Short-Term Effects of Mineral and Organic Fertilizer on Denitrifiers, Nitrous Oxide Emissions and Denitrification in Long-Term Amended Vineyard Soils

Short-term effects (i.e., 21 d) of mineral or organic fertilizer application on long-term (i.e., 8 yr of applications) amended soil on denitrifier community abundance, denitrification gene mRNA transcript numbers, denitrification rate, and emissions of N2O were explored. Soil was collected from a vineyard in Italy receiving annual applications of either mineral fertilizer (conventional management system, CS) or municipal compost (organic management system, OS). Each soil was incubated using three treatments: no amendment, NH4NO3, or municipal compost. Microcosms set up with soil treated with compost showed higher nirS, nirK, and nosZ abundance in comparison to conventional fertilization. Short-term compost addition increased nirK gene abundance over time in OS and CS soils, whereas nirS and nosZ gene abundance increased after compost addition only in OS soil. In OS soil, nosZ gene mRNA transcript numbers were higher at all time-points for all treatments compared with CS soil. Furthermore, nosZ gene mRNA transcript number increased over time after compost addition for both soils, N2O emissions were higher in both soils after NH4NO3 addition compared with no amendment and compost addition. Denitrification was higher in OS than CS soil following NH4NO3 treatment. Denitrification rates were much higher than N2O rates in all cases suggesting most emissions occurred as N-2. Our study demonstrated that long-term urban-waste compost application clearly changed soil denitrifier communities and the response of denitrification and N2O emissions to different short-term soil amendments.