Development of Resin Disc Soil Testing in Rice Crop in Relation to Kinetics of Nutrient Adsorption on Resin

The aim of this investigation was to develop a durable, rigid, and reusable resin disc for soil testing with the hypothesis that a uniformly shaped disc of cation/anion exchange resin placed in direct contact with the soil will accumulate ions from the soil by processes similar to those for living plant roots in the natural soil-solution-plant continuum. To develop regression equations for the relationship of resin-adsorbed quantity (RAQ) to yield of rice, soils were collected before sowing from different plots of a rice field where a fertility gradient had been created in the previous year by growing rice with different doses of fertilizers. For resin-disc soil testing, a soil sample is made into a saturated paste and placed in intimate contact with the resin disc. After 24 h (as decided from the kinetic experiment), the resin disc-soil assembly was dismantled. Ammonium, phosphate, sulfate, and potassium ions were extracted from the discs. Rice was grown in those plots without any fertilizer, and yields were recorded. Regression analysis was done between yield and nutrients adsorbed by the resin (NAR). The same soils were also analyzed for organic carbon, phosphate, sulfate, and potassium by the conventional chemical extraction method. Multiple regression analyses of grain yield (Y) as the dependent variable and resin-adsorbed N (RN), resin-adsorbed P (RP), resin-adsorbed K (RK), and resin-adsorbed S (RS) as independent variables produced the following relationships: Y = 5.95 + 5.13RN + 23.85RP -2.4RK + 1.05RS, multiple R-2 = 0.793. The resin-disc method gave much better regression with rice yield than the conventional chemical extraction method.