International Year of Chemistry, 2011

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Idea by Chitra Joshi   |   added on Oct 06, 2011 05:44PM Discussion Discussion
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Chemistry plays a vital role in feeding growing world poulation. There are a number of chemicals which help in increasing food production to keep pace with growing population of the world. A knowledge of positive and negative impact of these chemicals needs discussion among scientific community.












       The beginning of 'agro' or 'agriculture' marks the beginning of 'civilized' or 'sedentary' society. Climate change and increase in population during the Holocene Era (10,000 BC onwards) led to the evolution of agriculture. During the Bronze Age (9000 BC onwards), domestication of plants and animals transformed the profession of the early homo sapiens from hunting and gathering to selective hunting, herding and finally to settled agriculture. Eventually the agricultural practices enabled people to establish permanent settlements and expand urban based societies. Cultivation marks the transition from nomadic pre-historic societies to the settled neolithic lifestyle sometime around 7000 BC.

As per the modern definition of agriculture which would be" an aggregate of large scale intensive cultivation of land, mono-cropping, organized irrigation, and use of a specialized labor force", the title "inventors of agriculture" would go to the Sumerians, starting ca. 5,500 BC.

Modern agriculture depends quite heavily on the advances that have been made in science, and chemistry in particular, to maximize the yield of crops and animal products. Fertilizers, pesticides, and antibiotics play ever increasing roles in this field.

Fertilizer (or fertiliser) is any 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. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use.

Fertilizers are perhaps the most widely used form of chemical in agriculture. Fertilizers are added to the soil in which crops are growing to provide nutrients required by the plants. Fertilizers can be divided into two categories: organic and inorganic. Organic fertilizers are derived from living systems and include animal manure, guano (bird or bat excrement), fish and bone meal, and compost. These organic fertilizers are decomposed by microorganisms in the soil to release their nutrients. These nutrients are then taken up by the plants. Inorganic or chemical fertilizers are less chemically complex and usually more highly concentrated. They can be formulated to provide the correct balance of nutrients for the specific crop that is being grown. Both organic and inorganic fertilizers supply the nutrients required for maximum growth of the crop. Inorganic fertilizers contain higher concentrations of chemicals that may be in short supply in the soil. The major or macro- nutrients in inorganic fertilizers are nitrogen, phosphorous, and potassium. These fertilizers also may provide other nutrients in much smaller quantities (micro-nutrients). With the expansion of cities due to increases in population, there has been a loss of agricultural land. Appropriate use of fertilizers to increase crop yield has in part counterbalanced this loss of land.

Mined inorganic fertilizers have been used for many centuries, whereas chemically synthesized inorganic fertilizers were only widely developed during the industrial revolution. Increased understanding and use of fertilizers were important parts of the pre-industrial British Agricultural Revolution and the industrial Green Revolution of the 20th century.

Inorganic fertilizer use has also significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.

Fertilizers typically provide, in varying proportions:

·         six macronutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S);

·         seven micronutrients: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).

The macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0.15% to 6.0% on a dry matter (0% moisture) basis (DM). Micronutrients are consumed in smaller quantities and are present in plant tissue on the order of parts per million (ppm), ranging from 0.15 to 400 ppm DM, or less than 0.04% DM.

Only three other macronutrients are required by all plants: carbon, hydrogen, and oxygen. These nutrients are supplied by water and carbon dioxide.

The nitrogen-rich fertilizer ammonium nitrate is also used as an oxidizing agent in improvised explosive devices, sometimes called fertilizer bombs, leading to sale regulations.

The modern understanding of plant nutrition dates to the 19th century and the work of Justus von Liebig, among others. Management of soil fertility, however, has been the pre-occupation of farmers for thousands of years.


Fertilizers come in various forms. The most typical form is granular fertilizer (powder form). The next most common form is liquid fertilizer some advantages of liquid fertilizer are its immediate effect and wide coverage. There are also slow-release fertilizers (various forms including fertilizer spikes, tabs, etc.) which reduce the problem of "burning" the plants due to excess nitrogen.

More recently, organic fertilizer is on the rise as people are resorting to environmental friendly (or 'green') products. Although organic fertilizer usually contain less nutrients some people still prefer organic due to natural ingredients.

Inorganic fertilizer (synthetic fertilizer)

Fertilizers are broadly divided into organic fertilizers (composed of enriched organic matter—plant or animal), or inorganic fertilizers (composed of synthetic chemicals and/or minerals).

Inorganic fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia as the end product. This ammonia is used as a feedstock for other nitrogen fertilizers, such as anhydrous ammonium nitrate and urea. These concentrated products may be diluted with water to form a concentrated liquid fertilizer (e.g. UAN). Ammonia can be combined with rock phosphate and potassium fertilizer in the Odda Process to produce compound fertilizer.

The use of synthetic nitrogen fertilizers has increased steadily in the last 50 years, rising almost 20-fold to the current rate of 100 million tonnes of nitrogen per year.[7] The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000. A maize crop yielding 6-9 tonnes of grain per hectare requires 31–50 kg of phosphate fertilizer to be applied, soybean requires 20–25 kg per hectare.[8] Yara International is the world's largest producer of nitrogen based fertilizers.[9]

Controlled-release types

Urea and formaldehyde, reacted together to produce sparingly soluable polymers of various molecular weights, is one of the oldest controlled-nitrogen-release technologies, having been first produced in 1936 and commercialized in 1955. The early product had 60 percent of the total nitrogen cold-water-insoluble, and the unreacted (quick release) less than 15%. Methylene ureas were commercialized in the 1960's and 1970's, having 25 and 60% of the nitrogen cold-water-insoluble, and unreacted urea nitrogen in the range of 15 to 30%. Isobutylidene diurea, unlike the methylurea polymers, is a single crystalline solid of relatively uniform properties, with about 90% of the nitrogen water-insoluble.

In the 1960's the National Fertilizer Development Center began developing Sulfur-coated urea; sulfur was used as the principle coating material because of its low cost and its value as a secondary nutrient. Usually there is another wax or polymer which seals the sulfur; the slow release properties depend on the degradation of the secondary sealant by soil microbes as well as mechanical imperfections (cracks, etc) in the sulfur. They typically provide 6 to 16 weeks of delayed release in turf applications. When a hard polymer is used as the secondary coating, the properties are a cross between diffusion-controlled particles and traditional sulfur-coated.

Other coated products use thermoplastics (and sometimes ethylene-vinyl acetate and surfactants, etc) to produce diffusion-controlled release of urea or soluble inorganic fertilixers. "Reactive Layer Coating" can produce thinner, hence cheaper, membrane coatings by applying reactive monomers simultaneously to the soluble particles. "Multicote" is a process applying layers of low-cost fatty acid salts with a paraffin topcoat.

Besides being more efficient in the utilization of the applied nutrients, slow-release technologies also reduce the impact on the environment and the contamination of the subsurface water.[10]



Synthetic fertilizers are commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soy and sunflower. One study has shown that application of nitrogen fertilizer on off-season cover crops can increase the biomass (and subsequent green manure value) of these crops, while having a beneficial effect on soil nitrogen levels for the main crop planted during the summer season.

Nutrients in soil can be thrown out of balance with high concentrations of fertilizers. The interconnectedness and complexity of this soil ‘food web’ means any appraisal of soil function must necessarily take into account interactions with the living communities that exist within the soil. Stability of the system is reduced by the use of nitrogen-containing fertilizers, which cause soil acidification.


Applying excessive amounts of fertilizer has negative environmental effects, and wastes the growers' time and money. To avoid over-application, the nutrient status of crops should be assessed. Nutrient deficiency can be detected by visually assessing the physical symptoms of the crop. Nitrogen deficiency, for example has a distinctive presentation in some species. However, quantitative tests are more reliable for detecting nutrient deficiency before it has significantly affected the crop. Both soil tests and Plant Tissue Tests are used in agriculture to fine-tune nutrient management to the crops needs.

Disadvantages of organic fertilizers

·         Organic fertilizers may contain pathogens and other disease causing organisms if not properly composted

·         Nutrient contents are very variable and their release to available forms that the plant can use may not occur at the right plant growth stage

·         Organic fertilizers are comparatively voluminous and can be too bulky to deploy the right amount of nutrients that will be beneficial to plants

·         More expensive to produce

Comparison with inorganic fertilizer

Organic fertilizer nutrient content, solubility, and nutrient release rates are typically all lower than inorganic fertilizers. One study found that over a 140-day period, after 7 leachings:

·         Organic fertilizers had released between 25% and 60% of their nitrogen content

·         Controlled release fertilizers (CRFs) had a relatively constant rate of release

·         Soluble fertilizer released most of its nitrogen content at the first leaching

In general, the nutrients in organic fertilizer are both more dilute and also much less readily available to plants. According to UC IPM, all organic fertilizers are classified as 'slow-release' fertilizers, and therefore cannot cause nitrogen burn.[

Organic fertilizers from composts and other sources can be quite variable from one batch to the next. Without batch testing, amounts of applied nutrient cannot be precisely known. Nevertheless they are at least as effective as chemical fertilizers over longer periods of use.

Pesticides are another important group of agricultural chemicals. Since before 2000 BC, humans have utilized pesticides to protect their crops. The first known pesticide was elemental sulfur dusting used in ancient Sumer about 4,500 years ago in ancient Mesopotamia. By the 15th century, toxic chemicals such as arsenic, mercury and lead were being applied to crops to kill pestsThey are used to kill any undesired organism interfering with agricultural production. Subclasses of pesticides include: herbicides, insecticides, fungicides, rodenticides, pediculicides, and biocides. Many pesticides can be grouped into chemical families. Prominent insecticide families include organochlorines, organophosphates, and carbamates. Organochlorine hydrocarbons (e.g. DDT) could be separated into dichlorodiphenylethanes, cyclodiene compounds, and other related compounds. They operate by disrupting the sodium/potassium balance of the nerve fiber, forcing the nerve to transmit continuously. Their toxicities vary greatly, but they have been phased out because of their persistence and potential to bioaccumulate. Organophosphate and carbamates largely replaced organochlorines. Both operate through inhibiting the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses indefinitely and causing a variety of symptoms such as weakness or paralysis. Organophosphates are quite toxic to vertebrates, and have in some cases been replaced by less toxic carbamates. Thiocarbamate and dithiocarbamates are subclasses of carbamates. Prominent families of herbicides include pheoxy and benzoic acid herbicides (e.g. 2,4-D), triazines (e.g. atrazine), ureas (e.g. diuron), and Chloroacetanilides (e.g. <a href=

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Chitra Joshi
Oct 06, 2011 06:19PM


(e.g. alachlor). Phenoxy compounds tend to selectively kill broadleaved weeds rather than grasses. The phenoxy and benzoic acid herbicides function similar to plant growth hormones, and grow cells without normal cell division, crushing the plants nutrient transport system.[8]:300 Triazines interfere with photsynthesis. Many commonly used pesticides are not included in these families, including glyphosate.

Pesticides can be classified based upon their biological mechanism function or application method. Most pesticides work by poisoning pests. A systemic pesticide moves inside a plant following absorption by the plant. With insecticides and most fungicides, this movement is usually upward (through the xylem) and outward. Increased efficiency may be a result. Systemic insecticides, which poison pollen and nectar in the flowers, may kill bees and other needed pollinators.

In 2009, the development of a new class of fungicides called paldoxins was announced. These work by taking advantage of natural defense chemicals released by plants called phytoalexins, which fungi then detoxify using enzymes. The paldoxins inhibit the fungi's detoxification enzymes. They are believed to be safer and greener.

Fungicides are used to control infestations of fungi, and they are generally made from sulfur compounds or heavy metal compounds. Fungicides are used primarily to control the growth of fungi on seeds. They are also used on mature crops, although fungal infestation are harder to control at this later stage.

Herbicides are weed killers that are used to destroy unwanted plants. Generally herbicides are very selective, since they would be useless for most applications if they were not. A general non-selective herbicide can be used to clear all plants from a particular area. However, appropriate treatment must be carried out to remove the herbicide or render it ineffective if that area is to be used for subsequent plant growth. Herbicides can be used to kill weeds that grow among crops and reduce the value of the harvest. They can also be used to kill plants that grow in fields used for grazing by animals, since some plants can be poisonous to livestock or can add unpleasant flavors to the meat or milk obtained from the livestock. Breeding and genetic manipulation are used to introduce herbicide resistance to crops, allowing the use of more broad-spectrum herbicides that can kill more weed species with a single application. Herbicides include a wide range of compounds, such as common salt, sulfates, and ammonium and potassium salts. In the 1940s 2,4-D (2,4 trichlorophenoxyacetic acid) was developed and this herbicide is still widely used today.

Insecticides are chemicals that are used to kill insect pests. Insects can spread livestock diseases, can eat stored grain, and can feed on growing crops. Not all insects are harmful, and certain species of insects are needed to pollinate plants to ensure that they set seed. Insecticides work in a number of ways. Some are direct poisons (chrysanthemic acids, contact poisons, systemic poisons), while others are attractants or repellents that move the insects to a different location (fumigation acrylonitrile). Some insecticides will only attack a particular stage of an insect's life cycle and this can make them more specific.

Pesticides can save farmers' money by preventing crop losses to insects and other pests; in the U.S., farmers get an estimated fourfold return on money they spend on pesticides. One study found that not using pesticides reduced crop yields by about 10%. Another study, conducted in 1999, found that a ban on pesticides in the United States may result in a rise of food prices, loss of jobs, and an increase in world hunger.

Antibiotics and growth hormones are routinely used as feed supplements for a number of animals. These additives are supplied to keep the animals free from disease and to help them grow to a marketable size as quickly as possible.

The faster an animal gets to slaughter weight or the more milk an animal produces, the more profitable the operation. Approximately two-thirds of all beef cattle in the US are given growth hormones, and approximately 22 percent of dairy cows are given hormones to increase milk production. Recombinant bovine growth hormone (rBGH) causes cows to produce more milk.

  To combat mastitis and other diseases, cows and other farmed animals are given regular doses of antibiotics as a preventive measure. If a single animal in a herd or a flock is diagnosed with an illness, the entire herd receives the medication, usually mixed in with the animals’ feed or water, because it would be too expensive to diagnose and treat only certain individuals. Industrial farms have been mixing antibiotics into livestock feed since 1946, when studies showed that the drugs cause animals to grow faster and put on weight more efficiently, increasing meat producers' profits. Today antibiotics are routinely fed to livestock, poultry, and fish on industrial farms to promote faster growth and to compensate for the unsanitary conditions in which they are raised.

Modern industrial farms are ideal breeding grounds for germs and disease. Animals live in close confinement, often standing or laying in their own filth, and under constant stress that inhibits their immune systems and makes them more prone to infection. According to the Union of Concerned Scientists, as much as 70 percent of all antibiotics used in the United States is fed to healthy farm animals.

Perhaps the most drastic measure dairies take to boost milk production is the use of artificial hormones such as recombinant Bovine Growth Hormone, rBGH, or rBST (recombinant bovine somatotropin). Approved by the FDA in 1993, and produced by Monsanto under the name Posilac®, rBGH's effects are similar to human growth hormone or steroids. RBGH is said to increase per-cow milk yield by 10-15 percent.

Agricultural chemistry has provided us with more and cheaper food than ever before. It has also allowed food to be produced in areas that previously were unsuitable for agriculture. The application of chemicals to farming has been one of the chemical success stories of the twentieth century.

In addition to the applications outlined above, chemicals also have other agricultural uses. For example, sulfur dioxide can be used to keep grain fresh and useable for a longer period of time than untreated grain. Other chemicals can be added to promote the ripening of fruits or the germination of seeds. It is difficult to estimate the monetary value of agricultural chemicals, but many multi- national corporations are involved in their manufacture and use. Agricultural chemistry has increased the diversity of the human diet and has led to a greater overall availability of food, both animal and plant.

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