Soil aggregation under different management systems

Cibele Mascioli Rebello Portella,Christian Feller,Maria De Fátima Guimarães,João Tavares Filho,Inês Cristina De Batista Fonseca

doi:10.1590/s0100-06832012000600021

Abstract

Considering that the soil aggregation reflects the interaction of chemical, physical and biological soil factors, the aim of this study was evaluate alterations in aggregation, in an Oxisol under no-tillage (NT) and conventional tillage (CT), since over 20 years, using as reference a native forest soil in natural state. After analysis of the soil profile (cultural profile) in areas under forest management, samples were collected from the layers 0-5, 5-10, 10-20 and 20-40 cm, with six repetitions. These samples were analyzed for the aggregate stability index (ASI), mean weighted diameter (MWD), mean geometric diameter (MGD) in the classes > 8, 8-4, 4-2, 2-1, 1-0.5, 0.5-0.25, and < 0.25 mm, and for physical properties (soil texture, water dispersible clay (WDC), flocculation index (FI) and bulk density (Bd)) and chemical properties (total organic carbon - COT, total nitrogen - N, exchangeable calcium - Ca2+, and pH). The results indicated that more intense soil preparation (M < NT < PC) resulted in a decrease in soil stability, confirmed by all stability indicators analyzed: MWD, MGD, ASI, aggregate class distribution, WDC and FI, indicating the validity of these indicators in aggregation analyses of the studied soil.

Highlights

The soil under native forest (Figure 1) had the typical characteristics of a Red Oxisol, structurally organized in small stable granular aggregates, forming a rich network of pores by aggregate stacking, evidenced in the large portion of the profile organized as Cm
Under NT (Figure 1), there was a predominance of cracked structures (Cr) whose main characteristic is the separation of clumps resulting in crack porosity, predominantly, through which most roots grow
The profile consisted of compact aggregates with the presence of CrΔ and CrΔμ layers down to 53 cm

Summary

Introduction

Intensive soil use and systematic implementation of inappropriate agricultural practices, such as excessive topsoil preparation and high losses of crop residues and soil by erosion, alter the original soil properties (Carpenedo & Mielniczuk,1990), affecting the organic matter content (Pereira et al, 2010; Primo et al, 2011) and degrading the soil structure, as evidenced by increased soil density and reduced aggregate size, macroporosity, final infiltration rate and plant root development (Llanillo et al, 2006; Reichert et al, 2009; Ferreira et al, 2010; Tavares Filho & Tessier, 2010; Cunha et al, 2011).The adoption of cropping and management systems that conserve the soil and continually introduce fresh organic residues is fundamental to preserve a good soil structure (Lal & Greenland, 1979; Calegari et al, 2006; Tavares Filho & Tessier, 2010), with lower bulk density and better macro and micropore distribution (Tavares Filho et al, 2001; Schaffrath et al, 2008; Luciano et al, 2010).The vegetation and organic residues protect the surface layer aggregates against degradation by raindrop impact and abrupt variations in moisture content, and represent a source of energy for the microbial activity, which produces valuable byproducts that act as agents for aggregate formation and stabilization (Harris et al, 1966; Calegari et al, 2006; Salton et al, 2008; Coutinho et al, 2010).According to Castro Filho et al (1998), the notillage system with accumulation of plant organic residues on the surface improves aggregation by increasing organic carbon levels in the topsoil, raising the percentage of aggregates > 2.00 mm, as observed by Beutler et al (2001), and distributing the capillary system carrying water in the arable layer more evenly, resulting in higher infiltration and storage for longer periods.The continually interacting physical, chemical and biological factors, variations in crop yields over time, the relationship between soil formation and loss by erosion, the accumulation or loss of organic matter and the production of entropy (Addiscott, 1995; Reicosky et al, 1995) can be used to determine whether an agricultural soil is stable, improving or deteriorating.Bearing in mind that the management system used changes the dynamic equilibrium of the soil, the aim of this study was to assess the effects of management systems established for over 20 years on the aggregation of a dystrophic Red Oxisol. Intensive soil use and systematic implementation of inappropriate agricultural practices, such as excessive topsoil preparation and high losses of crop residues and soil by erosion, alter the original soil properties (Carpenedo & Mielniczuk,1990), affecting the organic matter content (Pereira et al, 2010; Primo et al, 2011) and degrading the soil structure, as evidenced by increased soil density and reduced aggregate size, macroporosity, final infiltration rate and plant root development (Llanillo et al, 2006; Reichert et al, 2009; Ferreira et al, 2010; Tavares Filho & Tessier, 2010; Cunha et al, 2011).

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