Soil: Our Eroding Asset
Contents |
The Vital Importance of Soil
When we think of resources, we typically think of our aquifers, lakes and rivers, our forest resources, our oil, gas and mineral reserves, and our terrestrial and aquatic plant communities. We don’t usually think of soil as a resource. Yet we rely on soil to produce our food, degrade our solid wastes, clean our water, and provide dependable habitat for the countless microbes (at least 10,000 species per gram of soil) that provide these vital ecological functions. Soil is the rich, diverse, and dynamic matrix within which terrestrial life functions.
Cropland soils are vital to our economy. In 2006, Ontario’s approximately 3.7 million hectares of cropland produced $8.8 billion in farm receipts. The Ontario farm and food processing sector generates over $30 billion in sales annually – representing more than 35 per cent of Canada’s agri-food sector GDP. Our agricultural exploitation of the soil resource has also become much more efficient over time; for example, the average seed-corn yield has doubled from about 3.5 tonnes per hectare 30 years ago to about 7.0 tonnes per hectare at present. Similar increases have been achieved with other important crops, such as soybeans.
Much of this increase in productivity is a direct result of fossil fuel based inputs, such as inorganic fertilizers, pesticides and mechanization, combined with agronomic advances in plant hybridization and genetics. More recently, however, the sustainability of this approach has been called into question. Should we not be asking whether this high level of productivity and the methods used to achieve it could be affecting the quality and quantity of available fertile soil? The ECO believes that it is time to take a close look at the status of Ontario soils and to consider whether we are managing them in a sustainable way.
Soil and Organic Matter
Soil consists of a mixture of organic and mineral particulate matter of various sizes and proportions. In the topsoil layer, the mineral portion contains sand, silt and clay, and the relative amounts of each of these determine the soil’s characteristic texture. Clay is the finest portion and provides for the water-holding capacity, while the larger particles of sand and silt provide pore spaces that keep the soil aerated and drained. Soils form slowly from parent material (rock) that has disintegrated through abrasion, chemical and physical processes and biological activity.
Overall, the amount of soil organic matter (SOM) ranges from one to ten per cent of the total dry weight of soil. The organic components of SOM include: raw plant residues (less than 10 per cent); a humus portion fairly resistant to further biological breakdown (40 to 60 per cent); and biologically “active” organic material (10 to 40 per cent). The active fraction – where microorganisms, particularly bacteria and fungi, break down the complex organic matter and recycle its nutrients – is a particularly important component of fertile soil. The microbes and other microfauna create what scientists call a “food web” – a biological matrix that improves soil structure, increases both water retention and infiltration, provides a slow-release nutrient supply appropriate for plant requirements, reduces nutrient loss through leaching, and increases system resilience to external impacts.
This biological matrix depends on organic matter to provide food for the organisms. If the food web is diminished due to the loss of organic matter, the soil becomes more liable to compaction and much more prone to erosion. The loss of water-holding and infiltration capacity makes crops more susceptible to short-term drought effects. A reduction in beneficial microbe populations or diversity reduces the soil’s overall productivity and necessitates greater dependence on potentially costly external inputs of fertilizer to the cropping system.
SOM declines when land is first cleared and put into agricultural use, with most of the loss occurring within the first ten years. Information on SOM levels and long-term trends in Ontario soils is extremely limited. One study, in the mid-1990s, found that for 16 study sites ranging across Ontario, deforestation and cultivation over the decades had released about 34 per cent of the soil carbon in the top 250 mm to 350 mm of soil.
The Problem of Soil Erosion
The substantial carbon losses described above greatly increase our croplands’ susceptibility to erosion. The most common agents of erosion are tillage, wind and water. Erosion caused by tillage on steep slopes is primarily a localized concern. Wind erosion may become a concern if climate change increases the frequency of droughts, but has not been a major problem to date because of Ontario’s humid climate. Water erosion, on the other hand, is widespread, sometimes highly destructive and, therefore, the major environmental concern.
How serious a problem is soil erosion in Ontario? To answer this big question, we need to know:
- How much topsoil is Ontario losing on an annual basis?
- What is the annual replacement rate for topsoil?
- In what direction is the trend moving? Are our efforts at soil conservation improving or failing?
Complete answers to these three questions are not available – a problem in itself – although there are some disturbing partial answers.
With regard to annual topsoil loss, estimates based on actual sampling and measurement are sparse to non-existent. However, Agriculture and Agri-Food Canada (AAFC) has compiled a comprehensive series of reports on “Agri-Environmental Indicators,” which use Census of Agriculture data and Soil Landscape of Canada maps to assess the risk of various rates of soil erosion for all provinces. These risk estimates are based on data regarding physical factors, such as slope, slope length and lack of cover, and fineness of the soil. They do not consider the level of organic matter. Table 1 summarizes the most recent estimates of water erosion risk in Ontario.
Table 1: Cropland Water Erosion Risk in Ontario 2001
| Erosion Risk Category | Annual Soil Loss Rate (tonnes/hectare) | Percentage of Soils in Risk Class (2001) |
|---|---|---|
| Very low | < 6 | 56 |
| Low | 6 – 11 | 15 |
| Moderate | 11 – 22 | 16 |
| High | 22 – 33 | 7 |
| Very High | > 33 | 6 |
- From: Agri-Environmental Indicator Report Series, Report No. 2 (AAFC)
According to this analysis, as of 2001, 44 per cent of our land had the potential to erode at rates greater than six tonnes per hectare per year. To put this into perspective, for almost half of our cropland, we are at risk of losing at least one tonne of soil for every tonne of grain corn produced. For up to 29 per cent of our arable land, the potential loss rate is at least twice that.
If the above represents our annual risk of soil loss, what would be a reasonable estimate of the replacement rate? Soil regeneration rates have been reported in the range of 0.5 to 1.1 tonnes per hectare per year. This is considerably lower than the six-tonne-per-annum level set by AAFC as “low risk,” meaning that even our low-risk croplands may be losing their topsoil at a rate well above that of natural replacement. We cannot say at what rate this is actually happening, because we do not have the data, but we can say that the risk of this type of unsustainable loss is very high for a very large proportion of our croplands.
From a policy perspective, both the Canadian and Ontario governments have defined “tolerable” (T) soil loss not in terms of soil replacement, but rather in terms of sustained crop productivity. This is because, in practice, soil loss risk could not be kept within soil replacement rate levels for row crops, such as corn and soybeans, unless very conservative practices or multi-year crop rotations with forage crops were implemented. The value for T has usually been set by determining soil loss rates below which crop yields have been noticed to decline. For instance, the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) uses a T value of 6.6 tonnes per hectare per year, while AAFC uses a T value of 7.0 tonnes per hectare per year.
Unfortunately, the concept of “tolerable” seems to have replaced the concept of “sustainable” in our soil management policy. Perhaps this is because the loss of quality topsoil can be an insidiously gradual process. It is masked by the use of inorganic fertilizers – at least until dire symptoms, such as noticeable erosion damage or marked declines in major crop yields, “suddenly” appear. According to OMAFRA, this lack of awareness of soil loss occurs because “continuous advances in soil management and crop production technology … have maintained or increased yields in spite of soil erosion” [emphasis added]. By ignoring the continuous loss of the natural soil resource, farmers are becoming locked into an expensive dependence on inorganic fertilizer that threatens the resilience and sustainability of our agricultural system.
The risk of soil erosion can be reduced through certain management practices, such as cover cropping and conservative tillage technologies. In terms of cover cropping, perennial covers of hay and pasture give a high degree of protection to the soil, as compared to widely spaced row crops such as corn, which provide very minimal soil protection. Other uses of cover crops include: protecting bare soil between harvest and next planting; covering the bare soil between rows of conventionally grown crops; and renewing the soil’s nutrient supply during fallow periods (e.g., green manures).
Conservation tillage practices that substantially reduce water (and tillage) erosion include: “no-till,” where seeds are drilled directly into the soil; “chisel ploughing,” where the main function is to loosen and aerate the soils without turning, while leaving crop residue at the top of the soil; and “disk harrowing,” where the soil’s surface layers are disked (cut) but not turned. The traditional mouldboard ploughing and associated secondary tillage, on the other hand, set up conditions that are conducive to water and tillage erosion, and to accelerating the loss of organic matter.
Soil Management Policy in Ontario
The above analysis certainly indicates that soil erosion is a serious concern in Ontario. Is the trend for the better, or for the worse? A short history of soil management policy in Ontario is illustrative in this regard. Serious problems with soil degradation in Ontario began occurring in the early 1960s. More sustainable practices, such as mixed livestock-cropping systems, high proportions of forage and cereal grain production, and multi-year crop rotations, had begun to be replaced by intensified crop production, crop specialization, the separation of livestock operations from crop production, and off-farm inputs of fertilizers.
It is particularly worthy of note that early soil conservation planning services for farmers, offered as extension services from the Ontario Agricultural College from 1945 until about 1958, were phased out due to growing interest in commercial fertilizers as a substitute for plant nutrients lost because of soil erosion. In 1978, a report by the Pollution from Land Use Activities Reference Group (PLUARG) showed the scale of erosion, sediment and nutrient runoff from land uses in the Great Lakes Basin and raised awareness in the agricultural community to begin to address these issues. It was not until the 1980s, however, that programs began to appear to assist farmers in addressing environmental issues and implement conservation practices. Several major programs were initiated over the period from 1983 to 1995, which brought some change to Ontario’s agricultural practices and resulted in some improvements. (Readers are referred to Section 7 in the Supplement to this Annual Report for a description and history of these programs.) Reductions in erosion risk by 2001 are evident in Table 2, comparing soil erosion risk category distribution for that year with 1981.
Table 2: Cropland Water Erosion Risk in Ontario, 1981 to 2001.
| Erosion Risk Category | Annual Soil Loss Rate (tonnes/hectare) | Percentage of Soils in Risk Class (1981) | Percentage of Soils in Risk Class (2001) |
|---|---|---|---|
| Very low | < 6 | 44 | 56 |
| Low | 6 – 11 | 22 | 15 |
| Moderate | 11 – 22 | 15 | 16 |
| High | 22 – 33 | 11 | 7 |
| Very High | > 33 | 8 | 6 |
- From: Agri-Environmental Indicator Report Series, Report No. 2 (AAFC)
Despite the modest improvements shown above, Ontario still had, as of 2001, one of the lowest proportions (56 per cent) of land in the very low risk class and the largest share (six per cent) of cropland in the very high risk class, compared with other provinces. The reader should bear in mind, furthermore, that the risk levels used in the above assessment are based on the concept of tolerable, rather than sustainable, soil loss.
The programs of the mid-1980s to mid-1990s expended over $100 million, and at their peak, 25-30 full- time OMAFRA staff were working on soil conservation programs directly with landowners, Conservation Authorities and farm organizations. As OMAFRA’s priorities began to shift, these staff were subsequently re-deployed and OMAFRA began to rely on farm organizations, such as the Ontario Soil and Crop Improvement Association (OSCIA), along with Conservation Authorities, to deliver cost-share programs to farmers, while the ministry focused on providing training to farm groups.
Canada’s Green Plan of the early 1990s introduced a pilot program to develop Environmental Farm Plans (EFPs), which were initiated, with OMAFRA technical support, in 1993. Environmental Farm Planning is a voluntary, confidential process used by farmers to identify environmental risks on their farm and to develop strategies to mitigate them. In the currently available federal-provincial funding for farm stewardship and conservation measures, EFPs are required before landowners qualify to receive cost-sharing dollars.
Most program initiatives to conserve soil now fall under federal-provincial agreements under the aegis of the Agricultural Policy Framework (APF). We do not yet know whether or not the more recent programs have continued the slight improvement trend that was started in the early 1990s. In 2008, the federal Commissioner of the Environment and Sustainable Development (CESD) audited the Environment Section of the Agricultural Policy Framework, to examine whether its objectives for environmentally sustainable agriculture were being achieved and to assess its ability to report on performance under this section. Among other concerns, the report identified a lack of monitoring data necessary to track the effectiveness of the programs.
ECO Comment
While some progress has been made since the 1980s, we still have a situation where a predominant portion of our agricultural soils are being managed in a way that is clearly not sustainable. We do not know how much of our soil is being lost each year at unsustainable rates, but the information that we do have suggests that almost half our cropland is at risk of losing topsoil at a rate that is much greater than its replacement rate. Moreover, we have no guarantee of sustainable soil loss rates on any of our croplands.
Reports within the last ten years indicate that agricultural soil conservation practices have been adopted over a relatively small percentage of the province’s croplands. No-till practices have increased substantially in the last 20 years, yet the percentage of overall cropped land under no-till remains less than 20 per cent.
Meanwhile, climate change appears to be changing Ontario’s weather patterns, increasing the likelihood of more intensive runoff events. One recent report has warned that more frequently occurring spring rain events, coming at a time when soil is left unprotected by crops, could potentially increase erosion rates by one or more orders of magnitude. Economic shifts are also coming into play. Agricultural operations continue to increase in size and specialization, and there is rising interest in production of grain for ethanol and soybeans for biofuel, and in the use of crops and crop by-products as alternative fuels for electrical generation. These trends may increase the amount of high-risk cropland brought into use at the same time as they create a demand for agricultural “wastes” that could substantially reduce the amount of organic matter returned to the soil.
We can only suspect the dimensions of the overall soil problem. We do not have enough information about actual soil erosion rates to be able to do a proper assessment, nor is there sufficient information upon which to evaluate the effectiveness of the most recent cost-sharing programs that have been available under the Agricultural Policy Framework.
Similarly, the monitoring of sediment loss from watersheds is insufficient to enable us to identify trends in soil loss related to changing practices or climate change and thus to prioritize watershed areas of concern. The last substantive effort, carried out under PLUARG in 1978, estimated the average annual transport of sediment via tributaries to the Canadian portion of the Great Lakes at 1,084,000 tonnes. We have no recent data to determine whether this situation has changed and, if so, by how much.
Finally, given its importance to soil health, it seems inconceivable that we know virtually nothing about our soil organic matter and how it is changing. This is information that could be of great value not only in saving and enriching Ontario’s soil, but in developing strategies for sequestering carbon to offset greenhouse gas emissions. We must find ways of overcoming the economic barriers to re-incorporating organic “wastes” back into agricultural soil.
The ECO encourages OMAFRA to set an aggressive soil conservation agenda for its part in the new federal-provincial programs, and to undertake comprehensive soil mapping review, soil erosion assessment and monitoring to support the evaluation of program effectiveness. The ECO also believes that successful programs, past and present, deserve to be re-assessed, and to have their best elements considered for re-institution. Historic cutbacks in staff who implemented technology transfer and extension programs also need to be reviewed. While farm organizations, such as the Ontario Federation of Agriculture (OFA) and OSCIA, are doing a good job of delivering programs, OMAFRA staff is needed to represent provincial interests in their interaction with these groups and directly with farmers. Experience has shown that the areas of the province that have the highest adoption rates of conservation practices are those that have benefited from the work of highly qualified field personnel and aggressive promotion of scientifically and economically based initiatives. Finally, the ECO suggests that OMAFRA consider replacing the concept of “tolerable soil loss” (which does not represent a sustainable level) with “net soil loss” (i.e., soil lost to erosion less natural and engineered replacement) and subsequently develop a long-term strategy to bring Ontario’s net soil loss down to zero. This could be done in conjunction with initiatives to sequester carbon as part of a joint soil conservation/climate change mitigation strategy.
Ecologist C.S. Holling defined resilience as “the ability of a system to maintain its structure and patterns of behaviour in the face of disturbance.” In the case of our croplands, resilience implies not only an ability to maintain productivity (i.e., in commercial terms, to produce a crop) in the face of climatic stresses, such as drought, heavy rainfall and other extreme events, but also an ability to maintain and renew itself on a sustainable basis. At a time when climate change and economic shifts are presenting significant new challenges to the agricultural community, we need to be assured that Ontario’s soils are in good standing.
| Recommendation 9:
The ECO recommends that OMAFRA commit to systematically monitoring, documenting and reporting on farm soil erosion risk levels, net annual soil loss rates and trends in soil organic matter. |
| Recommendation 10:
The ECO recommends that OMAFRA establish an aggressive soil conservation agenda, including a long-term strategy to bring Ontario’s net soil loss down to zero. |
| This is an article from the 2008/09 Annual Report to the Legislature from the Environmental Commissioner of Ontario. |
Citing This Article:
Environmental Commissioner of Ontario. 2009. "Soil: Our Eroding Asset." Building Resilience, ECO Annual Report, 2008-09. Toronto, ON : Environmental Commissioner of Ontario. 61-67.
