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Environmental Sustainability of Canada’s Agricultural Soils

Issue Context

Why should we be concerned about agricultural soil?

Sustainable agriculture is the continuous production of food and fibre into the future while conserving the health of natural resources on and off the farm. Healthy soils serve as the foundation of sustainable agriculture by:

• providing a medium for plant growth,
• holding water, air, nutrients, and soil biota, and
• receiving organic wastes and recycling their nutrients back to plants.

Agricultural soils can also have an influence on overall environmental sustainability, by, for example:

• exchanging gases with the atmosphere and influencing global climate, and
• holding and breaking down contaminants.

Virtually all available productive agricultural land in Canada is already under crop production. Some highly productive land has been (and is being) lost to urban and industrial uses. It is important to maintain the health of our remaining soil resources.

Water quality, biodiversity, and socioeconomic aspects of sustainable agriculture are not directly related to soils and will be covered under other issues. 

Indicators of agricultural soil sustainability

The cycle diagram below shows three broad components of the interactions between humans and the environment that are related to agricultural soils. Indicators are chosen to be representative of the cycle components (not necessarily an illustration of a particular cause–effect relationship). All the indicators presented in this bulletin are based on the detailed research underlying Agriculture and Agri-Food Canada’s Agri-Environmental Indicator Project.

Human activity: Fertilization and nutrient balance

Tillage, fertilization, and pest control are examples of human activities related to agriculture. Fertilization was chosen as the representative indicator since the focus of this bulletin is on soils. Pest control will be covered under other themes, and tillage is covered indirectly under the other two soil indicators.

Farmers must add nutrients to the soil to produce crop yields that satisfy human requirements and maintain soil fertility. The main sources of added soil nutrients are commercial fertilizers and animal manure. Sewage sludge and municipal compost are less commonly used. The major nutrients in these inputs are nitrogen, phosphorus, and potassium. 

Nitrogen is a nutrient that is particularly mobile in soil. Overfertilization can result in surface water and groundwater pollution or the release of greenhouse gases such as nitrous oxide. Other factors, such as weather, the permeability of the soil, and management activities, influence whether excess nutrients in the soil will result in environmental problems. Underfertilization can result in serious depletion of soil fertility.

The fertilization and nutrient balance (residual nitrogen) indicator shows whether we are achieving a balance between nutrient availability and crop requirements. 

Environmental condition: Soil degradation

A small grouping of indicators of risk of soil degradation was chosen to represent environmental conditions and effects. Soil organic matter content has good potential as an indicator representative of environmental condition, but existing data limitations need to be addressed to make it a better candidate for future bulletin updates. Soil may be degraded (e.g., through compaction and tillage erosion) by farming activities and by the natural processes of wind and water erosion. Some farming practices, such as summerfallow (soil left bare for one growing season), increase the risk of wind and water erosion. Other practices, such as conservation tillage and returning land to permanent cover, help to prevent erosion.

Soil salinization, another form of soil degradation, limits the ability of crops to take up water and nutrients. Some Prairie soils have naturally high levels of water-soluble salt, given the regional climate and geology, but inappropriate irrigation and cropping practices can worsen salinity problems. The risk of soil degradation indicator shows the proportion of cultivated land where the levels of risk for water erosion, wind erosion, and soil salinization are low enough for agricultural soils to be sustainable. With future updates, the trends will be more apparent and helpful in deciding on appropriate responses.

Societal response: What are we doing to protect soil?

Soil conservation has been promoted for decades in agricultural regions of Canada. Research is ongoing on the timing of fertilization, improved manure storage methods, methods of fertilizer application, and other techniques to improve nutrient management and maintain soil health. The crop and residue cover indicator reflects the degree to which farmers are adapting management strategies to enhance the sustainability of agricultural soils. Greater plant cover with fewer bare-soil days promotes higher organic matter content and contributes to reducing runoff and to holding nutrients in upper soil layers. 

Collectively, these indicators show an improvement in the management of Canada’s agricultural soils. However, large areas of agricultural land in Canada, particularly where cropping is intensive or where marginal land is cultivated, remain susceptible to soil degradation.

Acknowledgements:

These indicators were developed principally by a team at Agriculture and Agri-Food Canada (AAFC), with input from the Indicators and Reporting Office, Environment Canada and advice from AAFC's Public Advisory Committee. The input and collaboration of the Research Branch and the Policy Branch, AAFC, Ottawa, are gratefully acknowledged.