow yield paddy soils were 1.95% for total K. 215.6 ppm for slowly available k and 73.5 ppm for available K. The potassium contents in decreasing order were marine coastal salty paddy soilsandy leak paddy soil gleyed muddy paddy soilyellow clayey paddysoil. Indicating that the structural potassium of soil was rich while poor in available K. 2. The total amount of K separately extracted by INHNO3 seperately for 5 times from 4 main soils was significantly correlated to slowly available K r=0.972**. The rates of K-released to total K-extraction correlated signkficantly,r = 0.743*. The ability of potassium supply of different soils ranked as : coastal saltysandy leak paddy soil and calcareous yellow clayed paddy soilyellow clayed paddy soilgleyed muddy paddy soil. 3. As the K-depletion of yellow paddy soils, the available K decreased sharply and simultaneously the rice yield dropped markedly, r=0.9219**. Total K oupply for 5 continual crops (per pot) were 1164 mg on more fertilizer gray-yillow paddy soil, out of which 89.0% came from available K, and 1047 mg on yellow paddy soil. Out of which 44.9% from available K. The former gave significantly high grain output than the latter by 51.5%.