Qu’est-ce que la fertilisation des terres agricoles ?

Basic mineral amendments primarily serve to maintain or raise soil pH. These consist essentially of lime (CaO) and magnesia (MgO).

Organic amendments, particularly in the form of manure and compost applications, improve the microbiological and physical qualities of soil by increasing the capacity of the clay-humus complex to store nutrients. Organic matter gradually mineralizes to release the nutrients plants need for growth.

Applications of wastewater treatment plant and industrial sludges eliminate residual sludge from these facilities while providing crops with agronomically valuable elements at lower cost: organic matter, nitrogen, phosphorus, lime, and potassium and magnesia in smaller quantities. However, sludges may also contain undesirable elements: heavy metal traces (copper, chromium, lead, etc.); organic micropollutants (pesticides, paints, solvents); pathogenic microorganisms; and emerging pollutants (pharmaceutical residues, endocrine disruptors).

Synthetic mineral fertilizers are derived from chemically transformed substances. They increase crop growth and yield but do not improve long-term soil fertility. Some fertilizers are simple (for example, nitrogen fertilizers), while others are compound when they provide two or three different mineral elements. The percentage of each element is specified as follows: NPK 7-5-6 means the fertilizer contains 7% nitrogen (N), 5% phosphorus (P2O5), and 6% potassium (K2O). They can be supplemented with trace elements (boron, copper, iron, manganese, molybdenum, zinc, etc.) to address specific deficiencies. Mineral fertilizers are produced from ores extracted from the ground (phosphate, potash) or manufactured from atmospheric nitrogen. They can be a source of heavy metals, some of which are potentially radioactive. Depending on its extraction origin, mineral-origin phosphorus can be mixed with varying levels of toxic metals such as cadmium, chromium, mercury, and lead. There are three main families of synthetic fertilizers: nitrogen fertilizers: nitrogen is a fundamental component of proteins and chlorophyll and therefore a very important element for plant growth. While nitrogen is naturally present in the atmosphere, chemical fertilizers provide it in much greater quantities; phosphate fertilizers: they can provide soil with phosphorus, aluminum, nitrogen, and calcium depending on their composition; potassium fertilizers: potash is naturally present in soils, with some soils being richer than others. Certain plants are particularly demanding for potash, such as potatoes, beets, and grapes.

Organic fertilizers are composed of nutritive elements of animal or plant origin. These include animal waste (manure, slurry, poultry droppings, etc.) or industrial by-products such as leather, horn, beet vinasse powders, grape pomace, seaweed, oilcakes, etc. Certain wastewater treatment plant sludges are also intended for agricultural spreading. Their use is regulated due to the possible presence of metals, organic micropollutants, pathogenic microorganisms, and emerging pollutants.

Organo-mineral fertilizers contain both organic matter of plant and/or animal origin and mineral fertilizing materials. They must contain a minimum of 1% nitrogen of organic origin.

The first regulation governing the sale of fertilizers in France dates from 4 February 1888. It requires declaring nutrient content in N, P2O5, and K2O as a percentage of product mass. It establishes controls by the fraud prevention administration (Departmental Direction for Population Protection) through the adoption of official sampling and analysis methods. The Rural Code defines the procedures for placing fertilizing materials and growing media on the market, namely: approval (or provisional sales authorizations or import authorizations) after risk and benefit evaluation by the National Food, Environment and Work Safety Agency (ANSES).