THE IMPACT OF CROPLAND MANURE APPLICATION ON WATER QUALITY IN SURFACE WATER, DRAIN TILE DISCHARGE AND GROUNDWATER AT A UNIVERSITY DAIRY FARM

The problem of assessing and limiting agricultural impacts on water quality is compounded by high variability associated with soil/sub-soil type, hydrology, climate and farming/livestock practices. Thus, it is important to develop a variety of research sites in different locations to investigate transport pathways, water quality impacts and test the effectiveness of management practices. This talk focuses on investigations at a small research dairy (<250 milking cows) operated by the University of Tennessee. The site includes approximately 100 hectares of low-relief cropland underlain by 3 to 9 m of floodplain deposits (silt and sand, with some gravel layers), which is bounded on two sides by a 4^th order stream (the Little River) and on another side by a state-designated impaired 3^rd order stream (Ellejoy Creek). This talk focuses on the surface water quality response to seasonal applications of liquid manure in the central portion of the floodplain, where a drainage ditch collects surface runoff, drainage tile discharge and groundwater discharge from an area of about 40 hectares of rotational cropland. Water samples were collected from the ditch at 3 locations, from 4 proximate wells and 6 drainage tile discharge locations before and after application of liquid manure. Monitoring began prior to commencement of dairy operations in 2011 and increased in frequency beginning in April 2013. The data set includes 3 manure application events (May 2013, November 2013 and May 2014), each of approximately 2 million liters. The May 2013 application resulted in statistically significant increases in E. coli, Bacteroides and nitrates above background levels in many sampling points. Subsequent applications did not lead to significant increases in these parameters, relative to the fluctuating background levels common at the site. Manure applications were scheduled for periods when weather forecasts indicated a low probability of precipitation. This was intended to reduce runoff-related transport. Depth to the water table varied between different manure application events and this may have influenced fecal indicator parameter transport during/after the May 2013 event. Additional statistical evaluation of the data is underway and monitoring will continue for at least another year.