Towards identifying the fate of15N applied in spring as ammonium nitrate fertiliser to a kikuyu pasture

Abstract

Abstract Nitrogen was applied as ammonium nitrate in solution to kikuyu pasture at 225 kg N ha‐1, split into three equal dressings and applied in October, December and February. The first, at 75 kg N ha‐1 was labelled in the ammonium ion and the latter two dressings were not labelled. Herbage, soil and roots were sampled monthly to determine the proportions of the labelled N in the herbage, root and soil over the season. Total 15N recovered over the season, as a percentage of that applied as 15NH4NO3, was 99.0%. A total of 52.1% of the labelled N was recovered in the herbage over the season, the highest recovery being in November. Recovery rates declined from November through to March. However, the accumulated recovery of 15N was curvilinear over the season. The recovery rate of 15N in the roots was lower than in the herbage, and the highest percentage recovered was in December. The 15N recovered, as a percentage of that applied, in the soil depth classes showed similar trends. The highest percentage of I...