RESUMO

The sombric horizon is a diagnostic subsurface horizon defined in the soil classification system of the United States (Soil Taxonomy) and FAO (WRB), used to classify the soil at different categorical levels. The sombric horizon has a soil color darker than the overlying surface(s) horizon(s), and must show illuvial humus accumulation features, though they are not associated with aluminum (Al), as in the spodic horizon, nor associated with sodium (Na), as in the natric horizon. There are also criteria to distinguish it from buried A horizons. However, since the first references and proposed concept of the sombric horizon in African soils made by Sys and co-workers in the 1960s, and adopted by the Soil Taxonomy edition of 1975, few modifications have been made to its definition. Moreover, the pedogenic process involved in illuvial humus accumulation in these horizons remains inadequately clarified, making the distinction between the sombric and spodic or buried A horizon difficult and unclear. This review reports the historical evolution of the sombric horizon concept, its definition and inconsistencies under different soil classification systems, and the current hypothesis, together with its fragilities, proposed to explain the soil illuvial humus accumulation. Although it is recognized that further research is necessary, alternative criteria are proposed for the definition of the sombric horizon in the Brazilian System of Soil Classification.

The Araucaria forests of Southern Brazil have been drastically reduced as a result of anthropic intervention and are currently found at different stages of succession. The objective of our study was to understand the influence of forest fragmentation on the phytosociological composition of its tree component. The composition of floristic groups of the tree component and their correlation with the edaphic and environmental variables in a fragment of the Araucaria Forest in the municipality of Curitibanos, state of Santa Catarina, Brazil was analyzed. A hundred and ten permanent continuous plots (10 m²) with forest edges of different origins and formation times were established for sampling. Trees with diameter ≥ 5 cm at breast height (DBH) were measured and identified. Using TWINSPAN, data were analyzed for species importance values (including indicator species) in the formation of floristic groups. Floristic similarities resulted in separating groups conditioned by the forest succession. The presence of the invasive species Pinus taeda L. and pioneer species at the forest expansion border contributed to the formation of a spatially cohesive group. The other areas did not show influence of edge effects, being in an initial secondary succession stage, dominated by Jacaranda puberula Cham. Low edaphic variation among the classes of lithosols in a flat relief had no influence on the formation of floristic groups.

A agricultura biodinâmica desde sua concepção por Rudolf Steiner, junto com alguns agricultores alemães na década de 1920, tem buscado recompor o equilíbrio sistêmico no que se refere às relações entre o ser humano, a agricultura e o cosmo. Diante de algumas dificuldades criadas pela agricultura moderna em termos de sustentabilidade econômica, principalmente para a agricultura familiar, as proposições da agricultura biodinâmica podem ser uma possibilidade tangível de geração de renda e bem estar para os agricultores. Assim, este artigo busca apresentar um estudo introdutório acerca da viabilidade econômica da agricultura biodinâmica no planalto catarinense a partir de um experimento que analisou o Produto Bruto-PB, o Valor Agregado Bruto-VAB e as condições sistêmicas do organismo agrícola de uma área experimental durante o ano agrícola 2019/2020. Embora observadas algumas dificuldades de eficiência do manejo que precisam ser estudadas e aperfeiçoadas, a análise dos resultados econômicos mostrou-se satisfatória e promissora enquanto proposição para a agricultura familiar.