| | Slope can play a significant role in a farm operation. Producers need to be aware of the benefits in being able to calculate slope and the consequences of not calculating slope properly.
"Simply put, the outputs of slope, the eroded material running downhill from some upslope position, quickly become the inputs to some other ecological system, such as a body of water," says Jason Cathcart soil quality program coordinator with Alberta Environmentally Sustainable Agriculture (AESA), Alberta Agriculture, Food and Rural Development, Edmonton. "It can be said that field slope exerts a fundamental control on other parts of the landscape and environment."
Slope has an effect on soil quality as highly sloped land is subject to topsoil loss or a loss in soil quality as a result of erosion processes. These processes often result in field blowouts and the exposure of rocks, which can be potentially damaging to farm machinery. Furthermore, the loss of topsoil exposes the lower less fertile B- and C-horizons, which typically result in poor crop growth, less crop residue return, and greater field variability. This starts the downward spiral in soil quality that is often a result of the unequal distribution and loss of nutrients, organic matter and moisture.
"From a regulatory point of view, slope falls under the Agricultural Operation Practices Act (AOPA) with respect to establishing the minimum setback distance from a common body of water when producers are considering applying manure," says Cathcart. "These setback distances differ based on the degree of slope leading up to that body of water, and calculating that setback often requires specific knowledge of the field's slope length. The greater the slope leading up to the edge of a water body, the farther away manure application must be made to avoid surface water contamination."
Setback distances from water bodies for manure application
| Percent field slope | Minimum setback distance |
| Less than 4 per cent | 30 m (approximately 100 feet) |
| Between 4 and 6 per cent | 60 m (approximately 197 feet) |
| Between 6 and 12 per cent | 90 m (approximately 296 feet) |
| Greater than 12 per cent | No application permitted |
Adapted from "Manure Spreading Setback Distances: What is required by the Agricultural Operations Practices Act (AOPA)" (March 2005)
Knowledge of field slope is also required when filling in an Alberta Environmental Farm Plan (AEFP). Slope is considered on Worksheet 1 - Soil and Site Characteristics, where it is used to assess a farm's risk to water erosion and surface water contamination. In the EFP program, slope is classed as:
- Steep - more than 10 per cent
- Moderate - or 2 to 10 per cent
- Level - with field slope of less than 2 per cent.
Slope assessment in the AEFP program also requires knowledge on slope length, as determined using the visualization drive-by knowledge. Drive-by knowledge was described in the second part of this series and was featured in the July 3, 2006 issue of Agri-News.
"In wrapping up this series on field slope, I want to mention a few Beneficial Management Practices (BMPs) that can be employed by producers on both moderate and steep slopes," says Cathcart. "On moderate slopes, BMPs to assist in mitigating potential erosion problems include vegetative buffer strips, grassed waterways, and/or contour farming. On more severe slopes, recommended BMPs include strip cropping, terrace structures and/or the use of water drop structures. Which BMPs are used, depends on both the severity of slope and whether removal of this land from crop production and returning it to permanent cover is an option. The key goal of these six BMP's is to minimize slope length to reduce the potential for runoff accumulation and reduce the erosive energy of the flow."
Field slope affects erosion potential, surface water contamination and crop response by exerting detrimental effects on soil quality. There are two important parameters to slope, those being slope length and per cent slope. There are a number of methods producers can use to calculate these parameters, ranging from trigonometric calculations to simple visualizations and drive-by assessments. Finally, what must be remembered is that slope plays a significant role in maintaining farm soil quality, achieving AOPA Regulations and in filling out an Environmental Farm Plan.
For more info on AOPA, visit www.agric.gov.ab.ca and search AOPA. For more info on AEFP, visit www.albertaefp.com.
Contact: Jason Cathcart (780) 427-3432 |
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