Nitrogen–Potassium Concentrated Complex Fertilizers versus Nitrogen–Potassium Blends: Effects on Potassium Uptake by Perennial Ryegrass

Abstract

It was hypothesized that supplying potassium (K) in concentrated complex fertilizer (CCF) form with nitrogen (N) (NK CCF) to all fertilizer microsites, rather than in NK‐blended fertilizer form to a fraction of the total fertilizer microsites, should enhance the rate of K uptake by perennial ryegrass. Two complementary pot experiments were conducted to test this hypothesis. The results demonstrated that plants fertilized with an NK CCF absorbed K at faster rates than those fertilized with an NK blend and that use of K₂SO₄ in place of KCl as the K source lowered the rate of K uptake by plants regardless of fertilizer form. Form of fertilizer (i.e., CCF or blend), however, had no effect on NH₄ ⁺ or NO₃ ⁻ uptake. Unfortunately, the positive effects of the CCF on K absorption were only manifest during the second 2 weeks of regrowth and did not result in significant improvements in dry matter production by the end of the 5‐week regrowth periods.

Keywords:

• Blended fertilizers
• concentrated complex fertilizers
• perennial ryegrass
• potassium absorption

Acknowledgments

The authors thank Peter Scullion and staff in the Soil and Plant Nutrition Laboratory for analytical support and 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 Clare Purdy 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 do the research.