Crop rotation is a tactic that has been used for thousands of years to reduce the impact of pest and diseases on crops and to make better use of nutrients in the soil.
By planting crops in a tactical cycle you can avoid a build up of pathogen numbers or insect pests and their larvae in the soil reducing the stress placed on the plant in its effort to fighting off an overwhelming attack.
This cyclical planting also allows nutrients to be used in a successional pattern and for nutrients to be added at critical times in the cycle.
More on these concepts will be explained later.
Crop rotation does not have to be complicated but it does require a little bit of organisation and planning.
Reducing the impact of pest and diseases
Crop rotation reduces the impact of pests and diseases but not allowing the same type of plant to grow in the same area for repeated seasons.
In a crop rotation system there will be a number of years between seasons where a particular type of plant grows in one space.
Plants from the Solanaceae family i.e. tomatoes,potatoes,eggplants etc, can suffer from nematodes. By cycling different types of plants through an area for a few years before plants any of these types of plants in that area again will remove the nematodes favoured plant thereby breaking the life cycle and reducing or perhaps eliminating them from that area.
Making better use of nutrients in the soil.
By rotating crops through an area in a coordinated way you can taking advantage of the differing nutrient needs of the plants and the changing character of the soil.
If we start with legumes, they will add nitrogen to the soil.
This can then be followed with leafy greens which have a high nitrogen demand so they will benefit from the nitrogen fixed in the soil by the legumes.
This can then be followed by root vegetables that have a low need for and benefit from a lower soil nitrogen level in the soil.
Fruiting vegetables can then follow the root vegetables.
Soil should be improved before legumes and fruiting vegetables with compost to replenish nitrients used by the previous crops.
Crop rotation can be done with as many beds as you would like. More beds may be more beneficial in some ways, such as the length of time you can have between plantings of the same type of plant, but it can also reach a stage where it could be harder to manage.
Generally most home vegetable gardeners using crop rotation would use a four or six bed crop rotation.
Four Bed Crop Rotation
With a four bed crop rotation system crops can be separated into:
- Root vegetables i.e. onions, garlic, beetroot, carrots, leeks, shallots etc.
- Legumes i.e. beans, peas etc.
- Leafy greens i.e. lettuce, spinach, silverbeet etc, and
- Fruiting vegetables i.e. tomatoes, capsicum, eggplant etc.
You can start your crop rotation with any type of the vegetable types in a bed as the next planting will move on to a different type of vegetable until you have moved through the cycle to return to the beginning.
During the crop rotation cycle you can add compost to maintain a sufficient amount of organic matter in the soil. Good stages to add compost are before legumes and fruiting plants. You would not add compost before root vegetables as they prefer a less nutrient rich soil than other types of vegetables.
With 4 beds the crop rotation can be set up so that heavy feeders such as leafy greens and friuting vegetables will follow light feeders such as legumes and root vegetables.
As you can see in the diagram below leafy greens follow legumes to take advantage of the nitrogen fixed in the ground for the nitrogen hungry leafy greens. This followed by root vegetable that require less nitrogen. Compost can then be added for friuting vegetables with perhaps another addition before legumes that would then follow fruiting vegetables.
Using a four bed rotation such as this is very simple and does not require too much organisation.
Although it can be easier to have four separate beds it can also be done with the one bed divided into four separate areas.
Six Cycle Crop Rotation.
A six cycle crop rotation can be a little more complicated than the four cycle crop rotation but it is still very easy to maintain.
There are different ways to set up a six cycle crop rotation but the way I like to do it is to take the four cycle system and split leafy greens and brassicas and also split Solancae and corn/curcurbits to create the extra two beds in the cycle.
This six cycle crop rotation can be one bed divided into six sections but it is often easier to have six separate beds.
Using this method with six beds is very similar to the four cycle crop rotation with very little extra effort or complication invovled other than constructing two extra beds or planting areas.
It can also be beneficial to plant a green manure crop at some time in the cycle.
This green manure can be something like comfrey or lucerne and it is probably easiest to insert this crop during winter when it is usual only possible to grow a few groups of crops leaving one or more beds available for a green manure crop.
When using a green manure the crop is grown and before the crop flowers and produces seed it is chopped down and turned into the soil as a kind of compost.
It would also be benficial to use green manure crops in a four cycle rotation.
So whether you go with four beds or six beds crop rotation is a tried and true method for growing healthier crops with few pest and disease problems.
You also have the benefit of reducing the need for chemical pest controls and may even be able to eliminate them altogether.
Combine this with the addition of organinc material such as manure and mulch as well as green manure crops and the need to chemical fertiliser can also be reduced or eliminated.
This leads to healthier and tastier vegetables for you and your family.