Healthy soils are a key step towards reducing greenhouse gas (GHG) emissions from agriculture.
On this page, we deal with the following aspects of soil health:
- Conservation tillage
- Crop rotations
- Soil cover
- Crop residue
- Soil drainage
- Marginal land
- Organic farming
Click a link in the list above to jump to that topic on this page.
A balanced mixture of minerals, organic matter, living organisms, plant roots, water and gases are ingredients for a healthy soil. When soil components are in healthy equilibrium, nutrients will be available to provide food for the crop and micro-organisms alike. Natural nutrient cycling will limit the need for farmers to apply excess amounts of fertilizers and keep nutrients in forms that are good for the environment.(1) Soil with a wide diversity of soil organisms and nutrients will be more productive and sequester carbon (C) from the atmosphere.
The quality of soil is essential to efficient crop production and environmental health because it plays many key roles for the ecosystem:(2) Soil contributes to agro-ecological health by
- Supporting plant growth
- Controlling water loss, use, and cleanliness
- Acting as a recycling system by decomposing plant and organic residue
- Providing habitats to small mammals, reptiles, and micro-organisms
- Strongly influencing the cycling of gases between the soil and the atmosphere
One of the best indicators of soil quality is earthworm populations. Earthworms increase soil fertility and improve soil physical properties.(3) Worms create burrows that act as water drainage tunnels, aerate the soil and create pathways for crop roots to reach deeply stored nutrients. A minimum of 5 earthworms in a shovelful of soil under cool, moist soil conditions indicates a good worm population in agricultural systems.(4) Other large soil organisms in a healthy soil include nematodes and insects, or micro-organisms, such as bacteria, fungi or algae that live in the soil water and provide nutrients to plant roots.(5)
In agricultural systems, specific forms of nitrogen (N) and carbon (C) are the culprits that create atmospheric greenhouse gases. Farming practices have increased the amount of C and N cycling in the environment, leading to greater amounts of carbon dioxide (CO2) and nitrous oxide (N2O) in the atmosphere. Limited nutrients stay in the soil system, lessening soil organic matter and plant available N forms in the soil. Awareness of the cycling of these two nutrients is important to understanding how crop production can reduce GHG emissions.
Nitrogen is a naturally occurring element that is essential for strong root growth and plant development. Small amounts of N are moved into the soil by biological nitrogen fixation and lightning strikes, replenishing only a portion of N soil reserves. Decomposing organic material provides most of the natural N found in the soil.(6)
To ensure that adequate amounts of N are available for the crop, farmers must apply N fertilizers. Good soil and crop management will ensure that sufficient N forms and amounts are available to the crop throughout the growing season. Simply adding N fertilizer to a cropping system at planting will not ensure adequate and efficient use of the nutrient. For plant uptake, N needs to be in the form of ammonium (NH4+) or nitrate (NO3-). Synthetic fertilizers, such as anhydrous ammonia, urea and UAN that rapidly convert into these forms of N are generally used.(7)
A healthy soil will promote complete N cycling, reducing the likelihood of nitrous oxide (N2O) creation. Nitrous oxide is a potent greenhouse gas that is the byproduct of an incomplete nitrogen cycle and a major greenhouse gas.
Agricultural soils act as both a source of atmospheric carbon dioxide (CO2) gas and as a sink to store carbon (C).(8) Although various farming practices influence C cycling differently, sustainable and healthy soil management should moderate the amount of C leaving the cropping system and aim to enhance the amount of C that remains.
When forests, wetlands or pastures are converted into cropland huge amounts of natural C are released to the atmosphere as CO2 gas. The conversion of these systems releases C stored within the soil or in the plant biomass.(9)
The tillage that occurs in farming systems is a major agricultural source of C. Tillage allows more air and microbes to access soil organic matter (SOM) on a regular basis. Decomposition rates are increased, releasing huge amounts of CO2 to the atmosphere that would otherwise remain in the soil as organic matter.(10)
Soil acts as a C sink when CO2 is sequestered into the system. Using photosynthesis, plants store C in their foliage, seeds or roots. Some of the plant C will decompose to become part of the SOM, portions of which can be considered long-term storage. Organic matter is the component of soil that acts as a natural plant fertilizer and is fundamental to healthy soil.
Besides storing more organic matter and lowering GHG emissions, good soil management will provide economic benefits to a farmer by increasing crop productivity, improving nutrient use efficiency, and enhancing air and water quality.(11,12) Numerous farming practices can be implemented to improve soil health and enhance crop production. Several methods are discussed in the following sections.
Adopt conservation tillage
Conservation tillage, where crops are planted directly into the previous year’s stubble, limit the amount of carbon (C) loss and increase the amount of plant material returned to the soil. Conservation tillage also encourages plant root growth, helping hold soil particles together, improving soil structure and almost eliminating the risk of wind and water erosion. Also known as reduced- till or zero-till, these soil management practices have been shown to sequester C over time.(13,14)
The Soil Conservation Council of Canada estimates that conservation tillage, depending on weather and moisture conditions, can help store between 0.3 and 0.5 tonnes of C per hectare per year in the soil.(15) Research from Saskatchewan has shown there is more available organic nitrogen (N) in long-term zero tillage fields than in fields tilled using conventional methods.(16)
Conservation tillage is done using narrow, low disturbance openers (knives or discs). These openers have the advantage of minimal seedbed disturbance (less than 33 percent of the total surface area), encouraging sparser weed growth and improved crop production. Benefits also include moisture conservation, erosion control, and reduced labour and fossil fuel costs. Crop stubble that is left standing over the winter will help trap snow, increasing spring soil moisture and permitting the survival of over-wintering crops.(17)
Choose effective crop rotations
The best crop rotations should not only manage soil nutrients and reduce pest problems, but also improve soil quality. While the environmental benefits of certain crop rotations are clear, market demand or production constraints may limit which crops can be grown.
Here are some suggestions to improve crop rotation quality:
- Include legume and pulse crops in crop rotations to fix N. Perennial legumes, such as alfalfa or clover, provide valuable nutrients to subsequent crops and encourage the increase of SOM. Pulse crops, such as beans, peas or lentils, are also biological nitrogen fixers and encourage N accumulation in plant roots.
- Use crops with high N requirements, such as corn or cereals, as a follow-up to legumes. These crops need much N to grow and using the fixed N in the soil will help reduce the amount of fertilizer required at planting.(18)
- Remove surplus N by planting a winter cereal (i.e. winter wheat or fall rye) or a cover crop, such as mustard, vetch, or clover after harvest. Cover crops provide nutrients for subsequent crops, reduce weeds, host beneficial insects and improve soil quality.(19)
- Try planting multi-species crop mixtures, such as alfalfa-brome grass, or clover-winter wheat when using cover crops.(20) Crop mixtures help mimic a natural system and use soil nutrients more efficiently, reducing their potential to be lost to the environment.(21)
- Consider forages for their numerous indirect benefits on grain production. Perennial forages trap more atmospheric carbon dioxide (CO2) because they have extensive roots systems and grow for more months of the year than annual crops. Forage production not only improves the soil by increasing organic C, it suppresses pests, increases subsequent crop yield and quality and uses surplus soil nutrients.(22) Capable of absorbing excess water, forages are great for managing high water tables or soil salinity, by lowering the water table.(23) Reducing soil moisture also limits the risk of N losses by denitrification, cutting down the amount of N2O emitted to the atmosphere.
Increase soil cover
Improving crop rotation quality can also be achieved by eliminating the use of summer fallow. Besides leaving fields susceptible to wind and water erosion, fallow reduces the amount of plant residues returned to the soil and encourages residue decomposition by soil animals and microorganisms.(24)
Rather, a green manure cover crop or legume can be used in the crop rotation to increase the N and C content of the soil. The cover crop would be returned to the soil or left as surface mulch in mid-July when there are peak nutrients in the plant tissues. The nutritional residues reduce the need for synthetic fertilizer addition the following spring. Cover crops also limit the risk of wind or water erosion (25)
Manage crop residue
Properly managing crop residue can enhance soil organic matter and nutrients or improve soil moisture. Depending upon production practices, time and labour constraints, or equipment availability, there are different options to managing crop residues.
Opportunities for removing residues from the field include either stubble burning or baling. Stubble burning is strongly discouraged for many reasons:
- More than 90 percent of crop residue C is lost (mostly as CO2) when it is burned, returning little nutrients or organic matter back to the soil (26)
- Burning can turn into a health hazard, when smoke remains close to the ground and moves towards residential areas
Consider alternate uses for cereal straw such as chopping and spreading it back on fields or baling the straw to be sold for profit. Cattle farmers can either graze or bale the straw to be used for livestock bedding and feed.
A farmer may choose to incorporate crop residue. Under drought conditions or on soils prone to erosion, increasing crop residue is favorable.
On heavy clay soils or during wet conditions, fewer residues are ideal otherwise soils can take longer to warm up in the spring.(27) Harvest methods will influence the amount of residue left on the field. To effectively encourage straw and chaff residue decomposition, combine settings should be set so that straw is finely chopped and spread over the maximum amount of the width of cut.(28) Crop residue will slowly decompose, providing nutrients to subsequent crops and improving OM in the soil.
If a farmer chooses to leave crop stubble standing on the field from harvest to seeding, there are several benefits that can be achieved. Between 30 and 60 percent crop residue cover is recommended to prevent wind erosion. Crop residues also encourage the trapping of snow over the winter months. Adequate snow cover encourages the survival of over-wintering crops and increases the amount of spring soil moisture.(29)
Manage soil drainage
Saturated conditions during the growing season are more prone to producing nitrous oxide (N2O) through denitrification. Saturated soils also increase water stress for the plant, resulting in unhealthy, stunted plant shoots and roots from lack of oxygen.(30) Improving soil drainage will encourage efficient crop growth, increase nutrient and fertilizer uptake and may even extend the crop production season.(31)
Surface drainage of fields in the province is done using small drainage ditches within fields and large, deeper, permanent ditches around field edges. Proper drainage should remove excess ponding from the field within 24-48 hours of a precipitation event. Rapid water removal will reduce the potential for crop damage.
Sometimes a high water table can be an issue, resulting in extended, saturated soil conditions. In these scenarios, an increase in SOM to improve water infiltration, diversifying the crop rotation or planting perennial forage crops are management strategies recommended to improve drainage. A good indicator that inadequate surface drainage may be an issue can be local weeds. Indicator weeds that thrive in wet environments include horsetail, chickweed, and marsh smartweed. Even though retention ponds are a great idea for water conservation, it is not a viable option for farmers. They would have to purchase irrigation equipment, etc and it is not worth the money for most prairie crops. This could be a possible option for potatoes or veggie crops.(32)
Remove marginal land from production
Maintaining or improving soil drainage removes the need for the conversion of marginal land into agriculture. Flood-prone property or lands with excess moisture require the same inputs as productive crop land, but produce lower yields.
Marginal land, such as wetlands and marshes, are beneficial to the environment. They recharge groundwater, filter and recycle nutrients, and provide wildlife habitat. These lands should be protected from agricultural development when possible.
Consider organic farming methods
Organic farming adopts a whole-system management approach, with the farmer making decisions based on the farm ecosystem as a whole. Many organic farming methods have the potential to mitigate climate change by reducing greenhouse gas emissions and sequestering carbon dioxide (CO2). While numerous variables make it difficult to confidently say that organic systems are more environmentally sustainable than conventional systems, there are some key practices that favour organic agriculture.
Conventional farms will also benefit from many of these organic practices:
- The use of legumes has the potential to reduce agricultural emissions of greenhouse gases by reducing the need for synthetic fertilizers. Growing perennial legumes, such as alfalfa, is a proven way of replacing the need for synthetic N fertilizer in Prairie cropping systems.(33)
- A Manitoba study that compared two crop rotation types with organic and conventional production found that energy usage was 40-50 percent lower on organic farms. The major factor affecting energy use between the two systems was the use of inorganic (synthetic) fertilizer in the conventional system. Energy efficiency was determined higher in the organic system.(34)
- Organic agriculture sustains soil fertility by enhancing nutrient cycles, building soil organic matter and promoting biological activity.(35) The increased use of green and animal manure, intercropping and cover cropping, perennial forage crops and composting techniques may result in carbon (C) gains and help reduce soil erosion.
- A further benefit in organically farmed soils is increased water content. Soils with higher C content can capture more water, providing necessary water to plants. In a 12-year study in north-eastern U.S.A., water volumes were found to be substantially higher in two organic systems compared to a conventional agro-ecosystem.(36) Ability to conserve water might make this organic management practice important for adapting to climate change. However, the impact of greater moisture retention on emissions of N2O should also be considered.
For more information, download our publication “Farming in a Changing Climate in Manitoba – Crop Edition (2013)“