Negative effects of no-till on soil macrofauna and litter decomposition in Argentina as compared with natural grasslands

No-till (NT) has been recognized as a management system of low environmental impact when applied in combination with crop residue mulch and rotations involving cover crops. It has been suggested, however, that, if these conditions are not met, NT may result in physical, chemical and biological soil degradation. This study evaluates the effect of NT on the litter decomposition process and on soil macrofauna communities and how changes in soil physical, chemical, and physicochemical properties affect litter decomposition and soil macrofauna. We hypothesised (1) that macrofaunal abundance, richness and diversity would be lower in NT soils than in natural grasslands; (2) that this would be a consequence of unfavourable physical and chemical soil conditions and high inputs of agrochemicals; and (3) that these changes in macrofauna would influence soil functioning, reducing litter decomposition rate. The study was conducted during winter and spring 2007 on Typic Haplustolls from southern Córdoba, Argentina (32°41′ and 32°50′S; 63°58′ and 63°44′W). Macrofauna was sampled twice in NT and in natural grasslands (NA) - as a reference situation - by extracting five soil monoliths of 25cm×25cm×30cm at each plot. Soil properties were measured using standard methods. The decomposition rate was determined by the litterbag method, using a 2mm and a 10mm size meshes to evaluate litter decomposition mediated by macrofauna. NT greatly reduced richness (from 33 species in NA to 12 species in NT) and abundance (from 1870ind/m² in NA to 475ind/m² in NT) of macroinvertebrates, confirming our first hypothesis. Changes in macrofauna community under NT were mainly explained by high compaction and low organic matter content, confirming our second hypothesis. The reduction in earthworm abundance may also be explained by the influence of the intense use of toxic agrochemicals. No-till increased surface horizon bulk density (from 1.22 to 1.33g/cm³) and decreased organic matter content (from 3.51% to 2.58%) and pH (from 6.74 to 6.01) compared with NA. The litter decomposition rate was lower in NT, confirming our third hypothesis, and it was correlated with low earthworms abundance and activity. We conclude that in our study area the capacity of soils under NT to maintain ecosystem functions would be at risk.