Changes of photosynthetic pigments and phytol content at different levels of nitrogen fertilizer in Italian ryegrass fresh herbage and hay

Abstract

The content of photosynthetic pigments in herbage not only has a strong antioxidant function, but also can improve the health of animals and the quality of livestock products after being ingested by ruminants. Increasing the content of photosynthetic pigments can improve the feed value of herbage, which is of great significance in the process of animal feeding. The experiment aimed to investigate the effect of nitrogen (N) fertilizer levels on the contents of photosynthetic pigments and phytol in fresh Italian ryegrass (IR) herbages and their changes after drying under natural condition over two consecutive seasons. IR variety: Ace (for 2013–2014 season) and Inazuma (for 2015–2016 season) were planted in 3 blocks (4 × 6 m) from two separate fields (≥1 ha), three plots (2 × 2 m) were arranged in each block and three fertilization treatments, control: 0 kg N/ha, 60 N: 60 kg N/ha, and 120 N: 120 kg N/ha, were applied for each block. The results revealed that the crude protein, ether extract, photosynthetic pigments and phytol in IR (fresh herbage and hay) were increased with increasing N fertilizer levels. Photosynthetic pigments decreased obviously by hay preparation (chlorophylls: 40%–70%, phytol: 25%–47%, β-carotene: 72%–90%, lutein: 31%–69%). The decomposition of phytol and β-carotene was not affected by the growing year and N fertilizer levels. However, the decomposition of chlorophyll and lutein was affected by growing year, which was higher in 2014 than that in 2016. Also, the contents of total phytol and lutein of the fresh herbage and hay harvested in 2016 were higher (p < .05) than those harvested in 2014. In conclusion, higher N fertilizer levels could increase the photosynthetic pigments and phytol content in IR fresh herbage which contributes to improving the feed value. However, the content of photosynthetic pigments and phytol in IR hay decreased significantly. IR variety may also affect the nutrient content and their degree of decomposition during drying.