Effects of nitrogen fertilizer and harvesting stage on photosynthetic pigments and phytol contents of Italian ryegrass silage

Abstract

This study aimed to investigate the effects of nitrogen (N) fertilizer application and harvesting stage on the contents of chlorophyll, phytol and carotenoids (β-carotene and lutein) in Italian ryegrass herbage before and after ensiling, and the extent of phytol preservation after ensiling. Three rates of N fertilizer (0, 60 and 120 kg N/ha) were applied by top-dressing as an additional fertilizer. The herbage harvested at booting stage (27 weeks of age) or heading stage (29 weeks of age) were wilted for 1 day, then ensiled for 60 days using a small-scale pouch system. In the pre-ensiled herbages, increasing N fertilizer application increased the contents of crude protein and photosynthetic pigments, and these contents were also higher at the booting stage compared with the heading stage. In the silage, increasing N fertilizer application also increased the contents of crude protein, the photosynthetic pigments and their derivatives (pheophytin and pheophorbide), while harvesting stage did not affect the contents of β-carotene, chlorophylls or pheophorbide. Nitrogen fertilizer application and early harvesting of herbage increased lutein and phytol contents in Italian ryegrass silage. Lutein and phytol in Italian ryegrass herbage are indicated to be well preserved during ensiling.