Nitrogen availability from a mature urban compost determined by the 15N isotope dilution method

Land application of city refuse compost (CRC), produced from aerobic-thermophilic composting of the organic fraction of municipal solid wastes, is an attractive alternative for the disposal of these wastes, currently land-filled or incinerated. Knowledge of the availability of N in compost is particularly important, given the current concern about groundwater contamination by NO3--N. In this work we assessed the capacity of a CRC with a high degree of maturity to supply N to a barley crop over 2 months in a controlled-phytotron experiment. The CRC was applied at a rate equivalent to 60 t ha(-1), after incubation of the material (fraction < 2 mm) for 3 months at 24<degrees>C (40-45% moisture). The soil (Eutric Cambisol) was labelled using N-15 as ((NH4)-N-15)(2)SO4 with 9.614 atom% N-15 excess. Available N from CRC dilutes the isotopic N-15/N-14 ratio of the labelled soil in an important way; atom% N-15 excess in the plant material (aerial part) after 2 months was approximately 50% in the compost treatment with respect to the non-amended soil (0.625 and 1.201 atom% N-15 excess, respectively). Accordingly, CRC should not be considered as a poor-release N material when it has a high degree of maturity, i.e. it is highly biologically stabilised and "humified". (C) 2001 Elsevier Science Ltd. All rights reserved.