Waste Management Systems for Loafing Areas in Dairies

Waste Management Systems for Loafing Areas in Dairies

Summary

Dairy loafing areas present unique waste management problems that are not being addressed under present farm practices. These unpaved areas leading to milking barns have high animal densities and can be a source of contaminated surface runoff and subsurface leachate to groundwater. We have been studying an innovative waste management system recently installed in the participating farmer’s loafing area in Putnam County, Georgia, that will capture surface and subsurface flow in a gravel-covered geotextile fabric and buried subsurface drains and route this to a lagoon. The drains were installed under half of the loafing area so comparisons can be made with soil sampling, ground electromagnetic inductance measurements, and groundwater sampling to determine if the drains or gravel and liner significantly reduce nitrate leaching.

Therefore, the overall objective of this study was to install and test a pilot system of buried drains and gravel-covered surface geotextile fabric in the loafing areas of a participating farm to capture runoff and subsurface losses of nitrogen and phosphorus and route these to a lagoon.

Approach
The loafing system was installed on a farm in Putnam County, Georgia, during the month of December 1994. The area was fenced by late spring and an initial electromagnetic survey (EM) was conducted June 1995. A second EM survey was conducted on September 1996 and additional surveys are planned as a long-term effort to monitor the development of surface and any possible groundwater contamination from manure deposition on this loafing lot.

Monitoring equipment was installed to measure surface runoff and subsurface drainage. Surface and subsurface drainage are routed first to a settling basin, which then drains to a lagoon. Four-inch perforated drain lines were placed on 25 ft centers at approximately 3 ft depths on half of the loafing area. They combine into a main drain line that is routed to a 5 ft diameter culvert placed outside the lower end of the loafing area. A central slot takes a subsample of flow to a small reservoir that is pumped by a sampler at times based on flow. Samples are stored in an automated refrigerated sampler until retrieval for analysis.

For subsurface flow, the two halves of the loafing area are separated by a gravel trench that diverts flow from the non-tile drained side away from the tile drains. At the time of establishment approximately 240 background soil samples were taken incrementally to 2 m to determine initial soil inorganic and organic N levels. After a year of operation, nitrate, ammonia and soluble phosphorus in runoff was compared to nutrient content of surface soil samples.

Results
Three rainfall runoff events captured by the monitoring equipment suggest that very little of the water (less than 0.5 percent of the total rainfall) is infiltrating to the tile drains. This result suggests that most of the nitrogen and phosphorus being lost from this field is being lost as surface flow rather than subsurface flow. In spite of this, less than 5 percent of the estimated manure nitrogen being deposited on the surface of the loafing lot could be accounted for in this short one-and-a-half-year monitoring time. A definitive mass balance will likely require several more years of monitoring.

The EM survey results show little change over this time period. It is seen on the tile drain side that there is a spot in the center that has lower conductivity values that has developed over the period of study. On the non-tile side there is an area of higher values that has developed over this same period. This could possibly indicate a removal of solute by the tile drain and an accumulation of ions on the non-tile side. The individual soil chemical analysis produced a large standard deviation and cannot be used to confirm or deny this observation at the current time.

Impact of Results
At this point the results suggest that the geotextile fabric is significantly intercepting the water flow and moving it to the surface outlet under the surface of the gravel. Less than 0.5 percent of the rainfall is found to infiltrate below the fabric to the tile drains. At this rate and, concentration of nitrate observed in the tile drainage, contamination of subsurface water at nitrate concentrations and depths observed from previous EM surveys of other dairy sites would require in excess of 300 years.

Since the subsurface of these previous sites was contaminated in only 10-20 years, this result strongly supports the use of the gravel covered geotextile fabric as a groundwater protection device. The tile drainage system does not appear to be necessary since so little water in reaching it. Data will continue to be gathered over a three- to four-year period to confirm these results. However this first year's data strongly suggest that a gravel covered geotextile fabric delivering surface runoff to a lagoon can significantly lessen pollutant loading to the groundwater.

This project enabled us to establish a test plot to verify the usefulness of the technique of subsurface drain lines and surface geotechnical fabric with gravel in reducing phosphorus and nitrogen losses from dairy loafing lots to surface and groundwater.

The first year's data suggest that differences in surface nutrient accumulation are only just beginning to be apparent. Investigators at the University of Georgia and Clemson University will continue to monitor the development of nutrient profiles in the soil and water and nutrient concentrations discharged from this loafing lot over the next three years. It is expected that three to four years of operation will be required before a statistically valid accounting of nitrogen accumulating in the surface and subsurface can be made.

December 1996.