Nitric fertilizers have to be introduced taking into account the given analysis of the soil and plants. It must be kept in mind that the doses of nitric fertilizers recommended until recently were made without the content of nitrates in the soil. Therefore it is necessary to be guided by the minimum values of the recommended doses, and at research of the soils rich with nutrients, to reduce these doses by 30-40%. It is important to use slow-acting sources of nitrogen, for example, compost. It is better to introduce fertilizers small doses that will also reduce the content of nitrates in vegetables.
High doses of mineral fertilizers promote increase in productivity of vegetable plants. However application of the raised doses of nitric fertilizers conducts to the excess content of free nitrates which negatively influence health of the person. Besides the amount of solid of carbohydrates, some vitamins and microcells significantly decreases.
According to the Dutch scientists, the amount of usvoyaemy nitrate nitrogen in the top layer of earth (0 – 0,6 m) should not exceed 225 kg/hectare (225 g / 102). Acidity of the soil should not lower be better to grow up Spinach during the spring period and it is not necessary to hurry too with harvesting. It is desirable to clean in cool, but clear day.
Under potatoes recommend to bring to 80 g / 102 nitrogen. Ammoniac forms of nitrogen should not be brought under it as the content of nitrates thus considerably increases in tubers. Temporary alkalifying of reaction of the environment intensifies microbiological processes and decomposition of organic substance of the soil. As a result in a korneobitayemy layer of earth the increased amount of usvoyaemy nitrogen collects.
From amide fertilizers urea (CO(NH which else is called a carbamide is most widespread. It is the most concentrated solid nitric fertilizer, contains not less than 46% of nitrogen. The carbamide can be applied as the main fertilizer and in top dressing under many plants. However at introduction without seal into the soil losses of nitrogen owing to volatilization of ammonia from carbonic ammonium especially on carbonate soils are possible.
Special attention should be paid on cultivation of green plants (salad headed, spinach, cress – salad). Under them it is necessary to bring no more than 50 kg/hectare of nitrogen. At introduction of nitric fertilizers of 160 kg/hectare (160 g / 102) in salad the content of nitrates raises to 1100 – 2400 mg/kg. The lowest contents them is noted at use of the fertilizers containing nitrogen in an ammoniyny form. However the ratio of ammoniyny and nitrate forms of nitrogen in the applied nitric fertilizers has to be 1: The increase in the maintenance of an ammoniyny form leads to decrease in productivity of salad.
As the part of nitrogen in ammonium nitrate is presented by ammonium, from it less nitrates, than from sodium saltpeter are washed away. However and there are restrictions. In the conditions of sufficient moistening it is better to bring it in the spring under preseeding cultivation or top dressing. When using under potatoes the strict dosage is necessary: on cespitose and podsolic soils under early grades – no more than 80-100 kg/hectare (80-100 g/m, under late – 100-120 kg/hectare (100-120 g / 10 m nitrogen against manure and optimum forms of phosphoric and potash tuk. But nevertheless it is better to apply ammonium sulfate in the same doses here.
At cultivation of spinach, fertilizer (azotna in number of 70 – 100 kg/hectare, promotes accumulation of nitrates to 250 mg/kg, and at increase in a dose of fertilizers by 3 times the contents them increases to 4000 mg/kg. Increase of productivity is followed by increase in the content of nitrates and reduction of iron (with 100 to 64 mg), and also considerable deterioration of production.
The cucumber, in comparison with other vegetable plants, is characterized by the low content of nitrates (15 – 259 mg/kg of crude substance in fruits) and even at introduction of high doses of nitrogen they increase very slightly. An optimum dose of introduction of nitric fertilizers of 90 kg/hectare (90 g on 10 sq.m).