Fertilizer is any natural or industrially produced material that is applied to soil or to plant tissues to supply plant nutrients. Natural sources for fertilizers include manure, compost and minerals. Commercial fertilizers commonly focus on three main elements, nitrogen, phosphorus and potassium, and some fertilizers also contain additional nutrients such as calcium, zinc and magnesium. Fertilizers can be applied in dry, pelletized or liquid forms and using manual methods or agricultural machinery.
The increased use of synthetic fertilizers has been crucial in increasing crop yields to support the earth's rapidly expanding human population. However, improper or excessive application can cause environmental damage and harm public health. For example, it can lead to soil acidification, reducing microbial activity and diminishing soil fertility. It can also deplete essential nutrients in the soil.
Nitrates and phosphates from fertilizer runoff can contaminate groundwater, rivers, and lakes, causing eutrophication (excessive algae growth) and dead zones in water bodies. This can harm aquatic life, killing fish and reducing biodiversity, and it can make water unsafe for human consumption. Excessive nitrogen deposition can also damage terrestrial ecosystems. Some synthetic fertilizers also contain heavy metals or toxic compounds that can accumulate in the food chain.
The production and application of synthetic fertilizers also adds to air pollution, especially nitrous oxide and ammonia. The former is a potent greenhouse gas that contributes to climate change, while the latter leads to particulate matter formation and acid rain.