Healthy soils are essential for plants, animals and humans to live. Soils help sustain life by fulfilling our needs for food, feed and fiber plus a number of critical ecological services. Indeed, the essential macronutrients needed by plants to grow, nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) are to be found in soils, along with several micronutrients, such as zinc (Zn), iron (Fe) and many more (see our section “About Fertilizers” to learn more about macro and micro nutrients).
Plants can only take up nutrients in their mineral forms. Therefore, to be available to crops, organic nutrient sources must first be converted to mineral forms by soil microorganisms.
It all begins with soil: Chris Lambe, Director Strategic Initiatives, Agriculture and Food Security Center, The Earth Institute at Columbia University
Most soils lack some plant nutrients at some point, as growing crops and harvests remove them over time. Soil nutrients therefore must be replaced when removed and supplied when deficient.
Nutrient deficiencies becoming apparent in a rice field
Deficient soils, i.e. soils that lack one or several essential nutrients, pose serious risks for people’s food and nutrition security, and also raise environmental problems. Continuous soil depletion leads to low yield potential and conversion of natural habitats to cropping. In extreme cases, it can trigger desertification.
Desertification is the degradation of land in arid, semi-arid and dry sub-humid areas, primarily caused by human activities and climatic variations. Although other regions, mostly in Asia and Latin America, are also concerned, the most dramatic examples of desertification are found in Africa, where declining soil fertility is linked to declining agricultural productivity.
Traditionally, methods for restoring soil fertility entailed long fallow periods and shifting agriculture to new areas. However, these practices no longer suffice to meet the needs of the current and future population levels, and have raised serious environmental concerns, such as deforestation, as people tried to expand arable land.
The main nutrients in most fertilizers — nitrogen, phosphorus and potassium — come from the land and the air. They also exist in crop residues, manure and waste but these sources are not abundant enough for the yield level needed to produce food, feed, fibre and bioenergy to more than 7 billion people.
The fertilizer industry encourages farmers to use both organic nutrient sources and mineral fertilizers in an integrated manner,
together with appropriate soil and crop management practices. This practice is referred as “Integrated Soil Fertility Management”