What are fertilizers?

Fertilizers are any solid, liquid or gaseous substances containing one or more plant nutrients.

They are either applied to the soil, directly on the plant (foliage) or added to aqueous solutions, in order to maintain soil fertility, improve crop development, yield and/or crop quality.

The purpose of fertilizers are to supplement the natural supply of soil nutrients, build up soil fertility in order to satisfy the demand of crops, and to 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.

What are plant nutrients?

As a precondition for growth, health and the production of nutritious food, plants require essential nutrients (macro and micronutrients) in sufficient quantities.

Seventeen elements have been shown to be essential for plants: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulphur (S), magnesium (Mg), calcium (Ca), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), nickel (Ni). Furthermore, additional elements may be essential to a few plant species, e.g. sodium (Na) and cobalt (Co).

Carbon, H and O are obtained from the atmosphere and water, and are not considered mineral elements. The remaining essential elements can be divided into three groups: primary macronutrients (N, P and K), secondary macronutrients (S, Mg and Ca) and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl and Ni) based on average concentrations in plants. If a single essential plant nutrient is available in insufficient quantity, it affects plant growth and thus the yield.

Food and Nutrition Security

Half the food we eat today is produced thanks to mineral fertilizers

They provide crops with the essential nutrients to their growth and health, which helps increase yields and food production. Fertilizers are used in every corner of the globe to support sustainable agricultural production and food security. Food security exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food.

With the world population expected to reach 9.7 billion people by 2050, the agricultural sector needs to increase its productivity by 60% compared to 2005 levels to meet the increasing demand for food. This must be accomplished in the context of the shrinking availability of arable land. Achieving global food security today and in the future cannot be achieved without fertilizers.

Fertilizers contribute to a better nutrition for all through micronutrient fertilization.

Currently, billions of people, mostly in developing countries, suffer from micronutrient malnutrition, sometimes referred to as “hidden hunger”. The nutrient deficiencies most commonly associated with human health problems on a global scale are iron, zinc and iodine, but selenium and fluorine deficiencies are also widespread. Micro-enriched fertilization is considered one of the most promising ways to fight malnutrition, and to alleviate nutrient deficiencies worldwide.

In addition, micronutrient fertilization can extend the lifecycle of food, improve the post-harvest integrity of crops and thus reduce food waste: this is the case for calcium-based and boron-supplemented fertilizers, which help strengthen plant cells and make them more resistant post-harvest.

Types of fertilizers

Mineral fertilizers

Mineral or manufactured fertilizers are produced by the fertilizer industry. A wide range of products, supplying one or more essential mineral nutrients are available to farmers. Each fertilizer product has its advantages and shortcomings, which depends on the local argo-ecological and economic conditions in which they are used.

Manufactured fertilizers are classified according to different criteria as follows:

Number of nutrients

  • Single-nutrient or straight fertilizer (whether for macro or micronutrients);
  • Multi-nutrient/ compound (multiple nutrients) fertilizers with 2, 3 or more nutrients.

Type of Combination

  • Mixed fertilizers or "bulk-blends" are physical mixtures of two or more single-nutrient or multi-nutrient fertilizers.

Physical condition

  • solid (cystralling, powdered, prilled or granuals) of various size ranges;
  • liquid (solutions and suspensions);
  • gaseous (liquid under pressures, e.g. ammonia).

Nutrient release

  • quick acting (water-soluble and immediately available);
  • slow-acting (transformation into sobulble form required, e.g. direct application of phosphate rock);
  • controlled- release by coating;
  • stabilized by inhibitors.

Livestock manure

Livestock manure is a valuable nutrient source, yet its nutrient content of manure varies widely between sources and farm management practices. Before its application, manure should be analyzed for nutrient content.

Crop residues

Crop residues (such as leaves, stems and roots) release the nutrients they contain when left on/in the soil. Crop residues vary greatly in nutrient content.

Compost

Compost (organic matter that has been decomposed) can be added to soils to supply nutrients and serve as soil conditioner. Quality of composts can vary with raw materials and processes used.

Biological N fixation

Biological N fixation (BNF) is the conversion of inert atmospheric dinitrogen molecules (N2) into forms of N that can be utilized by plants. It is greatest in symbiotic systems developed in leguminous crops (e.g. beans, peas, alfalfa) and rhizoba. BNF rates range from 20 to 400 kg N/ha/year depending on plant species, length of the growing season and climatic conditions.

Previous applications

Soil nutrients from previous applications, which have not been taken up by previous crops, are either lost to the environment or stored in soils and potentially available to subsequent crops. Some nutrients such as N and S can be prone to significant losses in the year of application under wet conditions. Nutrients such as P and K remain in soils for longer periods, usually several years, subject ot soil types, rainfall and management practices.

It is important to note that crops respond to plant nutrients from all sources but they can take up nutrients only in their unorganic form. Organic nutrient sources must be mineralized (converted from an organic to an inorganic form) before being taken up by plants. The amount of nutrients provided by the different sources varies greatly between and within agro-ecosystems. Sustainable crop nutrition identifies and utilizes all available sources of plant nutrients.

IFA Publications

Fertilizers and their Efficient Use
Nutrient Management Handbook
Integrated Plant Nutrient Management