Alternation of crops, or crop rotation
Long-term cultivation of one crop at the same site degrades the nutrition and development of plants, causes depletion and depletion of the soil, leads to the accumulation of pests and pathogens in the soil. So, with the constant cultivation of cabbage, the soil becomes acidified, and on the sites with onion, as a rule, the number of nematodes sharply increases. In addition, many plants are characterized by increased removal of certain nutrients, which can also lead to fatigue of the soil in relation to this plant species.
Long-term cultivation of the same crop in one area is possible only if it does not leave pests, pathogens or plant parasites in the soil after it, which may cause a decline in the crop next year. However, such cases are rare, and therefore an annual crop rotation, also called crop rotation, must be observed at the site. The scientific rationale for the need for crop rotation is to disclose the mechanisms of mediated plant interaction through soil. The influence of the preceding plants on the following plants is manifested through changes in soil properties, enrichment or depletion of organic or mineral substances, loosening or compacting.
Indirect interaction of plants through the soil and their effect on the soil environment determines the rules for alternating vegetable crops in crop rotation.
Plant roots carry a variety of continuous work in the soil. They actively influence it, stimulating the life of the soil microflora, creating a lumpy structure. In the soil, internal changes constantly occur, there is a continuous exchange of substances between plants and soil due to light, heat, moisture and many other factors.
The roots of plants throughout the growing season with varying degrees of intensity release into the soil a large number of organic compounds of complex chemical nature, which consist of vitamins, sugars, organic acids, enzymes, hormones, phenolic compounds. The composition of the root secretions is not the same for different plant species. Phenolic compounds, called calenas, are the component that determines the toxicity of the root secretions of some species of crops for other plants. The action of colins is specific and varies depending on the type of culture that emits them. However, the accumulation of colins in the soil causes the phenomenon of fatigue of the soil, which occurs when the same type of plant is grown for a long time in one place. It is noticed that in this case the plants become worse and worse every year and finally degenerate completely. This is due to the fact that many plants are sensitive enough to their own root secretions accumulating in the soil. For example, beetroot can not be constantly grown in one place because the toxic root extracts left in the soil after the first year of cultivation are depressing for the plants of the next planting year, a sort of self-poisoning of the beet occurs.
The most sensitive to their own root secretions, or rather the toxic element in their composition, beets and spinach, are the least sensitive - legumes, corn, leeks, which can grow long in one place. Many colins remain in the soil after growing tomatoes, peppers, cucumbers, carrots, cabbages. The accumulation of colins in the soil is only one cause of fatigue.
It is interesting that mixed plantings can play an important role in solving the problem of interleaving crops. For example, beets and spinach, extremely sensitive to their own root secretions, accumulating in the soil, can grow in one place for a number of years only in a mixed planting. This is due to the fact that the landing partners, belonging to other species, absorb their roots and process the root extracts of beet and spinach, preventing them from accumulating in the soil.
Another, equally important, is the accumulation in the soil of pathogens and pests specific to the type of vegetable that has been growing for several years in one place. With the permanent cultivation of any one of the crops, pathogens of bacterial and fungal diseases such as cabbage, root rot, and root and leaf nematodes, cabbage, carrot and onion flies, fleas and other pests accumulate in one place in the soil. It is possible to fight these disastrous phenomena for cultures only through the alternation of cultures. As a rule, vegetables from the same family have the same set of pests and diseases that damage the vegetables of this family and do not pose a danger to other families. So, on the garden where cabbage grew last year, one should not plant radish and turnips. When cabbage appears, cabbage can not be returned to its original place before 6 years later, but during these years, in a garden where cabbage has grown, it is possible to grow a culture from another botanical family, for which cabbage whales are not dangerous. Another important factor that determines the need for alternation of crops is the extent to which they take out nutrients, and hence their effect on the fertility of the soil. Therefore, it is important to know what condition each type of vegetable leaves behind.
Soil is improved not only by leguminous crops, but also by plants of other families with developed powerful deep root system. They absorb mineral nutrients( potassium, phosphorus, calcium) from deep layers of soil and enrich them with the upper arable layer, where the root system of most vegetable plants develops.
In addition, plants with a deep root system have a positive effect on heavy clay soils, loosening and improving their structure, and therefore are good precursors for other crops. Such plants include cumin, buckwheat, flax, rapeseed and soy.
An important characteristic of each crop is the amount of nutrients it takes out of the soil, undergoing a full development cycle. It depends on it, how much the supply of nutrients is depleted and how much it requires replenishment after harvesting the crop. In accordance with this, vegetable crops are divided into strong, medium and weak consumers, which has already been described earlier. Vegetables of one family are very close to each other in terms of nutritional requirements, and if they are planted one after the other in one place, this will lead to unilateral depletion of the soil, since the cultures of one family carry out mostly the same elements from the soil in which the most stronglyneed.
The correct alternation promotes the complete and effective absorption of nutrients and moisture by plants, the appropriate use of fertilizers, the increase of soil fertility, and the successful control of weeds.
To avoid depletion of the soil, a crop rotation must be observed in the form in such a way that all 3 groups of crops are replaced in each area for 3 years. The following sequence is most favorable: in the first year, the demanding crops are planted, in the second - legumes, which restore nitrogen reserves and improve the structure of the soil, in the third - less demanding. Then everything repeats itself. Instead of legumes can be planted after strong consumers of culture with an average carrying out of nutrients.
In the scheme of alternation of crops, legumes occupy a special place, since they enrich the soil with nitrogen due to its accumulation in nodules on the roots of plants. Most of the nitrogen compounds during plant life remain closed in the nodules and become accessible to other plants only after the dying of the legumes, when the roots rot and release into the soil the nitrogen accumulated in the nodules. Thus, legumes enrich the soil with nitrogen and are the ideal precursors for any kind of vegetable crops.
The choice of predecessors of a vegetable crop is an important link in the planning of crop rotation and depends on many factors: the compatibility of crops, the belonging of crops to the botanical family, the susceptibility to certain diseases and pests, the degree of nutrient removal and depletion of the soil,including still little-studied factors. Based on the study of all the above-mentioned regularities in the effect of successive cultures, more and less favorable precursors were established for each other for many vegetable crops.
In the conditions of the suburban area for compliance with crop rotation, it is rational to proceed as follows. The garden plot is divided into 3 parts. In the first part of the garden place potatoes, in the second - cabbage, cucumber, pumpkin, zucchini, in the third - tomato, onions, beets, carrots, parsley, beans, peas. The next year, those crops that were sown in the second part of the garden, go to the first part - after the potatoes. Tomato, onions and other crops from the third section fall on the second section, and the potatoes - on the third. If a large part of the garden is provided for and given to potatoes, for example, half, then the breakdown is made differently. The whole area is divided into 4 parts. On the first part place cabbage, cucumber, pumpkin and zucchini. The second plant potatoes, the third - tomato, onions, peppers, legumes;on the fourth, again potatoes. There are many options for such a breakdown of a site for culture, it depends on your needs for the quantity of vegetable products of one kind or another.
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