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João Leonardo Miranda Bellotte, Sharlles Christian Moreira Dias e Frederico Alfenas Silva Valente

Nutrition Specialist, Technology Manager and Nutrition Coordinator at Eldorado Brasil Celulose


Technology of preparation and conservation of sandy soils

Mato Grosso do Sul has stood out in the expansion of eucalyptus planted forests to provide raw material for the pulp industries, from those already implemented to the expansion projects of the pulp sector in the region. Eucalyptus cultivation in the state already exceeds one million hectares and is concentrated on the east coast of Mato Grosso do Sul, which has, hegemonically, soils of low agricultural aptitude, with a predominance of sandy texture and great susceptibility to erosion.

In this region, eucalyptus plantations have occupied, notably, areas formerly cultivated with pastures, many in advanced stages of degradation. The climate in the region is characterized by a dry winter and a rainy summer, with an average annual rainfall of around 1,200 millimeters and average temperatures of 25 degrees centigrade. In addition, it is observed that extreme weather events, such as storms and strong winds, have occurred more frequently, favoring soil erosion processes.

The region is under the domain of the Cerrado biome and has weathered, deep, predominantly sandy soils with low natural fertility. The sandy texture is associated with source materials formed by quartz sandstones. The region where Eldorado Brasil operates has 78% of the areas with clay content below 15% (threshold for classifying soils as sandy). Generally speaking, neosols predominate quatzarenic and red oxisols.

More clayey soils have greater water storage capacity, greater cation exchange capacity and lower risk of erosion, compared to sandy soils, therefore texture assumes great importance in the sustainable management of the system. At Eldorado, soil conservation management begins in the land prospecting stage, whose objective is to assess the suitability of properties for forest plantations. This evaluation considers, in a preliminary way, three important variables: soil texture, physical impediment to root growth and forest productivity.

Very sandy areas, with a significant presence of gravel or hydromorphic soils (subject to flooding) and with low productivity expectations, are considered unsuitable for planting. This assessment of the physical and chemical characteristics of the soil, prior to the leasing and acquisition of land, promotes an integrated management approach, providing information for conservationist preparation that will be used in the next stages of the production process.

Since 2014, Eldorado uses previous mapping technologies with Unmanned Aerial Vehicles and drones , in addition to advanced technology the Geographic Information System for the planning, definition and construction of roads and carriers, the definition of planting alignment and subsoiling lines.

The roads and firebreaks are built respecting the slope of the land, so that the farm's cuttings are arranged in a “fishbone” shape (angle between 45 degrees or 60 degrees in relation to the main roads). The purpose of this provision is to guarantee the trafficability and maneuverability of the trucks when transporting wood. Another soil conservation practice is the construction of “minicurves” to drain rainwater from roads and firebreaks into the plots, allowing water to infiltrate gradually and without risk of erosion. The “minicurves” consist of a ridge positioned perpendicular to the road, with one or two water outlets extending into the field over a distance of 35 meters. These structures are built every 3 meters of uneven terrain.

The main objective of soil preparation is to provide suitable conditions for the establishment and growth of seedlings. For this, the soil is mechanically loosened using a subsoiling rod and a set of harrows (subsoiling). In the same operation, fertilizers are applied in depth. The prevailing conditions of flat to gently undulating relief in the region, with a slope of less than 8%, favor the performance of these mechanized operations.

Eldorado uses Real Time Kinematic Positioning technology plus automatic pilot to carry out subsoiling. With this technology, the accuracy between lines planned in the office versus lines executed in the field is up to 5 centimeters, ensuring repeatability, parallelism and the quality of the services performed.

Real Time Kinematic Positioning technology, topographic surveys are carried out by Unmanned Aerial Vehicles or drones to recreate the landscape three-dimensionally and simulate surface water runoff from digital elevation models. Planting lines are planned and drawn in the office, perpendicular to the flow of water from the plots, with a view to favoring water infiltration into the soil and minimizing erosion processes.

The soil preparation carried out is based on the concept of minimum cultivation, where only the strip that will receive the seedlings is prepared. In this model, it is recommended to maintain plant residues between the cultivation lines (which may be forest residue from the previous cycle or from sugarcane pasture in cases of implantation), in order to disturb the soil as little as possible, seeking a balance between the phases chemical, physical (protection against erosion and increase of water storage) and biological of the soil (to favor the community of microorganisms).

Throughout Eldorado's history, soil management has evolved based on the extension of results from the experimental network. Based on the acquired knowledge, it was possible to define soil preparations between 40 and 50 centimeters deep and 80 centimeters of lateral rumbling, prioritizing the preparation in more clayey soils for the rainy season, in order to coincide with the friable consistency of the soil and, thus minimizing the formation of clods and maximizing sustainability and conservation of the system.

In addition to the good soil preparation practices carried out, Eldorado uses the cut-to-length forest harvesting process, in which only the wood of the trees is exported from the production area, and the other compartments, bark, branches, leaves and litter, remain in the soil surface and contribute to the maintenance of soil fertility, reduce direct exposure to sunlight, promote increased water retention in the soil and minimize the effects of erosion and soil compaction resulting from subsequent mechanized operations.

The adoption of conservationist techniques for preparing and using the soil are fundamental for the preservation of the soil and the maintenance of the productive capacity of the sites throughout the cycles. Embedded technologies are here to stay and are valuable tools to ensure execution as planned and promote the least possible impact of silvicultural operations on the resource that sustains forestry production, the soil. Therefore, to guarantee “total protection of planted forests”, the forest manager must protect the resource that sustains them, the soil, and this involves the use of conservationist techniques, but with technological tools.