Vegetables are the main source of vitamins, minerals, dietary fiber, organic acids and antioxidants. However, vegetables are very prone to the accumulation of nitrate salts, as well as cadmium, zinc, lead and other heavy metals that are dangerous to our health.
It is known that nitrate nitrogen is necessarily present in plants, because it is used to form amino acids and then proteins. Its level depends on the conditions in which vegetables grow – illumination, moisture reserves in the soil, temperature of the root layer of soil and surface air, and the age of the plant. For example, nitrates are higher in leaves, young shoots, and unripe fruits than in old shoots and ripe vegetables. Nitrates in green onion tops in an open garden are less than in greenhouse onions, but more than in onions, and lettuce or spinach contain more unwanted nitrogen than carrot roots.
According to the level of accumulation, nitrogenous compounds, including nitrate nitrogen, accumulate unevenly in different organs of the plant. For example, in squash, a large amount of nitrates is “located” near the stalk, in table beets – at the tip of the root crop. However, a high level of nitrates at the time of harvest does not necessarily indicate poor quality vegetables. For example, in the heads of late-ripening cabbage varieties, a high level of nitrates is sometimes noted during harvesting, but when ripening during storage, by the time of consumption (December – June), their amount returns to normal.
Also note that the amount of nitrates in certain vegetables depends on their variety. For example, carrots of the Sonata and Dayana varieties, which are characterized by high marketability and yield, accumulate few nitrates. By the way, these varieties have some of the best indicators in terms of carotene content (15 and 18 mg/kg) and taste (5 points).
Of course, the level of nitrates also depends on the growing conditions. For example, table beets grown on ridges in the Moscow region contained less nitrates than those grown on flat beds. And there were more sugars in the root crops with the ridge method of cultivation.
The amount of nitrates in vegetables increases if excessive doses of fertilizers are applied in an attempt to significantly increase the yield. Nitrogen-containing mineral fertilizers are mostly responsible for this. But too generous application of manure and litter also worsens the quality of the crop: nitrates accumulate in vegetables, reaching 150% of the MPC (maximum permissible concentration – Ed.). In other words, nitrate accumulation is affected by overfeeding with nitrogen-containing fertilizers. That is why the plant nutrition system must provide optimal doses and ratios of nutrients. It is not for nothing that supporters of ecological farming, when applying manure to the site, must necessarily embed straw in the soil or mulch the beds with peat, sawdust of hardwoods.
Our experiments have shown that a high yield of white cabbage, table beets, carrots, radishes with a minimum nitrate content can be obtained by combining Biocomp or vermicompost and nitrogen, phosphorus, potassium mineral fertilizers (each 0.05 g / sq. M).
Unfortunately, there are few full-fledged organic fertilizers available now. Therefore, we recommend applying ready-made organic-mineral complexes (2/3 of the necessary elements) and compost to the soil when forming beds or planting holes. We advise you to feed with complex mineral fertilizers (1/3 of the dose) Kemira, Gidrocomlex, Aquarin, Polyfida. If there is no compost or other organic fertilizers or they are not enough, then to reduce the amount of nitrates in vegetables, we recommend incorporating crushed charcoal into the soil along with mineral fertilizers.