Extensive organic farming enhances soil macrofauna abundance in Humid Pampa, Argentina

DOMÍNGUEZ, A.; BEDANO J.C.; BECKER, A.

Coimbra

Congreso; XVI International Colloquium on Soil Zoology; 2012

In last years, organic farming has arisen as an alternative to conventional agriculture which has produced a high level of soil degradation. However, evidences about benefits of organic agriculture on soil biota are still scarce, especially in extensive organic systems and in comparison with no‐till system, which has been stated as another possible alternative with low environmental impact. The aim of the present study was to assess the effect of different agricultural management on soil macrofauna. Three farming systems were studied: organic farming with conventional tillage and occasional grazing (ORG), conventional farming with agrochemical use under conventional tillage (CT) or under no tillage (NT). Natural grasslands (GR) were included as reference situation. Macrofauna was sampled by digging five soil monoliths that were hand sorted to extract all macroinvertebrates present. Total macrofauna abundance was significantly higher in GR with respect to the agricultural systems, confirming the general negative impact of agriculture on soil biota. ORG supported significantly higher abundances than the two variants of conventional agriculture, which did not differ from each other. Beetles and earthworms were analyzed separately. Beetle abundance did not differ between GR, ORG and CT, but was significantly less abundant on NT. Nevertheless, the abundance of detritivorous beetles showed a clear gradient GR>ORG>NT>CT. Also earthworm showed significantly higher abundances in ORG, therefore it can be concluded that organic agriculture foster decomposer macrofauna, and consequently would enhance decomposition, a key ecological process. These results confirm expected benefits of organic farming not only in the frame of smallholder agriculture (where low tillage intensity and high crop diversity are common practices) but in extensive agriculture where organic practices are limited to avoid using synthetic pesticides and fertilizers. More unexpectedly, here we show that no tillage may not assert benefits for macrofauna and even could have a strong negative effect on its abundance. Thereby, soil functions and ecosystem services that depend on macrofaunal activity would be enhanced in organic agriculture and attenuated in conventional agriculture, both under conventional or no tillage