Beneficial management practices that impact water quality
Four beneficial management practices (BMP) were found to have different impacts on the water quality at their respective watersheds. These BMPs include: controlled tile drainage, cattle exclusion fencing, streambank fencing, and conservation tillage.
Controlled tile drainage
The controlled tile drainage (CTD) BMP at the South Nation Watershed in Ontario significantly reduced nutrient loads in receiving surface water, while providing producers with a modest economic gain.
CTD involves placing a structure at the head of tile drain outlets in order to raise the water table and retain water and nutrients in the field during the growing season. Water quality findings showed that this practice significantly reduced nutrient losses to surface water, both at the edge of individual fields and at the watershed outlet.
Furthermore, CTD increased crop yields by an average of 3% for corn and 4% for soybeans. Given that the structures have a lifespan of at least 25 years, this BMP has the potential to pay for itself in as little as four to five years.
Due in part to the research conducted under Watershed Evaluation of Beneficial Management Practices (WEBs), CTD has been included as a BMP that is eligible for cost sharing under the Canada-Ontario Farm Stewardship Program. The South Nation Conservation Authority and the City of Ottawa, under the Rural Clean Water Program, are offering an incentive to producers as well.
Cattle exclusion fencing
A study at the Salmon River Watershed in British Colombia found that cattle exclusion fencing of a riparian area resulted in a significant reduction in E. coli and fine sediment contamination of river water. Fencing also had a positive impact on other environmental indicators, such as riparian vegetation and aquatic invertebrates.
Fencing cattle out of rivers and riparian areas is often promoted as a BMP to help producers minimize negative impacts on the environment. Fencing cattle out of the Salmon River was effective in preventing direct manure additions and disturbance of river sediments. Fencing was also found to have a positive impact on the health of riparian vegetation. The amount of bare soil in the riparian areas decreased and the amount of vegetative cover increased. On unfenced reaches, there was vegetation damage due to browsing and there were numerous cattle trails leading to and from the river.
However, watershed-scale studies also determined that most fecal bacterial contamination in the Salmon River came from non-agricultural sources. Wildlife contributed over 60% of the E. coli bacteria in the river, while domestic livestock sources contributed just 20% of the E. coli entering the river.
The regional cool winter season also significantly contributed to the water quality. Snow melting contributed about 70% of the Salmon River's flow, often resulting in erosion and flooding in the spring. The model accurately simulated the observed field data and predicts that 70 to 80% of fecal coliform bacteria are transferred to the river through snowmelt runoff.
Furthermore, studies were unable to show a reduction in nutrient levels in the river resulting from cattle exclusion fencing. The aquatic life standards for total phosphorus were generally exceeded. Hence, fencing alone may not be sufficient to address excess phosphorus issues.
The use of cattle exclusion fencing will help achieve some water quality objectives. However, findings on a watershed-scale suggest that phosphorus impacts may not be entirely due to farming practices. Fencing alone is unlikely to address phosphorus concerns in this watershed. A combination of both agricultural and non-agricultural BMPs may be needed to effectively address such a specific water quality issue.
Agricultural sites with the healthiest riparian areas along this 75 kilometre transect also had insect communities most similar in species and abundance to the non-agricultural reference sites. These results suggest that fencing that enhances riparian vegetation due to reduced cattle activity is likely to promote the health of the adjacent aquatic insect community.
WEBs on-farm economics studies found that adopting the BMP would be cost-prohibitive for a ranching industry struggling with fluctuating commodity prices and increasing input costs during the study period. Ranchers implementing this BMP would also face additional maintenance costs such as labour and materials to repair fence damage due to cattle, vegetation, flooding or weather conditions. Additional cross-fencing may also be required to prevent cattle from moving along a stream and entering unfenced areas.
However, fencing may provide some on-farm economic benefits that could partially offset the costs. Fencing that results in recovered riparian vegetation may stabilize streambanks, thereby reducing slumping (collapse) of soils along the riverbank. This soil loss can add up to larger losses of agricultural land over time. Other research studies have suggested that even though source water quality might not pose a health hazard, provision of an off-stream water source may result in increased cattle weight gains due to a desirable increase in water consumption overall.
Since sport fishing, recreation and domestic water use are highly valued in this area of British Columbia, significant off-farm benefits from adopting BMPs that improve water quality and riparian and aquatic health might be expected.
The effectiveness of streambank fencing - including a fenced stream crossing and off-stream watering - were investigated in the Lower Little Bow River Watershed northeast of Lethbridge. The purpose of this study was to determine the impact of excluding cattle from the river on water quality, rangeland health and riparian health, and to determine the BMP's costs and benefits for cattle producers.
The study found that streambank fencing was successful at preventing further degradation of water quality in terms of the amount of nutrient (nitrogen and phosphorus) and sediment loading, and that the cattle crossing did not contribute to water quality degradation downstream. The impact of the fencing BMP on other water quality variables, however, was less clear.
The rainfall simulation trials detected less runoff from the cattle-excluded pasture than from the grazed pasture. There were no significant differences in runoff volume or water quality between the two pastures during the first year of the study, which was also the year with the highest rainfall. However, differences were observed in years two and three of the study, suggesting that the fenced-off area does provide a buffer zone that reduces nutrient runoff in certain years, with the amount of nutrient runoff likely related to yearly climatic changes.
Several years of fencing improved the score of the cattle-excluded upland pasture. This increase was due to improvements in ecosystem status, plant (or ecological) community structure and abundance of plant (or crop) litter.
Streambank fencing also significantly improved several aspects of local vegetation and soil properties in the cattle-excluded pasture, such as vegetative cover and standing litter. The fenced-off area had fewer patches of bare soil, improved live-plant area, and reduced soil compaction in the latter two years. These improvements seemed to protect the soil surface from water erosion and acted as a buffer for potential contaminants.
The first riparian health assessment following implementation of the BMP showed that riparian health increased after four years of fencing. However, a follow-up assessment showed that the health of the fenced-off riparian area had weakened from 'healthy' to 'healthy but with problems'. This decrease in riparian health was due to an increase in invasive plant species, and possibly the residual effects of soil compaction caused by cattle on the ability of preferred trees and shrubs - such as willows - to establish along the streambank. The results of the riparian health assessment would have been more favourable had the assessments stopped after four years, emphasizing the merit in long-term evaluations.
Another alternative to total cattle exclusion is periodic, short-term grazing of the riparian pasture to achieve a balance between using the forage resource and protecting water quality. This practice may also help to control the invasive plant species that entered the cattle-excluded pasture after several years of fencing, but should only be used when the riparian zone soil is dry enough to prevent compaction and damage to the soil by cattle.
Streambank fencing might be targeted to more ecologically sensitive or more severely degraded stream reaches, with the less expensive and less effective off-stream watering without fencing BMP applied in less critical areas.
It is estimated that streambank fencing, with its immediate reduction of available pasture area and added costs, could cause a 2 to 7% decrease in farm cash flow. However, the practice may result in benefits that could partially offset the costs.
Research elsewhere has shown that providing access to clean water, as with an off-stream watering source, may result in higher water consumption and cattle weight gains compared to lower-quality water accessed directly from the river. Access to higher-quality water may also lead to a decrease in herd health problems. And providing access to off-stream watering, with or without fencing, may result in increased grazing and pasture utilization.
Tillage practices can be divided into the following three main categories, which reflect a decreasing number of tillage passes and associated increase in remaining plant residue:
- Conventional tillage has at least one tillage pass in the spring and one in the fall.
- Minimum tillage has often only one tillage pass in the spring or fall.
- Zero tillage has no tillage.
The term conservation tillage can be applied to practices ranging from minimum tillage to zero tillage.
Conservation tillage aims to maximize the amount of crop residue remaining on the soil surface, and is a BMP widely promoted for its role in reducing soil erosion and the export of soil-bound nutrients into surface water. It can also play an important role in soil carbon sequestration.
Although conservation tillage significantly reduces soil erosion, a biophysical study at the South Tobacco Creek (STC) Watershed in south-central Manitoba has shown that conservation tillage can increase dissolved phosphorus (P) export in a cold climate region where spring snowmelt is a major portion of annual runoff.
To study the water quality impacts of conservation tillage, the STC study used a pair of small, adjacent agricultural watersheds to compare the effects of conservation tillage and conventional tillage under a cereal and canola rotation.
Research on clay-loam soils within the STC Watershed has shown no statistically significant difference in the amount of annual runoff between the conservation tilled and conventional tilled fields. This might be due to the fact that the majority of runoff in this watershed occurs during snowmelt, when the ground is still frozen and impermeable. However, on an annual basis, conservation tillage was highly effective in reducing annual sediment and total nitrogen (N) export as compared to conventional tillage.
Sediment and total N export were reduced on average by 65% and 69% per year respectively. However, total P export was 12% greater under conservation tillage. This is because while the export of particulate P (the small proportion of P lost that was attached to soil sediment) decreased by 37% under conservation tillage, the portion of dissolved P (the large proportion of P that was water soluble) increased by 36%, resulting in a net increase of 0.06 kg/ha in exported total P. The average P loading for conservation tillage was therefore 0.17 kg/ha.
Even though these nutrient losses may be minor from an agricultural production standpoint, they are ecologically significant, since as little as 1 to 2 kg of P/ha/yr is associated with the accelerated eutrophication of lakes.
These findings suggest that the increase in total P is due to an increase in dissolved P released from crop residues during freeze-thaw events, or from soil P that accumulates in surface soils because it has not been mixed during tillage. Results demonstrated that although conservation tillage can effectively reduce sediment and sediment-bound nutrient export from agricultural fields, it can increase the export of dissolved P occurring during snowmelt runoff. In these situations, it may be appropriate to implement additional management practices, such as intermittent tillage, to reduce the accumulation of P at or near the soil surface.
The economic response to conservation tillage is generally positive for cereals (wheat, barley and oats combined) but is negative for canola (Table 1). Producers are likely to focus on the tillage method that is the most profitable, with canola generally being a higher-income crop than cereals.
|Crop||Conservation tillage (area under canola and cereals production)||Conventional tillage (area under canola and cereals production)||Total (area under canola and cereals production)|
|% area (ha)||Net income/ha||% area (ha)||Net income/ha||% area (ha)|
|Canola||7.3 (261)||$88||30.1 (1,074)||$106||37.4 (1,335)|
|Cereals||19.7 (703)||$35||42.9 (1,532)||$10||62.6 (2,235)|
|Total||27.0 (964)||73.0 (2,606)||100 (3,570)|
| % area represents the portion of the total area (3,570 ha) under canola and cereals production.|
The results of this study could apply to much of the cold, semi-arid landscape of the Canadian Prairies, and may be relevant wherever snowmelt runoff dominates and dissolved P is the major form of P in runoff. Conservation tillage has many environmental and agronomic benefits; however, it is not a cure-all in terms of reducing P export from agricultural watersheds in the Lake Winnipeg Basin.
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