Jk. Whalen et Rw. Parmelee, Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches, OECOLOGIA, 124(4), 2000, pp. 561-573
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.