Corn & The Environment

Sustainability of Corn Production

Sustainable development was defined by the World Commission on Environment and Development (the "Bruntland Commission") as "development which meets the needs of the present without compromising the ability of future generations to meet their own needs ".

Corn production in Canada includes features which could be classed as sustainable, and others which are not. Sustainable features include the use of sunshine, carbon dioxide and rainfall as the principal ingredients for corn growth. Almost no corn grown for grain or forage is irrigated in Canada.

The decline in soil organic matter levels associated with older methods of corn production could be classed as non sustainable. However, with conservation tillage techniques and higher corn yields, future soil organic matter levels can be expected to increase when land is planted to corn.

Conservation tillage and crop rotations which leave the soil surface protected against the action of wind, rainfall, and melting snow have markedly reduced the amount of soil erosion traditionally associated with corn production.

Pesticides (mostly herbicides in the case of corn production) are currently made from petroleum, a non-renewable resource. However, the quantities used are low - generally 2 to 3 kg/hectare of active ingredient - and declining.

The same situation exists for fossil fuels. An average of about 53 litres of petroleum-based fuels per hectare are used in field operations to grow corn (Cemcorp, 1992). This quantity is declining. The U.S. Environmental Protection Agency (1991) has estimated that fossil fuel usage in field crop production can be reduced by almost 50% with no-till technology.

The technology exists to use ethanol made from corn, or "soy-diesel" made from soybeans, as on-farm fuels. Refuse from corn production - i.e. corn cobs and husks - can be, and is being, used as a fuel for grain drying and for on-farm heating. The extent to which these uses of renewable fuel energy in agriculture expand will depend on the efficiencies of new technology and economics.

There are no effective substitutes for potassium and phosphate fertilizers used in the production of corn - and virtually all other agricultural crops.

The supply of available potassium in Canada is enormous - sufficient to meet predicted market needs for at least many centuries - and the energy cost needed for mining, transportation and application is small (Cemcorp, 1992).

With phosphate fertilizer, large global reserves of rock phosphate exist - the closest to Canada being the southeastern United States - but some energy is needed to process this rock into available plant fertilizer. (The availability of phosphate to plants from rock phosphate is very low.) Corn biomass energy could be used to reduce rock phosphate, but this is not likely to occur unless the price of non-biomass energy becomes significantly higher. Fortunately, the annual phosphate fertility requirement by corn, and energy used in meeting this requirement, is generally smaller than for potassium or nitrogen (Cemcorp, 1992).

The manufacture of nitrogen fertilizer, using natural gas as the energy source and atmospheric nitrogen gas as the feedstock, represents about half of the fossil-fuel energy requirement for corn production (Cemcorp, 1992). A similar situation exists for most non-legume, high-yielding farm crops.

Efficient use of livestock manure represents one means of reducing the need for synthetic nitrogen fertilizers.

A second involves the use of high-nitrogen-fixing crops such as alfalfa in the crop rotation, although this can only occur if there is a use for the legume forage produced. This generally means production of ruminant livestock animals such as cattle and sheep.

Annual legumes such as soybeans, field beans, and even forage legumes grown as a part- season cover crop (for example, red clover after winter wheat) normally can provide only a modest percentage of the soil nitrogen compounds needed for successful production of corn the following year.

Non-agricultural products, for example urban wastes, could potentially serve as a source of nitrogen fertilizer. However, health hazards (to both plants and humans) can exist with this material, and procedures commonly used to reduce these hazards - such as composting - tend to reduce the fertilizer value. (About half, or more, of the nitrogen in plant wastes may be lost by leaching or volatilization during composting.)

Biotechnology may provide a solution if researchers are able to transfer nitrogen-fixing abilities, genetically, from legume species into corn.

Until this occurs, the requirement for nitrogen fertilizers will remain the least sustainable feature of corn production, given the impracticality and environmental risks of supplying all of the crop's needs using animal manure, perennial legumes or urban wastes as dominant sources of nitrogen supply. The combustion of biomass as an energy source for nitrogen fixation also seems impractical, given the size of the need, and the high scale efficiencies associated with nitrogen fertilizer manufacture in large, "world-scale" plants.

It should be noted that the limiting resource is energy, not supply of nitrogen gas. Global atmosphere is almost 80% nitrogen gas!

The source of fossil energy for nitrogen fertilizer manufacture is natural gas, and Canadian natural gas reserves are relatively large - unlike those for light crude petroleum. Known Canadian natural gas reserves are equivalent to about 30-40 years of Canadian consumption, and Canada is a substantial exporter of natural gas (National Energy Board, 1991).

This dependence on synthetic nitrogen fertilizers is not unique to corn. The requirement per tonne of grain or seed produced is similar for most major non-legume crops. Technology now being developed to permit the times and rates of nitrogen application to be more closely tailored to individual crop needs, should permit the overall need to be reduced significantly - though not eliminated.