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Practices to reduce nitrate-nitrogen losses from drained agricultural lands

by (Michael Reed), 1970- Burchell

Abstract (Summary)
BURCHELL II, MICHAEL REED. Practices to Reduce Nitrate-Nitrogen Losses from Drained Agricultural Lands. (Under the direction of Dr. R. Wayne Skaggs). Two practices were studied to reduce nitrate-nitrogen (NO3--N) losses from drained agricultural lands - shallow subsurface drainage systems and in-stream constructed wetlands. Twenty-one months (January 2001-September 2002) of data was collected from two drainage systems located in a swine waste application field with a bermuda/rye grass rotation at the NCDA – Tidewater Research Station near Plymouth, NC. Drains in Plot 1 were 1.5 m deep and 25 m apart, while the drains in Plot 2 were 0.75 m deep and 12.5 m apart. Decreased drain depth reduced drainage outflows by 42% during the study. Nitrate-nitrogen concentrations in groundwater at the 90-120 cm and the 150-180 cm depth were significantly lower in Plot 2 (22.9 and 0.1 mg/L respectively) than in Plot 1 (39.1 and 15.5 mg/L respectively) in 2002. This difference was most likely a result of higher water tables and a larger reduced zone formed with the shallow drainage system, which increased denitrification potential. However, the average NO3--N concentration in the drainage water from the shallower drains (7.6 mg/L) was significantly higher than in the deeper drains (2.4 mg/L) in 2001. In 2002, there was no significant difference in the average NO3--N concentration in the drainage water from the shallow drains (15.7 mg/L) and the deeper drains (12.8 mg/L). On average, NO3--N export from the shallow subsurface drains was 8 kg/ha in 2001 and 27 kg/ha in 2002. Nitrate export from the deeper drains was 6 kg/ha in 2001 and 37 kg/ha in 2002. During the entire study, an average of 8 kg/ha less NO3--N was exported from the shallow subsurface drainage system. Decreased export observed in 2002 from the shallow subsurface drainage system was significant at the 10% level, but not for the entire 21-month period. Lack of significant difference in export between the drainage systems was most likely due to a lack of long-term data collection, a reduced number of drain flow/water quality observations (only 3 drains per plot), and possible low application of swine waste on one area of the deeper drainage plot. To evaluate the long-term effect of installing shallow subsurface drainage systems, the model DRAINMOD was calibrated with these field observations. The results of these simulations indicated that shallow drains would reduce drainage outflows by 23% at this site. Using the observed average NO3--N concentrations in the drainage water at this site in 2002, the total mass of NO3--N exported could be reduced by as much as 16%, or nearly 11 kg/ha-yr, by installing shallow subsurface drains at this site. The second study consisted of a wetland mesocosm experiment to determine if organic matter (OM) addition to soils used for in-stream constructed wetlands would increase NO3--N treatment. Not all soils are suitable for wetland substrate, so OM addition can provide a carbon and nutrient source to the wetland early in its development to enhance denitrification and biomass growth. Eight batch studies, with initial NO3--N concentrations ranging from 10-120 mg/L, were conducted in 2001 and 2002 in 21 surface-flow wetland mesocosms. The results indicated that increasing the organic matter content of a Cape Fear Loam soil from 5% to 11% enhanced NO3--N wetland treatment efficiency in 7 of the 8 batch studies, but increases to 16% OM did not. Wetlands constructed with dredged material from the USACE Eagle Island Confined Disposal Facility in Wilmington, N.C., with initial OM of 12%, showed no improvement in NO3--N treatment efficiency when increased to 18%, but did show increased NO3--N treatment efficiency in 7 of the 8 batch studies when increased to 22%. Increased OM additions to the Cape Fear soil increased biomass growth in the wetlands in 2001, but not in 2002. Increased OM additions to the dredged material had no affect on biomass growth in the wetlands in either year. Results of this research indicate that increased OM in the substrate will reduce the area required for in-stream constructed wetlands to treat drainage water in humid regions. It also serves as a demonstration of how dredged material can be used successfully in constructed wetlands, as an alternative to costly storage by the USACE. Practices to Reduce Nitrate-Nitrogen Losses from Drained Agricultural Lands By Michael R. Burchell II A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Biological and Agricultural Engineering Department Raleigh 2003
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School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:north carolina state university

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