Fertilizer Nitrogen Source and Inhibitor Approaches for Sustaining Agronomic Productivity and Mitigating Nitrous Oxide Emissions in Intensively Managed Grassland.

Addition of inorganic fertilizer N to agricultural soils is a cornerstone of many intensive agricultural systems. Fertilizer N allows for targeted supplementation of the mineralized pool of soil nitrogen and potentially optimized crop productivity, which feeds a growing global population. However, environmental degradation at national and global scales is linked to N fertilization related nitrous oxide emissions from agriculture. Consequently, strategies which sustain productivity and mitigate nitrous oxide losses are needed.     

In Ireland 90% of the country’s agricultural area is dedicated to grassland. Currently the majority of the supplemental inorganic fertilizer N is applied through granular ammonium nitrate based fertilizers, fertilizers which provide rapidly available nitrate for plant uptake but which also prime the soil system for nitrous oxide loss via de-nitrification.

The current study is assessing two approaches for mitigating nitrous oxide loss potential and sustaining agronomic productivity a) fertiliser nitrogen source i.e. urea, ammonium nitrate, and urea ammonium nitrate based fertilizer N and b) urea in combination with either a urease inhibitor (N-(n-butyl) thiophosphoric triamide), or a nitrification inhibitor (dicyandiamide), or both inhibitors.  

Initial results show that nitrous oxide fluxes followed a trend calcium ammonium nitrate > urea with urease inhibitor > urea > urea with nitrification inhibitor/urea with both inhibitors. Results to date indicate that specific urea inhibitor combinations show promise for sustaining productivity and mitigating nitrous oxide losses from intensively managed grassland.