Physical, chemical, and microbiological evaluation of a compost conditioned with zeolites

Zeolites are minerals characterized by high cation exchange capacity (CEC). This study evaluated possible effects of zeolites on improving the composting process in terms of the physical, chemical, and microbiological quality of compost and the productivity of the test plant, Raphanus sativus L. Compost enriched with 1.5% ground zeolites exhibited 62% greater degradation of organic particles sized less than 0.125 mm and 26% higher CEC than compost prepared without zeolites, while total coliform and Escherichia coli content were 96 and 36% lower, respectively. Moreover, the dried root mass of R. sativus was 21% higher with zeolite-enriched compost, subject to complementary mineral fertilization with macronutrients. The addition of zeolites to the composting process improved the quality of obtained organic compost as well as the productivity of plants grown using this compost. Given that zeolites are used mainly in the treatment of effluents in Brazil, and considering their mineralogical properties, more study is necessary to explore the effects of zeolite-enriched composts on crops with longer phenological cycles and grown in low-fertility soils. Key words: Composting, clinoptilolite, rock dust, radish, Raphanus sativus L., cation exchange capacity.