Fertilization technology for pollution-free vegetable production

   Fertilization techniques for the production of pollution-free vegetables 1. Vegetable fertilization and nitrate content Vegetables are rich in vitamins, mineral elements, etc., and are indispensable foods for human beings. Vegetables are also hi-water and hi-fertilizer crops. In production, nitrates are often accumulated in the edible parts of vegetables due to improper fertilization . More than 80 % of the total amount of nitrates in the human body comes from vegetables. Nitrate itself is not toxic, but in the human gastrointestinal, nitrates can be converted into great danger of nitrite salt, the blood loses oxygen-carrying function. In addition, nitrite can further synthesize carcinogens, nitrosamines, with gums in the human gastrointestinal tract, leading to gastric cancer and esophageal cancer. Studies have shown that nitrate content in vegetables being subject to the kind of vegetables, varieties and cultivation methods outside influence, fertilization is the main factor affecting the nitrate content in vegetables. The relationship between fertilization and nitrate accumulation is as follows: ( 1 ) The effect of different types of fertilizers on nitrate accumulation in vegetables The order of nitrate content in fertilizers is: biological fertilizer ( green friends ) < high temperature compost < local fertilizer < chemical fertilizer. The application of different types of fertilizers showed the same trend as the above for the nitrate content of soil 0 to 60 cm. The content of nitrate nitrogen in soil not only affects the absorption of nitrate nitrogen by vegetables, but also affects the content of nitrate nitrogen in groundwater . Therefore, from the protection of the ecological environment and the prevention of the accumulation of nitrate in vegetable products, it is recommended to apply more organic fertilizers and minimize the amount of fertilizer and application. Nitrogen Nitrogen forms and their ratio has a great influence on the accumulation of nitrate. When nitrate fertilizer is used completely, the nitrate content is significantly higher than that of ammonium nitrogen and amide nitrogen. Nitrogen fertilizers should also be used with urea or ammonium sulfate. ( II ) Relationship between nitrate and fertilizer in vegetables The nitrate content in vegetables increases with the increase of fertilizer application; some are almost positively correlated, even for melon and fruit vegetables with low nitrate content. The increase of nitrate content is especially the increase of chemical fertilizer, and the increase of nitrate content of organic fertilizer is not large. Therefore, pollution-free vegetable production must significantly increase the amount of organic fertilizer, strictly control the amount of fertilizer, the content of nitrate salt vegetable products not excessive, meet the health standards of green food. ( 3 ) Nitrate content in vegetables and the time after fertilization The nitrate content in vegetables gradually decreases with the continuation of the time after topdressing. For vegetables harvested 15-20 days after top dressing , the nitrate content is generally lower. ( IV ) Relationship between light and nitrate content Light intensity directly affects the activity of nitrate reductase in plants. The light intensity in the solar greenhouse is only 40-60 % of the land , so the nitrate content of the vegetables produced is generally higher than that of the open vegetables. Transforming the light conditions in the solar greenhouse can reduce the accumulation of nitrate in vegetables. (E) nitrate accumulation of different types of vegetables, different sensitivity to nitrate accumulation of different types of vegetables, the general polarization-sensitive type (leafy), sensitive (rhizome vegetable species), are less sensitive (like cauliflower) Insensitive type ( fruit category ) . Bai Zhen et al. proposed the standard for vegetable nitrate safety limits ( see Table 7--4) . The People's Republic of China agricultural industry standards for pollution-free vegetables nitrate content also has specific criteria (see Table 7-5). Acidification, to increase the amount of calcium and magnesium leaching, soil structure is destroyed and the soil nutrient content of polluting ecological imbalance in the environment and the like, and the application of organic manure can slow the process described above. Most of the organic fertilizers are excreta of humans and animals, as well as animal and plant residues, and the sources are complex. In the production of pollution-free vegetables, attention should be paid to high-temperature disinfection and hygienic operation. Therefore, we must pay attention to the source of organic fertilizer, choose organic fertilizer with good environmental quality as much as possible, and gradually carry out pollution-free vegetable production according to the internal circulation industrial structure required by the International Organic Agriculture Movement Alliance. Third, the accumulation of organic fertilizer Traditional organic fertilizer system is not only effective in low nutrient content, but also consumes a lot of manpower and material resources, and is not sanitary. When the chicken farms and pig farms are operated on a large scale, because the manure treatment is not solved, it often brings pollution to the environment, soil and vegetables. Therefore, on the basis of absorbing foreign experience, major cities such as Beijing and Shanghai in China have carried out research work on organic fertilizer factory processing in recent years and achieved certain results. Beijing has trial-produced chicken manure as the main raw material in Haidian District. It uses modern industrial production methods and some equipments to carry out factory processing to produce high-efficiency organic fertilizer ( odorless chicken manure ) . At the same time, according to the needs of different vegetable types, The amount of inorganic fertilizer is added to produce a special organic-inorganic compound fertilizer suitable for different types of vegetable crops. For example, it is suitable for medium-fertilizer leaf-leaf special fertilizer, which contains organic matter 22 ; 1 %, nitrogen-containing 8 %, phosphorus 6 %, potassium 8 %, and calcium, magnesium, sulfur and various trace elements. This nutrient is complete, quick-acting and slow-acting, and has a good yield-increasing effect, and has a good fertilization and fertilizer-changing fertilizer, which is well received by the majority of vegetable farmers. The processing of human, livestock and poultry manure has reduced impurities, and the nutrient content has been greatly increased. The transportation volume has been greatly reduced, and the use is also convenient. At the same time, after processing, it has a killing effect on pathogens and parasite eggs in feces. After processing the fertilizer is not only no odor and hygiene, creating conditions for pollution-free vegetable production. In the production of pollution-free vegetables, in theory, the ecological cycle of matter should be closed, and the supply of nutrients depends mainly on the natural fertility of the soil . However, in actual production, it is often because the soil's own fertilizing capacity cannot fully meet the crop production needs, and it must be supplemented with external fertilizer. Exotic organic fertilizers may contain a certain amount of pollutants, and organic fertilizers must be treated in a pollution-free manner. Studies have shown that, for agriculture and other high-temperature solid waste composting can have the following effects: (a) of organochlorine pesticides BHC, DDT has effects due to the degradation of our agriculture has been widely extensive use of organochlorine pesticides in the history of BHC and DDT (there are still produced and used in some places), in soil and plants and animals and their waste (livestock and poultry manure and crop residues) can detect a wide range of organic residual chlorine. However, after high temperature composting, it can promote the accelerated degradation of residual BHC and DDT . Therefore, livestock manure and straw in vegetable production can be greatly reduced by recombination of residual organochlorine pesticides into the ecological cycle, thereby shortening the natural decay time in the farmland environment and contributing to the production of pollution-free vegetables. (B) kill the pathogen, eggs, weed effect decomposition temperature compost composting process, the heat can be released by the fermentation, so that the reactor temperature reached 55 - 70 ℃, lasts for 10 to 15 days, to kill pathogenic microorganisms, eggs and weed seeds in agricultural waste has a significant effect. ( 3 ) Accumulating heavy metals in organic fertilizers Because crop straw and livestock manure contain more or less a certain amount of heavy metal elements, the content of which is mainly used in addition to different crop types and feeds for livestock and poultry. Depends on the heavy metal content of the soil of these crops and feed. During the composting process, the volatile elements (such as carbon, hydrogen, oxygen, etc.) can be converted into carbon dioxide, water, ammonia, etc., but heavy metal elements such as mercury, lead, chromium, arsenic, etc. Part of the conversion to mercury vapor reduction, other elements generally accumulate during the composting process, which is related to the reduction in volume and weight of the compost material during the stacking process. Therefore, production of pollution-free vegetable feedstock organic fertilizer to be prepared from the region, the problem as to avoid accumulation of heavy metals in the organic fertilizer with. Foreign materials should be intensively tested and stacked using high temperature compost. High temperature composting is an effective measure agricultural waste harmless treatment, to prevent biological contamination of vegetable fields of the environment, reducing vegetable production and weed pests occur breed has a significant effect. 4. Fertilization technology for the production of pollution-free vegetables The production of pollution-free vegetables can be flexibly controlled according to their own circumstances. By strictly controlling the quality of fertilizers, screening fertilizer types, determining the amount of fertilizer and topdressing techniques, the fertilization of soil to ensure the high-yield and stable supply of vegetables requires nutrients, and it is beneficial to cultivate strong seedlings and strong pests that resist pests and diseases. The use of pesticides to ensure the production of pollution-free and high-quality vegetables under the premise of being harmless to the ecological environment, and obtain high economic and social benefits. ( 1 ) Determination method of vegetable fertilization amount Determination of reasonable fertilization amount and avoiding blind fertilization is the most important content in pollution-free vegetable fertilization technology. Since the capacity of soil for fertilizer, vegetable fertilizer utilization and absorption by the roots influenced by many factors, and calculated the amount of fertilizer is quite difficult. The existing scientific knowledge can only be calculated by the results and experience of the fertilizer test, giving a reference value. Beijing summarize relevant scientific research units to search based on years of research and tone, vegetables fertilization method proposed is worth learning. The general formula for determining the amount of application is: the method of carrying out the nutrient content of the crop and the soil can provide nutrient content. This method is simple and easy to perform, and can be calculated with various data, and is easy to popularize and apply in production. However, it is necessary to combine the characteristics of vegetable production, the fertility characteristics of the planted soil and the fertilizer characteristics of the vegetable crop itself, as well as the characteristics of the vegetable commodity price. Beijing Based on years of research and investigation summary, put forward a series to determine a variety of specific parameters and values related to the amount of fertilizer (Table 7--6), provides a practical method and basis for determining the reasonable amount of fertilizer vegetables. The sources and calculations of the data in the above formula are as follows: 1 . Crop nutrient carrying capacity Crop nutrient introduction amount = unit is the soil available nutrient utilization factor, soil available nitrogen 0 . 6 , soil available phosphorus 5 , soil speed potassium 1 . 0 . 0 . 15XaXbXc is actually a constant, calculated: Spring cultivation: soil alkaline nitrogen X00504 soil nitrogen supply ( kg, mu ) ; autumn cultivation: soil alkaline nitrogen X0 . 0864 General cultivation: Soil alkaline nitrogen X0072 Soil phosphorus supply ( kg/mu ) Spring: Soil available phosphorus PPm~0 042 Autumn: Soil available phosphorus PPm~0 • 072 General: Soil available phosphorus PPm X0 06 Upland available potassium PPm X0 . 084 on the soil quick-acting PPmX0 • 144 on the fast-acting potassium PPmX0 • 12 3 . Increasing the nutrient component coefficient When the soil nutrient is higher than the crop carrying amount, there will be a situation where the soil supply nutrient exceeds the nutrient carrying capacity, and it seems that the fertilizer can be not applied. However, considering the requirement of vegetables to provide nutrients with high soil strength, in order to meet the requirements of short-lived, fast-growing and high-yield vegetables, it is proposed to increase the nutrient coefficient, which is generally equivalent to 20 % to 40 % of the carrying amount . When the soil fertility is high, it can be applied less ( multiplied by 20 % ) , and when the soil fertility is low, it can be applied more (40 % ) . However, when the amount of soil supplied exceeds 1 to 2 times the amount of carry -over, it may not be applied. In particular, phosphorus and potassium fertilizers, such as soil available phosphorus above 150PPm , and available potassium above 250PPm , there is no need to increase phosphorus and potassium. 4 . Fertilizer nutrient utilization rate. Generally, nitrogen fertilizer is 30 % to 50 %, phosphorus fertilizer is 15 % to 30 %, and potassium fertilizer is 15 % to 40 %. The utilization rate of nitrogen, phosphorus and potassium in good organic fertilizers ( such as chicken and duck manure ) can reach 20-40% , and the soil fertilizer is 5-30% . Several common organic fertilizers can provide nutrients (see Tables 7-7 , 7-8 ). 1 . The base fertilizer is selected to conform to the organic fertilizer produced by pollution-free vegetables, which is applied in general and deep, and evenly mixed with the soil . 2 . Topdressing vegetables are big water and large fertilizer crops, especially fruit and vegetable vegetables with long growth period and continuous results. In addition to a large amount of organic fertilizer as a large amount of organic fertilizer as a base fertilizer, it also needs topdressing. In order to meet the production standards for pollution-free vegetables , it is necessary to optimize the types, dosages and topdressing periods of fertilizers. (1) Topdressing is not necessarily mineral fertilizer. It can use traditional Chinese manure, cake fertilizer and other organic fertilizers, and strictly control the amount of fertilizer; (2) topdressing time. For a one-time harvest of vegetables, in order to avoid the accumulation of nitrate in plants, in 15 pre-harvest - 20 days. For fruits and vegetables on the results, it should also be as 15 before the advent of peak harvest --20 administered one day. (3) According to the sensitivity of vegetables to nitrate accumulation, flexible measures to control the mouth and fertilize the soil. For example, when producing melon and fruit vegetables that are not sensitive to nitrate, a larger amount of organic fertilizer can be used as a base fertilizer and top dressing. When producing leafy vegetables and root-leaf vegetables sensitive to nitrate accumulation, it is necessary to not fertilize as much as possible. Or use less fertilization, and use the sputum with more fertilization before and after, and directly use the nutrients of the anterior sputum. All of these fertilizations are carried out under the conditions permitted by the production of pollution-free vegetables , so as not to pollute the ecological environment, the production of vegetable products meets the hygiene standards.