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.

Keywords:

• Ammonium and nitrate absorption
• calcium effect
• calcium sulphate versus calcium carbonate
• fertilizer filler
• labeled nitrogen
• perennial ryegrass

Acknowledgments

The authors thank Peter Scullion and staff in the Soil and Plant Nutrition Laboratory for analytical support and for assistance with experimental harvests, Michael Nicholson and Tony Poland in the Agricultural and Environmental Science Division for ¹⁵N and mineral N analyses, respectively, Alan Gordon and Erica Chisholm of Biometrics Division for assistance with statistical analyses, and the Department of Agriculture and Rural Development for Northern Ireland for awarding Trevor Kirkpatrick a postgraduate studentship, enabling him to conduct the research.