FERTILIZER

Definition

fertilizer: Any substance that isadded to soil in order to increase itsproductivity. Fertilizers can be of naturalorigin, such as composts, or theycan be made up of synthetic chemicals,particularly nitrates and phosphates.Synthetic fertilizers canincrease crop yields dramatically, butwhen leached from the soil by rain,which runs into lakes, they also increasethe process of eutrophication.Bacteria that can fix nitrogen aresometimes added to the soil to increaseits fertility; for example, intropical countries the cyanobacteriumAnabaena is added to rice paddiesto increase soil fertility.

Agricultural Uses

Any natural or manufactured solid or liquid material, added to the soil to supply one or more nutrients essential for the proper development and growth of a plant is called a fertilizer. Fertilizers, in the broadest sense, are products that improve the levels of the available plant nutrients and/or the chemical and physical properties of the soil, thereby directly or indirectly enhancing the growth, yield and quality of the plant. The term is generally applied to commercially manufactured materials other than lime or gypsum.
Fertilizers sold on a large scale are called commercial fertilizers. They have a specific ratio of nutrients, known as fertilizer ratio, also called plant food ratio. The fertilizer ratio is the ratio of the number of fertilizer units in a given mass of fertilizer expressed in the order N, P and K. Thus, it is the ratio of two or more nutrient percentages to one another. For instance, a fertilizer with a 5-10-15 grade has a 1-2-3 ratio, whereas a fertilizer with a 10-20-20grade has a 1-2-2 ratio. Fertilizer ratio is also defined as the relative proportion of primary nutrients in a fertilizer grade divided by the highest common denominator for the grade. For example, the grade 20-12-8 has a ratio of 5-3-2 of N, P and K, respectively.
Based on their chemical composition, fertilizers are classified as (a) mineral fertilizers containing inorganic or synthetically produced organic compounds, (b) organic products that are produced out of wastes of animal husbandry (stable manure, slurry manure, etc.), plant decomposition products (compost, peat, etc.), or products from waste treatment (composted garbage, sewage sludge, etc.), and (c) synthetic soil conditioners whose main function is to improve the physical properties of the soil.
Based on their nutrient content, fertilizers are classified as (a) straight fertilizers, generally containing one primary nutrient, (b) compound or complex or multinutrient fertilizers, containing several primary nutrients and sometimes micronutrients, and (c) micronutrient fertilizers, containing nutrients required in small quantities by plants.
Finally, fertilizers can be classified as solid or liquid fertilizers and as soil or foliar fertilizers. Solid fertilizers come in bags, while liquid fertilizers (used for spraying on an existing plant population) are sold in containers.
There are five types of manufactured chemical fertilizers consumed on a large scale, especially in developing countries. These types are nitrogenous, phosphatic, potassic, complex or those supplying more than one major plant nutrient, and fertilizer mixtures.
Natural materials like manures and other organic materials are also used as fertilizers and are called bulky organic manures. These have to be used in bulk, with appropriate precautions to prevent the spread of diseases among plants. Biofertilizers are materials of biological origin that are sold as fertilizers. These are commercially reared micro-organisms that fix nitrogen or solubilize phosphorus and are multiplied under special conditions. While biofertilizers are economical and ecologically safe, they supply only two nutrients (nitrogen and phosphorus), and are usually used as a supplement to chemical fertilizers.
Nutritional or fertilizer requirements vary with the crop and the soil composition. Ideal doses of fertilizers are available for a number of agriculturally important crop plants.
Fertilizer requirement can be defined as the quantity of additional nutrients required by a particular crop to increase its growth to the optimal level in a given soil.