1993 Volume 68 Pages 15-24
An introductory investigation on soil conditions in relation to K status and release characteristics of twelve soils reveal that the physical and chemical properties of the studied soils varied considerably with the variation of soil parent material, hydrology and climatic conditions. The texture of the soils varied from sandy to clay,organic matter content was rather low(6.9 —19.8g kg-1) .Except for Sara soil,the pH(l:1,water)of the soils ranged between 4.7 and 5.3,indicating that the soils are acidic. Sara soil contained about 60 g kg -1 CaCO3 and had an alkaline pH(8.2) .Among the twelve soils, seven soils had exchangeable K+ of more than 0.20 cmol(+)kg-1,which can be considered as the critical level of K for these soils.The exchangeable K+/exchangeable Mg2+ ratio of the soils varied from 0.05 to 0.14.The structural K was about 93 to 99% of the tota 1 K,while exchangeable(0.26—1.02%)and non—exchangeable (1.07 —8.33%)K comprised a small percentage of the total K. Non — exchangeable K in the soils determined by 0.7M H2SO4 and IM HNO3 methods varied from 0.11 to 3.26 and 0.44 to 3.94 cmol( + )kg-1, respectively. Rate of release of K from the soils was very high in the first extraction by both the IM CH3COONH4 (1.02—3.07mmol kg-1)and 0.3M NaCl(0.90—2.47 mmol kg-1)solutions.With IM CH3COONH4,the release of K was drastically reduced on the second day and virtually stopped on the third day of extraction. With 0.3M NaCl extraction,the rate of release of K was reduced gradually and even on the 11th day of extraction the release of K was considerable. Only K released with 0.3M NaCl showed a significant positive(r=0.70**)correlation with the non—exchangeable K.
