The residual value of fertiliser N in crop sequences: An appraisal of 60 years of research using 15N tracer

The similarity of the results from more than 100 studies, and a boot strapping analysis, suggested that dilution of the 15N by the large unlabelled mineralisable soil organic N pool compromises the use of the techniques to explore residual uptake of immobilised 15N. The isotope technique does, however, enable researchers to monitor the rate of incorporation of the N into microbial biomass and more recalcitrant organic N forms within the soil organic matter.