How to apply nitrogen fertilizer to vegetables? The performance of excessive nitrogen fertilizer in vegetables is not good. Why?

It is worth noting that as soon as nitrate ions encounter digestive enzymes in saliva, they are transformed into nitrosamines, and this chemical has been proved to be carcinogenic by the medical community. Professor Zheng Zhengyong therefore reminded the public that when the Department of Health encourages children to eat more fruits and vegetables, in fact, we should also pay attention to the problem of excessive nitrate hidden in vegetables.

In recent years, many farmers have generally applied nitrogen fertilizer to speed up the growth of vegetables, but experts warn that once there is too much nitrogen fertilizer and insufficient sunshine, the nitrogen fertilizer absorbed by vegetables will form nitrates, which may be harmful to health if eaten for a long time. Therefore, nutritionists call on the Agricultural Commission of the Executive Yuan to advise farmers on the correct use of nitrogen fertilizer so as to prevent consumers from being victimized.

Cheng Cheng-yung, a professor of horticulture at National Taiwan University, points out that many consumers are worried about pesticide residues in fruits and vegetables. in fact, there is another question that has been hidden for a long time, that is, whether there is too much fertilizer. He stressed that nitrogen fertilizer is one of the most commonly used fertilizers used by farmers at present, but after absorbing nitrogen fertilizer, the roots of plants will be converted into free forms of nitrate ions, and amino acids will be formed through assimilation and photosynthesis, but if excessive nitrogen fertilizer is applied or vegetables are harvested prematurely, the roots, stems and leaves of vegetables will be full of nitrate ions.

Professor Zheng Zhengyong has conducted many experiments with commercially available pakchoi. The stem of one centimeter of pakchoi is ground, and then the juice is dripped on a test strip to measure the concentration of nitrate ion, which soon shows a purple color higher than 500 ppm (1/1000000). He said that although all organisms contain nitrogen, and most foods may also contain nitrate ions, if they accumulate too much in the body, it can be harmful to health.

Professor Zheng Zhengyong, for example, said that Europe and the United States have found that some babies have "blue baby disease". The problem is that spinach from the source of baby food contains excessive nitrate. In addition to being converted into nitrosamines by digestive enzymes, he said, it has been confirmed by the medical community that it also hinders the oxygen-carrying function of red blood cells, so the body will feel tired and physical strength will decline if it is absorbed too much.

Professor Zheng Zhengyong stressed that at present, advanced countries in Europe and the United States, such as Germany and the Netherlands, have also begun to pay attention to the problem of high nitrate content in fruits and vegetables due to excessive application of nitrogen fertilizer, and stipulated that the nitrate concentration in fruits and vegetables should not be higher than 1500 to 3000 ppm, but domestic standards have not yet been established. He believes that since the concentration of nitrate ions in vegetables varies with whether the soil is over-fertilized, the amount of sunlight varies from place to place, and the harvest time of various vegetables varies, the most important way to prevent it is still that the Council of Agriculture should advise farmers not to apply too much nitrogen fertilizer, which can save costs and protect the health of consumers.

The Council of Agriculture of the Executive Yuan points out that the government's measures to guide farmers in the use of fertilizers are mostly through the peasant association system and promotion classes on special crops in various places to guide farmers to apply fertilizers. As for the misgivings about nitrates caused by excessive nitrogen fertilizer, according to the research done in Japan, there is still no final conclusion, but it is best to diversify the types of vegetables that people choose.

A dietitian, who spoke on condition of anonymity, said that for clean and pollution-free hydroponic vegetables, the whole vegetable grows in water, and the culture medium that simulates soil nutrients is used as the main nutrient for vegetable growth, and the most abundant fertilizer is liquid nitrogen fertilizer. the stems and leaves of vegetables are full of nitrates, so from the point of view of nutrition, consumers can only eat hydroponic vegetables occasionally. Do not take this as a staple food.

An official from the Agriculture and Grain Department of the Council of Agriculture pointed out that there is a theoretical basis for the formation of nitrate after nitrogen fertilizer is absorbed by plants, but the transformation process in the body when the human body absorbs various sources of nutrients is very complicated, and the organic composition in the soil varies from place to place. Whether to limit the use of nitrogen fertilizer by farmers may cause controversy. As for hydroponic vegetables, since no academic report has confirmed that hydroponic vegetables are harmful to human health, the Council of Agriculture still adopts a laissez-faire policy towards hydroponic vegetables.