Chemistry in Agriculture – A Review

Food is the basic requirement for sustenance of human life. Agriculture, for decades, has been closely associated with the cultivation of the soil, production of economically important crops and raising livestock which in turn contributes to national income. However, to meet the demands of the world’s ever-increasing population, it has become necessary to maximize the yield and productivity of crops and animal products which is why modern agriculture depends quite heavily on the use of advanced scientific techniques that have been contributed by science and chemistry in particular. In this review, the authors have made an attempt to discuss the contributions of chemistry in agriculture.


INTRODUCTION
Food is the basic requirement for sustenance of human life. Without food there is a seldom possibility of survival for human beings on earth for a long period of time. It is only agriculture that satisfies this need for the entire world's population (Chhibber, 2017 andBaokar et al. 2018). Agriculture, for decades, has been closely related to the cultivation of the soil, production of economically important crops and raising livestock which in turn contributes to national income (Anonymous, 2019). Thus, agriculture is considered as the backbone of a nation and plays a pivotal role in the growth of an economy. However, to meet the demands of growing hunger of the world's ever-increasing population with diminishing natural resources and unpredictable climate (Plant, 2010), it has become necessary to maximize the yield and productivity of crops and animal products which is why modern agriculture depends quite heavily on the use of advanced scientific techniques that have been contributed by science, and chemistry in particular. Chemistry, also known as the central science, is a scientific discipline that deals with the study of structure, composition, behaviour and changes during reactions involving elements and compounds composed of atoms, molecules and ions (Reinhardt, 2001 andBrown et al. 1999).
Available online at www.ijpab.com DOI: http://dx.doi.org/10.18782/2582DOI: http://dx.doi.org/10.18782/ -2845 ISSN: 2582 -2845 Ind. J. Pure App. Biosci. (2020) 8(3), 241-247 This discipline has known to have played a significant role in fulfilling the fundamental needs of crops from the basics of photosynthesis to the utilization of farm produce (Chhibber, 2017) by providing threemajorrequisites viz.,water and nutrients to cause the land to produce more abundantly, and protection against deterioration caused by pests and pathogens (Bewick et al., 2019). Thus, advancement in the field of agriculture has become possible due to active research carried out in chemistryas it forms an indispensable part from molecular to organ level (Chhibber, 2017) and henceforth, an endeavour has been made to categorize the contributionsof this discipline under various headings in this review.

Chemistry in manufacturing food through Photosynthesis
Photosynthesis is a natural phenomenonin which green plants transform light energy into chemical energy that can be used to power the operations of the crop, thereby supplying all the agricultural products with essential building blocks. This chemical energy is stored in carbohydrate molecules viz., sugars that are synthesized from carbondioxide and water (Bryant & Frigaard, 2006). The net equation: 6CO 2 + 6H 2 O ==> C 6 H 12 O 6 + 6O 2 better illustrates the total operation of photosynthesis. For survival and sustenance of any life form on earth, no chemical process is more consequential than photosynthesis as they cannot preparetheir own food like autotrophs andrely only on green plant for food. Thus, chemistry has enabled the researchers to understand the underlying principle and mechanism of photosynthesis and to optimize conditions for maximization of the same (Chhibber, 2017).

Chemistry in water purification
Chemistry has enabled humans to utilize various compounds for water purification that are available in different products or forms. The main purpose of purifying water is how best the undesired and toxic compounds (organic, inorganic, biological contaminants and suspended solids) are removed from the water in order to make it suitable for human consumption. A few of the chemical compounds extensively used for water purification are mentioned in Table 1 (Lenntech, 2020).  (Cheremisinoff, 1997) and about 40-60% of crop yields are attributed by the use of commercial fertilizers.
Fertilizers are subdivided into two broad categories: organic and inorganic and both are required for promising plant growth. As the name suggests, organic fertilizers are derived from living systems and include manure, fish and bone meal and compost whereas inorganic fertilizers contain higher concentrations of chemicals that may not be present in enough quantities in the soil (Chhibber, 2017). The decomposition of organic fertilizers is carried out by microorganisms that are present in the soil to facilitate the release of definite nutrients into the soil which are then taken up by plants and translocated in their system. Inorganic or chemical fertilizers, on the contrary, are highly concentrated withfewerchemical complexities and are synthesized using the Haber-Bosch process. These properties make them suitable to be formulated in a way that can provide nutrients in balanced concentrations required during the production of a specific crop (Chhibber, 2017). Nitrogen, phosphorous and potassium are the major or macro-nutrients present in inorganic fertilizers and are also known to supply micro-nutrients in much smaller quantities. Thus, the role of chemistry is inevitable in manufacturingfertilizers becausewith the increase in urbanization and a decrease in agricultural land, the use of fertilizers in appropriate quantities has become an important aspect to increase the yield of crops to counterbalance the loss in agricultural land.

Chemistry in manufacturing pesticides
Pesticide is a broad term used to refer to the organic, inorganic, synthetic and biological compounds that can either inhibit the growth and development of the pestor kill the pest of all kinds. Based on their chemical composition, mode of action, mode of entry, time of development and type of pests, pesticides are classified into insecticides (may include insect growth regulators, repellent, antifeedants), acaricides, termiticides, rodenticides, nematicides, molluscicides, herbicides, fungicides, bactericides (Randall et al., 2014). Herbicides are the most extensively used pesticides that alone can account for 80% of all pesticide use (Gilden et al., 2010). Pesticides are intended to serve as potential products that impart protection to plants by minimizing the damages caused by pests and pathogens without compromising the yield and productivity.

Chemistry in sustainable arable crop protection
Organic chemistry has been the mainstay of crop defense strategies for arable cultivation and food production for more than half a century. Through maintaining the extracted yield of the world's crops, the management of pathogenic infections, insect pests and weeds has rendered a critical contribution to food production worldwide. Inclusion of these compounds in the integrated pest management system is possible only when they shows environment friendly properties along with high specificity (inhibit the growth of target pest and pathogens) and biodegradable properties. Thus researchers are keen to understand the advances made during the discovery of newer molecules for sustainable crop production and protection by including series of tests to evaluate the toxicological, biochemical and physiological aspects of the compounds (Smith, 2018). This need has arisen due to the multiple factors related to development of resistance in pests and pathogens, pest resurgence, health and environmental hazards caused due to the indiscriminate use of pesticides. Therefore, chemistry has enabled the scientists to discover efficient newer molecules with new mode of actions without upsetting the ecological balance (Smith, 2018 andGodwin et al., 1992). e.g. development of azoxystrobin. Chemistry in other areas of agriculture  Chemistry in food processing and post harvest management of agricultural produce Chemistry plays a vital role in the food processing industry as it deals with various chemical reactions and interactions that occur between biological and non-biological compounds of food (Kumar et al., 2016 anddeMan, 1999). By exploiting the advances in chemistry, attempts are being continuously made by the researchers to upgrade the quality (in terms of flavour, taste, appearance and nutritional values) of food products,to counter the effects of deterioration and spoilage within a short period of time as well as to increase the shelf life (Kumar et al., 2016 andPotter &Hotchkiss, 1995). e.g. application of sulphur dioxide in grains helps in keeping the grains fresh and useable for a longer period; use of sodium benzoate and salicyclic acid as food preservatives increases the shelf life; development of new generation refrigerants; use of saccharin, sweeteners, enzymes, vitamins, hormones and minerals to enhance the quality of food products; etc. Thus, advancement in chemistry has led to increase in diversity of diet in humans and animals and also availability of food productsto a greater extent.
 Extensive use of plastic pipe in agriculture The development of plastic is a contribution made by chemistry. The manufactureof plastic pipes has enabled their usage massively in the agricultural sector for irrigation purpose (Chhibber, 2017).  Chemistry in production of chemicals from agricultural wastes Advancements in chemistry have played a major role in the development of processesthrough which conversion of bioproducts into bio-energy could be carried out. The residues produced from agricultural wastes are known to have rich sources of bioactive compounds that can be utilized as an alternate source for production of biofuel, biogas and other raw materials (Sadh et al. 2018). Utilization of these products not only helps in maintaining air pollution-free environment but also ensures sustainability in the long run as other natural resources like sources of petrochemical hydrocarbonsare present in finite quantities. e.g. development of antioxidants, antibiotics, vitamins, feeds of animals via solid state fermentation (SSF) (Bhargav et al., 2008); use of anaerobic digestion (AD); pre-treatment of biomass, hydrolysis and fermentation of enzymes, purification and catalytic conversion of lactic acid to acrylic acid.

CONCLUSION
The discipline, chemistry has been playing and will continue to play an inevitable role in the agricultural sector as it not only provides innovative ways to produce the crops but also provide remedies to mitigate or limit the potential problems related to various pests and diseases including nutrient deficiencies without hampering the yield, productivity and quality of the crops in an eco-friendly way.