Strategies to reduce nitrous oxide emissions from nitrogen fertiliser applied to dryland sorghum. Part 4. Using 15N to discover the fate of N fertiliser

Abstract

Key findings • For three seasons, we applied isotope-labelled urea (15N) to sorghum in small (0.75–1.0 m2) plots, then calculated nitrogen (N) recovery by comparing the amount applied with the total 15N found in grain, crop residues and soil. • Between 55–85% of the N fertiliser applied was recovered at harvest, meaning a 15–45% loss, presumably during wet soil conditions when nitrate denitrification led to N2 and N2O gaseous losses. • In very wet conditions, little of the applied N remained in the soil at harvest, while in a dry season there was more of the applied N found in the soil at harvest than in the plant.