Fertilizers are natural or artificial substances added to soil to make crops and garden plants grow better. Natural fertilizers such as manure and compost have been used since the earliest days of farming. Manure comes mostly from farm animals, though in some countries human waste is used. Manure contains the chemicals nitrogen, phosphorus and potassium plants need for growth. It is also rich in humus, organic matter that helps keep water in the soil. Artificial fertilizers are usually liquid or powdered chemicals (or occasionally gas), containing a mix of nitrogen, phosphorus or potassium. They also have traces of sulphur, magnesium and calcium. Nitrogen fertilizer, also called nitrate fertilizer, is made from ammonia, which is made from natural gas. The first fertilizer factory was set up by