Leaching and crop recovery of15N from ammonium sulphate and labelled maize (Zea mays) material in lysimeters at a site in Zimbabwe

The fate of¹⁵N-ammonium sulphate fertilizer that was applied to four lysimeters in the 1990/91 summer was studied over three consecutive growing seasons during which either maize or wheat was grown. Aboveground portions of¹⁵N-labelled maize plants from the first harvest were applied to four other lysimeters at 5 t ha^–1. Two lysimeters in each of the sets of four were assigned a low and a high moisture treatment using irrigation. In both moisture treatments, plant recovery of fertilizer-¹⁵N in the first season was 27% and a further 2% was recovered by plants during the next two seasons. During the second and third seasons, total recovery of¹⁵N by aboveground plant portions from lysimeters that received¹⁵N-labelled maize material was equivalent to 2.5% of applied fertilizer-¹⁵N. This corresponded to ca. 18% recovery of the¹⁵N added in maize material. Leaching of fertilizer-N over the three growing seasons did not exceed 0.3% in total. During the first season, a maximum of 0.25 kg N ha^–1, equivalent to 0.25% of the applied fertilizer-N, was leached in the high moisture treatment. This represented 1.8% of the nitrate load in leachates. Less than 0.002% of the applied fertilizer-N was leached in the low moisture treatment during the first season.