Surface charge characteristics and phosphorus availability in selected oxisoils and ultisoils of Kerala

Abstract

To meet the goal of increased food production in areas dominated by LAC soils, it is essential to alleviate specific physical and chemical soil related constraints. A major constraint identified in the Oxisols and Ultisols is the widespread deficiency of phosphorus and moderate to high P – fixation coupled with low nutrient holding capacity. The use of low grade silicates and lime suggested as a low input strategy for sound phosphorus management in these soils is tested in the present study. In addition to this objective the by – product effect of the application of phosphate and silicate in excercising cation protection by enhancement of CEC is also tested in these selected soils. The results of the studies are summarised and appropriate conclusions drawn. The electro – chemical properties of the two soils studied clearly showed that the inorganic components of the soils are of variable charge type. The results of the incubation experiment proved the beneficial effect of silicate application in enhancing the available ‘P’ status. Adsorption studies of phosphate and silicate showed that the Kandiustult of Kottarakkara exhibited extremely high adsorption capacity for ‘P’ indicating a higher ‘P’ fixing capacity than the Haplustox of Pachalloor. The column study conducted revealed that it is possible to increase the retention of cations by applying phosphate and silicate as soil amendments. Neubauer’s experiment conducted to determine the effect of silicate lime and phosphate application on ‘P’ availability, did not show any significant result. However, the trend was indicative of the beneficial effect of silicate application in increasing the phosphate release from the soil. This aspect of the study needs further elaboration through field experiments.