Fertilizers are substances that are added to the soil or plants to promote growth and productivity by providing essential nutrients required by the plants, including nitrogen, potassium, and phosphorus. They are used by farmers daily to increase crop yield and enhance the water retention capacity of the soil, thus increasing its fertility. Fertilizers are mainly classified into two main types: organic and inorganic fertilizers. Organic fertilizers are obtained naturally by the decomposition of dead plants and animals, while inorganic fertilizers are chemical substances that are not typically natural. Inorganic fertilizers are further classified as straight fertilizers or complex fertilizers, depending on whether they provide one nutrient or two or more nutrients, respectively. The NPK rating system is a way of describing how much nitrogen, phosphorus, and potassium are in a fertilizer.

Advantages of fertilizers include that they are quick in providing plant nutrients and restoring soil fertility, portable and easy to transport, and improve and increase the productivity of many crops such as wheat, maize, and rice. However, overuse of fertilizers can lead to environmental problems such as algal blooms in bodies of water, which can decrease the oxygen level of the water and prevent streams from moving freely.

In summary, fertilizers are substances added to the soil or plants to promote growth and productivity by providing essential nutrients required by the plants. They are mainly classified into two main types: organic and inorganic fertilizers. While they have advantages, overuse of fertilizers can lead to environmental problems.