In order to live the plants they draw their nourishment from sunlight, through photosynthesis, as animals draw their nourishment from food; as with animals, plants also need water to live better, in addition, they also need mineral salts, which they cannot obtain through photosynthesis, as happens for a human being who eats oranges for example to get vitamin C, which not found in other foods. The mineral salts that plants need are naturally present in the soil, in general, and are multiple; the main ones are Nitrogen, Phosphorus, and Potassium, but we could add Calcium, Iron, Boron, Magnesium and some other important minerals.
Not always in the garden soil are all the mineral salts our plant needs, and sometimes they are present but not in forms readily available at the roots; for this reason, in agriculture and gardening, mineral salts are added to the soil to ensure that the plants find everything they need.
Chemical fertilizers generally consist of salts containing the minerals the plant needs; those to be dissolved in the water remain in the soil for a short period of time, usually for a couple of waterings after the one with the fertilizer, slow-release fertilizers are instead washed away slowly, sometimes even for 4-5 months, before to dissolve completely. The waterings and rains dissolve these salts, make them more readily available to the plants, but at the same time they dilate them, transporting them to the aquifers and rivers.
As with so many things, even chemical fertilizers are useful in agriculture, but they are very harmful if used in excess, either because they can easily ruin the plant they are given to, or in the long term because the washout due to bad weather leads to adding large amount of fertilizers to rivers or groundwater, polluting them.
An example that we all remember is that of the mucilages present near the mouth of the river Po, the uncontrolled proliferation of these algae is often also due to the massive presence of chemical fertilizers in the rivers.
So let's remember to use these products with caution, and avoid the reckless excesses.
In addition to the mineral salts directly dissolved in the soil, the plants also need a substrate of good dough to develop; free of water stagnation, but also rich in organic substance, loose and not excessively compact, so that the root system can develop without finding obstacles. In a good soil the mineral salts tend to remain longer or to be more readily available for the plants.
For this reason, in addition to the fertilizers, plants often need a good soil clearing, or soil improvers to improve the dough.
Organic fertilizers: Biological fertilizers
While chemical fertilizers tend to be made up mainly or mainly of the mineral salts that the plant needs, organic fertilizers tend to have a more varied composition; generally they are products that improve the mixture of the soil and contain organic substances which, decomposing over the months, release the mineral salts necessary for the life of the plants. They are therefore made up of composting soil, leaf mold, animal manure, nails or horns, rocks particularly rich in chopped minerals.
Generally an organic fertilizer, in addition to providing the right mineral salt content for a long period of time, also improves the composition and texture of the soil, so as to allow the plant to develop a good root system without effort.
Surely we gardening enthusiasts have to work a little more: while a chemical fertilizer is simply spread on the ground or dissolved in the water of the watering, an organic fertilizer must be spread on the ground, to then hoe, or even dig the soil itself, in so as to mix the earth of the garden with the soil improver chosen by us.