A B S T R A C TThe use of compost in enhancing organic carbon content and aggregation in soil has been widely studied in the last decades. Recently, compost is used in new environmental applications for the remediation of both contaminated groundwater and soil. However, compost addition increases by 10 orders of magnitude the soil electrical conductivity and the nutrient content such as potassium. Subsequently, nutrient leaching in groundwater may increase water salinity. The present study investigates the effect of zeolite application on potassium release in sandy soils amended with municipal compost. Kinetic experiments show that zeolite addition in soil-compost mixtures have no effect on potassium desorption rate while it results in an 18-fold increase in bio-available potassium. Column tests show that zeolite application results up to six times decrease in total potassium leaching. Experimental results show high potassium affinity for the mixture soil-compost-zeolite in pH > 7, which is of paramount importance, considering that soils in southern Europe (Italy, Spain, south France, Albania and Greece) exhibit slightly alkaline pH in most cases. The findings of this study may be also used to predict the potential of groundwater contamination in agricultural areas as well as during the implementation of preventive measures.