Improvements to soil cation exchange capacity following additions of various forms of soil amendments

Abstract

Low cation exchange capacities (CEC) contribute to the low productivity of some Zambian soils. By modifying these soils with cation exchangers, nutrient retention and crop productivity may be improved. A pot experiment was done in the greenhouse to investigate the effectiveness of various amendments in improving soil cation exchange capacity (CEC) and reducing leaching of applied potassium. Bentonite, Charcoal, Compost and Zeolite were each added to a Mufulira series soil at two different application rates (12.5g kg'^ and 25g kg"^), and a control to give a total of nine treatments. The treatments were replicated three times in a Randomised complete block design (RCBD). Two crops of maize were each grown for six-week periods, in pots. Potassium (0.9g / pot) was applied to the soils a week after the first planting and there after subjected to leaching at 1, 5 and 11 weeks after application. The treated soils were analysed for CEC and pH(CaGi2) while the dry matter yields of crops were obtained. Leachates were analyzed for potassium concentration. Soil CEC was improved (P < 0.05) by all the amendments, rising from 3.57 cmol (+) kg-^ to 5.71 cmol (+) kg'^ and 6.14 cmol (+) kg-' (Bentonite, 12.5g and 25g kg'' of soil respectively), 4.88 cmol (+) kg"' and 5.61 cmol (+) kg"' (Charcoal, 12.5g and 25g kg'of soil respectively), 5.39 cmol (+) kg"' and 6.03 cmol (+)kg"' (Compost, 12.5g and 25g kg' soil respectively) and 4.89 cmol (+) kg"' (Zeolite at both rates). These improvements were significantly different between treatments (P < 0.05). Increasing the rate of soil amendment was positive in increasing CEC. As soil CEC increased, the K lost in the leachate decreased. All the pots showed an increase in pH with the addition of K, but not as a result of CEC values. Treatments did not significantly affect dry matter yield (P < 0.05).