Fertilization

Needs for the plants

To develop, the plants use Eau, Lumière, Carbone, Oxygène and biogenic salts.

the Air provides the Carbone (in the form of CO2) and the Oxygène, which are fixed thanks to the Photosynthèse.
the biogenic salts and water are provided by the ground. The principal biogenic salts used are the Azote, the Phosphore, the Potassium, the Magnésium, the Calcium and the Soufre. Minor elements, known as Oligo-élément S are also necessary in less quantity: the Iron, the Manganese, the Zinc, the Copper, the Boron, the Molybdenum for example.

The needs for the plant evolve/move during its development. At the stages where they are necessary, the biogenic salts must be able to be taken by the plant in the ground. They must be available in sufficient quantities and in a form available. If the elements are not available to the moment necessary, the growth of the plant will be limited and the weaker final output.

In the case of a not collected plant developing on the spot and, the biogenic salts are taken during the growth of the plant, but are restored on the ground when the plant dies. There are thus no really losses of elements minéraux.
On the other hand, during the culture of a species at agricultural ends , part of the Plante is not restored with the field (for example grains of the Blé, to in the case of see almost the totality of the plant the Maïs ensilage). A whole part of the biogenic salts taken in the ground, do not reinstate it, and are thus not available for the following culture. The nutritive elements missing for the later cultures can be brought in the form of produced fertilizing.

In order to guarantee at the same time an availability sufficient for the plant, and not to bring more than necessary (financial loss and ecological risk), it is useful to know exactly the amount exported (i.e. used) by the plant. It is what is called an assessment of export. The amount exported by the plant can be completely compensated, by contribution in the form of fertilizer.

Biogenic salts and requirement of the plants

Nitrogen

The nitrogen plays a central role in the Métabolisme of the plants. It is the constituent number one of the Protéine S, essential components of the living matter. It is thus of a growth factor, but also about quality (content of proteins of cereals for example).

Plants, except for the Leguminous S (Alfalfa, Clover, Garden pea…), cannot absorb nitrogen in its gas form. The nitrogen will have to thus be brought by the fertilizer S. On the other hand, it will not be necessary to bring nitrate fertilizers to leguminous plants. RETSA In the ground, the nitrogen is in organic form (Humus) or mineral (ammonium NH4+, nitrate NO3). The organic nitrogen comes from the residues of preceding harvests, organic manures, and must be transformed by the Bactérie S present in the ground into Nitrate S to be usable by the plants; it is what is called mineralization. The essence of the nitrogenized nutrition of the plants is ensured by nitrates.

The nitrogen in the form of ions nitrates, is a very soluble element, little retained by the ground. Brought in too great quantity, the surplus is washed (dissolved, then carried by water circulating in the ground) and thus lost for the plant. The nitrogen must thus be brought, as much as possible, right before its absorption by the plant, in order to avoid scrubbing towards the Ground water. In addition, the excess of nitrogen in cold weather and covered, involves the accumulation of nitrates in the plant (for example, in potatoes). However the nitrate excess in vegetable fabric is harmful for health.

These characteristics explain why its contribution generally annual, is even split.

See also biological Fixing of the nitrogen | Cycle of the nitrogen

Potassium

Potassium is not very mobile in the plant. He plays a central role in the absorption of the cations, the accumulation of the hydrates of proteins, the maintenance of the Turgescence of the cell and the regulation of the water saving of the plant. It is also an element of resistance of the plants to freezing, the dryness and the diseases. It is essential for the transfer of the assimilats towards the bodies of reserve (bulbs and tubers). For these reasons, it is particularly important for the cultures of the type potato, beets

Potassium in the ground is only in mineral form. It comes either from the decomposition of the organic matter and minerals of the ground, or of manures.

For certain minerals, the quantity present in the ground must be higher than the quantity necessary; indeed they can be present in the ground, but nonavailable for as much for the plant. Potassium is primarily retained by the humus or clay (in certain grounds, it could thus be lost in significant amount per drainage).

Potassium is often brought in only once, in an irregular way, in great quantity, because it is stored by the ground and is gradually released.

The very demanding potassium plants are the beet or the potato, whereas not very demanding plants are the common wheat, the durum wheat, the barley.

Phosphorus

Phosphorus intervenes in the energy transfers (ATP), in the transmission of the hereditary features (nucleic acid), the photosynthesis and the degradation of glucids. This element is essential for flowering, the nouaison, precocity, the enlargement of the fruits and the maturation of seeds.

It is in the ground in three forms:

an accessible form, related to the argilo-humic Complex by calcium and magnesium
a combined form: it is immobilized, partly, by the iron and aluminum hydroxides in the acid grounds (in this case, it is necessary to lime the ground to release it)
an insoluble form: in calcareous ground, phosphorus can be in the form of calcium phosphates, of which some are insoluble.

Only the phosphorus of the argilo-humic complex is quickly available (0.2 1 kg from P2O5 per hectare). It is thus a not very mobile element in the ground. For this reason, it is preferable to place it precisely where the roots take it. The risks of drainage are very limited.

The mycorhizes often play a fundamental role in the absorption of phosphorus by the plant. These last by secreting enzymes are able to absorb a phosphorus fixed by the ground (nonassimilable form by the plant directly) n the other hand to transmit it then to the plant sugars coming from photosynthesis (symbiosis racinaire). The cultivated grounds are less and less equipped with mycorhizes (work of the ground, rotation, fungicides,…). Phosphorus/mycorhize

The very demanding phosphorus plants are the beet, the potato, colza, the alfalfa. The not very demanding plants are the common wheat, the corn grain, soya, the sunflower, the oats, rye. Certain stages are more sensitive to the lack of phosphorus than of others: the stage of tillering for cereals, the stage from 4 to 10 sheets for corn for example.

Magnesium

Magnesium is constituent chlorophyl and thus plays a big role in photosynthesis. However, it is especially intended to improve the structure of the ground (and “to nourish” the plant not so much). It is rather brought in the form of amendments.

Calcium

Calcium is especially intended to improve the structure of the ground (and “to nourish” the plant not so much). It is rather brought in the form of amendment whereas for the plant it has two principal roles: role of structure and metabolic role.

Sulfur

Sulfur is necessary to the growth of the plants. It is constituent amino-acids. He plays a crucial role in the metabolism of the vitamins. The food of the sulfur plants is carried out primarily starting from sulfates, the roots absorbing ions SO4 present in the ground. It is responsible for the odor and the savor of certain plants (garlic, onion, cabbage).

Sulfur is especially useful to certain cultures like the Crucifère S (colza, cabbages, mustard), the Liliacée S (garlic, leek, onion). One frequently insists on the need for respecting a relationship between S and NR constantly of the vegetative cycle. For example, for the barley, report/ratio S/N recommended is of 1 per 3 for the complete plant and 1 per 4 for the grain. For corn, these two reports/ratios are of 1 per 2,5. For colza, the report/ratio is of 1 per 0,8 for the whole plant, and of 1 per 0,9 Po the grain (colza is a plant particularly rich in sulfur).

Generally, sulfur is only little fixed in the grounds; there can thus be risk of loss per drainage. Sulfur can be provided by the manure (on average 1,25 unit of SO3 per ton), or of mineral manures, such as the ammonia sulfate (SO3 60%), the simple lime superphosphate (more than SO3 27%) and it potassium sulfate (SO3 45%).

Sulfur is expressed out of SO3 (sulfur trioxide) on the labels of manure in accordance with the regulation. Even if the majority of the sulfur brought to the cultures are in form (SO4 sulfates--), there exist the other sulfur shapes like thiosulfate or mineral sulfur (S). Only the Sulfate form is directly assimilable by the plant and soluble in the solution of the ground. The other forms will have to oxidize under the action of the bacteria of the ground to make itself biodisponible, they will have different agronomic properties (reducing effect, acidifying action,…). the various sulfur shapes

Chlorine

Chlorine is regarded as essential to the plants to differing degree. So for certain plants, its sufficient content is very low, which makes a trace element of it, for others it represents a major element (in particular plants adapted to the coastal areas). Among the crop plants, this case meets at the Cocotier, palm tree tropical which needs large quantities of chlorine to ensure the good performance of its Stomates. The Chlore is not an element fixed in the ground, but it arrives permanently on the plants and the ground by the Aérosol S, more especially as one is close to the sea. It is brought also by manures the such potassium chloride, and even the sea salt (sodium chloride) épandu in certain cases in the cocoteraies.

Trace elements

The Oligo-élément S are more rarely brought. It can sometimes however exist specific deficiencies, according to the types of ground or of the composition of the aerosols. For example, from many Forêt S auvergnates suffer from a lack of Bore. One saw the case of the chlorine, which can be either a trace element or a major element (for example at the coconut). There exists within the world agriculture of the examples of deficiencies out of copper, zinc, iron (when iron is blocked in the grounds very limestones), out of manganese, boron (already quoted).

The assessment of import-export of the nutritive elements

In agriculture, a nutritive assessment is the difference existing between the quantity of nutritive elements provided by the Organic matter (after Minéralisation) and manures and the quantity of nutritive elements removed by the culture or lost, for example by the erosion or the drainage. A very precise calculation of the assessment is difficult to establish, more especially as it must take account of an objective of output which will not be inevitably respected, but an approximate calculation can be enough to indicate if the quantity of manure applied is too weak or too high.

To avoid the impoverishment of the grounds, it is necessary to compensate for the taking away made by the culture and the losses due for example to the Lessivage.

In practice, a total assessment consists in estimating, most precisely possible, the amount necessary to ensure the level of harvest wished and assembling it theoretically available. The balance of these two values indicates the level of fertilization to be brought. In short, the farmer seeks to bring neither too much, nor not enough.

The assessment of export

The assessment of export consists in estimating, most precisely possible, the quantity of an element used by a culture, and not restored on the ground. It is a technique which can be used in the various types of durable Agriculture (such as the reasoned Agriculture or the Organic farming) as in traditional agriculture.

For example, for a corn harvest, one estimates the quantity of nitrogen contained in each quintal of Grain, for a harvest of Ensilage of corn, it acts of the quantity contained in a ton of Matière dries of collected plant.

Thus, one can, for example, to estimate that the corn requires approximately 3 kg of nitrogen per quintal of grains produced. For a corn field giving an output of 80 quintals per hectare, one thus evaluates the total quantity of nitrogen necessary per hectare to 3*80 = 240 units of nitrogen. This amount constitutes a maximum of what must be brought in the form of nitrogen.

This amount of 3 kg nitrogen per production unit, is obviously different for each Culture, according to the species, of the variety and the accessible objective of output. For corn for example, this value can vary from 2,5 to 3,5 according to the varieties, which can results in a large difference into term in contribution.

One adds to exports, the amount lost by drainage or gas losses for example.

The assessment of the imports

It consists in estimating at the beginning of countryside, the amount who is or will be available. It is primarily about the remainder remaining of the preceding countryside, of the contributions resulting from the Minéralisation (i.e. the organic matter transformation into biogenic salt available), typically of the contributions of Fumier, the Paille S exits of the preceding culture, the reversals of old meadows), even the contributions by water of Irrigation.

Benefit of the fertilization

The fertilization is essential to improve the outputs. It must be correctly evaluated to be located at the economic optimum. There exists indeed, if one observes the evolution of the output according to the amount of fertilizing element brought, a technical threshold beyond whose the output decreases by effect of toxicity (surdose) and an economic threshold, lower than the precedent, beyond whose the additional profit does not cover any more the additional costs. Of course this threshold is delicate to evaluate because the output depends on other factors less better controlled, in particular in culture of full field, like pluviometry.

Nevertheless, a level of fertilization adapted is necessary to obtain the level of production permitted by the genetic potential of a given species. Progress in this field is especially in the methods of diagnosis (analyzes of the grounds, analyzes of the plants, for example foliar Diagnostic), in the comprehension of the interactions between the biogenic salts, the ground and the plants, and in the techniques of fertilization so as to answer most precisely possible, taking into account the technical constraints and economic, with the needs for the plants in growth while limiting the effects on the natural environment.

The development of the fertilization was one of the key components of the agricultural revolution. So in the Western countries, one probably reached a threshold of saturation, the level of fertilization is still definitely insufficient in the majority of the Third World countries.

Ecological risks

An excessive fertilization, in particular out of soluble mineral nitrogen, can involve a water pollution of surface, even of the ground water.

On the surface, Azote (Nitrate S, Nitrite S) and phosphorus (Phosphate S), which also comes from the effluents of breeding, urban waste water and the rejections of certain industries, can cause in the rivers a proliferation of algae which, in the long term causes a Asphyxie rivers (more Oxygène) and thus would result in the “death” of the rivers if fauna and Flore had suddenly disappeared

See the case of St. Lawrence river

Material used in fertilization

pendular Muck-spreader
Muck-spreader centrifuges
Localisateur of manure
Localisateur enfouissor of manure
Epandeur of manure
Epandeur of manure Agrospir

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