The problem of nitrates
Vegetables, along with fruits, are one of the main sources of vitamins, microelements, pectins and organic acids for the human body. However, it is with vegetables that the greatest amount of nitrates and nitrites enters the human body. Being a natural link in a single chain - a cycle of nitrogen in nature, in moderate doses, nitrates are absolutely harmless. In healthy people, they are quickly absorbed and quickly removed from the body. Admissible safe daily dose of them for human - 5 mg per 1 kg of mass. However, a prolonged and abundant supply of nitrates to the human body can adversely affect the health status.
A great danger to human health is the restored form of nitrates - nitrites. In plant foods, their concentration is usually very small, not more than 1 mg / kg wet weight, but when nitrates enter the body as a part of vegetable production, nitrites can be restored from nitrates in the gastrointestinal tract with a lack of special enzymes in it. Different types of vegetable crops accumulate nitrates in varying degrees: some are more inclined to concentrate them in tissues, others - less. The number of nitrates in vegetables depends on the biological characteristics of plants. Especially a lot of nitrates( 1000-1500 mg / kg) accumulate spinach, lettuce, radish, celery, cabbage, broccoli, and table beet. The average quantity was noted in white cabbage and cauliflower, cucumber, carrots( 100-1500 mg / kg).The lowest content of nitrates in onions, tomatoes, eggplant, pepper, green peas.
Plants, whose vegetative mass is affected by pests or diseases, accumulate nitrates more than unaffected. Many nitrates are found in unripe vegetables. Vegetables of the last fees usually contain less nitrates than in the first fees.
When using vegetables in food, it is necessary to take into account the different contents of nitrates in different parts and organs of plants. In vegetables nitrates are distributed unevenly. In leaf vegetables, nitrates accumulate mainly in the petioles and veins of the leaves. The content of nitrates in the fruits of zucchini and cucumber decreases from the stalk to the top, and at the patisson - from the surface layer to the core. In the tips of root crops of carrots, beets, radish, turnip, radish, the content of nitrates is greater, which is due to the presence of small suction roots in them. In the core of the carrots, the level of nitrates is higher than in the peel, and in the direction from the tip of the root to the apex, it decreases. Table beets have a lot of nitrates in the top and root of the root. The top leaves of cabbage contain about 2 times more nitrates than the internal ones, and the greatest amount of nitrates accumulates in the stump. The potato has a lower level of nitrate in the pulp of the tuber compared to the core.
The content of nitrates in vegetable production depends on soil and climatic conditions, biological characteristics of plants, agrotechnical methods, varieties, lighting conditions, balance in basic nutrients, soil microelements, the timing of planting and harvesting vegetables, and a number of other factors that can be controlled.
Often one of the main reasons for the high content of nitrates in vegetables is the introduction of unacceptably high doses of nitrogen fertilizers into the soil. This is to some extent true, but the reasons for the accumulation of nitrates in plants should be considered in the complex.
The source of excessive accumulation of nitrates in plants can be not only fertilizers, but also natural nitrogen reserves in the soil. The accumulation of nitrates in vegetable production increases under unfavorable weather conditions: in years with cold and cloudy summers, nitrates absorbed from the soil are not fully spent on building organic compounds and accumulate in plant tissues in free form. However, constantly high temperatures during the growing season also contribute to an increase in the concentration of nitrates in vegetables. The degree of illumination of plants has a significant effect on the process of accumulation of nitrates: in poor lighting and lack of solar radiation, the content of nitrates in vegetables sharply increases. Therefore it is very important not to thicken the crops and planting of vegetable crops and maintain the purity of glasses in the greenhouses.
In conditions of good moisture supply, the accumulation of nitrates in vegetables is intensified, and with prolonged deficiency, it decreases. The content of nitrate nitrogen in vegetables increases with imbalance in mineral nutrition, when high doses of nitrogen fertilizer are applied in spring and when late nitrogen is fed. The vegetable production of summer crops of nitrates contains more than in spring crops. This is most likely due to a greater intensity of solar illumination in the summer, as well as a change in nitrogen concentration in the soil after the spring application of nitrogen fertilizers.
The quality of vegetables can be significantly improved by observing a number of simple techniques, which include the optimization of mineral nutrition, the selection of varieties, the maintenance of optimum illumination of plants, the treatment and the regime of soil moistening, the timing of sowing and harvesting.