Indicadores de qualidade do solo em áreas de cana-de-açúcar dos Tabuleiros Costeiros de Alagoas

• Autor(a) principal: Sant'anna, Selenobaldo Alexinaldo Cabral de
• Data de Publicação: 2007
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/6639
• topic: Agroecossistemas; Diacetato de fluoresceína; Agregados de solo; Manejo do solo; Agroecosystems; Fluorescein diacetate; Soil aggregates; Soil management; CNPQ::CIENCIAS AGRARIAS

The sugarcane crop is the major agricultural activity in the coastal tableland ecosystems in Alagoas State, exerting a remarkable influence in the economical and social aspects. This activity has been continuously and intensively conducted for several years and the necessity of environmental conservation and preservation of the several natural resources in this agroecosystem makes the adoption of sustainable practices mandatory for this activity. Among these resources, soil assumes a primary role and the evaluation of its quality through the observation and analysis of physical, chemical and biological indicators that are sensitive to management practices and robust to seasonal variations may be used to define this agroecosystem sustainability. Therefore, the objective of this work was to select indicator variables of soil conservation that fulfill the criteria of sensitivity to management and robustness to seasonal variability. For this, ten composite soil samples (0-10 cm) were taken from areas grown with organic sugarcane (OS), unburned sugarcane (US), and burned sugarcane (BS), as well as from an adjacent native forest (NF) used as a reference of the undisturbed condition. Sampling was carried out at two dates: July 2005 (rainy season) and March 2006 (dry season). The following variables were analyzed: microbial biomass-C (MBC), total organic C (TOC), soil enzyme activity by the fluorescein diacetate (FDA) hydrolysis technique, the weighed mean diameter of water stable soil aggregates (WSA), and the percent of macroaggregates (PMA). MBC and TOC were higher in NF than in the cultivated areas. No differences were observed in these C pools between the three sugarcane management treatments. The response of FDA to the crop management was dependent on the sampling time. In the rainy period, the activity followed the order: NF > OS > US > BS; in the dry season, only NF differed from the other treatments. Irrespective to the sampling time, WSA and PMA decreased according with the order NF > OS = US > BS. The variables WSA and PMA were quite sensitive to discriminate between sugarcane managements, and, at the same time, robust to seasonal variations. As an additional study, we analyzed the distribution of enzyme activity (fluorescein diacetate hydrolisys) across different diameter classes of water stable aggregates in soil samples from NF and US in order to verify the relationship between these variables. It was suggested the occurrence of two pools of fluorescein diacetate catalyzing enzymes in soils from NF and US. A non-monotonic relationship was observed between aggregate diameter and FDA. For both soils, intermediate aggregate size classes (0.25 to 1.00 mm) had lower FDA values than the classes bellow and above this diameter range.