EVALUATION OF SOIL FERTILITY STATUS OF LOWLAND AREAS IN THE PHILIPPINES

Attempts were made to evaluate the regional fertility characteristics of the Philippine lowland soils and to identify the factors determining their productivity for rice cultivation. Eight soil characters, i.e. organic C, total N, available P2O5, total P2O5, exchangeable K, available SiO2, clay contents, and CEC for 52 surface soil samples were considered. By factor analysis, 3 factors were extracted, representing the organic matter status, available potassium and silica status, and available phosphorus status. The scores of these 3 fertility components were computed for each sample and based on the mean values for each region, regional characteristics of soil fertility status were determined. Based on the relationship between each of the 3 fertility component scores and rice yield for the 30 plow-layer samples, any of the 3 fertility components was found to be significant for rice production. Furthermore, the lowest among the 3 fertility component scores was considered to control the productivity for rice cultivation. Thus, emphasis was placed on identifying and alleviating the soil constraints, in order to achieve rational nutrient management for higher rice production. Discipline: Soils, fertilizers and plant nutrition Additional key words: factor analysis, fertility components, rice production, soil constraints, soil characters