Manufacture Process
The principal raw materials for fertilizer production are air (to provide nitrogen), natural gas (to provide hydrogen for ammonia synthesis) phosphate rock, potash and sulfur (for suifuric acid production and subsequent use in phosphate fertilizer production). Fossil fuels are also used for power generation in the mining and processing of raw materials. As with other industries, mining and treatment of each raw material may raise environmental problems.
Use of natural gas for fertilizer production contributes around 2 per cent of global carbon dioxide emissions. The increased availability of nitrogen from fertilizers, manures and leguminous crops further adds to greenhouse emissions by the formation of increased amounts of nitrous oxide. These sources together may contribute as much as 3 to 5 per cent of the long term greenhouse effect. However, use of fertilizers stimulates plant growth and photosynthesis, removing carbon dioxide from the air. The overall effect of fertilizers on greenhouse gas emissions is therefore likely to be a positive one. Further, should soil organic matter concentrations increase due to fertilizer use, more carbon becomes 'locked away' in the soil.
Mining of phosphates and potash may damage the landscape. Phosphate rock is usually open-mined, generating large amounts of waste overburden. large scale restoration of the landscape is required. Some phosphate rock contains minor amounts of radioactive elements (e.g. uranium) necessitating special storage for mining waste. Leaching of waste may cause water pollution. Potassium extraction may also lead to water pollution when brines are produced as a by-product. Large stockpiles of common salt (sodium chloride) are often generated during the processing of potash ores.
Extraction of sulfur from industrial smoke stack gases, e.g. metal processing plants and fossil fuel power stations, may in fact minimise environmental impact by utilising sulfur dioxide, which may otherwise be emitted to the atmosphere, possibly contributing to acid rain.
Some emissions may occur during the manufacturing processes. Nitrogen oxides, ammonia, fluorides and sulfur dioxide, along with fertilizer dust, may be emitted. Losses however are small, less than 1 per cent of the nutrients handled.
Type of Fertilizers
The nutrients of most concern are nitrogen and phosphorus given their widespread use.
Nitrogen Fertilizers:
Excessive or inappropriately applied nitrogen fertilizers can lead to emissions of ammonia (by volatilisation) and nitrous oxides (by denitrification). The latter may contribute to greenhouse effects. The dominant source of atmospheric ammonia is from farm animals and manures, with fertilizer use contributing only an estimated 10 per cent of atmospheric ammonia in Western Europe. While ammonia concentrations in the air are too low (of the order of micrograms per cubic metre) to affect air quality, they may contribute to acid rain and soil acidification in these densely settled and intensely cropped regions.
Nitrogen fertilizers readily convert to nitrate in the soil. The nitrogen in soil organic matter and organic fertilizers becomes available more slowly. Nitrate from all sources may be readily leached if not used by crops or pasture. Leaching is particularly likely in sandy soils following heavy rainfall. Leached nitrate may contaminate underground water. This is of concern if the water is to be used for human or livestock consumption, as high concentrations of nitrate may affect health. Nitrate combines with haemoglobin, interfering with oxygen transport in the blood, particularly in young children. World standards are set for nitrate levels in drinking water (10 mg/L NO3- N or 45mg/L N03-). Nitrate contamination of groundwater is not of concern in most parts of Australia as little use is made of shallow underground water for drinking, and Australia's agriculture is far less intensive than in Europe and North America. Leaching of nitrate can be minimised by good fertilizer management (recommended rates, soil and plant tissue analysis, application when maximum uptake occurs, split-application etc.).
The use of fertilizers, particularly nitrogen fertilizers can accelerate the natural process of soil acidification. The initial effect fertilizers have on soil pH in the immediate vicinity of the granules is usually of little consequence. While some fertilizers are acidic e.g. MAP and others basic e.g. DAP, their effects are confined to the point of application. Due to the relatively small volume of soil affected compared to total soil volume, there is little effect on sail pH. Some fertilizers e.g. anhydrous ammonia and urea may initially raise the soil pH at the site of application but in the long term acidify the soils. This occurs when ammonium is converted to nitrate.
Superphosphate is popularly held to be responsible for soil acidification. It does not directly cause soil pH to fall, but since it does promote legume growth and nitrogen fixation it will, like most nitrogen fertilizers, have an indirect effect on soil pH. Any practice which increases plant growth such as proper fertilization will lead to the gradual acidification of the soil by two main processes. They are the formation and loss of nitrate through the soil, and removal of nutrients in the form of farm produce.
Removal of plant and animal produce removes alkaline cations such as calcium and magnesium, along with some acidic elements. There is an overall acidifying effect on the soil. Any accumulation of organic matter in the soil increases the amount of nitrogen stored in the soil. Organic nitrogen is then converted to ammonium and subsequently to nitrate by nitrification. In the process, hydrogen ions are formed i.e. acid is produced. Much of this increased nitrogen comes from fixation by legumes, and from fertilizer application. Acid produced in the nitrification process can be used if the nitrate is taken up by plants or soil organisms, but if the nitrate is leached beyond the root zone, acidification occurs. The effect then of intensive agricultural systems is one of soil acidification.
The effects of soil acidification include reduced availability of the trace element molybdenum, development of aluminium and manganese toxicity and modulation failure in legumes. Soil analysis is used in diagnosing soil acidity problems. Lime may be required where acidity is a problem. Lime (obtained from naturally occurring calcium carbonate) neutralises soil acidity and acts as a soil conditioner. Application rates depend upon the soil type, degree of acidity and crop being grown and may vary from 1-10 tonnes per hectare. The use of acid tolerant plant species is another management strategy.
Phosphorus fertilizers:
Excess amounts of phosphorus have been associated with the eutrophication of lakes and waterways, and with algal blooms. Nitrogen may also contribute; the level of nitrogen influencing the algal type. When nitrogen levels are low, blue-green algae which fix their own nitrogen are favoured.
Blue-green algae (more correctly named Cyanobacteria) are naturally present in small numbers in healthy waterways. During periods of prolonged dry weather, water stagnates, evaporation is high and nutrient levels become concentrated. These conditions of still waters, strong sunlight and high nutrient levels (particularly phosphorus) lead to rapid multiplication of the algae, and consequent algal blooms. The blue-green algae release toxins which cause sickness in humans and livestock. The bloom is fed by phosphorus in a mixture of soil run-off, sewage, manure from farm animals and wildlife and decaying material which enters the waterways, plus recycling of nutrients from within the waterway.
Given that phosphorus is relatively immobile in soils, leaching of fertilizer phosphorus is unlikely to cause build-up in waterways. This has happened, however, on deep sands in the south-west of Western Australia. Phosphorus present in surface water run-off may originate from soil erosion or freshly top-dressed fertilizer. Erosion of fertile top-soil, where fertilizer nutrients accumulate is another source of nutrient input to waterways. Soil conservation and cultural practices which reduce soil erosion can significantly reduce phosphorus inputs into waterways.
While the use of fertilizers can contribute to nutrient overload and consequent algal blooms, the extent of the contribution has not been measured and defined. It is one of many sources, and possibly a minor one. Minimising potential impact of fertilizers involves good fertilizer practices (appropriate application rates, timing and application techniques) to minimise potential losses. Management practices (improved erosion and run-off control and buffer vegetation around waterways) also contribute to minimising environmental effects.
Phosphorus fertilizers contain various impurities from the phosphate rock and acid used in manufacture. Cadmium (Cd) is of most concern. levels of cadmium in fertilizer will vary with the phosphate rock source. As there is currently no commercial means of removing cadmium during fertilizer manufacture, the only control is to use fertilizer made from low cadmium phosphate rock, especially in areas of intensive use, e.g. vegetables.
Use of phosphorus fertilizers may lead to a build-up of the heavy metal cadmium in soils. Cadmium is normally present in soils at levels of 0.1-1.0 mg/kg soil. Phosphorus fertilizers contain higher levels of cadmium as an impurity, so prolonged use over time increases soil cadmium levels. Cadmium input to soils also occurs from the atmosphere e.g. near industrial centres, and in sewage sludge.
The use of phosphorus fertilizers may increase cadmium concentrations in farm produce, which in some situations may exceed maximum permissible levels. This is most noticeable with certain crops e.g. potatoes and leafy vegetables (lettuce and spinach) and in the offal (kidneys and liver) of animals. Use of fertilizers with a low cadmium content i.e. less than 100 mg of cadmium per kg of phosphorus (P) and preferably less than 50 mg of cadmium per kg P is recommended, especially in vegetable production.
Reference:
http://www.incitecfertilizers.com.au/environmental_facts.cfm
The principal raw materials for fertilizer production are air (to provide nitrogen), natural gas (to provide hydrogen for ammonia synthesis) phosphate rock, potash and sulfur (for suifuric acid production and subsequent use in phosphate fertilizer production). Fossil fuels are also used for power generation in the mining and processing of raw materials. As with other industries, mining and treatment of each raw material may raise environmental problems.
Use of natural gas for fertilizer production contributes around 2 per cent of global carbon dioxide emissions. The increased availability of nitrogen from fertilizers, manures and leguminous crops further adds to greenhouse emissions by the formation of increased amounts of nitrous oxide. These sources together may contribute as much as 3 to 5 per cent of the long term greenhouse effect. However, use of fertilizers stimulates plant growth and photosynthesis, removing carbon dioxide from the air. The overall effect of fertilizers on greenhouse gas emissions is therefore likely to be a positive one. Further, should soil organic matter concentrations increase due to fertilizer use, more carbon becomes 'locked away' in the soil.
Mining of phosphates and potash may damage the landscape. Phosphate rock is usually open-mined, generating large amounts of waste overburden. large scale restoration of the landscape is required. Some phosphate rock contains minor amounts of radioactive elements (e.g. uranium) necessitating special storage for mining waste. Leaching of waste may cause water pollution. Potassium extraction may also lead to water pollution when brines are produced as a by-product. Large stockpiles of common salt (sodium chloride) are often generated during the processing of potash ores.
Extraction of sulfur from industrial smoke stack gases, e.g. metal processing plants and fossil fuel power stations, may in fact minimise environmental impact by utilising sulfur dioxide, which may otherwise be emitted to the atmosphere, possibly contributing to acid rain.
Some emissions may occur during the manufacturing processes. Nitrogen oxides, ammonia, fluorides and sulfur dioxide, along with fertilizer dust, may be emitted. Losses however are small, less than 1 per cent of the nutrients handled.
Type of Fertilizers
The nutrients of most concern are nitrogen and phosphorus given their widespread use.
Nitrogen Fertilizers:
Excessive or inappropriately applied nitrogen fertilizers can lead to emissions of ammonia (by volatilisation) and nitrous oxides (by denitrification). The latter may contribute to greenhouse effects. The dominant source of atmospheric ammonia is from farm animals and manures, with fertilizer use contributing only an estimated 10 per cent of atmospheric ammonia in Western Europe. While ammonia concentrations in the air are too low (of the order of micrograms per cubic metre) to affect air quality, they may contribute to acid rain and soil acidification in these densely settled and intensely cropped regions.
Nitrogen fertilizers readily convert to nitrate in the soil. The nitrogen in soil organic matter and organic fertilizers becomes available more slowly. Nitrate from all sources may be readily leached if not used by crops or pasture. Leaching is particularly likely in sandy soils following heavy rainfall. Leached nitrate may contaminate underground water. This is of concern if the water is to be used for human or livestock consumption, as high concentrations of nitrate may affect health. Nitrate combines with haemoglobin, interfering with oxygen transport in the blood, particularly in young children. World standards are set for nitrate levels in drinking water (10 mg/L NO3- N or 45mg/L N03-). Nitrate contamination of groundwater is not of concern in most parts of Australia as little use is made of shallow underground water for drinking, and Australia's agriculture is far less intensive than in Europe and North America. Leaching of nitrate can be minimised by good fertilizer management (recommended rates, soil and plant tissue analysis, application when maximum uptake occurs, split-application etc.).
The use of fertilizers, particularly nitrogen fertilizers can accelerate the natural process of soil acidification. The initial effect fertilizers have on soil pH in the immediate vicinity of the granules is usually of little consequence. While some fertilizers are acidic e.g. MAP and others basic e.g. DAP, their effects are confined to the point of application. Due to the relatively small volume of soil affected compared to total soil volume, there is little effect on sail pH. Some fertilizers e.g. anhydrous ammonia and urea may initially raise the soil pH at the site of application but in the long term acidify the soils. This occurs when ammonium is converted to nitrate.
Superphosphate is popularly held to be responsible for soil acidification. It does not directly cause soil pH to fall, but since it does promote legume growth and nitrogen fixation it will, like most nitrogen fertilizers, have an indirect effect on soil pH. Any practice which increases plant growth such as proper fertilization will lead to the gradual acidification of the soil by two main processes. They are the formation and loss of nitrate through the soil, and removal of nutrients in the form of farm produce.
Removal of plant and animal produce removes alkaline cations such as calcium and magnesium, along with some acidic elements. There is an overall acidifying effect on the soil. Any accumulation of organic matter in the soil increases the amount of nitrogen stored in the soil. Organic nitrogen is then converted to ammonium and subsequently to nitrate by nitrification. In the process, hydrogen ions are formed i.e. acid is produced. Much of this increased nitrogen comes from fixation by legumes, and from fertilizer application. Acid produced in the nitrification process can be used if the nitrate is taken up by plants or soil organisms, but if the nitrate is leached beyond the root zone, acidification occurs. The effect then of intensive agricultural systems is one of soil acidification.
The effects of soil acidification include reduced availability of the trace element molybdenum, development of aluminium and manganese toxicity and modulation failure in legumes. Soil analysis is used in diagnosing soil acidity problems. Lime may be required where acidity is a problem. Lime (obtained from naturally occurring calcium carbonate) neutralises soil acidity and acts as a soil conditioner. Application rates depend upon the soil type, degree of acidity and crop being grown and may vary from 1-10 tonnes per hectare. The use of acid tolerant plant species is another management strategy.
Phosphorus fertilizers:
Excess amounts of phosphorus have been associated with the eutrophication of lakes and waterways, and with algal blooms. Nitrogen may also contribute; the level of nitrogen influencing the algal type. When nitrogen levels are low, blue-green algae which fix their own nitrogen are favoured.
Blue-green algae (more correctly named Cyanobacteria) are naturally present in small numbers in healthy waterways. During periods of prolonged dry weather, water stagnates, evaporation is high and nutrient levels become concentrated. These conditions of still waters, strong sunlight and high nutrient levels (particularly phosphorus) lead to rapid multiplication of the algae, and consequent algal blooms. The blue-green algae release toxins which cause sickness in humans and livestock. The bloom is fed by phosphorus in a mixture of soil run-off, sewage, manure from farm animals and wildlife and decaying material which enters the waterways, plus recycling of nutrients from within the waterway.
Given that phosphorus is relatively immobile in soils, leaching of fertilizer phosphorus is unlikely to cause build-up in waterways. This has happened, however, on deep sands in the south-west of Western Australia. Phosphorus present in surface water run-off may originate from soil erosion or freshly top-dressed fertilizer. Erosion of fertile top-soil, where fertilizer nutrients accumulate is another source of nutrient input to waterways. Soil conservation and cultural practices which reduce soil erosion can significantly reduce phosphorus inputs into waterways.
While the use of fertilizers can contribute to nutrient overload and consequent algal blooms, the extent of the contribution has not been measured and defined. It is one of many sources, and possibly a minor one. Minimising potential impact of fertilizers involves good fertilizer practices (appropriate application rates, timing and application techniques) to minimise potential losses. Management practices (improved erosion and run-off control and buffer vegetation around waterways) also contribute to minimising environmental effects.
Phosphorus fertilizers contain various impurities from the phosphate rock and acid used in manufacture. Cadmium (Cd) is of most concern. levels of cadmium in fertilizer will vary with the phosphate rock source. As there is currently no commercial means of removing cadmium during fertilizer manufacture, the only control is to use fertilizer made from low cadmium phosphate rock, especially in areas of intensive use, e.g. vegetables.
Use of phosphorus fertilizers may lead to a build-up of the heavy metal cadmium in soils. Cadmium is normally present in soils at levels of 0.1-1.0 mg/kg soil. Phosphorus fertilizers contain higher levels of cadmium as an impurity, so prolonged use over time increases soil cadmium levels. Cadmium input to soils also occurs from the atmosphere e.g. near industrial centres, and in sewage sludge.
The use of phosphorus fertilizers may increase cadmium concentrations in farm produce, which in some situations may exceed maximum permissible levels. This is most noticeable with certain crops e.g. potatoes and leafy vegetables (lettuce and spinach) and in the offal (kidneys and liver) of animals. Use of fertilizers with a low cadmium content i.e. less than 100 mg of cadmium per kg of phosphorus (P) and preferably less than 50 mg of cadmium per kg P is recommended, especially in vegetable production.
Reference:
http://www.incitecfertilizers.com.au/environmental_facts.cfm
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