Calcium Sulphate versus Lime as Fertilizer Filler: Effects on Ammonium and Nitrate Uptake by Perennial Ryegrass

Abstract

The recovery of ¹⁵N‐labelled nitrogen (N) by perennial ryegrass can be significantly increased by mixing gypsum (CaSO₄ · 2H₂O) into soil rooting medium at rates equivalent to 0.7 t ha^?1. Similar improvements in fertilizer N efficiency might be achieved, at less cost and more conveniently, by applying smaller amounts of CaSO₄ anhydrite more strategically to fertilizer microsites as a fertilizer filler or diluting agent, in calcium ammonium nitrate (CAN), in place of CaCO₃. With this in mind, two complementary pot experiments were conducted under simulated spring conditions in a controlled environment chamber. Use of CaSO₄ as diluting agent, in place of CaCO₃, appreciably enhanced (>30%) the uptake of labeled N by perennial ryegrass plants within the second week of regrowth, but thereafter, because losses of ¹⁵N‐labeled NO₃ ^?‐N from pots by denitrification or leaching had been minimal, plants in both treatments eventually recovered equal amounts of this N form from the soil.