Optimizing nitrogen use efficiency of six forage grasses to reduce nitrogen loss from intensification of tropical pastures

Summary

This two-phase field trial evaluated how nitrogen fertiliser type and application rate influence biomass production, nitrogen use efficiency, and nitrous oxide emissions in six tropical forage grass cultivars under Colombian conditions. Phase 1 identified large differences in NUE between cultivars and fertiliser types (ranging from 8.0% to 91.7%), whilst Phase 2 demonstrated that optimised nitrogen rates—20 kg N ha⁻¹ cut⁻¹ for Stargrass and Cayman, 30 kg N ha⁻¹ cut⁻¹ for Mombasa—balanced forage production with reduced N₂O emissions. The findings suggest that matching cultivar choice and fertiliser type can substantially improve nitrogen efficiency and reduce environmental losses in intensified tropical pasture systems.

Regional applicability

This study was conducted in tropical Colombian conditions and may have limited direct applicability to United Kingdom temperate grasslands, which experience different climate, soil types, and pasture species. However, the methodological approach and principles of optimising nitrogen fertiliser type and rate to improve NUE and reduce N₂O emissions are globally relevant and could inform UK pasture management practices, particularly for nitrogen application efficiency and greenhouse gas mitigation strategies.

Key measures

Forage dry matter yield; crude protein content; nitrogen uptake; nitrogen surplus; nitrogen use efficiency (% NUE); nitrous oxide emissions (N₂O); four nitrogen application rates (0, 10, 20, 30 kg N ha⁻¹ cut⁻¹); three fertiliser types (urea, calcium ammonium nitrate, urea-ammonium sulphate)

Outcomes reported

The study measured plant biomass production, crude protein content, nitrogen use efficiency (NUE), nitrogen uptake and surplus, and nitrous oxide (N₂O) emissions across six tropical forage grass cultivars under varying nitrogen fertiliser types and application rates. Results demonstrated that NUE and N₂O emissions varied substantially by grass cultivar and fertiliser type, with optimised application rates minimising emissions whilst maintaining forage production.

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