EFFECT OF ORGANIC FARMING PRACTICES ON FIVE ORCHARD SOIL BIO-INDICATORS

The goal of the study was to compare the effects of seven years of conventional and organic fruit production systems on soil biological and mineral properties. The experiment was conducted at Gembloux, Belgium on two adjacent experimental orchards, both planted in 2002 on a flat site with a common cultivation history. The first orchard was managed following organic guidelines and the second one was under conventional management over seven growing seasons. Soil management practices in the organic orchard included additions of composted cattle manure and organic fertilizers and the use of mechanical tillage for weed control. Conventional soil management practices included adding synthetic fertilizers and using herbicides for weed control. Both orchards received different kinds of fungicides. In year 2 (2003), the soil methane oxidation process was measured in order to compare the orchards� soil biological activities. In year 5 (2006), the overall soil microbial activity was assessed by measuring, during five short-term experiments from May to October, the basal respiration (BAS), the substrate-induced respiration (SIR) and the in situ soil CO2 efflux (CDE). Closed-dynamic-chamber systems were used to analyse the soil CO2 efflux in situ in the orchards. In year 5 and 7 (2006 and 2008), earthworm abundance was assessed together with chemical soil parameters. No significant difference in the methane oxidation rate was observed between the two orchard management systems in year 2. In year 5, however, the BAS, SIR and CDE values were higher in the organic orchard than in the conventional one on most sampling dates. Total earthworm abundance was strongly improved by organic practices. Soil mineral analysis and soil pH values did not show important differences between the two orchard management systems.