Author : Basilio, Pearl R.

Summary : The study was conducted to evaluate the potassium (K) status and exchange characteristics of 10 soils representing important lowland areas in Luzon the Philippines. An inventory of the K content of the soils was made using the following extracting solutions: hydrogen flouride (HF) for total K, sodium tetraphenylboron (NaTPB) for nonexchangeable K, and ammonium acetate (NH4OAC) for exchangeable K. Quantity/intensity (Q/I) parameters derived from the Q/I curves were tested against K availability indices to assess their value in characterizing K status. Q/I data described K status by relating the intensity (I) of K to the amount (Q) of labile K in the soil. A greenhouse experiment was conducted to determine the influence of K addition and K uptake on the Q/I parameters of selected lowland soils and at the same time assess their K supplying capacity. A high soil to plant ratio was used to exhaust available K supply in a short period. Eight of the soils studied contained 2:1 expanding type of clay minerals. Bantog and Tarlac were dominated by vermiculite. X-ray diffraction patterns of the sand fractions of all the soils showed the presence of quartz and feldspars. The soils varied in their chemical characteristics which include pH, cation exchange capacity, organic matter content, exchangeable K, NaTPB-xetractable K, ARKe, AK degree, and PBCK. The exchangeable K contents (NH4OAc extractable K) of eight soils were found to be below satisfactory level of exchangeable K for rice. Only San Manuel I and Bantog had exchangeable K level higher than 0.2 me/100g. Significant correlation were found between exchangeable K and ARKe (r = o.77) and Ko (r= -0.96). Sodium tetraphenylboron extractions.