Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches

Production was estimated for Aporrectodea spp. and Lumbricus spp. populatio ns in corn agroecosystems with a 5-year history of manure or inorganic fert ilizer applications during 1994-1995 and 1995-1996. Earthworm biomass and p roduction were greater in manure than inorganic fertilizer plots, although biomass and production declined by about 50% between 1994-1995 and 1995-199 6 due to unfavorable climatic conditions. Production was highest during the spring and autumn when soil temperatures were between 4 and 22 degrees C. Production was higher in Lumbricus spp. than Aporrectodea spp, populations due to greater Lumbricus spp. biomass. Aporrectodea spp, production was 3.4 7-16.14 g ash-free dry weight (AFDW) m(-2) year(-1), while Lumbricus spp. p roduction was 6.09-18.11 g AFDW m(-2) year(-1), depending on the fertilizer treatment and the method used to estimate production. However, production estimates from the instantaneous growth rate method were within 27% of the values calculated using the size-frequency method. Nitrogen flux through ea rthworms was used to estimate efficiency quotients. Net production efficien cy (P/A) ranged from 0.64 to 0.76, assimilation efficiency (A/C) ranged fro m 0.1 to 0.3, and gross production efficiency (P/C) ranged from 0.06 to 0.2 2. Annual N flux through earthworm populations was higher in manure than in organic fertilizer plots, and ranged from 2.95 to 5.47 g N m(-2) year(-1) i n 1994-1995 and 1.76 to 2.92 g N m(-2) year(-1) in 1995-1996. The N flux th rough earthworms represented an amount equivalent to 16-30% of crop N uptak e during 1994-1995 and 11-18% of crop N uptake during 1995-1996. We conclud ed that the effects of earthworms on N cycling in corn agroecosystems were substantial, and that N flux through earthworms was influenced significantl y by fertilizer amendments.