Evaluating Fertilizer Nitrogen Source and Inhibitors for Gaseous Nitrogen Loss Mitigation and Increased Nitrogen Use Efficiency in Temperate Humid Region Grassland.

Optimizing nitrogen (N) availability for crop growth is critical for productive agricultural systems and for minimizing potential negative economic and environmental impacts associated with N loss from agro-ecosystems. Grass is the largest crop in Ireland comprising 90% of the country’s agricultural area. Granular calcium ammonium nitrate (CAN) is the most widely used straight N source and provides rapidly available nitrate-N (NO₃-N) for plant uptake. However, NO₃-N is vulnerable to leaching and de-nitrification loss pathways. The use of Urea with inhibitors or combinations of CAN and Urea holds potential to improve N use efficiency (NUE) by reducing NO₃-N residence periods in the soil matrix and by synchronizing NO₃-N availability with crop N uptake. A shift towards greater Urea usage brings potential cost and transport savings over CAN. However, a challenge for greater adoption of Urea is potentially increased ammonia-N (NH₃-N) loss via volatilization, loss which contributes to eutrophication in aquatic and low-N input ecosystems through atmospheric transport and deposition. The present study is evaluating the performance of N source (CAN, Urea, and a CAN-Urea combination) and N inhibitor treatments (N-(n-butyl) thiophosphoric triamide and dicyandiamide in combination with Urea) for mitigating NH₃-N and nitrous oxide losses and for improving grassland N use efficiency in the temperate humid climate of Ireland.