Fundamentals of Soil Fertility

Plants need 17 different minerals to grow.  Carbon (C) and oxygen (O) they get from carbon dioxide in the atmosphere.  Hydrogen they get from water (H2O).  The other 14 elements are typically picked up from the soil.  Managing soil sustainably so that it remains agriculturally productive for the long haul is a function of the biological, physical and chemical characteristics of soil, as well as dependent on adding amendments to maintain adequate levels to replace crop removal. 

Six of the nutrients crops get from soil are needed in relatively large amounts and are called macro nutrients.  These include nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), and sulfur (S).  Availability of some nutrients, for example phosphorus (P), is simply a matter of which chemical forms are present in the soil.  Other nutrients, for example nitrogen (N), are very dependent on biological activity.  These will be discussed in later sections.  Some nutrients are commonly found in the soil as charged elements or compounds called ions, and so charged particles in the soil play a role in retention and availability.