Avaliação visual da estrutura do solo em área produtora de cana-de-açúcar com diferentes manejos agrícolas

Abstract

Assessing soil structure is important to identify the consequences of agricultural management, especially due to the close correlation between soil structure and the attributes that express the porous arrangement of the soil and its relationship with water storage and gas exchange. The type of management used in the cultivation of sugarcane interferes with the structure of the soil and must be evaluated by a practical, reliable and easily reproducible method. In this sense, there is a gap in the literature on investigations on these methods in soils in sugarcane producing areas in the Northeast. Therefore, this work investigated the methodology of Visual Evaluation of Soil Structure in areas of sugarcane cultivation with different agricultural management in the mesoregion of the florest zone of Paraíba. For that, samples were taken at the Miriri bioenergy and foods S/A plant, a sugarcane producer, belonging to the municipality of Santa Rita, in the state of Paraíba.Three different managements were sampled: SQV - Cultivation of sugarcane in rainfed areas with application of vinasse; IR - Irrigated sugarcane cultivation and IRV - Irrigated sugarcane cultivation with vinasse, in addition to an area of conserved native vegetation. The managements were sampled in the row (L) of cultivation and between the rows (EL), with the exception of the area of native vegetation conserved with 5 repetitions, totaling 35 collection points. The collection points consist of mini trenches (20 x 25 x 25 cm), with samples of deformed and non-deformed soils in the 0-10 and 10-20 cm layers for determination of physical attributes (granulometry, clay dispersed in water, flocculation and dispersion indices, soil density, particle density, total porosity, aggregate stability, hydraulic conductivity and soil penetration resistance) and chemical (pH, Ca2+, Mg2+, Na+,K+ and exchangeable Al3+, H+Al, cation exchange capacity (CTC), sum of bases (SB), electrical conductivity of the saturation extract and osmotic potential of the soil solution).To determine the Visual Evaluation of Soil Structure (VESS), scores or grades from 1 to 5 were assigned to the undeformed blocks collected in the mini-trenches. For data analysis, ANOVA, Scott-Knott mean comparison test (p <0.05) and Pearson correlation were used. In the analysis of VESS, there was no significant difference for the managements studied. The low values in VESS suggest an adequate structural condition for the evaluated managements. All the variables analyzed showed significant differences between the planting lines and between the lines. Through Pearson's correlation, the direct relationship between VESS and physical attributes was demonstrated, with a significant correlation, positive with soil resistance to root penetration and negative with total porosity and saturated hydraulic conductivity. It was possible to identify that there is a difference in the sampling location: line and between lines. Thus, the results found in the planting line indicate that, when using controlled machine traffic, these locations are less affected and provide better conditions for the establishment of the crop throughout its production cycle. Finally, the VESS method can be used by producers and field technicians in sugarcane production areas in the northeast region of Brazil, as a tool for monitoring soil structure and defining strategies for improvement or maintenance of these areas.