An optimum nutrient level is essential for productive agriculture. Nutrients can be supplied either by natural sources or in the form of synthetic chemical fertilizers. However, the use of both natural and chemical fertilizers may result in an excess of nutrients, which can cause problems in water bodies and to health. This excess use of various fertilizers may pollute food crops and groundwater; this process is commonly called agrochemical pollution. Nitrates are highly soluble and, therefore, may quickly reach water bodies. Phosphates tend to be fixed to soil particles and can reach watercourses when soil is eroded. Phosphate-saturated soils and high phosphate levels in groundwater are found in many countries. This entry describes the main types of agrochemicals, the reasons for their use, and their ...