SYNTHESIS AND EVALUATION OF AHOKO KAOLIN DERIVED ZEOLITE A AND PHILLIPSITE SUPPORTED FERTILIZER ON SELECTED AGRONOMIC CHARACTERISTICS OF TOMATO (Lycopersicon esculentum)

Abstract

The high leachability of soluble conventional fertilizers causes environmental pollution and the low cation exchange capacity of farmlands reduces soil fertility and agricultural yields. The aim of this study was to synthesise and characterise Zeolite A and Phillipsite from Ahoko Kaolin and to evaluate their plant nutrient delaying capacity on tomato growth, fruit yield, nutritional quality and postharvest soil residues. Zeolite A and phillipsite were synthesised from Ahoko kaolin using hydrothermal methods. The zeolites synthesis parameters of aging time, crystallisation temperature and time were optimised using central composite design. The zeolites surfaces were modified with Hexadecyltrimethylammonium (HDTMA) through an adsorption process and further enriched with Nitrogen, Phosphorous, Potassium (NPK). The isotherms, kinetics and thermodynamics parameters of zeolite A and Phillipsite were determined. The desorption rate of the synthesised zeolite A and phillipsite based fertilizers were determined through percolating columns. The effect of Zeolite A, Phillipsite based fertilizers and NPK 15:15:15 fertilizers were evaluated on the agronomic characteristics of tomato crop. The results showed that the crystallinity of synthesised zeolite A and Phillipsite were 99.92 % and 72.26 % respectively. The specific surface area of Zeolite A and Phillipsite were 296.178 m2 /g and 361.50 m2 /g respectively. The regression model revealed that crystallization time contributed the highest to the crystallinity of zeolite A and phillipsite. The modification of zeolite A with HDTMA gave the maximum adsorption capacity of 3.10 mg/g with an initial concentration of 162.6 mmol/L, contact time 8 h and temperature at 25 o C while the modification of Phillipsite with HDTMA gave a maximum adsorption capacity of 3.40 mg/g with initial concentration of 195 mmol/L, contact time of 16 h and temperature 25 o C. The specific surface area of surfactant modified zeolite A and phillipsite were 65.257 m2 /g and 312.429 m2 /g, respectively. The Freundlich isotherm model represented the best fit for the experimental adsorption data of zeolite A with correlation coefficient R2 = 0.7843 and the lowest error values of sum of square errors (SSE) (1.0377) and average relative error deviation (ARED) 24.5469. Dubinin Radushkevich isotherm model represented the best fit for the experimental adsorption data on Phillipsite with R2 = 0.9633 and lowest values of the SSE (0.0004) and ARED (0.4142). The pseudo-first-order model with R2 0.9992 and 0.7979 for zeolite A and phillipsite respectively represented the adsorption kinetics of the two zeolites. The Gibb‘s free energy for zeolite A and phillipsite were -27.045 kJ/mol and -61.799 kJ/mol respectively at temperature of 298K which points to the spontaneity of the adsorption processes. The negative enthalpies of -12.20 kJ/mol and -35.06 kJ/mol for zeolite A and Phillipsite showed that the adsorption processes were physical and exothermic. The phosphate loaded zeolite A based fertilizer showed slow release effect with the rate constant k2 of 1.8 x 10-3h-1 higher than KH2PO4 with its rate constant of 3.84 x10-3 h-1. The nitrate loaded zeolite A based fertilizer with rate constants 5.51 x 10-2 h-1 were slower than NH3NO3 fertilizer with rate constants 9.70 x 10-2 h-1 in the second phase of the leaching process. The slow release property of the zeolite A and Phillipsite based fertilizers were indicated through the leaf counts with mean value of 54.2 and 46.5 significantly higher to NPK 15:15:15 with a mean of 25.7 at 11 weeks after transplanting in 2018. Zeolite A and phillipsite based fertilizers produced fruit mean values of 84.69 and 83.36 g/plant significantly higher to NPK 15:15:15 with fruit mean value of 69.34 g/plant. Also, the vitamin C mean values 123.34 and 126.54 mg/100g of tomato fruit grown with Zeolite A and Phillipsite were significantly higher than those grown with NPK with mean 84.60 mg/100g. The results further showed that the soils with Zeolite based fertilizers significantly retained higher plant nutrients than soils treated with NPK at post harvest. The findings from this study revealed that zeolite based fertilizers significantly improved fruit yield, nutritive contents and postharvest soil content compared to NPK fertiliser.