Effects of Agricultural Practices on Soil Fauna Communities in Kiwifruit Plantations

Kiwifruit is intensively produced in Galicia (NW Spain) by either conventional (CONV) or organic (ORG) farming practices. In the former case, large amounts of chemical fertilizers, pesticides, herbicides and plant growth regulators are applied, whereas the ORG systems rely on natural amendments to minimise the adverse impacts on the environment. Soil fauna play a critical role on soil organic matter transformations and hence, any alteration in the structure of their communities could have important implications for soil fertility. Therefore, in this study, we compared the abundance and diversity of macrofauna (earthworms and macroarthropods) and mesofauna (enchytraeids, mites and collembolans) in organically and conventionally produced kiwifruits crops. Replicate soil samples (PVC cores: 83 cm2 and quadrats: 2500 cm2) were collected from CONV and ORG plots monthly from March 2013 to February 2014 and the soil organisms from each extracted, identified and counted. Results showed that management significantly affected total soil fauna abundances, with a 31% reduction in CONV treatments when compared to the ORG ones. Furthermore, agricultural practices also had a significant effect on the community structure and while earthworms were negatively affected by CONV treatments (76% reduction), mesofauna clearly benefited from these practices. In contrast, the soil communities under ORG systems were less diverse than those under the CONV ones. In conclusion, agricultural practices profoundly affect the numbers and kinds of organisms by altering their densities and the ratios of the different groups. In particular, larger bodied earthworms appeared to be the most sensitive organisms to external agricultural inputs.