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Soil Organic Matter Indicator

The Soil Organic Matter Indicator combines two separate indicator models - the Soil Organic Carbon Change Indicator and the Relative Soil Organic Carbon Indicator – to assess how organic carbon levels in Canadian agricultural soils are changing over time. The indicator gives a useful picture of soil health and an estimate of how much carbon dioxide has been removed from the atmosphere by plants and stored, or sequestered, as soil organic carbon in agricultural soils. This indicator has tracked soil organic matter associated with Canadian agricultural activities from 1981 to 2011.

Overall state and trend

Soil organic matter has been increasing on agricultural lands in Canada. In 2011 Canadian agricultural soils removed 11.9 million tonnes of carbon dioxide from the atmosphere. You can view these statistics in Environment Canada's National Inventory Report 1990-2011: Greenhouse Gas Sources and Sinks in Canada - Executive Summary.

Soil Organic Carbon Change Indicator

The Soil Organic Carbon Change Indicator looks at the rate of change in carbon levels in agricultural soils. Using this indicator we can see where soil organic carbon is increasing or declining, and at what rate it is doing so.

Use the interactive map below to zoom in and explore different regions. Note that in the Prairies, soil organic carbon is increasing primarily due to a reduction in tillage intensity and area under summerfallow – a practice of leaving fields bare. This increasing trend holds promise for correcting past practices that caused soil degradation and left many Prairie soils with very low organic carbon levels. Conversely, in regions of Canada east of Manitoba, where soil carbon levels were historically much higher, these levels are now generally decreasing due to the steady conversion of tame pastures and hayland to annual crops.

In addition to exploring the 2011 values, click the play button to view changes over time. Since 1981, there has been a significant increase in soil organic matter across the Prairies and a noticeable decline in soil organic matter in much of eastern Canada.

Generally speaking, the large improvements in the Prairies can be mainly attributed to the reduction in summerfallow as well as an increase in reduced tillage and no-till practices, which have increased plant residues and led to a build-up of organic matter in the soil. The decline in soil carbon elsewhere can be explained by shifts in cropping practices and crop types. Since 2006, the sharp decline in beef cattle production, as well as a longer-term decline in dairy herds since 1981 has reduced the area under pasture and forage production. Much of the area previously dedicated to these land uses have been converted to annual crops, such as corn, which do not increase soil organic matter as much as perennial crops. These declines in eastern Canada are more than offset by improvements in the Prairie Region and overall, the national trend is very favourable.

Soil organic carbon change (in kilograms per hectare, per year) in Canada in 2011

Legend: legend

If soil is well managed over a long period of time, the organic carbon content will stabilize and remain constant over time. An increase in soil carbon is not necessarily better than a stable situation. However, if soil degradation has occurred in the past, a significant increase in soil organic carbon is clearly desirable, as it indicates improvements in soil health and function. A loss of soil organic carbon represents a net release of carbon dioxide into the atmosphere and so is not desirable.

Soil Organic Carbon Change Index

The state and trend of the soil organic carbon change indicator can also be seen in the performance index below

Figure 2: Soil Organic Carbon Change Index
Description of this image follows.
Description - Figure 2
Year Index Value
1981 48
1986 53
1991 56
1996 63
2001 70
2006 74
2011 74

In 2011, the state of the environment, as it relates to soil organic carbon change resulting from farming activities in Canada, was in the "Good" category. The index illustrates a strong upward trend, from an index value of 48 in 1981, to a higher value of 74 in 2011, demonstrating a consistent improvement and an increase in soil organic carbon over this 30-year period. This national-scale improvement came about primarily as a result of widespread adoption of reduced (conservation) tillage and no-till, as well as decreases in the use of summerfallow in the Prairies.

The index tends to aggregate and generalize trends and so should be viewed as a policy tool to give a general overview of state and trend over time.

How performance indices are calculated

Relative Soil Organic Carbon Indicator

In addition to knowing how quickly carbon is accumulating in the soil, it is useful to have a means of assessing soil health and function, which varies across different climates and soil types, and for different farming practices. For this reason, a complementary indicator, the Relative Soil Organic Carbon Indicator, compares carbon levels against the optimum soil carbon scenario of an extensively grazed grass pasture. When combined with the Soil Organic Carbon Change Indicator, it can help to identify those areas most at risk from soil degradation.

Use the interactive map in Figure 3 to explore the current degradation risk in soil organic carbon. Areas like the Prairies that still have relatively low but increasing soil carbon levels are considered to be at a low risk of degradation. Areas that have soils with high organic carbon, like the majority of eastern Canada, but which are losing soil organic matter through changes in farming practices are considered to be at moderate risk and may not be sustainable in the long-term. Those regions with lower soil carbon levels that are also declining, as can be seen in parts of eastern Canada, are at the greatest risk of degradation.

Figure 3: Soil organic carbon degradation risk in 2011

Legend: legend

Specific trends

This section highlights a few other trends of interest. In some cases, these are occurring in certain regions and in others they are affecting certain sectors, such as the beef or dairy industries. This is not an exhaustive list; additional findings can be found in the full publication: Environmental Sustainability of Canadian Agriculture, Agri-Environmental Indicator Report Series - Report #4 .

Trend 1 – Soil conservation in the Prairies increases soil organic carbon

The Prairie Region has seen significant improvements in soil organic carbon over the past 30 years. The map below shows the cumulative changes in organic carbon, directly resulting from the reduction in tillage intensity and summerfallow. You can explore these improvements in the Prairies and also zoom out to see that these same improvements were not experienced in Eastern Canada over the same time period.

Figure 4: Cumulative Soil Organic Carbon change (in kilograms per hectare) from 1981 to 2011 due to changes in tillage and summerfallow

Legend: legend

Reasons for trend 1

The primary reason for the improvement in this indicator in Canada is due to the shift away from summerfallow and intensive tillage in the Prairie region. Both these practices remove or prevent the build-up of soil organic matter – and therefore carbon. Figure 5 shows the change in percentage of farmland – between 1981 and 2011 – under summerfallow, as well as under no-till for the Prairies (Alberta, Saskatchewan and Manitoba) as well as for British Columbia and Canada as a whole. Because the Prairie region accounts for over 85% of farmland in Canada, changes in these provinces significantly impact the national averages. Eastern Canada remained stable over this period because summerfallow was not a common management practice in this region.

Figure 5: Trends in summerfallow and no-till in Western Canada and the Prairies, 1981 to 2011. Note that Census data for tillage practices are available from 1991 onwards only.
Description of this image follows.
Description - Figure 5
Percentage area of summerfallow
1981 1986 1991 1996 2001 2006 2011
Manitoba 11 10 6 6 5 2 2
Saskatchewan 35 28 28 22 16 13 8
Alberta 18 17 14 11 9 7 4
British Columbia 7 10 7 5 4 3 2
Canada 22 19 17 14 10 8 5
Percentage area of no till
1981 1986 1991 1996 2001 2006 2011
Manitoba 5 9 13 21 24
Saskatchewan 10 22 39 60 70
Alberta 3 10 28 48 65
British Columbia 5 10 14 19 28
Canada 7 16 30 46 56

Trend 2 – Land-use changes in parts of Eastern Canada lead to lower soil organic carbon

While the national trend for soil organic carbon is extremely positive, this has been slightly offset by localized decreases in soil carbon in parts of eastern Ontario and southern Quebec, and in parts of the Maritimes. The map below shows the cumulative changes in organic carbon, directly resulting from land-use changes, most notably shifting between annual and perennial crops. You can explore trends in Eastern Canada and also zoom out to see that these land-use changes had a mixed effect in the Prairie Region.

Figure 6: Soil organic carbon change in Eastern Canada, 1981 to 2011

Legend: legend

Reasons for trend 2

Between 1981 and 2011, eastern Canada has experienced a gradual shift away from perennial crops such as pasture and forage, towards annual crops such as cereals and oilseeds. Annual crops tend to contribute very little to soil carbon reserves and so these changes have resulted in a reduction in soil carbon levels in these regions. The main reason for these changes in land use is due to the decline in Canada's cattle herd. Canada's beef cattle population peaked in 2006 and then experienced a decline primarily attributed to the bovine spongiform encephalopathy (BSE) crisis in 2003–2004. In the case of the dairy industry, increased efficiencies have led to fewer head of dairy cows (a decline from 1.8 million down to around 1 million head), without a decline in milk production.

Why this indicator matters

Soil organic matter has implications for a number of environmental processes and conditions relating to overall soil health, including soil structure, fertility, drainage and susceptibility to erosion. The carbon in our soils has important implications for climate change, as sequestering carbon in soils removes carbon dioxide from the atmosphere. Sequestered soil carbon is calculated as part of Canada's national greenhouse gas inventory, and reported as part of our commitment to the United Nations Framework Convention on Climate Change. Soil carbon also has implications for land productivity and crop yield and quality.

Agriculture has the potential to mitigate climate change by implementing beneficial management practices that increase soil cover and by limiting practices (such as summerfallow) that decrease soil cover.

Beneficial management practices

The same practices that reduce soil erosion and increase soil cover will increase soil organic carbon levels. In the Prairies especially, producers can increase soil organic carbon by reducing summerfallow and tillage intensity and by converting annual crops to perennial cropping systems.

In cases where low-residue horticultural or root crops are grown on farmland with relatively low soil organic carbon levels, it is important to include crops that produce abundant residues in the rotation. Examples of these higher residue cover crops include clover, alfalfa, ryegrass, oats and winter wheat. Manure spreading can also increase soil organic carbon, and quickly improve soil health and productivity. Other suitable methods may include intercropping lower residue crops with suitable companion plants.

How performance indices are calculated

The agri-environmental performance index shows environmental performance state and trends over time, based on weighting the percentage of agricultural land in each indicator class, such that the index ranges from 0 (all land in the most undesirable category) to 100 (all land in the most desirable category). The equation is simply "(% in poor class multiplied by .25) plus (% in moderate class multiplied by .5) plus (% in good class multiplied by .75) plus (% in desired class)." As the percentage of land in the "at risk" class is multiplied by zero, it is not included in the algorithm.

The table below shows the index classes. The index uses the same five-colour scheme as the indicator maps whereby dark green represents a desirable or healthy state and red represents least desirable or least healthy.

The index classes
Scale Colour scheme Class
80-100 Dark green Desired
60-79 Light green Good
40-59 Yellow Moderate
20-39 Orange Poor
0-19 Red At risk

The index tends to aggregate and generalize trends and so should be viewed as a policy tool to give a general overview of state and trend over time.

Related indicators

Additional resources and downloads

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