Abstract
In evaluation of soil quality for agricultural use, soil structure is one of the most important properties, which is influenced not only by climate, biological activity, and management practices but also by mechanical and physico-chemical forces acting in the soil. The purpose of this study was to evaluate the influence of conventional agricultural management on the structure and microstructure of a Latossolo Vermelho distroférrico típico (Rhodic Hapludox) in an experimental area planted to maize. Soil morphology was described using the crop profile method by identifying the distinct structural volumes called Morphologically Homogeneous Units (MHUs). For comparison, we also described a profile in an adjacent area without agricultural use and under natural regrowth referred to as Memory. We took undisturbed samples from the main MHUs so as to form thin sections and blocks of soil for micromorphological and micromorphometrical analyses. Results from the application of the crop profile method showed the occurrence of the following structural types: loose (L), fragmented (F) and continuous (C) in both profiles analyzed. In the Memory soil profile, the fragmented structures were classified as Fptμ∆+tf and Fmt∆μ, whose micromorphology shows an enaulic-porphyric (porous) relative distribution with a great deal of biological activity as indicated by the presence of vughs and channels. Lower down, from 0.20 to 0.35 m, there was a continuous soil volume (sub-type C∆μ), with a subangular block microstructure and an enaulic-porphyric relative distribution, though in this case more compact and with aggregate coalescence and less biological activity. The micromorphometrical study of the soil of the Memory Plot showed the predominance of complex pores in NAM (15.03 %), Fmt∆μ (11.72 %), and Fptμ∆+tf (7.73 %), and rounded pores in C∆μ (8.21 %). In the soil under conventional agricultural management, we observed fragmented structures similar to the Memory Plot from 0.02 to 0.20 m, followed by a volume with a compact continuous structure (C∆μ), without visible porosity and with few roots. In the MHUs under conventional management, reduction in the packing pores (40 %) was observed, mainly in the continuous units (C). The microstructure had well-defined blocks, with the occurrence of planar pores and less evidence of biological activity. In conclusion, the morphological and micromorphological analyses of the soil profiles studied offered complementary information regarding soil structural quality, especially concerning the changes in pore types as result of mechanical stress undergone by the soil.
Highlights
Most studies for the purpose of evaluating soil quality for crop production refer to the effects of characterization and quantification of cultivation and management practices on soil morphological, physical, chemical, and biological properties (Doran, 1987; Bertol et al, 2004; Marques et al, 2010).according to Drees et al (1994), changes resulting from management on soil properties are largely consequences of changes undergone by the soil structure
In the Memory soil profile, the fragmented structures were classified as Fptμ∆+tf and Fmt∆μ, whose micromorphology shows an enaulic-porphyric relative distribution with a great deal of biological activity as indicated by the presence of vughs and channels
The soil structure assessment described in this study was conducted in the fourth year of that trial, corresponding to the 2006/2007 crop, with maize grown under a conventional system (CS)
Summary
According to Drees et al (1994), changes resulting from management on soil properties are largely consequences of changes undergone by the soil structure. In the case of conventional systems, structural changes arising from intensive mechanization, such as compaction and accelerated soil erosion, may lead to significant changes in soil quality (Hakansson et al, 1988), with a negative effect on infiltration and plant water availability (Imhoff et al, 2000), and soil aeration (Xu et al, 1992), reducing the depth and exploitable volume of the soil by the roots (Weill and Sparovek, 2008). Structural changes in soil quality often lead to serious consequences both in terms of degradation of this essential, finite, and non-renewable resource, and in economic terms, by bringing about reduced yield or increased costs of production. Soil structure is a characteristic difficult to measure directly, which is why it is commonly assessed by other properties, such as soil density, porosity (Reynolds et al, 2008), available water (Dexter, 2004), infiltration (Thierfelder and Wall, 2010), soil resistance to penetration and limiting water range (Silva et al, 1994), air permeability (Ball and Schjonning, 2002), tensile strength of aggregates (Guimarães et al, 2009), and the S index (Dexter, 2004)
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