Agriculture is stone: To cultivate or not in soils with a stony texture?

It is estimated that in the state of Tocantins, 35% of pedological coverage is composed of stony soils (INDE, 2018). The so-called Plinthosols can be present in various ways. The most common are loose gravel, but They can also be presented in the form of a stone blade, not fragmented.

The precursor of gravel is plinthite, “an unhardened stone” (soft), which once dries through natural processes, hardens and forms petroplinthite, which constitutes gravel. It may be surrounded by earth (clay, silt and sand) consisting of in different proportions.

These soils occur diffusely across the landscape, in the upper third of the landscape (tops of areas), in the lower third of the landscape, other times associated with the presence of water in drainage headwaters. All these characteristics make it important when we realize that currently the Tocantins agriculture is developing on them. The presence of gravel, at first glance, would inhibit its use, but it brings with it an advantage fundamental: the price of land. The other advantage is the relief, which favors mechanization.

Despite this, production on these soils still does not have scientific information aimed at its management, despite the agricultural suitability do not recommend its use for agricultural crops, although the do it for pastures. Despite this, these soils often have presented very high levels of productivity.

The fact is that the presence of gravel and pebbles reduces the volume occupied by land fine (part of the soil made up of sand, silt and clay). But after all, what does this do you want to tell us?

That the producer is farming in non-recommended soils, or In other words, all the technology used to cultivate these soils is done today without no scientific support. Research involving studies on Plinthosols are of fundamental importance, both in technical terms, as it is known that it is It is necessary to adjust the management of these soils so that the use is appropriate to the real condition, and above all economic, when we refer to the use of inputs, as fertilization and liming recommendations are made only considering the land thin, that is, there is an overestimation of the doses of fertilizer and limestone. That means that the producer may be applying more than he really should, addressing a super relevant economic issue, especially considering the eminence the lack of fertilizers. Furthermore, we have the environmental issue that needs be rethought. Over dosing of fertilizers and lime means more loss of nutrients, either through leaching or surface runoff as a result of water erosion, resulting in contamination of groundwater, rivers and lakes.

A recent research carried out with Pétricos Plintosols in the state of Tocantins, proved the great variability of this soil. The proportion of gravel in relation to fine earth it varied from 20% to 77% within the same soil class. In other words, in extreme cases, more than 70% of the soil volume is not soil, is gravel (Castro & Ramos 2020). Does it mean a loss of inputs (fertilizer and limestone)? Or could these soils only produce Why are they super fertilized and super limed?

Other questions that we still don't have answers to, the water dynamics in these soils, how does it happen? What is the climate risk involved? Farmer insecurity in cultivating under these areas and not knowing the water storage potential, causes producers to cultivate these soils without the certainty that it will harvest and have good yields.

To answer these questions, we need more research that allow us to improve our understanding of chemical and biological fertility and the dynamics of water in these soils. In order to improve agricultural practices and obtain greater crop yields by making sustainable use of these soils peculiar.

Michele Ribeiro Ramos, Agricultural Engineer and higher education teacher at the State University of Tocantins – Unitins