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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #213409
Title: HYDROLOGY AND GROUNDWATER NUTRIENT CONCENTRATIONS IN A DITCH-DRAINED AGRO-ECOSYSTEM

Author
item Vadas, Peter
item SRINIVASAN, M - INVERMAY AGRIC CENTRE
item Kleinman, Peter
item Schmidt, John
item ALLEN, ARTHUR - UNIV OF MARYLAND EASTERN

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2007
Publication Date: 8/1/2007
Citation: Vadas, P.A., Srinivasan, M.S., Kleinman, P.J., Schmidt, J.P., Allen, A.L. 2007. Hydrology and groundwater nutrient concentrations in a ditch-drained agro-ecosystem. Journal of Soil and Water Conservation. 62(4):178-188.

Interpretive Summary: Loss of nitrogen (N) and phosphorus (P) from agricultural fields is a major water pollution concern for the Chesapeake Bay. Even though movement of N and P in groundwater from fields to open drainage ditches is an important loss pathway, it has not been studied well enough for us to understand how to control it. We monitored hydrology and groundwater N and P concentrations in 26 shallow wells for 27 months on a heavily ditched, poultry-grain farm on Maryland's Lower Eastern Shore. Hydrology data showed that groundwater flows continuously to deep ditches, but to shallow ditches only when water tables are high. Data showed N readily moves in groundwater throughout the farm in environmentally significant quantities. Very high P concentrations were often measured in groundwater, but only in areas of both high concentrations of soil P and high water tables. When soil P concentrations were less or groundwater flowed through deep subsoils, groundwater P movement was more restricted. Therefore, limiting soil P accumulation in near-ditch zones may help reduce P delivery to shallow ditches. Increasing the length of groundwater flowpaths through low-P subsoils may help reduce P delivery to deep ditches. Overall, however, data show these commonly occurring farms represent significant sources of N and P to the Chesapeake Bay.

Technical Abstract: Loss of nitrogen (N) and phosphorus (P) from agricultural fields is a major water pollution concern in the Chesapeake Bay watershed. Even though movement of N and P in groundwater from fields to commonly occurring open drainage ditches is an important loss pathway, it has not been studied well enough for us to understand how to control it. We monitored hydrology and groundwater N and P concentrations in 26 shallow (~3 m) wells for 27 months on a heavily ditched, poultry-grain farm on Maryland's Lower Eastern Shore. Hydrology data showed groundwater flows continuously to deep ditches, but to shallow ditches only when water tables are high. Water tables frequently perched on top of subsoil clay horizons. Although perching persisted only 24 to 48 h, N and P transport could be accelerated if rapid, lateral movement of water to ditches occurred. Frequent and widespread concentrations of groundwater NO3-N greater than 10 mg L-1 show that significant subsurface N loss from the farm is probable. Very high concentrations of dissolved P often existed in groundwater, but only in areas of both high concentrations of soil P and high water tables. In these areas, rain infiltrating through topsoils mobilized soil P into groundwater and moved considerably high concentrations of P as deep as 1.5 m, where elevated P concentrations persisted for several days. In areas where soil P concentrations were less or groundwater flowed through deep subsoils, groundwater P movement was apparently more restricted. Thus, limiting soil P accumulation in near-ditch zones may help reduce P delivery to shallow ditches, and increasing the length of groundwater flowpaths through low-P subsoils may help reduce P delivery to deep ditches. Overall, however, data clearly show these commonly occurring types of farms represent significant sources of N and P to the Chesapeake Bay.