Quantifying the contribution of dissolved organic matter to soil nitrogen cycling using 15N isotopic pool dilution

Dissolved organic matter (DOM) has been recognised as a key carbon and nitrogen (N) pool involved with soil-plant-microbe interactions. Yet few studies have quantified this contribution in agricultural soils. In this study we leached DOM from a. sandy loam and sandy clay loam soil under either grassland or arable cropping. Two weeks after DOM removal microbial respiration from soils was not altered. However, a significant (P<0.05) decline in microbial biomass-N, potentially mineralizable-N, gross N mineralization and gross nitrification occurred after leaching. This data illustrate that whilst DOM is a small component of the soil OM it contributed up to 25% of microbial N supply within these agricultural soils. (C) 2004 Elsevier Ltd. All rights reserved.