Fate of fertilizer nitrogen applied to grassland. II. Nitrogen‐15 leaching results

SUMMARY Results are presented from a 3‐year investigation into nitrate leaching from grassed monolith lysimeters treated with double ( 15 NH 4 15 NO 3 ) or single ( 15 NH 4 NO 3 ) labelled ammonium nitrate at three rates, 250, 500 and 900 kg N ha −1 a −1 . Over the 3 years of the experiment, 0.14%, 3.1% and 18.1% of the applied fertilizer was recovered in the leachate at 250, 500 and 900kg N ha −1 respectively. This represented 9%, 39% and 75% of the overall nitrate leaching at the three application rates. A significant proportion of the fertilizer leached as nitrate at the three application rates was derived, via nitrification, from the fertilizer ammonium. Increasing fertilizer applications caused a rise in the leaching of both soil and fertilizer derived nitrogen, although whether the increase reflected a true priming effect was not clear.