A model of nitrogen efficiency in contrasting grass-based dairy systems

Area of Science:

• Agricultural Science
• Environmental Science
• Animal Science

Background:

• Nitrogen (N) efficiency is crucial for sustainable agriculture.
• Dairy production systems face challenges in managing N surplus and losses.
• Ireland's grass-based systems require tailored N management strategies.

Purpose of the Study:

• To develop, evaluate, and validate an N balance model for Irish grass-based dairy systems.
• To assess N use efficiency and N surplus under different production scenarios.
• To predict N losses and identify environmentally sustainable dairy production practices.

Main Methods:

• Utilized a 5-year study dataset for model evaluation and validation.
• Compared grass-based and high-concentrate systems with three Holstein-Friesian (HF) dairy cow genetic strains (HP, HD, NZ).
• Incorporated N requirements for replacement animals into the N surplus calculations.

Main Results:

• Increased concentrate input led to higher N surplus per hectare and decreased N use efficiency (23% and 10% respectively).
• The high-production (HP) genetic strain showed a greater N surplus (156 kg N/cow) compared to HD (140 kg N/cow) and NZ (128 kg N/cow) when replacement animals were included.
• Model-estimated N leaching (8.1 mg NO(3)-N/L) aligned with site-specific measurements.

Conclusions:

• The developed N balance model effectively assesses N use efficiency and surplus in Irish dairy systems.
• Production system intensity (concentrate use) and dairy cow genetics significantly influence N surplus.
• The model provides valuable insights for optimizing N management towards more sustainable grass-based dairy production.