The Physiology of Tall Fescue as Affected by Cutting Height and Nitrogen Application

Livestock farmers in New England struggle with limitations due to land availability when allowing their livestock to graze. There is much discourse on what height tall fescue should be grazed in order to allow for efficient regrowth, and proper nutrition for cattle. There are also differing philosophies on how tall fescue should be grazed. We investigated several different philosophies. In this experiment, tall fescue was grown in a controlled greenhouse environment. There were three grazing treatments regarding height, including 1.5”, 4”, and 6.5”. The fescue was cut three times at these heights. Cutting events were staggered, and plants were grazed when each height treatment separately reached a height of thirty inches. This resulted in the 1.5” plants taking the longest time to regrow, and the 6.5” were the fastest. Nitrogen was applied to half the pots to find if nitrogen fertilizer would allow for more efficient regrowth, and more nutritive value. Nitrogen did allow for greater yield after the 2nd cutting event. The 6.5” plants had the least yield after both cutting events but the most biomass after both cutting events suggesting that grazing tall could allow for more aboveground biomass and less short-term yield. Photosynthesis and plant height values were highest within the 6.5” plants, which could be correlated to the observation that the 6.5” plants having most amount of stored WSC and fructans within their root crowns after the final cutting event as excess photosynthesis results in stored carbohydrates. Photosynthetic parameters such as photosynthesis, chlorophyll, transpiration, and stomatal conductance were lowest in the 1.5” plants suggesting less efficient regrowth. The 1.5” plants also had the lowest regrowth rate after both cutting events. Forage analysis revealed that while the 6.5” plants had the least desirable forage quality results, the results were within acceptable nutrition guidelines as recommended by literature for certain livestock. Grazing tall could be more beneficial to farmers in order to allow for faster rates of pasture turnover due to the improved regrowth efficiency, but there is a tradeoff of less yield and worse RFV. Therefore, since the 4” plants had higher yield and better RFV, that cutting height may be more suited to high energy-requiring livestock, whilst the 6.5” cutting height may be more beneficial for higher grazing frequency and nutrient deficient soil.