Availability of the residual nitrogen from a single application of N-15-labelled fertilizer to subsequent crops in a long-term continuous barley experiment

In an earlier paper we presented data from an experiment in which nitrogen- 15-labelled fertilizer was applied in spring to barley on the Rothamsted lo ng-term Spring Barley Experiment, at rates of 48, 96 or 144 kg N ha(-1). A substantial proportion (between 28 and 39%) of this N-15 remained in the so il (0-70 cm) and stubble at harvest, mostly in organic form. The present pa per follows the fate of this 'residual' N-15 over the following 2 years. Sm all amounts of 'residual' N-15 were recovered in the following two spring b arley crops; 8% in the first and 3% in the second. The overall loss of 'res idual' N-15 (i.e. 'residual' N-15 not recovered in crops and soil to a dept h of 70 cm) over the 2 years was 23%. This is equivalent to just 8% of the total N-15 originally applied. There was surprisingly little difference in the behaviour of the 'residual' N-15 in soils containing very different qua ntities of soil organic matter.