Relationship between microbial community properties and nitrogen mineralisation in soils after amendment with two forms of nitrogen

Abstract

Microbial diversity in soils is considered important for maintaining sustainability of agricultural production systems. However, the links between microbial diversity and ecosystem processes are not well understood. This study was designed to gain better understanding on the effect of farm management practices on the microbial community and key soil processes. Two soils with organic and conventional management histories that had similar fertility levels were amended with equal amounts (100 kg/ ha) of nitrogen in organic (as lupin (Lupinus angustifolius L.)) and mineral form (urea). Over 91 days, microbial biomass C and N, dehydrogenase enzyme activity, community structure of eubacteria and actinomycetes (by PCR-DGGE) and gross N mineralisation were measured. The addition of lupin stimulated the microbial community, resulting in an increase in microbial biomass and enzyme activity in both soils, while urea and control treatments were not significantly different from each other. Microbial community structure was more strongly influenced by substrate availability rather than by the form of fertiliser (lupin or urea); however, the effects were not sustained over time. No direct relationship existed between microbial structure, enzyme activities and N mineralisation, and that microbial community structure was more strongly influenced by inherent soil and environmental factors than by short-term management practices. The findings indicate that amendment with green manures improved soil biology irrespective of management history, that no direct relationship existed between microbial structure, enzyme activity and N mineralisation, and that microbial community structure was more strongly influenced by inherent soil and environmental factors than by short-term management practices.