Trees, plants, vegetable gardens and all fruit plants need sixteen elements during their growth. Carbon, potassium, oxygen, phosphorus, hydrogen, nitrogen, iron, calcium, chlorine, magnesium, molybdenum, sulphur, manganese, zinc, copper and boron. Natural nutrients are obtained from air and water to a plant; they are oxygen, hydrogen and carbon. The primary nutrient is crucial to their growth and they are potassium, phosphorus, nitrogen. Secondary nutrients are available in soil with certain limitation as per geographic and they are sulphur, calcium and magnesium. Micronutrient is the remaining element from the above briefed sixteen.
Classification of inorganic fertilizers:
Inorganic fertilizers are those which are manufactured by a chemical process synthetically without using any biomass. It is classified into 1) Direct 2) Indirect. This classification is made based on agrochemical nature.
- Direct fertilizers: plants directly assimilates the nutrient element present in the fertilizer
- Indirect fertilizers: These are supporters and developer of the soil conditioning. They make the soil suitable by improving it mechanical, biological or chemical properties.
- Direct fertilizers are classified based on the domination of the chemical element present in the compound mixture. They are termed as magnesium, potash, phosphatic and nitrogenous types.
- Based on the presence of basic nutrient elements in a compound fertilizer, that fertilizer is termed as simple, double or triple fertilizers.
- Micro fertilizers are those which contain micronutrients.
Classification based on preparation:
- If by using mechanical mixing to form a final fertilizer with the various individual element that it is called mixed fertilizer.
- Complex fertilizers are those formed by the chemical reaction of the element.
Classification based on solubility:
- Water soluble fertilizers that are easily soluble in water present in the soil, liquid fertilizer spray are used for this process but they are washed away easily if mass water flows over the soil for that reason liquid fertilizer applicators are used for the constant application. Example: potash and nitrogenous compounds
- Fertilizers soluble in acids present in soil which have slow dissolution property. Example: phosphate types
Categorized based physical property:
- Powder and Granulated form are mostly used, but for small gardens and lawns liquid types are also available. Granulated forms of fertilizers are preferred in the most case due to its non-cake forming and less hygroscopic nature. They can be easily sprayed by the machinery in the farms; they gradually supply the element to plants.
Based on effect on the environment (The controversy on fertilizer consumption):
Agricultural activities strongly depend on fertilizers and man-made fertilizers contain heavy metals along with macro nutrition. Continuous use of non-organic fertilizers increases the concentration of cadmium, chromium, nickel, mercury arsenic and lead in soils to the pollution level that harm human health. Plants absorb these metals and store them in the food chain. Even groundwater becomes harmful due to the accumulation of metal in soil.
Effects due to excess use of fertilizers
- Accumulation of nitrate
- Soil salinity
- Heavy metal accumulation
- Water eutrophication
- The increase of naturally occurring radioactive materials (uranium and thorium ) in soil and underground water, leads to cancer.
Water polluting fertilizer: Organic nitrogen fertilizers pollute water due to nitrate leaching and water drainage by the water flow at agricultural land.
Air polluting fertilizer: Harmful nitrogen oxides gases highly generated and released into the atmosphere due high consumption of nitrogen-based fertilizers.
Soil polluting fertilizer: Ammonium chloride, ammonium nitrate, potassium chloride, potassium sulfate, sodium nitrate are the main source of soil structure demolishing. Ammonia sulphate increases the pH and makes soil acidic. High utilization of potassium fertilizers affects the microorganisms in the soil.