Soil management
By  Manitoba Eco Network

Besides storing more carbon and making more efficient use of nitrogen, good soil management will provide economic benefits through increased productivity, more efficient use of nutrients, and improved air and water quality.

Agricultural soils act as efficient repositories for carbon, but under certain conditions soils also release carbon dioxide back into the atmosphere.

Plants fix atmospheric carbon into foliage and roots, which eventually becomes soil organic matter.

Soil organic matter is fundamental to healthy soil.

While much of the stored carbon is released back into the atmosphere when plants decay, some of it remains trapped in the soil as organic matter.

Through denitrification and other processes soils also release excess nitrogen into the atmosphere as nitrous oxide and nitrogen gas.The following farming practices can reduce the amount of greenhouse gas emissions from soils.

"Low till" (Conservation tillage)

In conservation tillage, crops are directly planted into the previous year’s stubble, with minimum or no tillage. This practice not only reduces fossil fuel consumption, but also increases soil organic matter (compared to conventional tillage*) that otherwise would be emitted as carbon dioxide. Conservation tillage, along with reduced use of summerfallow, can store from 0.3 to 0.5 tonnes of carbon per hectare per year in the soil, depending on weather and moisture conditions.

As well, research from the University of Saskatchewan has shown there’s more available organic nitrogen in long-term zero tillage fields than in fields tilled using conventional methods.

Choosing to seed with narrow, low disturbance openers (knives or discs) has the further advantage of minimal seedbed disturbance. Crops seeded with low disturbance disc and knife openers have shown improved production and fewer weeds over crops seeded with higher disturbance openers, such as spoons or sweeps.

Additional benefits of conservation tillage include enhanced water infiltration, moisture conservation, reduced labour requirements, and less runoff and soil erosion due to wind and water.

Crop rotations

The best crop rotations should not only effectively manage nutrients and reduce pest problems, but also improve soil quality. While the environmental benefits of certain crop rotations are clear, market constraints may limit which crops are included. Some suggestions:

The addition of legume crops in crop rotations will fix nitrogen. Perennial legumes, such as alfalfa, increase soil organic matter, while the residues contain nitrogen, which can easily be broken down to be used by subsequent crops.

Crops with high nitrogen requirements, such as corn or cereals, used as a follow-up to legumes will capitalize on the fixed nitrogen in the soil.

Planting a winter cereal or another cover crop after harvest (if timing permits) will help remove surplus nitrogen. Cover crops also store nutrients for the crops that follow them, as well as reduce weeds, host beneficial insects, and improve soil quality.

Forage production is a further way to reduce emissions. Increasing forage production not only increases soil organic carbon, but it also uses surplus soil nutrients, reducing the risk of nitrogen losses, including denitrification.

Crop mixtures, such as alfalfa-bromegrass, use soil nitrogen more efficiently and reduce the potential for nitrogen losses to the environment.

Marginal land

Marginal lands require the same inputs as productive land, but produce lower yields and profit. By planting these marginal or fragile lands to perennial cover, farmers can improve profit margins, create a carbon sink and provide natural habitat.

The best solution for flood-prone areas or lands with excess moisture may be restoring them back to wetlands. Wetlands can remove carbon dioxide from the atmosphere, reduce downstream flooding, help to clean water and provide wildlife habitat.
 

Stubble burning

On average, more than 90 percent of all carbon in crop residues is lost (mostly as carbon dioxide) when it is burned. Alternate uses for cereal straw include chopping and spreading back onto the fields, baling, grazing, and using for bio-energy feedstock and bio-fibre.

Soil drainage

Since saturated soils during the growing season are more prone to denitrification and producing nitrous oxide emissions, improving drainage encourages efficient crop growth and uptake of nitrogen fertilizer.

Drainage improvements may include enhanced surface drainage, installation of tile drains, or the use of trees, shrubs and other perennial crops to remove excess water. In some cases, it may be more appropriate to store water and refrain from annual crop production and fertilizer applications.

Soil cover

Crop residues left on the surface help prevent soil erosion. Manitoba Agriculture recommends that 60 percent of the soil surface should be covered with crop residue in the fall to prevent erosion.

Summerfallow

Summerfallow is already a dying practice in Manitoba. But it is worth noting that besides leaving fields susceptible to wind and soil erosion, soils that were frequently summerfallowed usually had reduced soil organic matter compared to continuously cropped soils.

This practice reduces the rate of organic matter breakdown compared to conventional tillage methods. Tillage buries stubble and aerates the soil. This increases the rate of soil organic matter breakdown. Conservation tillage doesn’t increase soil organic matter compared to forest or prairie.

 

October, 2013

Source:  Climate Change Connection