Runoff under natural rainfall from small tall fescue catchments in the Georgia Piedmont, United States

Authors: Endale, Dinku; Franzluebbers, Alan; STUEDEMANN, J - Retired ARS Employee; Seman, Dwight; Franklin, Dorcas; Schomberg, Harry

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2013
Publication Date: 11/1/2013
Citation: Endale, D.M., Franzluebbers, A.J., Stuedemann, J., Seman, D.H., Franklin, D.H., Schomberg, H.H. 2013. Runoff under natural rainfall from small tall fescue catchments in the Georgia Piedmont, United States. Journal of Soil and Water Conservation Society. 68(6):474-486.

Interpretive Summary: Over 90% of tall fescue in the USA, the most widely used cool season forage source for pastures and hay fields, is infected with a fungal endophyte. While the endophyte, through production of certain chemicals (alkaloids), gives the plant good agronomic characters such as persistence, competitiveness, summer survival, and yield, the alkaloids on the other hand negatively impact foraging animal health and performance resulting in over $600 million annual revenue loss to the cattle industry. To counter this researchers have developed fescue varieties with no endophyte (hence no alkaloid) or others with endophyte but low level of alkaloid. The impact of these altered varieties on the environment is not known and needs to be investigated. Scientists at the USDA-ARS in Watkinsville GA compared differences in runoff in fourteen 2.5-acre paddocks over 8 years (2002-2010) under the following management schemes. A pair of randomly selected paddocks were assigned one of either broiler litter or ammonium nitrate as fertilizer source, and one of 3 Jesup tall fescue-associations: one that is endophyte infected producing high alkaloid, a second also endophyte infected but producing little alkaloids, and a third that is endophyte free. These 12 paddocks were all grazed. Two more paddocks were assigned to the endophyte infected and low alkaloid fescue and were only hayed and received ammonium nitrate as fertilizer. The study coincided with some of the driest and wettest periods in 74 years (62% receiving below monthly average rainfall). Out of 77 runoff events recorded, 21 occurred during 60 calendar months where monthly rainfall was below average compared to 56 during 37 months of average or above average rainfall. Runoff among paddocks was variable partly due to variability of landscape features. Management treatments had significant effect on runoff. Paddocks fertilized with ammonium nitrate had ~31% greater runoff than those with broiler litter fertilization, but this effect was primarily due to a strong effect with endophyte-free paddocks and no difference between fertilizer treatments in other endophyte associations. No other management effects were significant. Grazed Piedmont pastures of endophyte infected but low alkaloid Jesup tall fescue (MaxQ) fertilized with broiler litter do not appear to pose any additional risk of runoff than more traditionally managed pastures. The findings are useful for cattle producers and personnel from different agencies interested in learning more about the rainfall runoff process. Such long-term data are not easy to come across, especially when they cover very dry and wet periods.

Technical Abstract: The environmental outcomes of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] pastures managed with different levels of endophyte (Neotyphodium coenophialum) infection and alkaloid production are not known. Rainfall-runoff relationships need to be established as a first step in this evaluation. We isolated landscape and management factors controlling rainfall-runoff relationships in fourteen 1-ha paddocks from April 2002 to April 2010 near Watkinsville in the Georgia Piedmont. Two fertilizer sources (inorganic and broiler litter) and three ‘Jesup’ tall fescue-endophyte associations (endophyte infected high alkaloid – Wild; endophyte infected low alkaloid – MaxQ; and endophyte free - Free) were factorially arranged and replicated twice on 12 grazed paddocks. A treatment of hayed MaxQ receiving inorganic fertilizer was imposed on two additional paddocks. The study coincided with some of the driest and wettest years in 74 yr recorded history. Of 77 runoff events, 21 occurred during 60 calendar months where monthly rainfall was below average compared to 56 during 37 calendar months with average or above average monthly rainfall. Runoff among paddocks (geometric mean runoff per event of 1.3 to 5.5 mm) was variable. Spatial variability in landscape attributes within and among paddocks contributed to this variation. Management treatments had significant effect on runoff. Inorganically fertilized paddocks had ~31% greater runoff than those with broiler litter fertilization, but this effect was primarily due to a strong effect with endophyte-free paddocks and no difference between fertilizer treatments in other endophyte associations. No other management effects were significant. Grazed Piedmont pastures with MaxQ tall fescue fertilized with broiler litter do not appear to pose any additional risk of runoff than more traditionally managed pastures. These observations underscore the need for long-term data that capture impacts of weather variability on environmental outcomes.