Influence of clinoptilolite and compost on soil properties

Compost from municipal sewage sludge. bark plus zeolite, and zeolite alone were used in this study to evaluate their influence on soil properties and humus characteristics. Two incubation experiments were conducted in two low humus content soils from Bulgaria (Typic Xerochrept) and Greece (Typic Rhodoxeralf). Soil alone, soil with zeolite, and soil with compost in various rates were incubated for 90 days (24 +/- 1degreesC, moisture content about 60% of field capacity). The experimental design was randomized complete blocks with four treatments each replicated four times. At the end of incubation experiment samples were taken., and the basic chemical properties as well as humus composition were determined. The pH, electrical conductivity and NO3-N concentration were determined in samples taken every 15 days. The results showed that zeolite increased soil pH and exchangeable potassium (K). Compost increased available phosphorus (P) in the low P Bulgarian soil and electrical conductivity. A strong positive relationship between electrical conductivity and NO3-N was recorded. Soil pH was negatively correlated with NO3-N concentration for Bulgarian soil. Composted sewage sludge also significantly increased soil organic matter content and led to formation of condensed humic acids.