Fertilizers, fertilizers and soil improvers: what they are and what the differences are

In nations with more advanced economies, in Italy as in much of the West, the search for a healthier and more sustainable food is one of the driving forces in the sales of agricultural products, as evidenced by the ever-increasing availability of organic or zero km products in the markets and for several years also in large-scale distribution. In the wake of this trend, it is increasingly common to come across products grown “without the use of fertilizers and chemical additives” or similar. Even in organic farming, however, products, generically called, can be used fertilizersto improve crop yields. Fertilizers are generally associated with a natural origin, while fertilizers are often understood as synthetic products. We also often hear about soil improvers in relation to fertilizers and manures. But what exactly is the difference between these product categories?

Fertilizers, fertilizers, soil improvers: what they are and what they are used for

Both product categories serve the same purpose, nourish the soil providing the useful substances to make it fertile and able to support crops. But there are very specific differences that are established by law. In particular, the law 748/1984 provides the definition of fertilizer:

any substance which, due to its content of nutritional elements or due to its particular chemical, physical and biological characteristics, contributes to the improvement of the fertility of agricultural land or to the nourishment of cultivated plant species or, in any case, to their better development.

Fertilizers are further divided into fertilizers And soil improvers (or corrective). A fertilizer And

any substance, natural or synthetic, mineral or organic, suitable for providing crops with the chemical element or elements of fertility necessary for them to carry out their vegetative and productive cycle

while a improver And

any substance, natural or synthetic, mineral or organic, capable of modifying and improving the chemical, physical, biological and mechanical properties and characteristics of a soil.

Basically, fertilizers they provide nutrients to the soil, while the soil improvers improve fertility; the two categories together fall within the generic definition of fertilizer.


Law 748/1984 also provides the list of chemical elements associated with soil fertility:

  • main elements (nitrogen, phosphorus, potassium);
  • secondary elements (calcium, magnesium, sulfur);
  • trace elements (boron, manganese, zinc, copper, molybdenum, cobalt, iron).

The characteristics of fertilizers, manures and soil improvers

When it comes to fertilizersoften refers to those products capable of release quickly large quantities of nutrients, especially the main ones (nitrogen, phosphorus and potassium), which is why they are classified according to the N/P/K nomenclature based on the chemical symbols of the 3 elements (N indicates nitrogen, P phosphorus and K potassium):

  • nitrogenous (N);
  • phosphates (P);
  • potassium (K);
  • nitrogen-phosphates (NP);
  • phospho-potassium (NK);
  • nitrogen-phospho-potassium (NPK).

The speed of release allows rapid growth of crops, and it is easy to adjust the quantity of each individual element based on the needs of the different plants, but excessive exploitation leads toimpoverishment of the land and declining yields.

THE fertilizers they are typically products derived from animal productslike the manure from farms or slaughter waste, but also products of vegetal or mineral origin such as volcanic ash. These are usually slower-releasing products, with smaller amounts of nutrients per kg of material, but the concentrations included can vary greatly depending on the source.

The soil improvers they are typically produced as obtainable compost also from treated domestic waste (our “organic” recovered through separate waste collection, but also wood chips, cut grass, etc.) which help to “give structure” to the soil, enriching it with substances capable of retaining greater quantities of water and promoting absorption into the soil of elements such as phosphorus or carbon.


This happens thanks to substances such as humic acids, a family of organic compounds derived from the decomposition of organic matter: a component of which forest soils are very rich, thanks to the large quantities of vegetal material which falls to the ground and is digested by bacteria or worms, but of which cultivated land or English lawns are decidedly lacking. Soil improvers can typically be purchased in bags and used by mixing them into the soil with a rake or spade.