Mixed Fertilisers
In ancient times the farmers discovered the excreta of animals and their decomposing bodies are food for plant life . American Indians used fish and wood ashes for fertiliser. The Chinese have maintained the fertility of their soil for 5000 years by the application of this principle . Manures have been applied on large scale to maintain better plant yields . Before 1900, more than 90 percent of all fertiliser nitrogen was in the form of natural organics ; by 1950, the proportion has decreased to 90 percent. Bones have served to supply phosphorus.
The production of and fibre at high rates required by the present large population depends largely upon fertilisers containing multinutrients . Where fertiliser return as much nutrient material to the soil as has been removed by the harvested crops, fertility can be maintained , but in much of the world insufficient fertiliser use is slowly reducing the ability of the soil to produce the necessary crops.
The major three elements needed for the plant growth are: (1) nitrogen, required to promote development of stem and leaves; (2) phosphorus , which stimulates growth and accelerates fruit and seed formation ; and (3) potash, which is essential to the development of starches, sugars, and fibres and helps to prevent disease and lessens the effects of excessive nitrogen application . Plants require materials other than NPK , but the quantity needed is really slight . these trace elements include Ca, Mg, Na and S and those need in even smaller quantities , micro nutrients, B, Cu, Fe, Mn, Mo and Zn. these are usually added locally , as needed . the sources of these materials are by-products of other chemicals or mining operations . In excess, some of the micro nutrients are toxic to plants . When thee unused parts of plants ( stem , leaves, hulls ) are returned to the soil , fertility is retained longer and the organic materials contained are helpful in retaining moisture . Some nutrients are added by natural causes, e.g., lightning forms NO2 which uses rain as transport.
Granulated or Pelleted Products
During the last 20 years , fertiliser technology and production have greatly altered. Fertilisers have become more concentrated , easier to apply, and more tailored to individual needs . the physical form of most fertilisers has been improved , causing less wastage and making `application easier . Many more fertilisers have become available in liquid form . Aerial application with mixtures of fertilisers and pesticides has become common . High-analysis water-soluble fertilisers are cheaper to transport and to handle. These products are less likely to cake ( making useless tombstones) than powdered materials and are less dusty and corrosive . Uniform- sized particles improve the uniformity of distribution during application , and the this is very important. In 1950 , there were no granular fertilisers . By 1960, 60 percent of all mixed fertilisers were marketed in the form of granules and pellets. It is possible to coat pellets to regulate and slow down the rate of release of the the contents , but this has been used mainly for house plants and home gardens .
Bulk Blending and Distribution
Distributors often play an important role in adapting mixed fertilisers to meet local conditions. Dry bulk blenders make an attention to meet the customer's need possible . Where complete plant food is supplied by the manufacturer , this is somewhat more difficult . Nearly half of the fertiliser used is supplied to the farmer in bulk instead of bags , giving him a considerable saving.
Liquid Mixed Fertiliser
More and more fertiliser is consumed in liquid for. liquids are far easier to apply and are particularly applicable for aerial application. The liquids formed must be free of solids to avoid clogging the spray nozzles. Concentrated phosphoric acid (called super phosphoric acid) is used as the basis for high-analysis liquids. When reacted with ammonia . it gives a neutral solution which does not crystallise at low temperature . If ammonia under pressure , ammonium poly phosphate forms. This can be stored and shipped as solid and dissolved readily when needed. Another favourite fertiliser is liquid anhydrous ammonia , vaporised to a gas and plowed directly into the soil.
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