کودهای کند رهش: راه حلی امیدوارکننده برای کاهش آلودگی محیط زیست

Abstract
Nitrate is the most abundant and common pollutant in Iran's underground water sources. More than half of the nitrogen fertilizers are wasted and returned to the environment due to nitrogen solubility in water, sublimation, oxidation and reduction, nitrification, and denitrification. Therefore, the use of slow-release fertilizers can be one of the appropriate solutions for its waste. Also, the use of slow-release fertilizers saves money and improves product performance. The results of this research show that slow-release fertilizers enhance the quality of water. This study also shows that natural slow-release fertilizers are not harmful to the environment and can even benefit plant growth. Slow-release urea fertilizers release nitrogen for a more extended period. In addition to reducing pollution, these fertilizers can also improve crop performance. This is because they provide a more stable nitrogen source for plants, which helps prevent nutrient deficiencies. The use of slow-release nitrogen fertilizers dramatically increases the duration of nitrogen release in water and the environment, and this ensures a healthier environment and will be much more economical than conventional fertilizers.
Introduction
The exponential growth of the population has increased the need for food. One of the ways to increase the yield in cultivated areas is by using fertilizers and agricultural pesticides. The function of fertilizer is to supply nutrients to plants to improve crop yield. Therefore, increasing the need for food increases the need for more fertilizers globally. The primary nutrients in plant growth are phosphorus, nitrogen, and potassium. Although fertilizers are essential for plants and crops; However, the excessive use of chemical fertilizers is ineffective in increasing the yield per unit area and has adverse effects. Excessive use of chemical fertilizers destroys soil fertility and also introduces various types of pollution to the environment. The production of the product is expensive from an economic point of view. Therefore, proper and sufficient use of chemical fertilizers increases productivity and has no adverse effects on nature. Plants absorb nitrogen from the soil in the form of nitrate or ammonium. Absorbed nitrate and ammonium are transferred to other plant tissues through wood vessels. After using nitrogen fertilizers, a large part of it is not absorbed by the roots, and due to its high solubility in water, it enters the surface and underground waters during irrigation and rainfall. The most abundant and common pollutant in confidential water sources is nitrate. In recent years, the concentration of nitrates in underground water has increased due to the increase in population, the growth of industry, and the development of agricultural activities. The leading causes of groundwater contamination with nitrates are the entry of sewage and agricultural runoff into groundwater sources. In many countries, such as England, China, Australia, and Turkey, high concentrations of nitrates in underground water have been reported. About half of the nitrogen fertilizers are lost due to drainage. According to the Food and Agriculture Organization of the United Nations (FAO) estimates, about 40-70 percent of these fertilizers are wasted through drainage. Also, less than half of the urea used in agriculture is wasted in about three mounth. Nitrogen solubility in water, evaporation, oxidation and regeneration, nitrification, and denitrification are among the influential factors in wasting nitrogen fertilizers. During irrigation or rain, nitrate ready to be absorbed by the roots enters the surface and underground waters. In very alkaline soils, evaporation is an essential mechanism for nitrogen removal. First, nitrogen is converted into NH4+, NH3 then transferred to the air. Due to oxidation and regeneration, some bacteria and fungi can convert nitrogen into nitrate, nitrite, nitrous, nitrogen gas, and nitrogen oxide. Therefore, part of the nitrogen is wasted. Also, two reactions occur in the phenomenon of nitrification. First, ammonium is converted into nitrite in the presence of bacteria called Nitrosomonas. Then, in the presence of oxygen and Nitrobacter, nitrite turns into nitrate. Denitrification depends on soil bacteria and is performed in saturated or dense soils with limited oxygen. Certain bacteria can use nitrate oxygen as an alternative energy source when oxygen is unavailable. Gaseous forms of nitrogen are created and enter the atmosphere by removing oxygen from nitrate.

Methodology
To review various articles related to the problems and diseases caused by the use of nitrate and nitrite-contaminated water as well as the use of slow-release fertilizers based on natural polymers to prevent nitrogen wastage and pollute surface and underground water, Google Scholar, ScienceDirect, ResearchGate databases with keywords nitrate-contaminated water, diseases caused by nitrates and nitrites, slow-release fertilizers, lignin, slow-release fertilizers, natural polymers in coating fertilizers were searched. The extracted texts included articles, web pages, and thesis. Web pages were not examined due to the general nature of the content. The thesis was used less; Because the valuable contents of them have been published as articles. Therefore, their reports were examined. This article investigated diseases caused by nitrate and nitrite-contaminated water in more detail. Finally, the criterion of this work was the use of articles published in reliable scientific databases.

Conclusion
Excessive use of nitrogen fertilizers is not economical. It is also very problematic from an environmental point of view. Among these problems can be increased water and soil pollution, hardening, salinization and loss of soil structure, various diseases, creation of low quality and unhealthy products, contamination of surface water and underground pointed to nitrate and nitrite and the reduction of plant access to phosphorus, copper, iron and manganese. Only 30 to 35% of its nutrients are absorbed when chemical fertilizers are given directly to plants. The most widely used nitrogen fertilizer is urea, which has only 50% nutrient consumption efficiency. With nitrate-contaminated drinking water, nitrate is first converted into nitrite in the stomach. Then nitrite reacts with blood hemoglobin; the product of this reaction is methemoglobin. As a result, people exposed to nitrates usually suffer from oxygen deficiency. Nitrates and nitrites can be very dangerous if nitrosamines are formed. Nitrosamines can be developed due to high heat and increase cancer risk. Control-release fertilizers offer a safer, more economical, and more effective way to use nutrients; Because they keep nutrients in the soil for a more extended period. This method can help improve the performance of nutrients in lower doses and reduce pollution and environmental risks. Fertilizers are divided into slow-release and controlled-release. In slow-release fertilizers, nutrients are released slower than usual, and in controlled-release, the rate of nutrient release is a function of the plant's life cycle and can be adjusted. These fertilizers reduce pollution and side effects in a certain period and increase the efficiency of plant use of nutrients. Usually commercial controlled-release fertilizers with polymer coating are often made of thermoplastic resins, including polyolefin and polyvinylidene chloride, which are difficult to decompose for the soil. When the coated urea is placed in an aqueous environment, water penetrates the coating layer and reaches the surface of the urea. Urea dissolves quickly in water, So the urea concentration becomes saturated in water. According to the Whitman-Lewis theory, there is no resistance in the typical phase. As long as there is solid urea, the concentration in the usual stage of water and urea remains saturated. Coatings can be divided into two general categories, organic and inorganic polymers. Sulfur, phosphogypsum, and bentonite are among inorganic coatings, and polymers such as polyethylene, polyurethane, polyether sulfone, polystyrene, and alkyd resin are among organic coatings. Also, natural coatings are included in the group of organic coatings. Chitosan, cellulose, Lignin, starch, alginate, and silicon dioxide are in the group of natural coatings. Phosphogypsum and sulfur-based gypsum are inorganic coatings due to their solubility in water. They do not change the pH of the soil, and they can easily give their sulfate to the plants, which in this respect has more advantages than sulfur coating. Synthetic polymers can be used to achieve the desired characteristics of release control fertilizers, but these polymers are non-degradable and have a destructive effect on the environment. The polymer components of the coating remain after the release of the contents and lead to environmental pollution. Since natural polymers are not harmful to the environment, they can be used more.