Towards an understanding of the dynamics of compost N in the soil-plant-atmosphere system using [sup.15]N tracer

Aims The principal aim of the present review is to synthesize and evaluate published information on the N fertilizer value of composts, and their effect on the utilization of conventional N fertilizers by crops. Methods We have examined the literature where the dynamics of N in the soil-plant-atmosphere continuum are traced using composts that were either artificially enriched in the [sup.15]N stable isotope (in units of atom% [sup.15]N excess) or had a natural [sup.15]N abundance (5[sup.15]N in units of[per thousand] or per mil) due to isotope discrimination processes that occur during composting. The methods used to produce artificially-enriched composts and to test uniformity of labelling are reviewed. Results Limited data show that composts are generally inferior sources of N for crops compared with their raw materials due to a lower N mineralization capacity. Immobilization of fertilizer N increases in compostamended soils and may reduce recovery by a crop, but fertilizer N losses are reduced overall. However, coapplication of compost and urea should be avoided due to the risk of increased N[H.sub.3] volatilization due to the action of compost-derived urease. High annual rates of compost application can exacerbate environmental problems including nitrate contamination of groundwater. Conclusions Efforts are required to improve the N fertilizer value of composts by minimizing N[H.sub.3] volatilization losses during composting. More attention should also be given to the use of the natural [sup.15]N abundance of compost as a tracer. Keywords Compost * Nitrogen * [sup.15]N * [delta] [sup.15]N * N mineralization * N immobilization * N fertilizers