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R.H. Dowdy

Publications and source records attributed to R.H. Dowdy.

8 recordsLinked to original sources
USGS1998

Effects of farming systems on ground-water quality at the management systems evaluation area near Princeton, Minnesota, 1991-95

Ground-water quality in an unconfined sand and gravel aquifer was monitored during 1991-95 at the Minnesota Management Systems Evaluation Area (MSEA) near Princeton, Minnesota. The objectives of the study were to: (1) describe the effects of three farming systems on groundwater quality, and (2) evaluate the factors affecting ground-water quality and transport of agricultural chemicals at the site. Concentrations of nitrate nitrogen (nitrate-N) in the upper 1 meter (m) of the saturated zone were greatest beneath the two cropped areas having a potato-sweet corn annual rotation (median concentrations of 23 and 22 mg/L). Concentrations of nitrate-N were least beneath a cropped area having a field cornsoybean annual rotation (median of 14 mg/L); another cropped area having the field corn-soybean rotation had similar nitrate-N concentrations to those beneath a cropped area having field corn in consecutive years (continuous corn)(medians of 17 mg/L). Concentrations of atrazine plus metabolites de-ethylatrazine (DEA) and de-isopropylatrazine (DIA), atrazine plus metabolites, were significantly greater during 1994-95 than during 1992- 93 beneath all cropped areas in the upper 1 m of the saturated zone. Concentrations of atrazine plus metabolites during 1994-95 were greatest beneath the continuous corn (median of 1.07 ( μ g/L), intermediate beneath one cropped area with the potato-sweet corn rotation (median of 0.37 μ g/L), and least beneath the other cropped area with the potato-sweet corn rotation, the field corn-soybean rotation, and background areas (medians ranging from 0.11 to 0.21 μ g/L), for which concentrations were not significantly different. Concentrations of atrazine plus metabolites during 1992-93 were mostly similar beneath the different cropped areas and background areas. DEA was the predominant atrazine-metabolite detected in ground water; the average DEA to atrazine ratio was 8.0. The herbicides metribuzin, alachlor, and metolachlor were rarely detected in ground water at trace levels and could not be linked to the MSEA farming systems, with the exception of metribuzin detections during 1993-94 at concentrations of 0.14-1.24 ( μ g/L beneath one cropped area where metribuzin was applied to potatoes. Peak concentrations of chloride and bromide tracers were usually detected in the upper 2 m of the saturated zone 11 to 19 months after application. Peak concentrations of nitrate-N and atrazine plus metabolites were usually detected about 13 to 27 months and 2 years after application, respectively. The estimated proportion of applied nitrogen that reached ground water ranged from about 13 to 50 percent with an average of 30 percent. Differences in the concentrations of nitrate-N in ground water between different cropped areas were related to varying nitrogen application rates, timing of nitrogen application, timing of recharge in relation to crop rotation, and differences in nitrogen uptake by crops. In order of importance, plant uptake and leaching to ground water likely account for most of the nitrogen applied. Denitrification likely is an important mechanism affecting nitrate-N concentrations at depths greater than 2 m below the water table. The proportion of applied atrazine in ground water, detected as atrazine or its metabolites, ranged from 0 to about 1 percent with an average of 0.37 percent. The small proportion of applied atrazine detected in ground water indicates that atrazine was predominantly affected by processes occurring in the soil such as adsorption and degradation. Concentrations of atrazine plus metabolites were related to application rates.

Minnesota↗
USGS1997

Water-quality and hydrogeologic data used to evaluate the effects of farming systems on ground-water quality at the Management Systems Evaluation Area near Princeton, Minnesota, 1991-95

The Minnesota Management Systems Evaluation Area (MSEA) project was part of a multi-scale, inter-agency initiative to evaluate the effects of agricultural management systems on water quality in the midwest corn belt. The research area was located in the Anoka Sand Plain about 5 kilometers southwest of Princeton, Minnesota. The ground-water-quality monitoring network within and immediately surrounding the research area consisted of 73 observation wells and 25 multiport wells. The primary objectives of the ground-water monitoring program at the Minnesota MSEA were to: (1) determine the effects of three farming systems on ground-water quality, and (2) understand the processes and factors affecting the loading, transport, and fate of agricultural chemicals in ground water at the site. This report presents well construction, geologic, water-level, chemical application, water-quality, and quality-assurance data used to evaluate the effects of farming systems on ground-water quality during 1991-95.

Minnesota↗
USGS1995

Effects of 1992 farming systems on ground-water quality at the management systems evaluation area near Princeton, Minnesota

The Management Systems Evaluation Area (MSEA) program was a multiscale, interagency initiative to evaluate the effects of agricultural systems on water quality in the midwest corn belt. The primary objective of the Minnesota MSEA was to evaluate the effects of ridge-tillage practices in a corn and soybean farming system on ground-water quality. The 65-hectare Minnesota MSEA was located in the Anoka Sand Plain near the town of Princeton, Minnesota. Three fanning systems were evaluated: corn-soybean rotation with ridge-tillage (areas B and D), sweet corn-potato rotation (areas A and C), and field corn in consecutive years (continuous corn; area E). Water samples were collected four different times per year from a network of 22 multiport wells and 29 observation wells installed in the saturated zone beneath and adjacent to the cropped areas. Bromide and chloride were used as tracers of water recharged through the cropped areas during 1992. Bromide applied in May 1992 was first detected above background levels between August 1992 and April 1993. Thus, the time of travel of water and bromide moving through the unsaturated zone during 1992 ranged from 3 to 11 months. Chloride applied to area C (sweet corn) in April 1992 was first detected above the residual levels of 1991 chloride applications in April 1993, 12 months after the chemical was applied. Chloride applies to areas A, B, D, and E in April 1992 was not detected above the residual effects from 1991 chloride applications. Nitrogen (N) fertilizer applied in 1992 on area C (potatoes) was first detected above background concentrations and the residual effects of the 1991 farming practices in April 1993, 12 months after application. Effects of 1992 N fertilizer applications on area E (continuous com) generally could not be distinguished from the effects of downgradient of area E were consistently greater than background concentrations during August 1992 through April 1993. These concentrations greater than background levels indicate that some N fertilizer applied to the continuous com crop during 1991 reached the water table. Nitrogen fertilizer applied on areas A, B, and D during 1992 could not be distinguished from the residual effects of the 1991 fanning practices but were detected above background concentrations. Atrazine concentrations beneath the cropped areas were generally indistinguishable from background concentrations. Atrazine was detected in 58 percent of the 361 ground water samples collected beneath cropped and buffer areas during June 1992 through April 1993. Most detections were at trace levels, between the detection limit of 0.01 micrograms per liter ( μ g/L) and the reporting limit of 0.04 μ g/L. De-ethylatrazine (DEA) was detected more frequently during June 1992 through April 1993 (78 percent of the 361 samples) and in greater concentrations than any other herbicide or herbicide metabolite, with a median concentration of 0.07 μ g/L. The maximum DEA concentration of 0.77 μ g/L was detected near the water table in the middle of area E (continuous corn) during April 1993. The likely source of this DEA detection was application of atrazine to area E during 1991-93. Additional data will be needed to conclusively evaluate whether atrazine applied as part of the MSEA farming systems reached the water table. Results indicate that the effects of the 1992 potassium-chloride and N fertilizer applications were reduced compared to the effects of 1991 applications. The most important factors associated with these differences were lower chemical application rates and lower recharge rates during 1992 than during 1991. Some of the chloride and N fertilizer applied to the cropped areas in 1992 likely did not reach the saturated zone in 1993 due to a 60-percent reduction in recharge compared to 1991. Therefore, analysis of data from additional years will be required to fully evaluate the effects of the fanning systems on ground-water quality.

Minnesota↗
USGS1992

Hydrologic research at the Princeton, Minnesota management systems evaluation area

The Management Systems Evaluation Area (MSEA) program is part of a multi-scale, inter-agency initiative to evaluate the effects of agricultural management systems on water quality. The program resulted from the integration of the U.S. Department of Agriculture (USDA) Research Plan for Water Quality and the U.S Geological Survey (USGS) Mid-Continent Herbicide Initiative and is part of the President's Water Quality Initiative. The mid-continental corn belt was selected for study because it is an area where about 60% of the Nation's pesticides and nitrogen fertilizers are used.

Minnesota↗