EARTHWORM EFFECTS ON SOIL RESPIRATION IN CORN AGROECOSYSTEMS RECEIVING DIFFERENT NUTRIENT INPUTS

Available evidence suggests that earthworms enhance the mineralization of carbon in soil, but there are few data from field experiments that demonstrate that earthworms increase soil respiration under natural e nvironmental conditions. We measured soil respiration (CO2 flux) durin g 1993-1994 in 20-m(2) held enclosures in which earthworm populations had been decreased, increased, or left unmodified (the latter serving as a control). The enclosures were in corn agroecosystems receiving on e of three different nutrients: legume cover crop, cow manure or inorg anic fertilizer (NH4NO3). Soil respiration was measured in the enclosu res by the static diffusion method. Earthworms had significant effects on soil respiration, but their effects varied seasonally and were inf luenced by environmental conditions. There were significant difference s in respiration rates among earthworm treatments on seven of the 24 s ampling dates, and where significant differences did occur, respiratio n rates were greatest in plots with increased populations and lowest i n plots with decreased populations. Most of the significant effects of earthworms on soil respiration were observed during the growing seaso n (June-August) of 1994. A severe drought in the summer of 1993 decrea sed overall respiration rates relative to 1994, and also inhibited ear thworm activity. Soil respiration was significantly greater, during th e growing season, in the organically-amended plots than in plots treat ed with inorganic fertilizer; there were no differences in soil respir ation among nutrient treatments in the autumn or in the spring before amendments were added. Our results show that earthworms had a signific ant influence on soil respiration in the field, but that their influen ce was seasonal, depended on environmental conditions, and was affecte d by temporal patterns in C supply. (C) 1997 Elsevier Science Ltd.