RESUMO A intensa antropização no baixo do rio São Francisco e áreas adjacentes geram risco de degradação ambiental e, sobretudo, torna essa área mais suscetível a processos erosivos. O objetivo do estudo identificar e correlacionar os atributos físicos e químicos que potencializam os processos erosivos e estabilidade dos taludes em margens de curso de água no baixo curso do Rio São Francisco, estado Sergipe, Brasil. As amostras de solos deformada e indeformadas foram coletadas na região do Baixo rio São Francisco, município de Amparo de São Francisco, Sergipe, em Neossolo Flúvico. Foram realizadas análises físicas (densidade, porosidade e textura) e químicas (pH, Capacidade de Troca de Cátions, saturação por bases, micro e macronutrientes no solo). Os camadas superficiais (Ap e AC) apresentaram superiores atributos físicos e maior teor de carbono orgânico que os demais camadas. O carbono orgânico, fosfóro e os micronutrientes obtiveram correlação negativa com a densidade do solo, onde um maior teor destes elementos nos camadas Ap e AC resultam em menor densidade do solo. As caracteristicas pedologicas das camadas do perfil avaliado não proporcionam uma resistência a erosão hidrica.

ABSTRACT The intense anthropization in the lower São Francisco River and surrounding areas can lead to environmental degradation risks and, above all, makes the area more susceptible to soil erosion. This study aimed to identify and correlate the physical and chemical properties able to enhance erosive processes and slope instability in the watercourse margins of the lower São Francisco River, in Sergipe State, Brazil. To this end, disturbed and undisturbed samples of an Entisol-Fluvent soil were collected in the region, specifically in the city of Amparo de São Francisco. Physical (density, porosity, and texture) and chemical (pH, cation exchange capacity, base saturation, micro-, and macronutrients) analyses were performed. All physical properties and organic carbon contents were higher in the surface layers (Ap and AC) compared to the others. Organic carbon, phosphorus, and micronutrients had a negative correlation with soil density, showing higher contents and lower soil densities in the Ap and AC layers. The pedological characteristics of the evaluated soil layers are unable to provide soil resistance to water erosion.

ABSTRACT In the tropics, water erosion is one of the most important factors leading to the degradation and deterioration of agricultural land. Olive orchards have a low canopy coverage, especially during the first years after planting, due to the low density of olive trees. Given the fast expansion of olive orchards in Brazil, this study aimed to evaluate the effect of cover vegetation on soil and water losses under natural rainfall. In addition, it was assessed the crop performance and the vegetation cover index in different management systems in olive orchards. The study was carried out in soil erosion plots, where water and sediment were sampled and measured over two crops season, under the following treatments: in the first season, bare soil with olive cultivation (OBS); olive trees intercropped with spontaneous vegetation (OSV); olive trees intercropped with jack beans (OJB); olive trees intercropped with millet (OM) and, as a control, only bare soil (BS). In the second season, the OM treatment was replaced by olive trees intercropped with sunn hemp (OSH). On bare soils, soil loss was the highest reaching 303.9 Mg ha-1 yr-1 and where the surface runoff amounted to 484.8 mm yr-1. However, in the absence of competition for resources with other crops, olive trees performed best under this system. The olive orchards planted in shallow and sloping soils without cover crops showed unsustainable soil loss, crusting, and sealing in the superficial soil layer, which can progress quickly for soil degradation in the future. The efficiency in the reduction of loss in relation to bare soil was 4.11 and 12.93 % for the soil loss and 12.15 and 25.17 % for water loss, respectively, for olive with spontaneous vegetation and olive with jack beans. Cover crops combined with olive trees, and reconciled with the crop performance aspects of cultivation in tropical regions, is of great relevance for improving sustainability, especially regarding the reduction of soil and water losses due to water erosion.

ABSTRACT Through the lack or non-use of conservationist criteria for adequate land use and management, the scarcity of natural resources becomes ever more evident. This study aimed to analyze the origin of the sediments in the Posses catchment, municipality of Extrema, state of Minas Gerais, Brazil, throughout the fingerprinting technique and portable X-ray fluorescence. Samples from soils under agriculture, pasture, and roads; and from the subsoil of theses land uses were taken in a widespread and representative manner from the entire Posses catchment. Lag deposits and river bed sediment samples were collected downstream from the catchment outlet. A total of 45 geochemical elements were analyzed in the samples by a portable X-ray fluorescence device (pXRF). The outlier test, Kruskal-Wallis test, multivariate discriminant analysis, and a mixing model were used to estimate the contribution of each source in relation to the sediments that arrive at the mouth of the catchment. The elements selected as geochemical tracers were Sr, Al2O3, Ba, Rb, Ti, Fe, and Zn, which combined correctly discriminated 81 % of the sediment sources. The largest and smallest proportion of sediment from the Posses catchment outlet comes from rural roads and agriculture, respectively. The contribution of the subsoil was higher for lag deposits or lower for river bed sediments, than the pasture. There was a low degree of uncertainty (<8 %) for predictions made by the model employed. The types of use, selected as potential sediment sources in the Posses catchment, are adequately discriminated through the geochemical tracers quantified through the pXRF. The fingerprinting technique estimates that the contributions to outlet sediments are dominated by rural roads, following by subsoil or pasture (depending on the type of sediment evaluated) and by agriculture. The sediment sampling strategies used in this study provided similar results for the period studied. Our results showed the potential of the fingerprinting technique and the pXRF for use as tools by the program of Payment for Environmental Services in the monitoring of catchment areas.

Resumo A compreensão das características físicas da chuva e sua interação com a paisagem possibilita o desenvolvimento de modelos matemáticos mais condizentes com a realidade além de auxiliar no planejamento eficiente de obras e práticas agrícolas. O objetivo deste estudo foi caracterizar a precipitação interna de um povoamento de Eucalyptus no município de Lavras, Minas Gerais, associado a padrões hidrológicos e potencial erosivo. Para individualização dos eventos de precipitação interna foram adotados os intervalos de 3 e 6 horas entre chuvas. Para cada abordagem foi realizada a classificação do padrão hidrológico da precipitação, incidente e interna, e, associados a estes, as características das chuvas: lâmina precipitada, tempo de duração, energia cinética, intensidades média e máxima, e erosividade. A precipitação interna no povoamento de eucalipto representou 79,2% da precipitação externa. A precipitação interna mostrou-se 36,4% menos erosiva do que a precipitação externa, na qual o padrão avançado foi identificado como predominante na série analisada em ambas as metodologias de individualização dos eventos.

Abstract The understanding of rainfall physical characteristics and their interaction with the landscape allow the development of more feasible mathematical models to be applied on the planning of agricultural conservation practices. However, only a few studies have tried to characterize the throughfall in planted forests, like eucalyptus plantation. The objective of this study was to characterize the throughfall behavior under Eucalyptus canopy, at Lavras county region, southern Minas Gerais state, relating it to the hydrology pattern and erosive potential of the rainfall. For that, rainfall events were individualized by means of two criteria: 6 and 3 hours between the events, consecutively. For each one of the approaches, both gross precipitation and throughfall were classified in terms of the rainfall hydrology pattern linked to the following rainfall features: rainfall depth, rainfall duration, kinetic energy, average and maximum intensities and erosivity. On average, throughfall events have corresponded to 79.2% of the gross precipitation. In addition, it has showed to be 36.4% less erosive than gross precipitation. The advanced rainfall pattern was identified as predominant considering both methodologies for rainfall events individualization.

ABSTRACT Erosion prediction models are a useful tool for soil use planning and soil conservation. This study aimed to apply the Universal Soil Loss Equation (USLE) in an experimental sub-basin located in the municipality of Teixeira de Freitas, in the southern end of the state of Bahia, Brazil. The following variables were calculated: rainfall erosivity factor, using the precipitation data; soil erodibility factor, by the correlation between erosivity and soil losses obtained from a standard plot installed in the field; topographic factor; vegetation cover and management factor; and conservation practices factor. The product of these factors corresponded to the soil losses in the sub-basin. Data from erosion plots were used to validate the model. The USLE predicted higher soil losses than that observed in the plots, and the eucalyptus proved to be efficient at reducing soil losses by erosion.

Resumo A erosão é a principal causa de degradação do solo, comprometendo a produtividade e a sustentabilidade do solo. A matéria orgânica do solo (MOS) é um indicador chave da qualidade; deste modo, o presente estudo objetivou avaliar o efeito de diferentes manejos da oliveira na matéria orgânica e em suas frações presentes no solo (Cambissolo) e no sedimento de erosão, no sul de Minas Gerais. Foram instaladas parcelas com 5 tratamentos: solo descoberto, cultura de oliveira em solo descoberto, oliveira em consórcio com feijão-de-porco, oliveira em consórcio com milheto e oliveira com vegetação espontânea, além de uma área contígua de vegetação nativa como referência. O carbono do solo e do sedimento foi determinado via oxidação úmida com aquecimento externo, enquanto o fracionamento da MOS e do sedimento foi realizado com base na granulometria. O Índice de Manejo de Carbono (IMC) foi determinado por meio das proporções das frações da MOS. Os resultados indicaram que a MOS associada aos minerais é a mais presente no solo e no sedimento de erosão, independentemente do manejo adotado. O IMC apontou os sistemas oliveira com milheto e oliveira sob vegetação espontânea como os mais favoráveis ao estoque de carbono no solo.

Abstract Erosion is the main cause of soil degradation, compromising soil productivity and sustainability. As soil organic matter (SOM) is a key indicator of quality, this study aimed to evaluate the effect of different olive tree managements on SOM and its soil fractions in soil (Inceptisol) and erosion sediments. Five treatments were installed: bare soil, olive cultivation in bare soil, olive tree intercropped with jack bean, olive tree intercropped with pearl millet, and olive tree cultivated with spontaneous vegetation; a contiguous area of native vegetation was used as reference. Carbon in soil and sediment were determined by wet oxidation with external heating, while the fractionation of SOM was performed based on granulometry. The Carbon Management Index (CMI) was determined by the proportions of SOM fractions. The results indicated that SOM associated with minerals is the most present in soil and sediment erosion, regardless of the adopted management. Results on CMI showed that the systems olive tree intercropped with pearl millet or with spontaneous vegetation are the most favorable to increase the carbon stock in the soil.