They provide the essential macronutrients needed by plants to grow, nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg), along with several micronutrients, such as zinc (Zn), iron (Fe) and many more.
Fertilizers play an important role for soil health: they supplement the natural supply of soil nutrients, build up soil fertility in order to satisfy the demand of crops with a high yield potential and compensate for the nutrients taken by harvested products or lost by unavoidable leakages to the environment, in order to maintain good soil conditions for cropping.
Integrated plant nutrient management
Most agronomists agree that optimal nutrient management entails starting with on-farm organic sources of nutrients and then supplementing them with manufactured fertilizers to achieve the farmer’s yield goal , contrary to some beliefs that supporting the use of manufacture fertilizers implies opposing the use of organic sources of nutrients.
Manufactured fertilizers and organic sources of nutrients can, and should, be used in a complementary fashion.
Integrated use of organic and mineral nutrient sources can improve soil fertility, enhance soil organic matter content and improve physical, chemical and biological soil properties. This integrated approach is an appropriate strategy for effective and responsible plant nutrition.
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IFA therefore advocates for:
Sound science as the basis for food and environmental safety standards, applied equally to all nutrient sources used for food production;
Uniform descriptions of available nutrient content for all commercial fertilizer products, whether of organic or mineral origin.
It should be noted that organic sources of nutrients, like mineral fertilizers, can have negative environmental impacts if not properly managed.
The integration of organic and mineral sources of nutrients should be seen in the context of overall crop production, which includes the selection of crop varieties, pest control, efficient use of water, soil management and other aspects of integrated farm management.
Soils and water
Soil fertility management must take water into consideration in order to be effective: indeed, the accumulation or depletion of nutrients in soils is directly affected by the movement of water in soils.
Water is fast becoming a scarce resource in certain regions of the world, and farmers need to be very careful in managing inputs (water and nutrients) to ensure high yields while reducing adverse effects of this management on the environment.
The three main considerations that govern the relation between water and nutrients in soil fertility management are:
Soil water stress will limit soil nutrient use at the plant level;
Soil-supplied nutrients can be taken up by plants only when sufficient soil solution allows mass flow and diffusion of nutrients to roots;
Soil water content is the single most important factor controlling the rate of many chemical and biological processes, that influence nutrient availability.
Soil degradation and desertification
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.
Restoration of degraded soils through soil conservation practices and the widespread adoption of fertilizer best management practices , can reverse the historic losses of soil carbon worldwide and restore the fertility of depleted soils.
