What is Crop Rotation?

What is Crop Rotation?

What is Crop Rotation? The basic principle of crop rotation is to keep closely related vegetables together and grow them on a different piece of land each year. The crops are moved around in a regular sequence so that they do not return to the same spot for three or four years, or longer.


Benefits

There are several reasons for crop rotation: it helps to control pests and diseases and weeds; it maintains soil fertility and also helps to improve soil structure.


Pest and disease control

The most commonly recognized benefit is that it helps to avoid problems of soil pests such as eelworm and diseases such as onion white rot, which attack only a closely related range of crops. By growing crops belonging to different botanical families in successive years, you can prevent such pests and diseases building up.


Weed control

Rotation helps weed control. Moving weed-suppressing crops such as potatoes and squashes from plot to plot can minimize problems for crops that follow, and help to prevent any one weed from getting out of hand.


Soil fertility

Rotation is equally important for maintaining the soil fertility. Different crops make different demands on the soil, and growing one crop continually may exhaust the ground of a certain nutrient. Changing crops from year to year (and hence also the soil management) allows the soil reserves to be replenished. Many leguminous crops like peas and broad and runner beans add nitrogen to the soil, which helps to feed the following crop.


Soil structure

Similarly, rotation helps to improve the soil structure. Alternating between crops with deep tap roots and those with a mass of shallow fibrous roots benefits the soil at all levels.


Problems

In practice it is not always easy to adhere to a strict crop rotation. This is particularly true if you have a small garden.


Weather

The weather may upset sowing and harvesting times by several weeks.


Garden conditions

There may also be parts of the garden that are ideally suited to — or indeed the opposite and completely unsuitable for — certain crops. Only one end of the plot may be sunny and sheltered enough to grow tender crops such as tomatoes, for example.


Clubroot

Where clubroot is a problem, it may even be advisable to keep aside one area for brassicas, and improve it for them by liming until the pH is high.


Is it worth it?

It is sometimes argued that crop rotation is not worthwhile in a small garden, since some dis- eases such as clubroot and white rot persist in the soil for much longer than four years and crops can only be moved a few metres.

However, even if rotation cannot guarantee complete control of pests and diseases, in most cases it does help towards it. In any event, it is still valuable for improving the soil. This is particularly the case in an organic garden, where fertility building relies on different organic materials and green manures being used in conjunction with different crops.


Planning a Crop Rotation

The first step in planning a rotation is to divide the garden up. Next, select your crops and then start cultivating the ground.


Dividing up the garden

Divide your vegetable garden into equal sections, one for each year of the rotation. This can mean anything from simply putting in wooden marker pegs at the side of the bed to physically dividing it with a network of paths.

In most gardens, there is only space for a three- or four-year rotation. On a bed system, you will need to group beds together into three or four groups.


Selecting crops

Decide which crops you are going to grow together and which are going to follow which.

This will be determined in first by their botanical families, and second by their soil and nutrient requirements. Salsify and scorzonera (the Compositae family), for example, can be grown with the Umbellifers (carrots and parsnips) because they have similar soil and nutrient requirements. If these follow a crop to which manure or compost was applied the previous year, their needs will be satisfied.

Another factor which can affect the crop groupings is their sowing and harvesting times. It is more convenient if you can clear a good part of a plot (or a whole bed on the bed system) at more or less the same time so you can prepare it for replanting. For example, leaf beet fits well with overwintering brassicas such as purple sprouting broccoli because, as well as having similar nutrient requirements, they both need to stay in the ground until harvesting is finished in spring.

Green manures must also fit in with the crop rotation.


Putting crop rotation into practice

While it is no use sticking slavishly to a rotation if it is to the detriment of the crops, it is still worth having an overall plan. On the bed system, a plan for a crop rotation is easier to make and is more flexible in practice. Records are also valuable. Keep a note, not only of what is grown where, but of when the crops are sown and when they are cleared. This will help you to plan more accurately in future.

The vegetables you grow and the quantities in which you grow them are a matter of personal choice, so it is almost impossible to follow an off-the-peg rotation plan exactly. The traditional four-year rotation of potatoes—brassicas—legumes—roots assumes that potatoes and brassicas make up much of the bulk of the plot. This might still be the case on an allotment, but in a small garden you are more likely to concentrate on vegetables that are best picked fresh or are difficult or expensive to buy, for example, salads, spinach and unusual crops such as kohlrabi and celeriac. Thus a different plan may be required.


Vegetable Families

The groups of vegetables given below are organized according to botanical families. When planning a crop rotation, keep vegetables in the same family together and “rotate” them so they grow in different ground in subsequent years.

Brassicas (Cruciferae)

Brussels sprouts, cabbage, broccoli, calabrese, cauliflower, kale, radish, swede, turnip

Legumes (Leguminosae)

Pea, bean (broad, French and runner) Potato family (Solanaceae) Potato, tomato

Umbellifers (Umbelliferae)

Carrot, parsnip, parsley, celery, celeriac, Florence fennel

Daisy family (Compositae)

Lettuce, chicory, endive, scorzonera, salsify

Onion family (Alliacae)

Onion, garlic, shallots, leeks

Beetroot family (Chenopodiaceae)

Beetroot, spinach, Swiss chard, spinach beet

Cucurbits (Cucurbitaceae)

Cucumber, courgette, marrow, squash, pumpkin

Not related to any other vegetable

Jerusalem artichokes, sweetcorn

28. January 2011 by Dave Pinkney
Categories: Kitchen Garden, Organic Gardening | Tags: , | Comments Off on What is Crop Rotation?

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