While nitrogen is the key component of all agricultural production systems, if used inappropriately, it can pollute waters, lead to greenhouse gas emission and further accelerate climate change. The ability to trace nitrogen as it moves through agricultural ecosystems is therefore essential to maximize its use while protecting the environment. Nitrogen-15, a stable isotope of nitrogen, is an ideal tracer. It can be easily measured in soils, plants, water and air to ensure that agricultural practises are environmentally sustainable and that farmers can minimise the quantity they apply.