Phosphorus application can double the productivity of eucalyptus plantations

Phosphorus is a very important element for all living organisms because it is part of cell components, biological reactions and compounds that act in the storage and transfer of energy. After nitrogen, it is the most important element for plants.

It is absorbed by plants in the form of phosphate (PO4-), remaining unchanged as a constituent of organic compounds. The phosphorus cycle is limited to the absorption of phosphate from the soil solution by the roots of the plants and incorporation into the organic components. The amount of phosphate immobilized by microorganisms is minimal, being more common in the addition of organic matter when the microbial community is increased.

In general, after the application of soluble fertilizers, the phosphate ions released in the soil solution have high reactivity, where they can be complexed by sodium, potassium, magnesium, calcium, manganese, iron and aluminum. So, it is very important to keep the soils with a pH around 6.0 in order to have the maximum phosphorus absorption. In this pH range, aluminum may have already been complexed, therefore, without interfering with phosphorus absorption.

Fertility of Brazilian soils

In Brazil, most plantations of eucalyptus and other forest species are found on marginal soils in terms of natural fertility. They are generally very weathered soils, with a predominance of secondary minerals.

The situation is even worse when the area has been affected by extreme degradation, with strong evidence of erosion of the surface layer and poverty of organic matter and primary minerals. But, worse than this is the fact that many forest stands are installed on soils naturally low in phosphorus, where experience has shown that economic productivity of eucalyptus can only be achieved with applications of a good dose of phosphorus.

Phosphorus sources

There are two sources of phosphorus for plants - readily soluble phosphorus, coming from phosphate fertilizers, such as super simple, super triple, monoammonium phosphate, etc. As the name implies, after the application of soluble fertilizer, phosphorus will be available, reducing its availability over time.

These fertilizers were produced from natural phosphorus-rich rocks reacted with strong acids, and are indicated for corrected soils, after the application of lime so that the readily available phosphorus is not immobilized by the acidity of the soil.
On the other hand, there are also phosphate rocks, which have not undergone chemical processing, having only been ground to be distributed in the soil. They need natural acidity to make phosphorus available, which is a slower process of nutrient release than acidified phosphates.

In this group are the natural phosphates that are recommended for uncorrected soils, where the natural acidity of the soil will be in charge of making the nutrient available. When these rocks undergo a partial chemical treatment to solubilize phosphorus, they are called partially acidulated phosphates.

It should be noted that the ability to solubilize natural phosphates after application depends on the conditions of the environment, especially the soil, which can represent the sum of different factors. Lately, there are many phosphate rocks available, such as Araxá phosphate, Gafsa phosphate, etc.

Until recently, there was Patos phosphate, produced in Patos de Minas (MG), however, there is no longer an economic advantage to commercialize this phosphate.

Benefits for forests

The use of natural phosphates (partially acidified or not) is very suitable for forest species. This is because initially the seedlings do not have active roots to absorb all the phosphorus from the fertilizers readily available.

It is expected, then, that the volume of roots will increase in line with the gradual availability of phosphorus (PO4-) contained in natural phosphates. Part of the phosphorus applied as a readily available fertilizer is fixed in the soil clays (mainly until the end of the first year). So, our effort is to provide the phosphorus for the seedlings and they will be absorbed as they grow.

Another difficulty we have for the absorption of this nutrient is that it is not very mobile in the soil. Being negatively charged, it is adsorbed (which can be understood as partially adhered) to clays that are positively charged.

Source: AgroRuralNews