The Stimulation of Nitrification in an Organically Enriched Soil by Zeolitic Tuff and its Effect on Plant Growing

The adsorption and ion-exchange properties of natural zeolite minerals such as phillipsite, clinoptilolite and mordenite are well studied and these microporous minerals are known to have a high selectivity towards the ammonium ion. Natural zeolites are often found as alteration products of volcanic glass, in deposits of volcaniclastic sediment. In such rocks they are very abundant and commonly exceed 80 percent of the mineral assemblage. Due to their high selectivity towards ammonium ions, rocks containing these minerals can be used to adsorb ammonia from sewage and organic farm waste. It has now been found that a composted mixture of the crushed zeolitic tuff and organic waste will enhance nitrification in soils, when added as an amendment. During composting ammonia, derived from the biological degradation of the organic waste, is adsorbed and ion-exchanged by the zeolite minerals present in the mixture. When added to a soil, nitrification occurs as a result of oxidation of the ammonium ions, first to nitrite and then further to nitrate, together with the production of protons. These reactions were studied in a time-course experiment using the analysis of aqueous leachates taken from untreated and amended soil substrates. Nitrification trends were observed and a linear relationship was found between the electrical conductivity (EC) and the nitrate concentration of the leachates; demonstrating how the ionic mobility of the substrate porewater increases with increase in the degree of nitrification. A comparison of plant growth in substrates without zeolitic tuff with those amended with the organo-zeolitic mixture, showed that plant growth in the amended soil is greatly increased