Curvas de compactação de um Latossolo Vermelho-Amarelo: com e sem reúso de amostras

Abstract

RESUMOA curva de compactação do solo é determinada pelo ensaio de Proctor, normal ou modificado, amplamente empregado na engenharia civil; entretanto, seu uso agronômico apresenta limitações já que a configuração da curva parte do reúso de uma única amostra, desconsiderando a estrutura original do solo. Diante disto, objetivou-se avaliar a configuração da curva de compactação a partir do reúso e não reúso de amostras de um Latossolo Vermelho-Amarelo considerando-se diferentes sistemas de manejo. Verificou-se, ao comparar o procedimento com e sem reúso da amostra que, independentemente dos manejos e camadas avaliadas, foram obtidas diferentes curvas de compactação do solo. Por outro lado, o procedimento com reúso aumenta os valores de densidade do solo pela fragmentação dos agregados e reorganização das suas partículas. Portanto, para fins agrícola a curva de compactação é adequadamente caracterizada sem reúso de amostras visto que, neste ensaio, os agregados da amostra não são totalmente fracionados, sejam eles oriundos do solo sob vegetação nativa ou de áreas antropizadas.Palavras-chave: umidade ótima de compactação, densidade máxima de compactação, Proctor normal, estabilidade de agregados, matéria orgânica do solo Soil compaction curves of an Oxissol:With and without reuse of samples ABSTRACT The soil compaction curve is determined by the Proctor test, normal or modified, widely used in civil engineering, however, its use has agronomic limitations, since the configuration of the curved part of the reuse of a single sample, disregarding the original soil structure. In this context, the objective of the study was to evaluate the configuration of the compaction curve based on with and without reuse of samples of an Oxissol, considering different management systems. While comparing the procedure with and without reuse of the sample, it was found that regardless of managements and layers evaluated, curves of soil compaction obtained were different. Furthermore, the procedure to reuse samples increases the density of the soil due to fragmentation of the aggregates and reorganization of its particles. Thus, for agricultural purposes, the compaction curve is suitably characterized without reuse of samples, since with this test, the aggregates of the sample, are not fully fractionated, both aggregates from soil under native vegetation or anthropized areas.

Organic Carbon and Total Nitrogen in the Densimetric Fractions of Organic Matter Under Different Soil Management

“…Several authors have stressed the importance of organic matter in determining soil quality because it influences, among other properties, the stability of the aggregates and the structure of the soil (HICKMANN et al, 2012;RAMOS et al, 2013); the rate of water infiltration and retention (RAWLS et al, 2003); biological activity and cation exchange capacity (SILVA; MENDONÇA, 2007); the complexation of metals (BEZERRA et al, 2009); the cycling and availability of nutrients to plants (SILVA et al, 2009); and the release of CO 2 and other gases (LAL;BRUCE, 1999).…”

Estimate of the least limiting water range based on relative density of an oxisol in Brazil

“…The M optimal value indicates where traffic of machinery should be avoided, because the increase in water content makes the soil easier to compact. In contrast, according to Ramos et al (2013), reduction in the water content can cause stronger coherence of the particles, making the soil less susceptible to compaction. Based on this, it was found that the gravimetric water contents that resulted in the highest compaction density in each soil layer were approximately 5% below the volumetric moisture equivalent to the field capacity (θCC = 10 kPa) for each layer, that is, by substituting the values in the water retention equations (Table 2) (Figure 3).…”

“…This would make it unnecessary to determine the LLWR for each type of soil, because it would be sufficient to estimate the RBD value and use 0.90 as the upper threshold. However, it is important to standardize the method for determining the compaction curve to obtain the maximum soil density, preferably without reuse of samples for considering the soil structure, as urged by Ramos et al (2013). In this study, the proportion of the BD or RBD values ≥ BD critical (LLWR = 0) for the depths of 0.20 to 0.30 m and 0.30 to 0.40 m were, respectively, only 8 and 2% of the 117 samples collected.…”

“…The samples were placed in polyethylene boxes and taken to the laboratory, and the techniques described in Ramos et al (2013) was applied. Based on the data pairs of the gravimetric moisture (GM) and bulk density (BD) the model were adjusted, that is by regression, applying a polynomial quadratic equation (BD = y0+aGM -bGM 2 ), where y0, b and c are the estimated coefficients.…”

“…The configuration of the compaction curve depends on, among other factors, the granulometry and organic carbon content. For agricultural purposes, it is recommended to determine the curve without reuse of soil samples (Ramos et al, 2013).…”