In a preceding study, converting conventional tillage (ConvT) to conservation tillage (ConsT) was reported to decrease nitrogen (N) but to increase phosphorus (P) losses during snowmelt runoff. A field-scale study was conducted from 2004 to 2012 to determine if conversion of ConsT to rotational tillage (RotaT), where conservation tillage was interrupted by a fall tillage pass every other year, could effectively reduce P losses compared with ConsT. The RotaT study was conducted on long-term paired watersheds established in 1993. The ConvT field in the pair has remained under ConvT practice since 1993, whereas tillage was minimized on the ConsT field from 1997 until 2007. In fall 2007, RotaT was introduced to the ConsT field, and heavy-duty cultivator passes were conducted in the late fall of years 2007, 2009, and 2011. Runoff volume and nutrient content were monitored at the edge of the two fields, and soil and crop residue samples were taken in each field. Greater soil Olsen P and more P released from crop residue are likely the reasons for the increased P losses in the ConsT treatment (2004-2007) relative to the ConvT treatment (2004-2007). Analysis of covariance indicated that, compared with ConsT (2004-2007), RotaT (2008-2012) increased the concentrations of dissolved organic carbon (DOC) by 62%, total dissolved N (TDN) by 190%, and total N (TN) by 272% and increased the loads of DOC by 34%, TDN by 34%, and TN by 60%. However, RotaT (2008-2012) decreased soil test P in surface soil, P released from crop residue, and duration of runoff compared with ConsT (2004-2007) and thus decreased the concentrations of total dissolved P (TDP) by 46% and total P (TP) by 38% and decreased the loads of TDP by 56% and TP by 42%. In the Canadian Prairies, where P is a major environmental concern compared with N, RotaT was demonstrated to be an effective practice to reduce P losses compared with ConsT.
Small dams and associated reservoirs have notable effects on soil and water dynamics in prairie streams. In this study, we developed a simulation module of small dams in the soil and water assessment tool (SWAT) to evaluate their long-term effects on stream flow and water quality at a watershed scale. To overcome the challenges in characterizing small storage and short retention time in small reservoir routing, concepts of equivalent reservoir storage and equivalent reservoir discharge are applied by which the average daily storage and daily discharge of the small reservoirs are calculated. Accordingly, the sediment deposition and nutrient abatement within the reservoir are computed using available SWAT routines. The effects of small dams in reduction of daily peak flow, sediment, and nutrient loads at the watershed outlet are obtained by summing the effects of all small dams within the watershed considering both reservoir and channel processes. The model is applied to the 74.6-km2 South Tobacco Creek watershed located in Southern Manitoba of Canada. A total of 26 small dams exist in the watershed with surface area ranging from 0.002 to 0.492 km2 and storage capacity from 3,380 to 642,000 m3. The simulation results show that the combined effect of these small dams can reduce daily peak flow by 0–14% at the watershed outlet depending on climate and initial reservoir storage conditions. The estimated average annual sediment, total nitrogen and total phosphorus reductions at the watershed outlet are about 4.51, 3.59, and 2.96%, respectively. However, the on-site effects of individual small dams are much higher depending on its size, location, shape, drainage area, and land use compositions in the contribution area. The simulation results also show that snowmelt-flooding events have higher reduction amounts but lower relative reduction rates compared to rainfall storm events and the back-flood small dams have greater impact on sediment, nitrogen, and phosphorous abatement followed by multipurpose small dams and dry dams in the study watershed.
Beneficial management practices (BMPs) are designed to minimize environmental impacts and provide on- and off-farm benefits such as improved farm economics and enhanced water quality for domestic consumption, recreation and healthier aquatic ecosystems. Adoption of BMPs depends on the willingness of producers to implement them and on producer capacity to finance the investment. The Watershed Evaluation of Beneficial Management Practices (WEBs) project was initiated in 2004 under Agriculture and Agri-Food Canada (AAFC) to investigate water quality issues and economics related to agricultural production. The project selected nine watersheds across the country where BMPs were implemented to determine the effect on water quality in terms of nutrients, pathogens and sediment and on-farm economics. The South Tobacco Creek (STC) watershed, located in southern Manitoba, was one of the nine watersheds selected. Several BMPs were investigated in STC, including land management changes, the use of small dams and retention ponds to control the runoff from livestock yards from entering the water ways. The objective of the WEBs STC economics component was to assess on-farm economic costs and to identify and assess potential on-farm and off-farm benefits of applying the selected BMPs. The STC economic results have shown that some of the BMPs tested contribute positively to improved farm economics and financial returns but there are some BMPs whose revenues will not fully offset BMP costs. Certain off-farm benefits resulting from BMP implementation have also been identified. Reduced tillage BMP was shown to have significant benefits to producers based on combined experimental and model results. For the small dam/reservoir BMP the net present value based on only flood damage control was shown that the financial payback period can be less than 35 years. Significant additional potential benefits in terms of irrigation, sediment and nutrient entrapment, and recreational activities have also been determined. For land conversion to forage BMP, the cost saving of inclusion of forage to annual crop rotation was not enough to compensate the loss of opportunity through the loss of net income in annual crops. Similarly, the farm benefit of the holding pond which built to capture run-off from an upstream winter cattle containment area was not enough to justify its instalment cost, although nutrients, sediment and pathogens export (off-farm benefits) were reduced significantly. The STC research provided producers, governments, and watershed groups with credible information that can be used to promote adopting and maintaining BMPs.
A long-term, field-scale study in southern Manitoba, Canada, was used to identify the critical factors controlling yearly transport of nitrogen (N) and phosphorus (P) by snowmelt runoff. Flow monitoring and water sampling for total and dissolved N and P were performed at the edge of field. The flow-weighted mean concentrations and loads of N and P for the early (the first half of yearly total volume of snowmelt runoff), late (the second half of yearly total volume of snowmelt runoff), and yearly snowmelt runoff were calculated as response variables. A data set of management practices, weather variables, and hydrologic variables was generated and used as predictor variables. Partial least squares regression analysis indicated that critical factors affecting the water chemistry of snowmelt runoff depended on the water quality variable and stage of runoff. Management practices within each year, such as nitrogen application rate, number of tillage passes, and residue burial ratio, were critical factors for flow-weighted mean concentration of N, but not for P concentration or nutrient loads. However, the most important factors controlling nutrient concentrations and loads were those related to the volume of runoff, including snow water equivalent, flow rate, and runoff duration. The critical factors identified for field-scale yearly snowmelt losses provide the basis for modeling of nutrient losses in southern Manitoba and potentially throughout areas with similar climate in the northern Great Plains region, and will aid in the design of effective practices to reduce agricultural nonpoint nutrient pollution in downstream waters.
In western Canada, dugouts are the primary source of water for beef cattle during the summer months. Over time, drought conditions and/or direct access by grazing animals have a negative effect on water constituents and overall water quality. A study was conducted to determine the effects of improvements in water quality on cattle performance. The effect of pasture water quality on weight gain of beef cattle was assessed with 44 Hereford yearling steers over 5 years and 40 Angus cow–calf pairs over 3 years. From 1999 to 2003, cattle were allocated to 1 of 4 treatments, which comprised untreated dugout water pumped to a trough, aerated water pumped to a trough, and coagulated and chlorinated water pumped to a trough, all compared with direct access by livestock to the water source. Data were collected on livestock weight gains, water consumption, fecal parasites, environmental conditions, water chemistry, biological constituents, and forage production and quality. Water treatment by aeration or coagulation tended to improve steer weight gains (P < 0.05) over untreated water from a dugout in 3 of 5 years. Daily weight gains tended to be improved slightly by simply pumping water to a trough without treatment. Water aerated and pumped to a trough in early summer tended to produce greater (P < 0.05) weight gains in calves than those drinking directly from the dugout. The effect of treatment on improving cattle weight gains appeared to be related to improved water palatability, which increased water and feed consumption. Water chemistry and biological constituents analysed did not identify significant differences among treatments. These results suggest that improving water quality with aeration and pumping to a trough will improve weight gain 9–10% over a 90-day grazing period in most years.
Beneficial management practices (BMPs) are designed to minimize environmental impacts and provide on- and off-farm benefits such as improved farm economics and enhanced water quality for domestic consumption, recreation and healthier aquatic ecosystems. Adoption of BMPs depends on the willingness of producers to implement them and on producer capacity to finance the investment. The Watershed Evaluation of Beneficial Management Practices (WEBs) project was initiated in 2004 under Agriculture and Agri-Food Canada (AAFC) to investigate water quality issues and economics related to agricultural production. The project selected nine watersheds across the country where BMPs were implemented to determine the effect on water quality in terms of nutrients, pathogens and sediment and on-farm economics. The South Tobacco Creek (STC) watershed, located in southern Manitoba, was one of the nine watersheds selected. Several BMPs were investigated in STC, including land management changes, the use of small dams and retention ponds to control the runoff from livestock yards from entering the water ways. The objective of the WEBs STC economics component was to assess on-farm economic costs and to identify and assess potential on-farm and off-farm benefits of applying the selected BMPs. The STC economic results have shown that some of the BMPs tested contribute positively to improved farm economics and financial returns but there are some BMPs whose revenues will not fully offset BMP costs. Certain off-farm benefits resulting from BMP implementation have also been identified. Reduced tillage BMP was shown to have significant benefits to producers based on combined experimental and model results. For the small dam/reservoir BMP the net present value based on only flood damage control was shown that the financial payback period can be less than 35 years. Significant additional potential benefits in terms of irrigation, sediment and nutrient entrapment, and recreational activities have also been determined. For land conversion to forage BMP, the cost saving of inclusion of forage to annual crop rotation was not enough to compensate the loss of opportunity through the loss of net income in annual crops. Similarly, the farm benefit of the holding pond which built to capture run-off from an upstream winter cattle containment area was not enough to justify its instalment cost, although nutrients, sediment and pathogens export (off-farm benefits) were reduced significantly. The STC research provided producers, governments, and watershed groups with credible information that can be used to promote adopting and maintaining BMPs.
An 8-yr field-scale study, 2005 to 2012, investigated effects of agricultural land use on nutrient and sediment losses during snowmelt runoff from four treatment fields in southern Manitoba. In 2005, two fields with a long-term history of annual crop (AC) production were planted to perennial forage (PF), while two other fields were left in AC production. In 2009, the AC fields were converted to PF, while the PF fields were returned to AC. Runoff flow rates were monitored at the lower edge of the fields, and nutrient concentrations of runoff water were determined. The effects of AC and PF on selected variables were similar for the spatial (between-fields) and temporal (within-field) comparisons. The flow-weighted mean concentrations (FWMCs) and loads of particulate N, P, and sediment were not affected by treatment. Soil test N and the FWMC and load of NO (NO + NO) were significantly greater in the AC treatment, but the FWMC and load of NH were greater in the PF treatment. Loads of total dissolved N (TDN) and total N (TN) were not affected by treatment, although the concentrations of TDN and TN were greater in the AC treatment. The PF treatment significantly increased FWMCs and loads of total dissolved P (TDP) and total P (TP). On an annual snowmelt runoff basis, the PF treatment increased the FWMC of TDP by 53% and TP by 52% and increased the load of TDP by 221% and TP by 160% compared with the AC treatment. The greater P and NH losses in the PF treatment were attributed mainly to nutrient release from forage residue due to freezing.
