Nitrogen fertilizers animal derivatives

Plants, like humans and animals, need adequate water, protection from disease, and certain chemical compounds to grow. Soil fertility where no agriculture occurs is maintained at an even level when the waste products derived from plants are returned to the soil. Human agriculture prevents this from occurring. Fertilizers are materials given to plants to promote growth. Nitrogen, phosphorus, and potassium are the most important elements in fertilizers. 

Nitrate (NO.D in natural waters is derived from sources such as fertilizers and undertreated animal and human waste. U.S. environmental regulations set a maximum of 10 ppm NO3 nitrogen in drinking water. Nitrate is commonly analyzed by reduction to nitrite (NO2), followed by a colorimetric assay of NO2. Metallic Cd has been the most common reducing agent for NO3. However, the use of toxic Cd should be curtailed to protect the environment. 

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