Approximately 25% of the world’s crop yield is estimated to be directly attributed to the use of chemical fertilizers. The use of chemical fertilizers has increased significally over the last few decades and is expected to rise even higher. Fertilizers are very valuable, as they replace the soil nutrients used up by plants. The three primary soil nutrients often in short supply are potassium, phosphorous and nitrogen compounds. These are commonly referred as “macronutrients”. Certain other elements like boron, zinc and manganese are necessary in extremely small amounts and are known as “micronutrient”. When crops are harvested, a large amount of macronutrients and a small amount of micronutrients are removed with the crops. If the same crop is grown again, depleted levels of the nutrients can result in decreased yields. These necessary nutrients can be returned to the soil through the application of fertilizers. In addition to fertilizers, a large amount of pesticides (chemicals used to kill or control populations of unwanted fungi, animals or plants often called pests) are also used to ensure a good yield. Pesticides can be subdivided into several categories, based on the kinds of organisms they are used to control. Insecticides are used to control insect populations while fungicides are used to control unwanted fungal growth. Mice and rats are killed by rodenticides, while the plant pests are controlled by herbicides.
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