Availability of the residual nitrogen from a single application of 15N-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 long-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 soil (0-70 cm) and stubble at harvest, mostly in organic form. The present paper follows the fate of this 'residual' N-15 over the following 2 years. Small amounts of 'residual' N-15 were recovered in the following two spring barley crops; 8% in the first and 3% in the second. The overall loss of 'residual' N-15 (i.e. 'residual' N-15 not recovered in crops and soil to a depth 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 quantities of soil organic matter.