No abstract

The degradation of pastures can be characterized by several factors, mainly due to the management adopted, so in view of the country's territorial extension and the peculiarity of each region and soil type, it is essential to develop research to improve the monitoring of the system. The objective of this study was to evaluate the effect of different sample densities to establish a mesh that gives precision in maps of spatial variability of soil mechanical resistance to root penetration to pasture areas in the coastal tableland region of Northeast Brazil. In a pasture area, three sampling meshes were demarcated for georeferenced evaluation of soil mechanical resistance to root penetration: mesh 1 established in the dimensions of 50 × 50 m, mesh 2 of 100 × 100 m and mesh 3 of 150 × 150 m, totaling an area of 9 ha. The soil resistance to penetration was measured using an automated apparatus, coupled to a tractor. The variation found in the values of penetration resistance in subsurface can be related to the management adopted in the area, as well as the trampling of the animals. Data on soil penetration resistance in pasture showed that the most compacted zone was always below 30 cm depth by using different sample densities. The results allow us to conclude that the higher the density of the sampling mesh, the greater the accuracy of the data and that, independently of the sample mesh, it was possible to identify the layer of higher soil mechanical resistance to root penetration.

ResumoO avanço do conhecimento da variabilidade espacial dos atributos do solo, por meio do uso de ferramentas da agricultura de precisão e geoestatística, tem sido considerado como uma estratégia de manejo que visa maximizar a produtividade agrícola. Objetivo foi avaliar a eficiência de malhas amostrais na caracterização da variabilidade espacial dos atributos físicos do solo na cultura do fumo. O trabalho foi desenvolvido na Fazenda Capivari, no município de Governador Mangabeira, Bahia. Avaliou-se: resistência do solo à penetração de raízes e condutividade hidráulica em duas malhas regulares, de 15x15 e 25x25 m, georreferenciadas. A resistência à penetração foi avaliada mediante o uso de penetrômetro de impacto. A determinação da condutividade hidráulica foi realizada por meio de ensaios em permeâmetro de carga constante. Os valores de resistência à penetração da malha 1 (15x15m) concentraram-se na faixa de pouca limitação a penetração de raízes, enquanto que na malha 2 (25x25m) no perfil abaixo dos 0,40 m valores superiores a 2,6 MPa, o que já implica em algumas limitações à penetração de raízes. Os dados demonstram que a malha amostral de maior dimensão apresenta grande potencial em detectar diferentes escalas de variabilidade espacial dos atributos físicos avaliados em Latossolos sob cultivo de fumo. Palavras-chave: Compactação do solo; condutividade hidráulica; fumo AbstractThe improvement in the knowledge of the spatial variability of soil attributes through the use of precision agriculture and geostatistics tools, have been considered as a management strategy to maximize agricultural productivity. The aim of this study was to evaluate the efficiency of sample meshes in characterizing the spatial variability of soil physical attributes in the tobacco crop. The work was developed at Fazenda Capivari, in the municipality of Governador Mangabeira, Bahia. It was evaluated: soil resistance to root penetration and hydraulic conductivity in two regular meshs, 15x15 and 25x25 m, georeferenced. The penetration resistance was evaluated using an impact penetrometer. The determination of hydraulic conductivity was made by means of constant load permeability tests. The values of resistance to penetration by the mesh 1 (15x15m) were concentrated in the range of little limitation to root penetration, whereas in the mesh 2 (25x25m) in the profile below 0,40 m values greater than 2,6 MPa, the Which already implies in some limitations to the roots penetration. The data demonstrated that the larger sampling mesh shows great potential in detecting different scales of spatial variability of the physical attributes evaluated in Oxisols under tobacco cultivation