Short-Term Response of Soil Microbial Biomass to Different Chabazite Zeolite Amendments

Zeolitites (ZTs) are rocks containing more than 50% of zeolite minerals and are known to be a suitable material for agricultural purposes by improving soil physicochemical properties and nitrogen (N) use efficiency. However, little is known about their effects on soil microbial biomass. This study aimed to evaluate short-term effects of different chabazite-rich ZT (CHAZT) amendments on soil microbial biomass and activity. A silty-clay agricultural soil was amended in three different ways, including the addition of natural (5% and 15%) and NH4+-enriched (10%) CHAZT. Soil dissolved organic carbon (C), total dissolved N, NH4+, NO3-, NO2-, microbial biomass C and N, and ergosterol were measured periodically over 16 d in a laboratory incubation. To verify the microbial immobilization of the N derived from NH4+-enriched CHAZT, a high N-15 source was used for enriching the mineral to measure the microbial biomass delta N-15 signature. An increase in the ergosterol content was observed in the soil amended with 5% natural CHAZT. However, no similar result was observed in the soil amended with 15% natural CHAZT, suggesting that the fungal biomass was favored at a lower CHAZT application rate. In the soil amended with NH4+-enriched CHAZT, microbial biomass N was related to NO3- production over time and inversely related to NH4+, suggesting high nitrification process. Isotopic measurements on microbial biomass confirmed immediate assimilation of N derived from NH4+-enriched CHAZT. These results suggested that the NH4+-enriched CHAZT used in this study supplied an immediately available N pool to the microbial biomass.