Potassium status and exchange characteristics of some lowland soils in Luzon [Philippines].
1988
Basilio P.R.
Eight of the soil studied contained 2:1 expanding type of clay minerals. Bantog and Tarlac [Philippines] were dominated by vermiculite. X-ray diffraction patterns of the sand fractions of all the soils showed the presence of quartz and feldspars. The soil varied in their chemical characteristics which include pH, cation exchange capacity [CEC], organic matter content, exchangeable K, NaTPB - extractable K, K availability at equilibrium, change in exchangeable K, and potential buffering capacity of soil for K. The exchangeable K contents (NH4 OAC extractable K) of eight soils were found to be below the satisfactory level of exchngeable K for rice. Only San Manuel 1 and Bantog had exchangeable K level higher than 0.2 me/100 g. Significant correlation were found between exchangeable K and K availability of equilibrium (r = 0.77) and change in exchangeable K (r = -0.96). Sodium tetraphenylboron extractions gave higher values for K than NH4OAC extractions since H was able to extract even the "difficult available" K. Although the soils contained low exchangeable K, most of the soils with the exception of La Paz, Tarlac, and Buenavista, have high buffering capacities. Significant correlation between buffering capacity and clay content (r = 0.81) and CEC (r = 0.87) were recorded. The Q/I relations of the soils used in the greenhouse experiment (Maligaya I and San Miguel I) redetermined after K addition and after the soils have been depleted of K by crop uptake were transposed vertically on the direction expected.
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