Fatty acid concentrations in timothy (Phleum pratense L.) and meadow fescue (Festuca pratensis Huds.): Effects of seasonal variations at different nitrogen fertilization levels

Timothy (Phleum pratense L.) and meadow fescue (Festuca pratensis Huds.) were subjected to three different nitrogen (N) fertilization regimes (30+30, 90+90, and 120+90 kg N ha(1); N-30, N-90, and N-120 treatments, respectively) and harvested at three different stages of maturity during spring growth and at two different maturity stages during summer growth. In addition, N-90 plots were sampled on one additional occasion during spring growth and two additional occasions during summer growth. Total fatty acid concentrations and concentrations of the four major fatty acids (C16:0, C18:1n-9, C18:2n-6, and C18:3n-3), which account for 9094 g 100 g(1) of the total fatty acid contents of both grasses, declined over time during both growth periods in both grass species (p < 0.001), irrespective of N-fertilization level. Moreover, the relative proportions of the four fatty acids were affected by the harvest date (p < 0.001); C16:0, C18:1n-9, and C18:2n-6 increased in abundance at later harvest dates, while the opposite was true for C18:3n-3. There were differences (p < 0.05) between timothy and meadow fescue in terms of the concentrations of C16:0, C18:1n-9, C18:2n-6, and C18:3n-3, and in the relative proportions (p < 0.001) of C16:0, C18:2n-6, and C18:3n-3. Meadow fescue contained higher concentrations of C16:0, C18:1n-9, and C18:3n-3, while timothy contained higher concentrations of C18:2n-6. However, the total fatty acid concentrations for both species were similar. The N-fertilization level did not directly affect (p > 0.05) the concentrations or relative proportions of the different fatty acids, but positive linear relationships (p < 0.001) were identified between the concentrations of fatty acids and crude protein. Consequently, there is a scope for adjusting the fatty acid profile and content of forage by changing the grass species used and the time of harvest, with the latter having the greatest influence.