down on the farm

Many people go out of their way to buy organically grown produce because of the guarantee that such produce is free from pesticides, but there are other benefits that are often overlooked or not understood. In particular, the use of synthetic nitrate fertilizers is banned under Soil Association rules in the UK, and probably by other accreditation bodies elsewhere, because this has an important effect on the uptake by plants of trace elements from the soil. All nitrates are extremely soluble in water and therefore dissolve preferentially; as a result, trace elements are not taken up by a crop that is fertilized in this way, and its nutritional value is thereby reduced.

There are two main strands to the practice of organic farming: crop rotation, which includes the planting of legumes, and soil conditioning. Legumes such as clover have nodules on their roots that are home to colonies of nitrogen-fixing bacteria, so when the crop is ploughed back into the soil at the end of the growing season, this becomes a vital source of nitrogen given the prohibition on synthetic nitrates. Animal manure provides an additional nitrogen source, but this material also has an important effect on soil condition.

Soils vary considerably depending on the underlying bedrock, the use to which land is put and the materials that are added, but all soils are complex ecosystems that need to be managed carefully. Soils that have a low organic content (humus) do not retain moisture efficiently, while soils with a high content of clay minerals easily become waterlogged. It follows that soil health depends on having plenty of humus, so that air can enter the pore spaces between soil grains and thus support the bacteria and small invertebrates (earthworms, burrowing insects, etc.) that are essential if the organic material is to decompose, making nutrients available to the growing crop. Roots also need air to function properly, so soil condition is of crucial importance whatever the crop.

An often neglected aspect of sustainable arable farming is composting, although ploughing unwanted plant material back into the soil is a viable alternative. However, the best way to deal with organic waste is to place it in a compost heap, where it will decompose aerobically, with the aid of invertebrates and micro-organisms that invade from the underlying soil, to form a material rich in humus that can be added to the soil.

Pests are dealt with in organic farming by introducing natural predators, which commercial pesticides are likely to kill in addition to the target pest. Another useful technique is intercropping: for example, planting pungent herbs such as rosemary and sage among rows of carrots deters the carrot root fly, the larvae of which can devastate a carrot crop. Ensuring that plants are healthy makes it less likely that they will be seriously affected by fungal infections and other plant diseases. The end result is foodstuffs that are healthier to eat and contain more trace nutrients than the same foods produced by conventional means, which in addition to being less nutritious are often completely lacking in flavour.

However, there is one major drawback to organic farming: crop yields are lower, and with the world’s population already approaching unsustainable levels, this is not a problem that can be ignored. The choice is therefore between producing less nutritious food in greater quantities and organically grown produce, which costs more and can feed fewer people. This begs an unavoidable question: is it socially responsible to insist on buying organic produce when the priority should be to feed everyone, not just those who can afford the higher prices that come with lower yields?