Simulação de produção de sedimentos em microbacias em função de cenários de restauração florestal

In São Paulo state, deforestation and agriculture activities are increasing soil losses processes, especially in areas of susceptible soils where properties not adopt soil conservation practices. Environmental adequacy at property level regarding Permanent Protection Areas and Legal Reserves is considered a factor on reducing soil losses and considering that we assessed soil losses of different scenario of environmental adequacy. Simulations of erosive process were carried out in 15 catchments of Corumbataí river basin, according to different forest restoration scenarios, as well as the current situation of land use/land cover. The scenarios include the implementation of Permanent Preservation Areas (PPA), the reforestation of variable source areas, and two scenarios, the Legal Reserve installation in 20% of each catchment, being one of them for most critical areas in terms of erosion and the other at random. It was observed that the establishment of PPA and the reforestation of hydrologically sensitive areas, offered only a small contribution to the control of the erosive process, resulting in a reduction of 10% and 7,8%, respectively, while the legal reserve in critical areas has a significant reduction of 69,8%. The random scenario, in turn, resulted in a reduction of only 21,4%. Results show that reforestation could reduce soil losses, but previous studies of land prioritization and planning could increase significantly its efficiency at this process.

Simulação geoestatística e classificação numérica para o delineamento de unidade de mapeamento de atributos e erosão do solo

Pós-graduação em Agronomia (Ciência do Solo) - FCAV

Perdas de solo e índices de vegetação: proposta metodológica para a determinação do fator C (MEUPS) em pastagens e cana-de-açúcar

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Modelagem do aporte de sedimentos aplicada à bacia hidrográfica contribuinte da PCH Costa Rica (MS) e proposta de mitigação do assoreamento

Pós-graduação em Engenharia Mecânica - FEG

Avaliação dos modelos de predição da erosão hídrica MEUPS e WEPP: contribuição em bacias hidrográficas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Perdas de água e solo sob diferentes padrões de chuva simulada e condições de cobertura do solo

Este trabalho foi realizado com o objetivo de determinar as perdas de solo e água em um Argissolo Vermelho-Amarelo, submetido a quatro diferentes padrões de precipitação de chuva simulada e duas condições de cobertura: área com solo descoberto e com palhada após plantio de milho. O experimento foi conduzido no Campo Experimental da Embrapa-Agrobiologia, localizado no município de Seropédica-RJ, e consistiu na aplicação de chuvas simuladas com diferentes padrões, caracterizados como avançado (AV), intermediário (IN), atrasado (AT) e constante (CT), em uma área amostral de 0,80 m de largura por 1,0 m de comprimento. Utilizando um simulador de chuvas portátil, foram aplicadas chuvas com 30 mm de lâmina total durante 60 minutos. Nos padrões com intensidade variada, o pico de precipitação foi de 110 mm h-1. Os resultados obtidos possibilitaram concluir que a cobertura do solo com resíduos de milho reduziu substancialmente as taxas e perdas de água e solo, principalmente para o padrão de chuva constante, indicando que a palhada deixada sobre o solo após a colheita auxilia de maneira efetiva no controle da erosão.

Efecto de la labranza y la cobertura vegetal sobre el escurrimiento y la pérdida de suelo en la región central de la provincia de Buenos Aires

El objetivo de este trabajo fue evaluar a campo la efectividad de diferentes tipos de labranzas junto con distintos grados de cobertura vegetal (CV) del suelo sobre el escurrimiento (E) y la pérdida de suelo (Ps). Se seleccionaron 34 sitios experimentales bajo labranza tradicional (LT) y siembra directa (SD), con diferentes niveles de CV (C1- < 49, C2- 50-79% y C3- > 80%). Se utilizó un diseño experimental completamente aleatorizado con 4 tratamientos y desigual número de repeticiones: 1) SD-C3, 2) LT-C3, 3) LT-C2, y 4) LT-C1, resultante de combinar el tipo de labranza con CV. Se realizó un ANOVA (p ≤ 0,05) y un análisis de contrastes ortogonales: 1) SD-C3 vs LT-C3, 2) LT-C1 vs LT-C2, y 3) C3 vs LT-C2+C1. Al cabo de cada simulación de lluvia se obtuvo el E y Ps. Se determinó: contenido de materia orgánica (CMO), contenido hídrico (CH) y densidad aparente del suelo (DA) en los 10 cm superficiales, y la pendiente (P) del terreno. La LT presentó mayor E y Ps en todos tratamientos evaluados respecto de SD. El mayor E (26,8 mm) se registró en LT-C2, y el menor (0,5 mm) en SD-C3. La Ps mostró igual tendencia que el E con 11,6 y 0,1 g respectivamente. Los contrastes mostraron E estadísticamente diferentes para los tres contrastes, mientras la Ps fue estadísticamente diferente en los contrastes Nº 2 y 3. Escurrimiento y Ps se correlacionaron entre sí (R2 = 0,98) y con P (R2 = 0,83 y 0,72 respectivamente). Los resultados obtenidos demuestran la importancia del efecto protector de la CV del suelo. Sin embargo, el CMO y CH, y la P y DA deben ser considerados también en el proceso de E - erosión del suelo.

Feedbacks between vegetation pattern and resource loss dramatically decrease ecosystem resilience and restoration potential in a simple dryland model

Conceptual frameworks of dryland degradation commonly include ecohydrological feedbacks between landscape spatial organization and resource loss, so that decreasing cover and size of vegetation patches result in higher water and soil losses, which lead to further vegetation loss. However, the impacts of these feedbacks on dryland dynamics in response to external stress have barely been tested. Using a spatially-explicit model, we represented feedbacks between vegetation pattern and landscape resource loss by establishing a negative dependence of plant establishment on the connectivity of runoff-source areas (e.g., bare soils). We assessed the impact of various feedback strengths on the response of dryland ecosystems to changing external conditions. In general, for a given external pressure, these connectivity-mediated feedbacks decrease vegetation cover at equilibrium, which indicates a decrease in ecosystem resistance. Along a gradient of gradual increase of environmental pressure (e.g., aridity), the connectivity-mediated feedbacks decrease the amount of pressure required to cause a critical shift to a degraded state (ecosystem resilience). If environmental conditions improve, these feedbacks increase the pressure release needed to achieve the ecosystem recovery (restoration potential). The impact of these feedbacks on dryland response to external stress is markedly non-linear, which relies on the non-linear negative relationship between bare-soil connectivity and vegetation cover. Modelling studies on dryland vegetation dynamics not accounting for the connectivity-mediated feedbacks studied here may overestimate the resistance, resilience and restoration potential of drylands in response to environmental and human pressures. Our results also suggest that changes in vegetation pattern and associated hydrological connectivity may be more informative early-warning indicators of dryland degradation than changes in vegetation cover.

Influência do uso e ocupação do solo na qualidade da água e no processo erosivo da bacia de captação do Rio Barro Preto, Coronel Vivida-PR

This study was developed in objecting to investigate the use and occupation of land in 1999, 2005, 2011 e 2015 and estimate soil degradation by laminar erosion and the relation with water quality in 2015 in the catchment basin of the Barro Preto river, Coronel Vivida – PR. For multitemporal analysis of use and occupation of land in the basin used in the Landsat 5, 7 and 8 images and Geographic Information System. The laminar erosion was estimated by the Universal Soil Loss Equation through the systematization of calculations of the factors that compose the equation in SPRING/INPE. The water quality of the studied river section was evaluated according to the Water Quality Idex and the Resolution CONAMA n. 357/2005. The multitemporal analysis of the use and occupation of land has demonstrated that basin is predominantly agricultural in all years studied, as well as the permanent preservation area presents it not regularized during the period in accordance with the Brazilian Forest Code in force. In relation the quantification of laminar soil erosion in the study period, the rainfall and runoff factor was estimated considering the rainfall data from 1986 to 2014 and resulted in a value of 11.573,47 MJ/ha.mm/a. The Dystrophic Red Latosol, Dystrophic Red Nitisol, Fluvisol and Leptosol soil erodibility factor were 0,0138, 0,0137, 0,0207, 0,0196 t.ha.h/ha.MJ.mm/a, respectively. The topographical factor has demonstrated that the catchment basin has the rough terrain because the moderate and moderate strong classes are dominant in the study area. The cover and management and support practice factors were estimated according to the multitemporal analysis of the use and occupation of land in the basin and the values ranged from 0,0006 to 0,0688. The soil losses by laminar erosion were simulated with agriculture areas with corn and soybeans in no-till. The soil losses with maize crop in no-till in 1999, 2005, 2011 and 2015 were 9.782,75, 10.592,71, 9.636,61 e 11.058,26 t/year, respectively, and soybeans crops in no-till were 15.140,01, 16.645,20, 14.662,14 e 17.049,85 t/year, respectively. In relation with water quality of the section studied river, the average of Water Quality Index during the season were 55,47, 53,09 and 49,72, for the first, second and third sample point, respectively. Indication a decrease in water quality since the source to the last sample point. It is concluded that the use and occupation of land in the catchment basin interferes in the water quality, as well as in soil degradation.

Comparação da eficácia de tecnologias para o controlo da perda de solo em áreas ardidas no Nordeste de Portugal aplicando modelo de erosão

As florestas exercem grande influência nos meios físico, biótico e socioeconômico, evitando a degradação do solo pela erosão, controlando a qualidade da água, fornecendo matérias-primas e alimentos, abrigando a maior parte da fauna e flora terrestre. As áreas florestais estão todavia sujeitas a significativo risco de incêndio. Como consequência dos incêndios, e entre outros impactos, o solo fica exposto à ação erosiva da chuva determinando perdas de solo muito significativas e a degradação deste recurso. Deste modo, o controle da erosão após o incêndio é essencial para a mais rápida recuperação das áreas ardidas suportada em medidas de conservação do solo eficazes. O trabalho propõe-se fazer uma avaliação quantificada da eficácia de técnicas de conservação do solo no controle da erosão em áreas ardidas, centrada em medidas de baixo custo e aplicável ao NE de Portugal, em especial o Distrito de Bragança. A metodologia de avaliação seguida inclui a construção de cenários regionais de aplicação simulada de uma seleção de medidas, mediante exploração de um modelo de erosão (Equação Universal de Perda de Solo – USLE). Através das simulações realizadas fazendo variar a distribuição de barreiras ao longo da encosta e o seu grau de retenção, foi possível avaliar a eficácia desta técnica para a redução da erosão nas condições definidas como cenários de base. Observou-se que o grau de retenção tem maior influência na redução de perda do solo do que a distância entre barreiras. Isto evidencia a necessidade de uma implementação adequada desta medida, com a instalação de barreiras de elevado grau de retenção. Aplicada apenas no primeiro ano pós-fogo, e de forma isolada, a técnica da sementeira não se mostrou suficientemente eficaz. Porém, se após um ano se realizar uma nova sementeira na área afetada, mostrou-se que pode ocorrer uma diminuição dos valores de perda de solo relativamente grande, pelo que será aconselhável a realização de uma ressementeira no ano seguinte à primeira aquando de intervenções pós-fogo com esta técnica. Uma possível combinação entre os métodos anteriores iria proporcionar uma situação ótima, como observado nos resultados das simulações efetuadas, onde a maioria dos cenários apresentou valores estimados de perda de solo menores ou iguais a 2 ton/ha.ano, limiar que separa condições de risco de erosão baixo e moderado e corresponde à tolerância de perda de solo para solos delgados e de substrato não renovável.

Effect of clearing native forest (Caatinga) strips on some hydrologic components of micro-watersheds.

The influences of clearing native vegetation (Caatinga) in contour strips at 25 cm vertical interval on evaporation losses in cleared strips, annual runoff efficiency and annuall soil loss on gently sloped micro-waterheds in the arid zones of Northeast Brazil are reported. The alternate native vegetation (Caatinga) strips function very effectively as windbreaks thus reducing evaporation losses substantially in the leeward cleared strips. The runoff measured at the micro-watershed with cleared strips was many-fold lower than the runoff obtained at a completely denuded watershed even when it was protected by narrow based channel terraces. However, the annual runoff efficiency can be significantly increased in a strip cleared watershed if narrow based channel terraces are provided on the lower side of cleared strips. The annual soil losses in strip cleared watersheds as well as completely denuded waterhed of gentle slopes were negligible. Thus clearing land in alternate contour strips on a micro-watersheds shall substantially improve crop water use efficiency without creating any significant erosion problems. Additionally this treatment will increase runoff for water harvesting for irrigation purposes.

O papel da agricultura de conservação na luta contra a erosão do solo em particular em Angola

A agricultura de conservação, conseguindo reduzir as perdas de solo por erosão e aumentando o seu teor em matéria orgânica, permite aos agricultores produzirem mais alimentos com menos trabalho. Oferece-lhes uma possibilidade de melhorar a sua qualidade de vida. Várias abordagens sobre agricultura de conservação do solo, incluindo rotação e consorciação de culturas, são componentes deste sistema aplicável a diferentes níveis. A sementeira direta e o menor distúrbio de solo, são princípios primordiais da conservação do solo, fornecem benefícios direitos para a agricultura e o meio ambiente, questões da maior relevância para a agricultura Angolana, apesar da pouca importância que atualmente lhes é dedicada. Logo, é preciso uma conversão e transição de tecnologias e técnicas para implementar a agricultura de conservação e o controle da erosão dos solos no país. As técnicas de conservação utilizadas pelos pequenos e grandes produtores, embora sejam bem-intencionadas, não oferecem a proteção contra a erosão do solo e a conservação da água. Tanto as entidades políticas, como o Programa de Acão do Ministério da Agricultura e do Desenvolvimento Rural (MINADER) e os agricultores angolanos devem entender a importância da agricultura de conservação para a segurança alimentar e dar continuidade para as gerações futuras. Não basta a reformulação e consolidação dos objetivos traçados no período de 2009 a 2013, sem que haja a aplicação prática. Portanto, para sair do atual conceito oficial de agricultura tradicional/convencional e optar para agricultura capaz de responder às necessidades de Angola é necessário seguir modelos semelhantes aos desenvolvidos por países tropicais de condições naturais semelhantes às de Angola; The role of conservation agriculture in the fight against soil erosion particularly in Angola ABSTRACT: Conservation agriculture, managed to reduce soil losses by erosion and to increase its content of organic matter, allow farmers to produce more food with less work. It offers them a chance to improve their quality of life. Several approaches to soil conservation agriculture, including rotation and intercropping, are components of this system applicable to different levels. Direct sowing and less soil disturbance, are key principles of soil conservation providiy benefits for agriculture and the environment, issues of great importance for the Angolan agriculture, in spite of the little importance that is currently dedicated to them. Therefore, we need a conversion and transition technologies and techniques to implement conservation agriculture and soil erosion control in the country. Conservation techniques used by small and large producers, although well-intentioned, do not offer protection against soil erosion and water conservation. Both political entities, such as the Program of Action of the Ministry of Agriculture and Rural Development (MINADER) and Angolan farmers should understand the importance of conservation agriculture for food security and continuity for future generations. Not just the redesign and consolidation of the objectives outlined in the period 2009 to 2013, without practical application. Therefore, to exit the current official concept of traditional / conventional farming and opt for agriculture able to meet the needs of Angola is necessary to follow models similar to those developed by tropical countries of natural conditions similar to Angola.

Soil and nutrient losses in erosion gullies at different degrees of restoration

The most advanced stage of water erosion, the gully, represents severe problems in different contexts, both in rural and urban environments. In the search for a stabilization of the process in a viable manner it is of utmost importance to assess the efficiency of evaluation methodologies. For this purpose, the efficiency of low-cost conservation practices were tested for the reduction of soil and nutrient losses caused by erosion from gullies in Pinheiral, state of Rio de Janeiro. The following areas were studied: gully recovered by means of physical and biological strategies; gullies in recovering stage, by means of physical strategies only, and gullies under no restoration treatment. During the summer of 2005/2006, the following data sets were collected for this study: soil classification of each of the eroded gully areas; planimetric and altimetric survey; determination of rain erosivity indexes; determination of amount of soil sediment; sediment grain size characteristics; natural amounts of nutrients Ca, Mg, K and P, as well as total C and N concentrations. The results for the three first measurements were 52.5, 20.5, and 29.0 Mg in the sediments from the gully without intervention, and of 1.0, 1.7 and 1.8 Mg from the gully with physical interventions, indicating an average reduction of 95 %. The fully recovered gully produced no sediment during the period. The data of total nutrient loss from the three gullies under investigation showed reductions of 98 % for the recovering gully, and 99 % for the fully recovered one. As for the loss of nutrients, the data indicate a nutrient loss of 1,811 kg from for the non-treated gully. The use of physical and biological interventions made it possible to reduce overall nutrient loss by more than 96 %, over the entire rainy season, as compared to the non-treated gully. Results show that the methods used were effective in reducing soil and nutrient losses from gullies.

Soil, water and nutrient losses by interrill erosion from green cane cultivation

Interrill erosion occurs by the particle breakdown caused by raindrop impact, by particle transport in surface runoff, by dragging and suspension of particles disaggregated from the soil surface, thus removing organic matter and nutrients that are essential for agricultural production. Crop residues on the soil surface modify the characteristics of the runoff generated by rainfall and the consequent particle breakdown and sediment transport resulting from erosion. The objective of this study was to determine the minimum amount of mulch that must be maintained on the soil surface of a sugarcane plantation to reduce the soil, water and nutrient losses by decreasing interrill erosion. The study was conducted in Pradópolis, São Paulo State, in 0.5 x 1.0 m plots of an Oxisol, testing five treatments in four replications. The application rates were based on the crop residue production of the area of 1.4 kg m-2 (T1- no cane trash; T2-25 % of the cane trash; T3- 50 % trash; T4-75 % trash; T5-100 % sugarcane residues on the surface), and simulated rainfall was applied at an intensity of 65 mm h-1 for 60 min. Runoff samples were collected in plastic containers and soon after taken to the laboratory to quantify the losses of soil, water and nutrients. To minimize soil loss by interrill erosion, 75 % of the cane mulch must be maintained on the soil, to control water loss 50 % must be maintained and 25 % trash controls organic matter and nutrient losses. This information can contribute to optimize the use of this resource for soil conservation on the one hand and the production of clean energy in sugar and alcohol industries on the other.

Short-term temporal changes of soil carbon losses after tillage described by a first-order decay model

Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO2) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: dC(sail)(t)/dt = -kC(soil)(t) and that soil C-CO2 emission is proportional to the C decay rate in soil, where C-soil(t) is the available labile soil C (g m(-2)) at any time (t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till (F-NT) and tilled (F-Gamma) fluxes, which is: F-T = a1F(NT)e(-a2t), where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient (R-2), index of agreement and model efficiency, with R-2 as high as 0.97. The two parameters included in the model are related to the difference between the decay constant (k factor) of tilled and no-till plots (a(2)) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage (a,). These two parameters were estimated in the model ranging from 1.27 and 2.60 (a(1)) and - 1.52 x 10(-2) and 2.2 x 10(-2) day(-1) (a(2)). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters. (C) 2008 Elsevier B.V. All rights reserved.