Soil infertility implies lack of the qualities which enable it to provide nutrient elements and compounds in adequate amounts and in proper balance for the growth of specified plants. Nutrient-weak soil may be aggravated by poor soil mechanics, particularly poor binding properties which do not hold soil particles together in a porous, water-stable structure. Soil binding is the result of microorganisms exuding gummy substances during organic decomposition. Infertile soils lacking in decomposing organic matter such as manure, will lack nutrients and binding qualities as well.
For healthy growth, all plants require certain nutrients from the soil. There are 16 elements (carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulphur, calcium, iron, magnesium, boron, manganese, zinc, copper, chlorine and molybdenum) which, in varying quantities, are essential to plant growth. If any of these is absent from the soil or present in insufficient quantities, then the soil is said to be deficient.
Soils have been found to be naturally deficient in one or more of all the essential elements. Almost all soils that have been cropped without fertilizer for 100 years or more will have become deficient in one or more of the plant nutrients. Nitrogen is deficient in all of the agriculturally important soils of the world. Phosphorus and potassium deficiencies are also very common. Zinc, manganese, iron, and copper deficiencies are commonly associated with sands and alkaline soils, while boron and molybdenum deficiencies are usually associated with the older, highly weathered soils. Calcium and magnesium deficiencies, which sometimes occur in the humid and semihumid temperate regions, are less of a problem since such soils are acid and the deficiencies are automatically corrected in the required liming programme.