Local Effects Of Agriculture On The Environment

Even though no farm is isolated in terms of atmospheric interchange (which affects gases, odours, small particles of spray, etc.), the extent to which water and soil movement occur vary greatly. Effects on the environment may remain local depending on the type of soil, the agricultural practices, the hydrology of the area and the degree of isolation and separateness of the farm. But even if these effects are confined within the farm, they are themselves not negligible since they may affect the health of the farm family and workers, and they may accumulate to the point where they have a wider impact.

Land may become seriously polluted with the accumulation in the soil of heavy metals such as lead, cadmium, zinc, copper and nickel. They are all highly toxic if found in large amounts and do not degrade or disappear. In general, these metals accumulate in soils due to long-term deposits, the source of which varies from air pollution from nearby highways to continuous applications of fertilizers with these elements as micronutrients. The heavy metals build up in the soils as most crops need only very minute amounts to grow. After a length of time, heavy metals may become concentrated enough that the crops can no longer thrive.

Once accumulated, heavy metals are very difficult to remove. Physical or chemical methods of removing are extremely expensive and almost unrealistic. For example, scraping one meter of topsoil from an entire field containing a few kilograms of heavy metals would result in 3,000 tonnes of contaminated soil per hectare!

Fortunately, there are other methods that can be used to decontaminate land. One of them is to utilize some plant species in the crop rotation that can use up large amounts of heavy metals without being adversely affected. These plants are known as 'hyper-accumulators' and are able to take up thousands of times more metal than most crop species.

Other local effects of agriculture may also have long-term consequences for the environment, mainly within the soil. One of them is the dramatic reduction of the population of microorganisms in the soil after many years of applying fertilizer, herbicides and pesticides.

Micro-fauna and micro-flora play a major role in maintaining and improving soil condition and fertility. Beneficial insects, earthworms and other invertebrates also help to control pests and to aerate the soil. But the use of agri-chemicals (generic term that includes pesticides, herbicides and fertilizers) can destroy the fragile balance within the soil that allows life to survive.

Such a situation can be corrected by stopping or limiting certain agri-chemical inputs, but it may take up to seven years to restore a balance within the soil. The length of time may also depend on the type of organisms: the smaller the organism, the less the problem. However, bigger organisms, such as earthworms, spread very slowly. Conversely, creatures that fly, such butterflies, beetles, flies, birds, etc., are not so constrained.