Agricultural Chemistry

What is Agricultural Chemistry?

Agricultural chemistry is a science concerned with studying the completed cycles of interactions between living and nonliving components in soil ecosystems. This complex interaction occurs on different levels. For example, the photosynthetic activity of some living organisms results in the production of carbon compounds that enter the soil. Microorganisms living in the soil degrade these compounds and catalyse their transformation into nutrients consumed by the plant for its development and growth. Agricultural ecosystems depend on productivity and stability of these interactions, especially the ones involving conversions of organic matters into phosphorous and nitrogen compounds. Humans can influence the agricultural ecosystems by introducing pesticides or fertilizers that change the natural ecosystem processes. Even though these influences can benefit plant growth and crop production, they can also result in adverse environmental consequences that can pollute ground waters, poison food and kill wildlife. 

What are the Agricultural Ecosystems’ Inorganic Components?      

Soil (ground or earth) is the essential medium of agricultural ecosystems. It is the place where chemical reactions and biological activity take place. The soil is a system that contains solid, gas, and liquid phases. Around half of its volume is made of solid matter that consists of one to five percent organic and 99 to 95 inorganic compounds. The rest of the soil volume is filled with gasses such as oxygen or carbon dioxide and varying water amounts of water. Many factors influence how soil will react with other chemicals. For example, inorganic particles in the soil’s solid phase have different sizes which give different properties. The smallest or sand-sized particles range between 0.05 and 2 millimetres. These are followed by silt-sized (0.002 to 0.5 millimetres) and clay-sized particles that are 8x10^-6 to 0.002 millimetres. The smaller the size of particles, the more surface per unit of weight the soil has, which means that clay can have around eight-hundred meters of surface area in a single gram. The surface area is important in agriculture because it influences the absorption of pesticides and fertilisers as some of most essential compounds used to catalyse chemical reactions.

Another important factor that influences the way soil would react with other chemical is its charge, which determines whether fertilizers or pesticides would remain or be washed away from the soil. For example, a clay-sized fraction of soil contains phyllosilicates or crystalline layer that play an essential role in ion exchange processes. Iron and aluminium oxides have anion exchange capacity because they usually hold a positive net charge. Soils containing these two oxides that regulate anion exchange are usually found in tropical regions of the world.  Contrastingly, the majority of phyllosilicates attract cations because they hold a negative net charge can be found in temperate regions.

What are the Agricultural Ecosystems’ Organic Components?

The solid phase of soil contains a small portion of organic compounds compared to its total weight. Still, organic matters are essential for controlling physical and chemical reactions and processes that occur in soil. Organic compounds can either take the form of smaller molecules such as organic acids or protein, or be grouped in large polymers that are known as humus. Humus is mostly made of acidic functional groups (−OH and −COOH) that hold a negative net charge and control the exchange of negative ions. Humate matter molecules have a unique spatial structure and three-dimensional conformation that gives them hydrophobic properties essential for attracting and retaining synthetic nonionic compounds such as pesticides.

Soil also contains many kinds of microorganisms such as fungi, bacteria, viruses, some algae and protozoa invisible to the naked human eye. Out of all microorganisms, soil contains the largest number of bacteria that process various chemical components. Bacteria activity produces different types of intracellular and extracellular enzymes that reduce and oxidise both inorganic and organic compounds, and increase reaction rates and degrade complex organic compounds into smaller particles used by plans during growth. Fungi present in the soil is more important in agriculture than bacteria because their activity produces the most biomass per given unit of soil weight. Fungi is also responsible for many diseases that attack and damage crops, so agricultural chemistry needs to find ways to maintain a delicate balance between beneficial and harmful properties of fungi.

References

Holmberg, K. (2017). 14.13 Cationic Surfactants in Agricultural Formulations. In , Handbook of Applied Surface and Colloid Chemistry, Volumes 1-2 John Wiley & Sons.

Jeschke, P. (2016). Progress of modern agricultural chemistry and future prospects. Pest Management Science, 72(3), 433-455. doi:10.1002/ps.4190

Kumar, S., Suyal, D. C., Bhoriyal, M., & Goel, R. (2018). Plant growth promoting potential of psychrotolerant Dyadobacter sp. for pulses and finger millet and impact of inoculation on soil chemical properties and diazotrophic abundance. Journal of Plant Nutrition, 41(8), 1035-1046. doi:10.1080/01904167.2018.1433211

Manahan Stanley, E. (2014). 16. Soil and Agricultural Environmental Chemistry. In, Environmental Chemistry (9th Edition) Taylor & Francis.

Morra, M. J. (2004). Agricultural Chemistry. Gale.

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