Effect of pasture renewal and nitrogen fertilization on dry matter yield and feed quality of perennial ryegrass-white clover swards under temperate dairy systems

Abstract:

A two-year field experiment was conducted at the Lincoln University Pastoral Research Farm, Canterbury, New Zealand, during 2023-2025 to evaluate the combined effect of pasture renewal and nitrogen fertilization on Dry Matter (DM) yield and feed quality of perennial ryegrass-white clover swards. A split-plot design with two pasture conditions (renewed and unrenewed) as main plots and five nitrogen levels (0, 50, 100, 150 and 200 kg N ha⁻¹ yr⁻¹) as subplots, replicated thrice, was followed. Renewed swards consistently outperformed unrenewed swards, yielding 10.2 to 16.9 t DM ha⁻¹ against 7.8 to 12.7 t ha⁻¹ in unrenewed plots. Crude protein in renewed plots was 2.5 to 2.8 percentage points higher, while metabolisable energy was elevated by 1.0 to 1.2 MJ kg⁻¹ DM. White clover content declined from 28.4% at 0 kg N to 11.6% at 200 kg N ha⁻¹ in renewed swards. Apparent nitrogen use efficiency fell from 48 to 34 kg DM kg⁻¹ N in renewed swards as nitrogen rose from 50 to 200 kg N ha⁻¹. The findings indicate that pasture renewal combined with moderate nitrogen application of 100 to 150 kg N ha⁻¹ yr⁻¹ offers the optimum balance between productivity, forage quality and legume persistence under temperate New Zealand dairy systems.