Crop rotation is not a new concept; it has been practised for thousands of years. Basically the science of crop rotation is based on the facts that it is never a good idea to grow the same crop on the same piece of land two seasons running, for two main reasons: Every type of crop takes different nutrients from the soil, leaving these depleted for crops that follow.
In case of the crop disease or pest outbreak, the residues are left in the soil and can attack the subsequent season. If a different crop is growing on same piece of soil, it is unlikely to be attacked as pests are more than often specific to a certain plant.
Growing the same crop in the same place for many years (monoculture) leads to an increase in pests and soil-borne diseases.
With crop rotation, various crops are grown in such a way that no crop is planted on the same piece of land more than once in at least three (preferably four) planting cycles.
While crop rotation improves soil and is good for conservation purposes, its greatest benefit is to reduce the level of disease in the soil.
Many pathogens (germs) can survive in the soil after the crop has been harvested. If you fail to practise crop rotation, this infestation will get worse, leading to higher pest management costs.
The common practice for farmers is companion planting which helps protect plants from pests. Companion plants growing next to a food crop disrupts the pest’s pattern. They detect the host plants but become confused because of the diverse distribution of plants.
For example when growing cabbages or broccoli separate the rows with a row of onions. Also growing tomatoes next to cabbages deters caterpillar and growing leeks next to carrots repels carrot flies.
Planting marigold between vegetables may reduce unwanted nematodes in the soil. Nematodes occur naturally in the soil, but monoculture can lead to a build-up of species harmful to specific crops.
These nematodes may feed on the root system of host plants and cause considerable damage. Basil planted with tomatoes and lettuce may deter insects, and oregano planted with broccoli may repel cabbage flies.
How crop rotation works
Simply divide your growing space into a number of distinct areas, identify the crops you want to grow and then keep plants of the same type together in one area.
Every year the plants grown in each given area are changed, so that each group (with its own requirements, habits, pests and diseases) can have the advantage of new ground.
Most crop rotation schemes tend to run for at least three or four years, as this is the number of years it takes for most soil-borne pests and diseases to decline to harmless levels.
If your beds are divided into four groups, this means that members of each plant family won’t occupy the same spot more than once in a four-year period.
Perennial vegetables such as soft fruit, rhubarb, asparagus and globe artichoke aren’t replanted each year, so they may need their own dedicated bed.
Grow brassicas followed by legumes. Sow crops such as cabbage, cauliflower and kale on soil previously used for beans and peas.
The latter fix nitrogen in the soil, whilst the former benefit from the nutrient-rich conditions thus created. Potatoes also love nitrogen-rich soil, but should not be planted alongside brassicas as they like different pH levels.
Very rich soil and roots don’t mix: Avoid planting root vegetables on areas which have been heavily fertilised, as this will cause lush foliage at the expense of the edible parts of the plant.
Sow parsnip on an area which has housed demanding crops (such as brassicas) the previous season, since they will have broken down the rich compounds.