Fertiliser organic or inorganic material of natural or synthetic origin (other than liming materials) that is added to a soil to supply one or more plant nutrients essential to the growth of plants. Any inorganic salt such as ammonium sulphate, or an organic substance, such as urea, used to promote crop production by supplying plant nutrients is considered to be a 'commercial' fertiliser. Specifically there are three different kinds of fertilisers: (i) chemical fertilisers, (ii) organic fertilisers, and (iii) biofertilisers. Fertilisers are the most important agricultural input throughout the world. Synthetic fertilisers contain nutrients in concentrated form. Naturally occurring inorganic materials are also rich in nutrients. Consequently, relatively lower amounts of fertilisers are needed to meet the crop requirement compared to naturally occurring organic materials.
Soil is the principal supplier of plant nutrients. Plants derive 14 essential nutrients out of 17 from the soils. But soils vary considerably in their inherent capacities to supply nutrients which gradually decline over time due to intensive cropping with high yielding varieties, very little or no use of organic materials and improper soil and crop management practices. As a result, crops suffer from inadequate supply of nutrients which is reflected in poor yield and quality. Therefore, there is a need to add nutrients to the soil through fertilisers in order to get desired yields.
Materials of plant and animal origin that are applied to the soil for increasing yield of crops are called organic fertiliser or manure. These are generally voluminous substances used in raw or processed condition. A variety of organic fertilisers are applied to the soils in different countries of the world. In the past, organic fertilisers were mainly used for crop production in Bangladesh. With the advent of chemical fertilisers in 1960s the use of organic fertilisers first gradually and then drastically reduced. However, animal manure, compost, green manure and biofertiliser are among the organic fertilisers, which are used in Bangladesh.
Fertilisers are indispensable for the crop production systems of modern agriculture. Among the factors that affect crop production, fertilisers play a crucial role in yield increase. In fact, inorganic fertilisers hold the key to the success of the production systems of Bangladesh agriculture, being responsible for about 50% of the total production. However, the contribution of fertilisers to crop yields may vary depending on the crop, cropping intensity, season, soil characteristics and management conditions.
Chemical (inorganic) fertilisers were introduced into this country during the early nineteen fifties as a supplemental source of plant nutrients. But their use increased steadily from the mid-sixties in line with the introduction and expansion of modern varieties and the development of irrigation facilities. The increasing trend of fertiliser use, particularly urea-N, still continues.
Until 1980, three primary major plant nutrients - nitrogen (N), phosphorus (P) and potassium (K), along with one secondary major nutrient calcium (Ca), were supplied from fertiliser to bangladesh soils. The importance of sulphur (S) and zinc (Zn) for rice culture in particular was recognised during the early eighties. Gypsum, zinc sulphate, and zinc oxy-sulphate were then introduced to supply these nutrients. Very recently, magnesium (Mg), boron (B), and molybdenum (Mo) deficiencies have been reported for some soils and crops. Appropriate fertilisers to supply these nutrients will be needed in the future.
Among the fertilisers, nitrogen occupies pivotal position because of the low nitrogen content of the soils and the quick visual action of nitrogenous fertilisers on crop growth, which drew attention of the farmers. Other fertilisers drew less attention because of their less visual response, although their need cannot be ignored.
A variety of organic fertilisers are applied to the soil such as cowdung, urine, poultry manure, farmyard manure, compost, dried blood, bone meal, fish meal, groundnut cake, oil cake, dhanicha, sunhemp, cowpea, blackgram, mungbean, rice and wheat straw, sugarcane leaves, weeds, ash etc. Of these however, animal manure, compost, green manure, and oil cake are the most important.
The preparations with living or latent specific microbial strains that are associated with the cycling of nitrogen, phosphorus and carbon assisting the supply of plant nutrients are popularly known as biofertilizers. Blue-Green Algae (BGA), Rhizobium, Azotobacter, Azospirillium, Vesicular Arbuscular Mycorrhizal fungi and Phosphobacterin are the commonly known examples of biofertilisers. The benefits of Rhizobium for pulses and other legumes, and BGA in association with azolla for rice have been well demonstrated in Bangladesh through many experiments, but their use at the farm level is yet to gain widespread acceptance. bacteria of the genus Rhizobium and Bradyrhizobium have the unique ability to fix atmospheric nitrogen in association with plants of the legume family.
In 1962-63, a total of 20,235 tons of fertiliser nutrients were used in Bangladesh, of them, the amounts of N, P and K were 18,916, 661 and 703 tons, respectively. In the year 1995-96, the total amount of fertiliser nutrient consumption raised to 11,79,390 tons. In that year, the amounts of consumption of different fertiliser nutrients were nitrogen 9,42,771 tons, phosphorus 68,866 tons, potassium 77, 940 tons, sulphur 89,468 tons and zinc 345 tons.
The production of fertilisers in 1997-98 in Bangladesh was 1.873 million tons of urea, 50 thousand tons of triple superphosphate (TSP), 100 thousand tons of single superphosphate and 3 thousand tons of ammonium sulphate. Gypsum, however, is produced as a by-product of TSP industry.
Table The products and the enterprises involved in fertiliser manufacturing
|KAFCO (Karnafuli Fertiliser Co)||Chittagong||Urea|
|Chittagong Urea Fertiliser Ltd||Chittagong||Urea|
|Jamuna Fertiliser Co Ltd||Jamalpur||Urea|
|Zia Fertiliser Co Ltd||Ashuganj||Urea|
|Urea Fertiliser Factory Ltd||Ghorashal||Urea|
|Natural Gas Fertiliser Factory||Fenchuganj||Urea and Ammonium Sulphate|
|Palash Urea Fertiliser Factory||Ghorashal||Urea|
|Chittagong Triple Superphosphate Complex||Chittagong||TSP and Single Superphosphate|
Some fertilisers contain single nutrient element while some others contain more than one nutrient. The latter ones are called multinutrient fertilisers. For practical purpose, more than one fertiliser is mixed together and such a mixture is called mixed fertiliser. In Bangladesh urea is used to meet almost all the N requirements of crops. In addition, ammonium sulphate is used for some crops, especially for tea plantation. Phosphorus is supplied from TSP and diammonium phosphate (DAP). In addition to phosphorus, DAP also provides nitrogen for the crops. Other chemical nutrients applied include Potassium (muriate of potash), Gypsum, Zinc Sulphate and Zinc Oxide, Ammonium Molybdate and Solubor and Borax. It has been estimated that about 108 kg nutrient per hectare was used in Bangladesh in 1994 compared to 18 kg nutrient per hectare in 1973. This figure is far below as compared fertiliser nutrient consumption in Republic of Korea (467 kg/ha/yr) and China (309 kg/ha/yr) in 1994, bit higher than that of India (80 kg/ha/yr) and Pakistan (102 kg/ha/yr).
In addition to their capacity to supply plant nutrient fertilisers also exert other effects on soil properties. Organic fertilisers have favourable effects on chemical, physical and biological properties of soil. Constituents released through decomposition exert these diverse effects and the effects are also long lasting on the contrary. The effects of synthetic fertilisers are quick but short lasting. [Sirajul Hoque]