Organic nitrogen fertilization benefits selected soil fauna in global agroecosystems

Soil fauna plays an essential role in agricultural productivity as it mediates nutrient cycling and soil organic matter dynamics, alters soil physicochemical properties and supports plant growth. Nitrogen fertilization may have a positive or negative influence on soil fauna in a manner that alters ecosystem functioning, but these links have not yet been quantified. We present the results of a global meta-analysis of available literature data on the effects of N fertilization on taxonomic and ecological groups of soil fauna. Our results show that organic N fertilization increases the density of springtails, mites and earthworms, as well as the biomass of earthworms compared to when no fertilizer is applied. The meta-analysis for different nematode feeding groups and ecological categories of springtails and earthworms as well as different mite orders showed that organic fertilization has an overall positive effect on most groups as opposed to inorganic fertilization, which has neutral or negative effects on most groups, alone or in combination with organic fertilizers. Additional meta-analyses showed that the effects of N fertilization on soil fauna depend on the N application rate, on soil texture and on climatic conditions. Our findings suggest that the adoption of less intense farming practices such as organic fertilization combined with site-specific N fertilization regimes is a suitable strategy for protecting and enhancing functional communities of soil fauna.