Nitrogen turnover by earthworms in arable plots treated with farmyard manure and slurry

Abstract

Important studies on the effects ofearthworms on nitrogen turnover have been made by Satchell (1967) in woodland and Syers et al. (1979) in grassland but data are sparse for arable soils. Most arable crops are able to utilize about 70%of the available inorganic N and the balance of their growth requirements must be met from the pool of organic N after mineralization. This study attempts to assess the contribution of earthworms to the turnover of organic N on plots receiving farmyard manure (FYM) or slurry (SLU) in relation to the crops’ N demand. It assumes that the output of mineralizable tissue N from dead worms, or eventually from their predators, is equivalent to the amount produced in new tissue, disregarding cocoon production. Estimates are calculated on an annual basis recognizing that if the system is not in balance, pulses of input and output may not coincide temporally. N output in earthworm faeces, urine and mucus undergoes microbial immobilization and may become partially adsorbed on clay colloids or stable organic matter complexes. Inputs and outputs of these N fractions similarly will vary with, inter alia, different agricultural operations, climate and changes in earthworm population density. To render their analysis less intractable they are nevertheless treated here as being in steady state.