Conservation management systems increase soil C and N pools. However, their effects on particulate (>53 μm) and mineral‐associated (<53 μm) soil organic matter (SOM) fractions are less understood under subtropical climatic conditions. This study evaluated the long‐term (12‐yr) effects of three no‐till cropping systems {bare soil, BS; oat (Avena strigosa Schreb.) + vetch (Vicia sativa L.)/maize (Zea mays L.) + cowpea (Vigna unguiculata L. Walp.), O + V/M + C; and maize + Cajanus [Cajanus cajan (L.) Millsp.], M + C} on C and N pools in particulate and mineral‐associated SOM. The study was performed in southern Brazil, on a sandy clay loam Acrisol. Cropping systems that included cover crops increased C and N pools in both particulate and mineral‐associated SOM when compared with BS. Mineral‐associated SOM had five to nine times more C and 13 to 26 times more N than particulate organic matter and was responsible for 69 to 80% of total atmospheric CO2 sequestred by soil in O + V/M + C (38 Mg ha−1) and M + C (51 Mg ha−1). The higher C and N pools were associated with greater recalcitrance of mineral‐associated SOM to biological decomposition, resulting from its interaction with variable charge minerals. The negative relationship between decay rates of SOM and the concentrations of Fe oxides and kaolinite demonstrated the physical stability of SOM caused by interaction with variable charge minerals. Power saturation curves of electron spin resonance (ESR) spectroscopy in the 20‐ to 53‐, 2‐ to 20‐, and <2‐μm granulometric fractions also reinforced this hypothesis. The SOM interaction with variable charge minerals plays an important role in preserving SOM storage, enhancing the potential of tropical and subtropical soils to act as an atmospheric CO2 sink.

RESUMOO objetivo deste estudo foi investigar o processo de transmissão do conhecimento relacionado às plantas medicinais entre as gerações familiares, no contexto de agricultores de base ecológica da região sul do Rio Grande do Sul. Trata-se de um estudo qualitativo realizado com oito famílias de agricultores, totalizando 19 entrevistados, residentes nos municípios de Pelotas, Morro Redondo, Canguçu e Arroio do Padre, entre janeiro e maio de 2009. A análise dos dados foi realizada através do método hermenêutico-dialético. A família foi referida como a principal fonte na transmissão do conhecimento em relação às plantas medicinais. A maioria dos sujeitos informou primeiro realizar o tratamento com as plantas medicinais para em seguida buscar o serviço formal de saúde. A construção do conhecimento relacionado às plantas medicinais pelas famílias é predominantemente oral, realizada através do convívio diário entre seus membros e compartilhada com os demais membros da comunidade na qual estão inseridos. DESCRITORES

a b s t r a c tThe Brazilian oil shale byproducts resulting from the Petrosix pyrolysis (retortage) process were submitted to a set of analytical techniques to evaluate their possible use as agricultural soil conditioners. Liquid dichloromethane extracts from the solid samples were analyzed using capillary column gas chromatography-mass spectrometry. The results showed that of the 16 PAHs designated by the U.S. EPA as priority pollutants, only phenanthrene, fluorene and naphthalene, present in the retorted oil shale sample taken from inside storage piles; benzo[k]fluoranthene, present in the dolomite limestone layer between the two layers of oil shale in the mine structure; and naphthalene, present in powdered raw oil shale, were above the limits established by the EPA. The solid Brazilian oil shale byproduct samples were also analyzed by X-ray diffractometry (XRD), diffuse reflectance ultraviolet-visible spectroscopy (DRUV-VIS), X-ray fluorescence spectroscopy (XRF) and electron paramagnetic resonance (EPR) spectroscopy. The XRD analysis showed that the pyrolysis process produces a "weathering" transformation, for example with the appearance of kaolinite diffraction lines in the retorted samples. The DRUV-VIS and XRF spectroscopy results indicated iron oxide goethite interactions with the PAHs present in the solid samples studied. The EPR spectroscopy showed that the samples row oil shale (g = 2.0044) and the powder oil shale (g = 2.0035), before the dichloromethane extraction, presented organic free radical signals associated with oxygen atoms. The other Brazilian oil shale byproduct samples, before and after the dichloromethane extraction, showed organic free radical signals associated with carbon atoms (g = 2.0022-2.0031).

RESUMO Objetivou-se com este estudo avaliar o carbono orgânico total e as frações físicas e químicas da matéria orgânica