As any model of real-world phenomena, soil erosion models must be tested against empirical evidence to have their performance evaluated. This is critical to develop knowledge and confidence in model predictions. However, evaluating soil erosion models is complicated due to the uncertainties involved in the estimation of model parameters and measurements of system responses. Here, we undertake a term co-occurrence analysis to investigate how model evaluation is approached in soil erosion research. The analysis illustrates how model testing is often neglected, and how model evaluation topics are segregated from current research interests. We perform a meta-analysis of model performance to understand the mechanisms that influence model predictive accuracy. Results indicate that different models do not systematically outperform each other, and that calibration seems to be the main mechanism of model improvement. We review how soil erosion models have been evaluated at different temporal and spatial scales, focusing on the methods, assumptions, and data used for model testing. We discuss the implications of uncertainty and equifinality in soil erosion models, and implement a case study of uncertainty assessment that enables models to be tested as hypotheses. A comment on the way forward for the evaluation of erosion models is presented, discussing philosophical aspects of hypothesis testing in environmental modelling. We refute the notion that soil erosion models can be validated, and emphasize the necessity of defining fit-for-purpose tests, based on multiple sources of data, that allow for a broad investigation of model usefulness and consistency.

R ESU M OPlantas com alto índice de cobertura e elevada produtividade de fitomassa propiciam melhor proteção ao solo, amortecendo o impacto das gotas de chuva sobre a superfície do solo reduzindo, consequentemente, os processos erosivos. Objetivou-se avaliar a influência das plantas de cobertura e dos espaçamentos de plantio no controle das perdas de solo, água e nutrientes por erosão hídrica, visando à conservação do solo. O experimento foi conduzido em um Argissolo Vermelho-Amarelo, cujos tratamentos foram definidos por três espécies de plantas de cobertura: crotalária júncea, feijão-deporco e milheto e com dois espaçamentos entrelinhas (0,25 e 0,50 m). Para a quantificação das perdas de solo, água e nutrientes, utilizaram-se parcelas de 4 x 12 m em que a maior dimensão obedeceu ao sentido do declive. Nos meses de dezembro e janeiro ocorrem os maiores valores de erosividade requerendo, neste período, melhor cobertura da superfície do solo. O feijão-de-porco foi a espécie que apresentou maior potencial no controle dos processos erosivos; quanto ao espaçamento a melhor proteção do solo para todas as culturas foi obtida no espaçamento de 0,25 m, propiciando menores perdas de solo, água e nutrientes. Palavras-chave: crotalária júncea, feijão-de-porco e milhetoCover crops to control soil, water and nutrient losses by water erosion A B ST R A C T Cover plants with high coverage index and biomass productivity provide a better soil protection, cushioning the impact of the raindrops on the soil surface, thus reducing the erosion process. The objective of this study was to evaluate the influence of cover crops and plant spacing in the control of soil, water and nutrient of this study losses by water erosion, aiming the soil conservation. The experiment was conducted in the Red-Yellow Argisol, with three treatments of cover crops; sunn hemp, jackbean and millet, in two row spacing (0.25 and 0.50 m). To quantify the loss of soil, water and nutrients, plots of 4 x 12 m were used, and the larger dimension followed up and down slope. During the months of December and January there were the highest erosivity values, requiring in this period a better coverage of the soil surface. The jackbean was the species with the highest potential in the erosion control; and the spacing that promoted the best soil protection for all crops was 0.25 m, providing lesser losses of soil, water and nutrients.

Purpose Soils are important regulators of Critical Zone processes that influence the development of geochemical signals used for sediment fingerprinting. In this study, pedological knowledge of tropical soils was incorporated into sediment source stratification and tracer selection in a large Brazilian catchment. Materials and methods In the Ingaí River basin (~1200 km 2), Brazil, three source end-members were defined according to the interpretation of soil and geological maps: the upper, mid, and lower catchment. A tributary sampling design was employed, and sediment geochemistry of three different size fractions was analyzed (2-0.2 mm; 0.2-0.062 mm, and < 0.062 mm). A commonly used statistical methodology to element selection was compared to a knowledge-based approach. The mass balance un-mixing models were solved by a Monte Carlo simulation. Modeled source contributions were evaluated against a set of artificial mixtures with known source proportions. Results and discussion For the coarse fraction (2-0.2 mm), both approaches to element selection yielded high errors compared to the artificial mixtures (23.8% and 17.8% for the statistical and the knowledge-based approach, respectively). The knowledgebased approach provided the lowest errors for the intermediate (0.2-0.062 mm) (10.9%) and fine (< 0.062 mm) (11.8%) fractions. Model predictions for catchment outlet target samples were highly uncertain for the coarse and intermediate fractions. This is likely the result of the spatial scale of the source stratification not being able to represent sediment dynamics for these fractions. Both approaches to element selection show that most of the fine sediments (median > 90%) reaching the catchment outlet were derived from Ustorthents in the lower catchment. Conclusions The different element selection methods and the artificial mixtures provide multiple lines of evidence for evaluating the fingerprint approaches. Our findings highlight the importance of considering pedogenetic processes in source stratification, and demonstrate that different sampling strategies might be necessary to model specific sediment fractions.

R E S U M OO solo é um dos recursos naturais de maior importância cuja heterogeneidade reflete na variabilidade de seus atributos químicos e físicos. Esta heterogeneidade é decorrente do processo de formação natural e do uso e manejo realizados pelo homem. Assim, o objetivo deste estudo foi avaliar a variabilidade espacial dos atributos químicos e físicos do solo e elaborar seus mapas de distribuição espacial na Sub-Bacia das Posses, Extrema. Para isto foram coletadas amostras em 150 pontos nas profundidades de 0-0,20 e determinados os atributos físicos e químicos. As variáveis: Ca, Mg, K, P, pH, matéria orgânica (MO), diâmetro médio geométrico dos agregados (DMG cp ), diâmetro médio ponderado dos agregados (DMP cp ) e índice de floculação (IF). IF apresentaram estrutura de dependência espacial, o que permitiu seu mapeamento a partir de técnicas geoestatísticas. O P, DMG sp e DMP sp apresentaram estrutura com efeito pepita puro, possivelmente decorrente de uma distância insuficiente para captar dependência espacial na amostragem para esses atributos e interferências antrópicas. A variação verificada para o Ca pode ser explicada pela aplicação localizada de calcário, a qual foi realizada em algumas pequenas propriedades localizadas nas subbacias. O DMG p , DMP p , e IF avaliados foram ajustados em conformidade entre si indicando boa agregação do solo. Variability of soil attributes under pasturing and Atlantic Forest on the watershed basin scale A B S T R A C TSoil is one of the most important natural resource and its heterogeneity reflects the variability of its chemical and physical attributes. Soil heterogeneity occurs due to the natural process of formation and use by men and management. The objectives of this study were to evaluate the spatial variability of physical and chemical soil attributes and map the spatial distribution of these in Posses sub-basin, Extrema, representative of the Atlantic Forest biome present in southern Minas Gerais. For this, samples (0-0.20 m depth) were collected at 150 points, and their physical and chemical attributes were determined. Variables: Ca, Mg, K, P, pH, organic matter (MO), geometric mean diameter of aggregates (DMG cp) , weighted mean diameter of aggregates (DMP cp ) and flocculation index (IF) showed spatial dependence structure, which allowed mapping from geostatistical techniques. P, DMG sp and DMP sp presented structure with nugget effect, possibly due to an insufficient distance to capture spatial dependence in the sample for these attributes, and human interferences. The variation for Ca can be explained due to lime application, which occurred in some small properties located in the sub-basin. The DMG cp , DMP cp , and IF evaluated were adjusted in line with each other, indicating good soil aggregation. ISSN 1807 -1929 v.18, n.5, p.517-526, 2014 Introdução O Brasil é um país rico em recursos naturais distribuídos em seus diversos biomas. A Mata Atlântica é considerada, atualmente, seu bioma mais importante em razão do seu estado crítico -nela se concent...

RESUMOO cultivo das plantas de cobertura pode proporcionar melhorias e reestruturação de atributos químicos e físicos do solo, reduzir a resistência do solo à penetração e aumentar a permeabilidade do solo à água reduzindo, assim, a erosão hídrica, razão pela qual se objetivou com este trabalho, avaliar o potencial de espécies de plantas de cobertura no recondicionamento dos atributos químicos e físicos do solo. O experimento foi instalado no município de Lavras, região Sul do Estado de Minas Gerais, sendo as espécies de plantas de cobertura cultivadas sobre um Argissolo Vermelho Amarelo distrófico. Os tratamentos instalados foram: Crotalaria juncea L. (crotalária), Canavalia ensiformis DC. (feijão-de-porco) e Pennisetum sp Rich (milheto), cultivadas nos espaçamentos de 0,25 e 0,50 m entre linhas. Os atributos químicos e físicos analisados foram: pH em água, macronutrientes, matéria orgânica do solo, densidade do solo, volume total de poros, microporosidade, macroporosidade, condutividade hidráulica do solo saturado, umidade e temperatura do solo, estabilidade de agregados e resistência do solo à penetração. As plantas de cobertura influenciaram a disponibilidade de potássio e fósforo porém os demais atributos químicos não foram modificados. A densidade do solo, volume total de poros, micro e macroporosidade não foram alterados após o cultivo das plantas de cobertura, independente dos espaçamentos utilizados. As plantas de cobertura reduziram a resistência do solo à penetração para valores não restritivos ao crescimento das raízes, até a profundidade de 0,25 m. Palavras-chave: Argissolo Vermelho Amarelo, Fabaceae, Poaceae Potential of cover plant species in reconditioning of physical and chemical properties of soil ABSTRACTSoil cover crops may provide improvement and restructuring of chemical and physical soil properties, reduce the soil resistance to penetration and increase soil permeability, thus reducing water erosion. Therefore, this work aimed to evaluate the potential of cover crops in the reconditioning the chemical and physical properties of soil. The experiment was conducted in Lavras in the region south of Minas Gerais State, and the cover crops were planted on a distrophic Hapludult. The treatments consisted of Crotalaria juncea L. (sunn hemp), Canavalia ensiformis DC. (jack-bean) and Pennisetum sp Rich (pearl millet), grown in between-rows with spacings of 0.25 and 0.50 m. The chemical and physical properties analysed were pH, macronutrients, soil organic matter, bulk density, total porosity, microporosity, macroporosity, saturated hydraulic conductivity, soil temperature and moisture, aggregate stability and soil penetration resistance. There was influence of cover crops on the potassium and phosphorus availability in soil, but other chemical properties were not modified. The bulk density, total porosity, micro and macroporosity were not changed after cultivation of cover crops, regardless of row length used. The cover crops reduced the soil penetration resistance values for nonrestrictive to root ...

Sheet erosion is common on agricultural lands, and understanding the dynamics of the erosive process as well as the quantification of soil loss is important for both soil scientists and managers. However, measuring rates of soil loss from sheet erosion has proved difficult due to requiring the detection of relatively small surface changes over extended areas. Consequently, such measurements have relied on the use of erosion plots, which have limited spatial coverage and have high operating costs. For measuring the larger erosion rates characteristic of rill and gully erosion, structure-from-motion (SfM) photogrammetry has been demonstrated to be a valuable tool. Here, we demonstrate the first direct validation of UAV-SfM measurements of sheet erosion using sediment collection data collected from erosion plots.Three erosion plots (12 m × 4 m) located at Lavras, Brazil, with bare soil exposed to natural rainfall from which event sediment and runoff was monitored, were mapped during two hydrological years (2016 and 2017), using a UAV equipped with a RGB camera. DEMs of difference (DoD) were calculated to detect spatial changes in the soil surface topography over time and to quantify the volumes of sediments lost or gained. Precision maps were generated to enable precision estimates for both DEMs to be propagated into the DoD as spatially variable vertical uncertainties.The point clouds generated from SfM gave mean errors of ~2.4 mm horizontally (xy) and ~1.9 mm vertically (z) on control and independent check points, and the level of detection (LoD) along the plots ranged from 1.4 mm to 7.4 mm. The soil loss values obtained by SfM were significantly (p<0.001) correlated (r 2 = 95.55%) with those derived from the sediment collection. These results open up the possibility to use SfM for erosion studies where channelized erosion is not the principal mechanism, offering a cost-effective method for gaining new insights into sheet, and interrill, erosion processes.

RESUMOO uso dos sistemas de informações geográficas (SIG) possibilita extrapolar informações pontuais permitindo maior rapidez, menor custo e elevada acurácia no planejamento de uso do solo em bacias hidrográficas. O objetivo deste trabalho foi utilizar o SIG como apoio ao planejamento de uso do solo na sub-bacia das Posses (Extrema, MG); para isto, o modelo digital de elevação (MDE) foi determinado pelo método topogrid e a qualidade da interpolação avaliada de duas formas: por meio da comparação das curvas de nível geradas pelo MDE e das curvas originais da sub-bacia (escala 1:10.000) e identificação do erro do modelo através da raiz quadrada do erro médio (RSME); a partir do MDE as classes de planejamento de uso do solo foram expandidas e interpretadas para toda a sub-bacia conforme o Sistema de Classificação da Capacidade de Uso do Solo utilizado para o Brasil. Os usos dos solos mais recomendados para a sub-bacia das Posses são as pastagens nativas, reflorestamentos e conservação ambiental; a Sub-bacia das Posses possui 11% de suas terras subutilizadas, 12% acima da capacidade de uso, 58% dentro do uso adequado, 18% de áreas de preservação permanente e um 1% de estradas.Palavras-chave: adequação do uso do solo, capacidade de uso das terras, modelo digital de elevação hidrologicamente consistente Geographic information system on the land use planning ABSTRACTGeographic information system (GIS) can be used on the extrapolation of the specific information, allowing more rapid, lower cost and high accuracy in the land use planning at catchments. The goal of this study was to use GIS as support in the land use planning at Posses catchment (Extrema, MG, Brazil). For this, the digital elevation model (DEM) was determined using the method topogrid and the interpolation quality was evaluated of two ways: comparing contour lines from survey of the catchment (scale 1:10,000) and contour lines derived from DEM and identification of model error by root mean square error (RMSE). From the DEM class of land use planning were expanded and interpreted for the catchment according the Land Use Capability Classification System used for the Brazil. Land uses recommended for the Posses catchment were native grasslands, reforestation and environmental conservancy. Posses catchment has 11% of its lands underutilized, 12% with use above the land use capability, 58% in the appropriate use, 18% of the permanent preservation areas and 1% of the roads.

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