Effects of Nitrogen Rate and Regrowth Interval on Perennial Ryegrass Fatty Acid Content during the Growing Season

The content of fatty acids (FA) in herbage is important for forage quality and animal-source foods, but there is a lack of knowledge on effects of agronomic practices, and on environmental factors related to seasonal variation in FA concentrations and FA composition. This research investigated the effects of N applications and forage cutting intervals in a factorial combination on FA composition of perennial ryegrass (Lolium perenne L.). The research was conducted during 2 yr that evaluated early, intermediate, and late cutting regimes during various seasons. Positive effects of N application and negative effects of extended regrowth interval on FA concentration and profile were found that appeared to be consistent within periods and years. The total concentration of FA was 32 to 53% higher in spring than in summer, and 18 to 25% higher in autumn than in summer. A positive relationship (P <0.001; r2 = 0.84) between concentrations of total FA and N was observed within and across a wide range of samples. Concentrations of total FA and N were on average 30% higher (P <0.001) in early-cut highly fertilized herbage than in late-cut unfertilized herbage. In generative canopies in late spring, the changes in FA concentration were related to differences in leaf blade proportion (P <0.001; r2 = 0.64). In contrast, in vegetative canopies the changes in FA concentration were associated with seasonal changes in solar radiation and temperature. Overall, applying high rates of N and harvesting perennial ryegrass after short regrowth intervals resulted in higher fatty acid concentrations in herbage.