Runoff nutrient losses from tall fescue pastures varying in endophyte association, fertilization, and harvest management

Authors: Endale, Dinku; Schomberg, Harry; Franzluebbers, Alan; Seman, Dwight; FRANKLIN, DORCAS - University Of Georgia; Stuedemann, John

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2020
Publication Date: 1/10/2021
Citation: Endale, D.M., Schomberg, H.H., Franzluebbers, A.J., Seman, D.H., Franklin, D., Stuedemann, J.A. 2021. Runoff nutrient losses from tall fescue pastures varying in endophyte association, fertilization, and harvest management. Journal of Soil and Water Conservation. https://doi.org/10.2489/jswc.2021.00164.
DOI: https://doi.org/10.2489/jswc.2021.00164

Interpretive Summary: Tall fescue is an important forage crop cultivated in approximately 37 million acres across the United States. Most is infested with a naturally occurring endophytic fungus Neotyphodium coenophialum (Wild variety) that adversely affects grazing animal performance and productivity associated with certain types of alkaloids the endophyte produces (a disorder referred to as fescue toxicosis).However, the endophyte helps tall fescue tolerate drought, disease, insects, and grazing pressure, thus imparting vigor. Research since the 1970s, when poor cattle performance was first associated with the endophyte, has led to the development of tall fescue varieties that are either endophyte free (Free) or do not have the type of alkaloid that affects animal performance (Novel endophyte). Cattle producers need better information to improve fescue, fertilizer and animal performance while reducing environmental impacts associated with grazing management systems. An eight year study conducted near Watkinsville, GA demonstrated that use of a novel endophyte-associated fescue (MaxQ) had no net negative effect on edge-of-field losses of nitrogen or phosphorus compared with wild endophyte or endophyte-free fescue. Based on this and previous companion results that showed that it poses no additional risk of runoff and has improved stand persistence and average daily gain by cattle, its adoption in the southeastern U.S., regardless of fertilization source, is encouraged. Weather variability had impact on assessed variables. Mean total runoff across all paddocks during above average (27.2%) and average (20.6%) monthly rainfall periods were 15.2- and 1.9-fold greater than that from the below average (52.2%) monthly rainfall period.

Technical Abstract: Tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbysh.] is a widely adopted cool-season perennial forage in southeastern USA. Historically, tall fescue contained a symbiotic fungal endophyte, Epichloë coenophiala, that produces an ergot alkaloid toxic to livestock. New fescue biotypes have been developed that are endophyte free or include endophytes that produce low-toxicity alkaloids. Ecological implications of these biotypes are not fully understood. We evaluated nutrient runoff for three tall fescue biotypes (common, high alkaloid endophyte [wild]; low alkaloid endophyte [novel]; and endophyte free [free]) under two fertilizer sources (broiler litter [BL] and inorganic fertilizer) in grazed systems and a hayed system with inorganic fertilization of endophyte free fescue. The seven treatments were replicated twice on 1.0 ha paddocks near Watkinsville, GA. Grazed paddocks were stocked in September each year with weaned Angus (Bos taurus) heifers (2002-2007) and steers (2008-2009) at rates of ~3 to 6 head paddock-1 adjusted every 28 days to maintain 1 to 3 Mg ha-1 of available forage. Weather conditions varied from very dry to very wet and allowed 15 grazing periods (50 to 198 days). Tall fescue with novel-endophyte association had lower or equal runoff concentrations and loads for inorganic N, TN, ortho-P, and TP than fescue with wild- or free-endophyte association (fescue treatment mean concentrations mg L-1: < 0.8 inorganic N, < 4.0 TN, < 3.5 ortho-P and TP; mean loads kg ha-1: < 0.08 inorganic N, < 0.40 TN, < 0.30 ortho-P and TP; all original untransformed data). This indicates increased adoption of novel-endophyte fescue, as previously recommended, presents no additional risk for nutrient losses regardless of fertilization source. Weather variability had impact on assessed variables. Mean total runoff across all paddocks during above average (27.2%) and average (20.6%) monthly rainfall periods were 15.2- and 1.9-fold greater than that from the below average (52.2%) monthly rainfall period. Nutrient loads also were greater: 3.4-fold (TP) to 14.6-fold (ammonium-N). Pollutant loads in the upper quartile (approximately a third of the overall data) were several fold greater than those from the rest of the data. The presence of cattle increased ortho-P load up to three-fold compared with periods with no cattle.