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The aim of this study was to characterize humic and fulvic acids using infrared spectroscopy and nuclear magnetic resonance (NMR) in aggregates collected from areas under different crop and soil management systems. Soil samples were collected at depths of 0.00-0.10 m in a trial set up in 1989 with four management systems (no-till, no-till with chiseling every three years, disk harrowing and heavy disking) under two production systems (succession and rotation). In the laboratory, the soil was sieved and separated into two fractions: particle size of 2 mm or more, and less than 2 mm. From each of the samples an aliquot was extracted and the humic and fulvic acids purified for FTIR, UV-VIS and NMR-1 H analysis. The results obtained showed that the structural characterization of the humic and fulvic acid fractions were linked to organic matter left on the soil surface, especially where the agricultural system involved species diversity. Aggregates !2 mm produce higher NMR, UV-VIS and FTIR spectral magnitudes in aromatic and aliphatic structures than those <2 mm. Aggregates collected from soil under no-till retained their aromatic and aliphatic chemical structures, resulting in higher spectral amplitude.

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SUMMARYThis study had the purpose of evaluating the effects of two management types of sugarcane: harvesting of burnt cane (BCH) and mechanized harvesting of unburnt green cane (MCH), on some soil physical properties of a dystrophic Rhodic Haplustox. The data were then compared with results for the same soil type under native forest. A completely randomized design was used, with three treatments and 20 replications. The following characteristics were determined: organic matter, aggregate stability, soil bulk density, and porosity at depths of 0-0.20 m and soil penetration resistance. After 15 years of cultivation, there were some alterations in the soil under cane burnt before harvesting, evidenced by a drop in the weighted average diameter of stable aggregates in water and increased soil bulk density. Significant changes were also detected in total porosity and pore distribution under both harvesting systems. Critical values for penetration resistance were observed in the area under mechanized sugar cane harvesting, with a value of 4.5 MPa in the 40-55 cm layer. This value is considered high and could indicate compaction and restriction of root growth. Soil properties under the green cane (unburned) management system were closest to those of the soil under native forest.Index terms: Saccharum officinarum, soil bulk density, porosity, soil penetration resistance, soil aggregate stability.(

SUMMARYSoils are the foundation of terrestrial ecosystems and their role in food production is fundamental, although physical degradation has been observed in recent years, caused by different cultural practices that modify structures and consequently the functioning of soils. The objective of this study was to evaluate possible structural changes and degradation in an Oxisol under different managements for 20 years: no-tillage cultivation with and without crop rotation, perennial crop and conventional tillage, plus a forested area (reference). Initially, the crop profile was described and subsequently, 10 samples per management system and forest soil were collected to quantify soil organic matter, flocculation degree, bulk density, and macroporosity. The results indicated structural changes down to a soil depth of 50 cm, with predominance of structural units ∆µ ∆µ ∆µ ∆µ ∆µ (intermediate compaction level) under perennial crop and no-tillage crop rotation, and of structural units ∆ ∆ ∆ ∆ ∆ (compacted) under conventional tillage and no-tillage. The soil was increasingly degraded in the increasing order: forest => no-tillage crop rotation => perennial crop => no-tillage without crop rotation => conventional tillage. In all managements, the values of organic matter and macroporosity were always below and bulk density always above those of the reference area (forest) and, under no-tillage crop rotation and perennial crop, the flocculation degree was proportionally equal to that of the reference area.Index terms: crop profile, soil physical properties, organic matter, soil quality. RESUMO: MUDANÇAS ESTRUTURAIS E DEGRADAÇÃO DE ATRIBUTOS DE LATOSSOLO VERMELHO SUBMETIDO A DIFERENTES MANEJOS POR 20 ANOSO solo integra os ecossistemas terrestres e o papel dele na produção de alimentos é essencial, embora nos últimos anos tenha se constatado sua degradação física em razão das diferentes práticas culturais utilizadas que modificam sua estrutura e, consequentemente, seu funcionamento. O objetivo deste trabalho foi avaliar possíveis mudanças estruturais, bem como a degradação de Latossolo Vermelho submetido a diferentes manejos por 20 anos. As avaliações foram realizadas em diferentes manejos: semeadura direta com e sem rotação de culturas; cultura perene; e preparo convencional, além de uma área de mata (referência). Inicialmente, fez-se a descrição do perfil cultural e, na sequência, coletaram-se 10 amostras de solo em cada manejo considerado e sob mata nativa para quantificar o teor de matéria orgânica, o grau de floculação, a densidade e a macroporosidade do solo. Os resultados indicaram mudanças estruturais até 50 cm de profundidade com predomínio de unidades estruturais ∆µ (nível intermediário de compactação) nos manejos cultura perene e semeadura direta com rotação de culturas e unidades estruturais ∆ (compactado), nos manejos preparo convencional e semeadura direta. A degradação do solo, da menor para a maior, ocorreu na seguinte ordem: Mata => semeadura direta com rotação de culturas => cultura perene => semeadura dir...