For example, consider a corn crop growing in a field. The corn plant extracts minerals needed for growth from the soil. These include nitrogen, phosphorus, potassium, sulfur, calcium, iron and many others. Most of these minerals are abundantly available in the soil and the corn plant's needs are easily met by what is in the soil. However, many soils have too little of some minerals and crops grown on these soils without fertilizers will have lower yields.