Keith Reid


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One size does not fit all: Toward regional conservation practice guidance to reduce phosphorus loss risk in the Lake Erie watershed
Merrin L. Macrae, Helen P. Jarvie, Roy Brouwer, Grant E. Gunn, Keith Reid, Pamela Joosse, Kevin W. King, Peter J. A. Kleinman, Doug Smith, Mark R. Williams, Martha Zwonitzer
Journal of Environmental Quality, Volume 50, Issue 3

Agricultural phosphorus (P) losses to surface water bodies remain a global eutrophication concern, despite the application of conservation practices on farm fields. Although it is generally agreed upon that the use of multiple conservation practices (“stacking”) will lead to greater improvements to water quality, this may not be cost effective to farmers, reducing the likelihood of adoption. At present, wholesale recommendations of conservation practices are given; however, the application of specific conservation practices in certain environments (e.g., no-till with surface application, cover crops) may not be effective and can even lead to unintended consequences. In this paper, we present the Lake Erie watershed as a case study. The Lake Erie watershed contains regions with unique physical geographies that include differences in climate, soil, topography, and land use, which have implications for both P transport from agricultural fields and the efficacy of conservation practices in mitigating P losses. We define major regions within the Lake Erie watershed where common strategies for conservation practice implementation are appropriate, and we propose a five-step plan for bringing regionally tailored, adaptive, and cost-conscious conservation practice into watershed planning. Although this paper is specific to the Lake Erie watershed, our framework can be transferred across broader geographic regions to provide guidance for watershed planning.


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Contribution of preferential flow to tile drainage varies spatially and temporally
William T. Pluer, Merrin L. Macrae, Aaron Buckley, Keith Reid
Vadose Zone Journal, Volume 19, Issue 1

Tile drainage of agricultural fields is a conduit for nutrient losses. Preferential flow in the soil can more directly connect surface runoff with tile drainage compared with matrix flow, which may also increase P losses. In this study, water temperature was monitored in surface runoff and tile drainage and electrical conductivity (EC) was measured in tile drainage at two sites in southern Ontario with different soil types (i.e., clay and loam). These data were used to estimate the percentage of preferential flow in tile drainage based on end member mixing. Estimates using temperature were compared with estimates using EC, and both were evaluated across seasons and hydrographs and compared with P concentration and load data. There was strong correlation (r = .83) between estimates of preferential flow using the two methods, but due to variability in surface temperatures, EC provided a less flashy estimate for preferential flow (Durbin–Watson statistics of 0.34 for temperature and 0.09 for EC). Preferential flow accounted for a higher percentage of tile drainage flow in clay soil than loam, but percentages were not significantly different between seasons or timing within events. Phosphorus concentrations and loads were weakly correlated with preferential flow, suggesting that P transport was influenced by other factors as well. Although further work is necessary to calibrate these methods for estimating preferential flow from continuously monitored temperature and EC, this technique can be applied to already collected data to model and test posited explanations of observed phenomena in P, other nutrients, and water transport from tile‐drained agricultural land.


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Nutrient Loss in Snowmelt Runoff: Results from a Long‐term Study in a Dryland Cropping System
Kimberley D. Schneider, B.G. McConkey, Arumugam Thiagarajan, J. M. Elliott, Keith Reid
Journal of Environmental Quality, Volume 48, Issue 4

Snowmelt runoff often comprises the majority of annual runoff in the Canadian Prairies and a significant proportion of total nutrient loss from agricultural land to surface water. Our objective was to determine the effect of agroecosystem management on snowmelt runoff and nutrient losses from a long-term field experiment at Swift Current, SK. Runoff quantity, nutrient concentrations, and loads were estimated after a change in management from conventionally tilled wheat ( L.)-fallow (Conv W-F) to no-till wheat-fallow and subsequently no-till wheat-pulse (NT W-F/LP) and to an organic system with a wheat-green manure rotation (Org W-GM). The conversion from conventional tillage practices to no-till increased snowmelt runoff likely due to snow trapping by standing stubble after summer fallow. Relatedly, runoff after no-till summer fallow had higher dissolved P losses (0.07 kg P ha). Replacing summer fallow with a pulse crop in the no-till rotation decreased snowmelt runoff losses and nutrient concentrations. The Org W-GM treatment had the lowest P loss after stubble (0.02 kg P ha) but had high dissolved P concentrations in snowmelt following the green manure (0.55 mg P L), suggesting a contribution from incorporated crop residues. In this semiarid climate with little runoff, dissolved reactive P and NO-N loads in snowmelt runoff were smaller than those reported elsewhere on the prairies (averaging <0.05 kg P ha yr, and <0.2 kg NO-N ha yr); however, the nutrient concentrations we observed, in particular for P, even without P fertilizer addition for organic production, question the practicality of agricultural management systems in this region meeting water quality guidelines.