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Fertilizer schedule

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Sixteen plant elements have been recognized as being essential to all plants for their normal growth and development. Carbon (C), hydrogen (H) and oxygen (O) are derived from the air and water. Nitrogen (N), phosphorus (P) and potassium (K) are used in large quantities by the plants and are called as major or "primary nutrients". Calcium (Ca), magnesium (Mg) and sulphur (S) are required in relatively smaller but in appreciable quantities and hence named as "secondary nutrients". Iron (Fe), zinc, (Zn), manganese (Mn), copper (Cu), boron (B), molybdenum (Mo) and chlorine (Cl) are needed in small quantities and are called as "micronutrients" or trace elements. In addition to the above, some elements are required by a particular group or species of plants. They are vanadium (V), silicon (Si), iodine (I), selenium (Se), gallium (Ga) and aluminum (AI). Apart from these elements other elements like rubidium (Rb), strontium (Sr), nickel (Ni), chromium (Cr) and arsenic (As) may be required at very low concentrations by some plants. These are often referred as beneficial elements or "microelements".

Plant nutrients are essentially supplied through manures and fertilizers. Manures are organic in nature and applied in large quantities. They are also called as organics or organic manures. They are of animal or plant origin and contain more than one nutrient element. Nutrient content in the organic manures is low. Fertilizers are inorganic or synthetic and the nutrient content is higher than in manures. Fertilizers are available for a particular nutrient or combination of nutrients.

Organic manures
Organic manures are the valuable by-products of farming and allied industries derived from plant and animal sources. Organic manures are broadly classified as bulky organic manures and concentrated organic manures. Bulky organic manures are applied in large quantities and contain low amount of plant nutrients. e.g. farm yard manure, compost, night soil, Sewage and Sludge, Vermicompost, Green Manure, Sheep and Goat Manure, Poultry Manure etc. Concentrated organic manures contain higher percentage of major plant nutrients. e.g. various oil cakes and waste products of animal origin like dried blood, bone meal, fish manure, etc.

Green manuring is growing the plants in the field usually belonging to leguminous family and incorporating into the soil after sufficient growth. The plants that are grown for green manure are known as green manure crops. The most important green manure crops are sunnhemp, dhaincha, Pillipesara, clusterbeans and Sesbania rostrata. Application to the field, green leaves and twigs of trees, shrubs and herbs collected from elsewhere is known as green leaf manuring. The important plant species useful for green leaf manure are neem, mahua, wild indigo, glyricidia, Karanji (Pongamia glabra) calotropis, avise (Sesbania grandiflora),Subabul and other shrubs.

Biofertilizers also play a vital role in maintaining long term soil fertility and sustainability. The term" biofertilizers" includes selective microorganisms like bacteria, fungi, and algae which are capable of fixing atmospheric N or convert insoluble phosphate in the soil into available forms to plants.  Biofertilizers are cost effective, eco-friendly and renewable sources of plant nutrients to supplement chemical fertilizers. Based on the type of microorganisms, the biofertilizers can be classified as follows: 1. Bacterial biofertilizers: e.g. Rhizobium, Azospirillum, Azotobacter and Phosphobacteria, 2. Fungal biofertilizers: e.g. Mycorrhiza, 3. Algal biofertilizers: e.g. Blue Green Algae (BGA) and AzolIa, 4. Actinomycetes biofertilizers:e.g. Frankia.
 
Fertilisers
Fertilisers are industrially manufactured chemicals containing plant nutrients. Fertilizers are inorganic/synthetic substances containing one or more plant nutrients in easily soluble and quickly available form. Because of their availability in concentrated form they have the advantage of being small for bulk storage and transport and handling are easier. In addition, crops may be supplied with exact quantity of nutrient required for their growth and development in soils of varying fertility levels. Nutrient content is higher in fertilisers than in organic manures and nutrients are released almost immediately.

Classification of fertilisers
1. Straight fertilizers:  Straight fertilizers are those which supply only one primary plant nutrient, namely nitrogen or phosphorus or potassium. eg. Urea, ammonium sulphate, potassium chloride and potassium sulphate.

2. Complex fertilizers:  Complex fertilizers contain two or three primary plant nutrients of which two primary nutrients are in chemical combination. These fertilisers are usually produced in granular form. eg. Diammonium phosphate, nitrophosphates and ammonium phosphate.

3. Mixed fertilizers: are physical mixtures of straight fertilisers. They contain two or three primary plant nutrients. Mixed fertilisers are made by thoroughly mixing the ingredients either mechanically or manually.

According to the nutrients constitution, they are grouped as
1. Nitrogenous fertilizers
2. Phosphatic fertilizers
3. Potassic fertilizers
4. Complex or mixed fertilizers
5. Micronutrients                                                       

Fertilisers can also be classified based on physical form as
1. Solid fertilizers
2. Liquid fertilizers

Solid fertilizers are in several forms viz.
1. Powder (single superphosphate),
2. Crystals (ammonium sulphate),
3. Prills (urea, diammonium phosphate, superphosphate),
4. Granules (Holland granules),
5. Supergranules (urea supergranules) and
6. Briquettes (urea briquettes)

Liquid fertilizers
1. Liquid form fertilizers are applied with irrigation water or for direct application.
2. Ease of handling, less labour requirement and possibility of mixing with herbicides has made the liquid fertilisers more acceptable to farmers.

Nutrient supply is one of the most important factors influencing growth and productivity of the horticultural crops. Adequate supply of plant nutrients is important to ensure efficient crop production. Adding animal and vegetable manure to the soil to restore fertility is the practice from time immemorial. As the use of the chemical fertilizers increased due to their large availability and easy-to-adopt technique, organic manure application slowly declined. Since the nutrient turn-over in soil plant system is considerably high under intensive farming, neither the chemical fertilizers nor the organic or biological sources alone can achieve a sustainable production. Choice of manures and fertilizers and their application at right quantity and time are important to get higher production.

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