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The Importance of Crop Rotation and Succession in Organic Gardening

Crop rotation is a fundamental practice to prevent soil fertility loss. Here's how to implement it correctly.

by BioGrow

Crop rotation is a fundamental practice in organic horticulture. To prevent soil fertility loss and overall “exhaustion,” it’s necessary to plan the proper succession of crops. In conventional agriculture, the logic of soil conservation and fertility is replaced by commercial interests. This leads to cultivating the most profitable species, often belonging to the same botanical family. This creates an imbalance, which is attempted to be masked by heavy use of mineral fertilizers and phytosanitary products. However, in the long run, such a logic only leads to agricultural system instability, eventually resulting in soil loss and inexorable desertification. Organic agriculture must be environmentally sustainable.

The first rule for adequate sustainability is maintaining biodiversity. This is primarily achieved through rational agronomic practices, such as crop rotation. Let’s explore the fundamental principles of this practice and discover some practical suggestions.

What does “soil exhaustion” mean and what problems does it cause?

Incorrect crop rotation can lead the soil to develop exhaustion phenomena. The phenomenon of soil exhaustion has been studied agronomically for centuries. It starts from the assumption that all cultivated plants (although to varying degrees depending on the species) do not thrive when repeated.

Soil productivity

The first consequence of this exhaustion is the decrease in soil productivity itself. This problem, as mentioned, is compensated for in conventional agriculture by resorting to chemistry.
However, operating in monoculture or mono-succession, i.e., repeating the same crop several times in the same piece of land, causes problems on multiple levels.
For example, there is the continuous absorption by plants of the same nutrients. This does not allow the soil itself to find a balance and thus depletes it of organic matter.
Furthermore, monoculture always exploits the same soil layers, regardless of the type of soil on which it is planted. This happens because the root systems exploring the soil are always the same.

Proliferation of pests

Another direct consequence of improper crop rotation is the proliferation of parasitic agents, both animal and vegetal. These multiply much faster by repeating the same crop. A glaring example could be a parasite like the Colorado potato beetle, a highly damaging insect that is difficult to eradicate. If one year we cultivate potatoes and experience a mild infestation of the beetle, if we repeat the same cultivation on that same plot of land the following year (or cultivate a plant from the same family, such as the eggplant), we can be certain that the Colorado potato beetle invasion will worsen.

Weed proliferation

Another problem with poor or absent crop rotation is the increasing difficulty of controlling weeds. They become more specific to the crop and more resistant. Sometimes even a good mulching may not be enough to control their proliferation.

Accumulation of substances

Finally, incorrect crop rotations and repeating the same crops on the same soil can lead to the accumulation of substances that plants naturally secrete. At high concentrations, some of these substances, such as nitrates, can become toxic.

Accumulation of Substances

Finally, incorrect crop rotations and repeating the same crops on the same soil can lead to the accumulation of substances that plants naturally secrete. At high concentrations, some of these substances, like nitrates, can become toxic.

The Benefits of Crop Rotation

Crop rotation divided into garden bedsOrganic cultivation, unlike conventional farming, is constantly seeking sustainable production processes. The goal is always to respect the soil’s biological balance and increase its fertility. With adequate crop rotations, the problems and disadvantages seen previously are reversed in favor of the farmer. For example, problems with pests and fungi do not affect all plants indiscriminately. For this reason, the first solution for their containment is varying the type of crop. In this perspective, proper crop rotation becomes a preventive and sometimes even curative strategy. For example, in the case of soil nematodes (whose presence indicates soil fatigue), action can be taken by using Brassicaceae in crop succession, which have specific natural biocidal activity. At this point, the cycle becomes virtuous, and there is no need to use synthetic chemical pesticides. For residual control of pests and pathogens, natural macerates are sufficient. Some, like those of horsetail, garlic, nettle, or tomato, can be made by ourselves with the plants present in our soil. Soil fertility is also favored because some plants consume more of certain elements than others. With adequate rotation, the system remains balanced, and there is no need for heavy mineral fertilization. It is enough to amend the soil with simple natural organic substances, such as manure, compost, or earthworm humus. Weeds also decrease and cause fewer problems with proper crop rotation. This is because they face more competition from diversified crops. A good natural mulch is enough to keep them under control. Finally, several agronomic studies have shown that crop rotation (and similar practices) greatly alleviate the problem of soil erosion. A clear example is the practice of cover cropping.

Classifying Vegetables Based on Nutrient Consumption

To design a home garden or manage agricultural land with adequate crop rotations, it is necessary to first understand the characteristics of the plants that will be cultivated. A first and simple classification is based on the consumption of organic matter by the crop. In this sense, we distinguish between “heavy consumers,” “medium consumers,” “light consumers,” or “nutrient producers,” particularly nitrogen. Among the heavy consumers, we have:

Among the medium consumers, we have:

They are nutrient producers and generally light consumers:

According to this widely accepted approach, an excellent crop rotation scheme involves abundant manuring, followed by the cultivation of heavy consumer crops. These are followed by medium consumer crops and finally a cycle of crops that are light consumers or soil improvers.

Rotation Based on Botanical Families

The general scheme of crop rotations based on nutrient consumption needs to be further explored by understanding the specific botanical families to which vegetables belong. An absolute rule dictates that crops from the same family should not follow one another in succession. It should also be noted that there are conflicts between certain different families.
Let’s look at some examples with the main crops commonly found in home gardens.

Chenopods

Let’s start with the Chenopod family, which includes Swiss chard and spinach. The rule is that they should never follow each other, not even alternately.

Composites

Then we have the Composites, primarily artichokes, a perennial plant that, once its cycle is complete, should not return to the same soil for at least 5 years. Within this family, we also have endives, escarole, lettuces, and radicchio. Given their widespread cultivation, it’s easy to make mistakes, but they also follow the general rule of not repeating themselves and not following each other. A good succession is with spinach and leeks.

Crucifers

Crucifers, on the other hand, are a large family that includes several species cultivated in vegetable gardens. Among the best-known vegetables, we have cauliflower, broccoli, cabbage, savoy cabbage, and turnip. These are all plants that significantly deplete the soil. In their crop rotation, they should not follow themselves, and they should also avoid plants from the Solanaceae and Umbelliferae families. Other Crucifers include radishes and arugula, which, although not heavy consumers of soil nutrients, should not follow themselves. This precaution helps, for example, to avoid problems with flea beetles.
A good rotation for these plants is instead with peas or cereals.

Cucurbits

Then we have the Cucurbitaceae family, including watermelon, cucumber, melon, squash, and zucchini. For the crop rotations of this family, it’s important not to repeat the same crops in the same soil for at least two consecutive years, not even by interchanging them with each other. Many recommend also avoiding succession with the Solanaceae. Good successions are with cabbages, legumes, salads, cereals, and leeks.

Legumes

Moving on, we have the Legumes, including beans, snap peas, fava beans, peas, lentils, chickpeas, lupins, and peanuts. These are soil improver plants as they can fix atmospheric nitrogen with their roots. They are suitable for crop rotation with any other plant, but they should not be repeated among themselves.

Liliaceae

Another important family is the Liliaceae, among which we find asparagus, a perennial crop. After its cycle, it should not return to the same soil for 5 years. Asparagus should never be followed by potatoes or carrots. They are instead suitable for rotation with cereals and strawberries.
In this family, we also have garlic, onions, and leeks. These crops should never follow themselves and should also avoid potatoes and beets. Suitable for rotation are instead tomatoes, cabbages, cucumbers, and legumes.

Umbellifers

Next, we have the Umbellifers, including carrots, fennel, parsley, and celery. With these crops, especially in the presence of diseases, crop rotation requires a period of 3 to 5 years before repeating the cultivation. They should also not be grown after beets. Without disease problems, they are suitable for rotation before and after most other crops.

Solanaceae

Let’s finally consider the Solanaceae family, which includes eggplant, potato, pepper, and tomato. These are among the most demanding crops in terms of nutrients and consume a lot of soil. Their crop rotation should never involve successive plantings of the same crop or even within the same family. It’s also advisable to avoid Cucurbitaceae and Chenopodiaceae. An excellent rotation after these plants is with legumes or, at a stretch, with crucifers.

Resting the Soil and Green Manures

When crop rotations are not respected, we may encounter phenomena of soil exhaustion. In such cases, it’s advisable to consider a period of soil rest. Resting the soil is not a bad thing; on the contrary, it’s an opportunity to fertilize it properly. A typical resting period is at least six months. During a period of rest, one option is to use green manure (or cover crops). The most suitable plants for this cultural operation are legumes, such as clover or vetch.

Crop Rotations in Home Gardening

How should one proceed in a home garden to follow a crop rotation plan? This is a problem that every gardener faces, but it becomes more pressing if space is limited. An idea for efficient planning is to divide the plot of land into several parts (usually at least 4) and design it according to the crop rotation rules seen earlier. It’s always better to keep one part fallow. Another important precaution is to write everything down, keeping a sort of farm notebook. While working from memory may be feasible for the first few years, it’s wise to have a written reference over time. The division can be done by creating beds, but also just theoretically, with hypothetical divisions. In this way, even those with a small plot of land can follow a valid crop rotation scheme. By doing so, you’ll ensure healthy and flourishing productions, greatly reducing problems related to diseases and pests, as well as disappointments arising from intensive and repeated cultivation.

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