RESUMO

The process of water erosion occurs in watersheds throughout the world and it is strongly affected by anthropogenic influences. Thus, the knowledge of these processes is extremely necessary for planning of conservation efforts. This study was performed in an experimental forested watershed in order to predict the average potential annual soil loss by water erosion using the Universal Soil Loss Equation (USLE) and a Geographic Information System (GIS), and then compared with soil loss tolerance. All the USLE factors were generated in a distributed approach employing a GIS tool. The layers were multiplied in the GIS framework in order to predict soil erosion rates. Results showed that the average soil loss was 6.2 Mg ha -1 yr -1 . Relative to soil loss tolerance, 83% of the area had an erosion rate lesser than the tolerable value. According to soil loss classes, 49% of the watershed had erosion less than 2.5 Mg ha -1 yr -1 . However, about 8.7% of the watershed had erosion rates greater than 15 Mg ha -1 yr -1 , being mainly related to Plinthosol soil class and roads, thus requiring special attention for the improvement of sustainable management practices for such areas. Eucalyptus cultivation was found to have soil loss greater than Atlantic Forest. Thus, an effort should be made to bring the erosion rates closer to the native forest. Implementation of the USLE model in a GIS framework was found to be a simple and useful tool for predicting the spatial variation of soil erosion risk and identifying critical areas for conservation efforts.Index terms: Forest systems, soil losses, USLE, GIS, coastal plain. RESUMOO processo de erosão hídrica ocorre em todo mundo sendo fortemente afetado por influências antrópicas. Assim, o conhecimento desses processos é extremamente necessário para o planejamento de práticas de conservação do solo. O estudo foi conduzido em uma bacia hidrográfica experimental florestada com o objetivo de estimar o potencial médio de perdas de solo anuais por erosão hídrica, utilizando a Equação Universal de Perdas de Solo (EUPS) inserida no Sistema de Informação Geográfica (SIG), e comparar com a tolerância de perdas de solo. Todos os fatores da EUPS foram gerados de forma distribuída utilizando a plataforma SIG. Os mapas foram multiplicados no ambiente SIG para estimar as taxas de erosão do solo. Os resultados mostraram que a perda de solo média foi de 6,2 Mg ha -1 ano -1 . Em relação à tolerância de perdas de solo, 83% apresentaram taxas de erosão menores que o valor de tolerância permitido. Com relação às classes de perdas de solo, 49% da bacia tiveram perdas de solo menores que 2,5 Mg ha -1 ano -1 . Entretanto, cerca de 8,7% da área da bacia apontaram taxas de erosão maiores que 15 Mg ha -1 ano -1 , estando, principalmente, relacionada à classe de solo Plintossolo e as estradas, exigindo uma atenção especial para conduzir um manejo sustentável nessas áreas. O cultivo de eucalipto mostrou perdas de solo maiores que a Mata Atlântica. Desse modo, um esforço deve ser realizado a fim de aprox...

SUMMARYKnowledge on the factors influencing water erosion is fundamental for the choice of the best land use practices. Rainfall, expressed by rainfall erosivity, is one of the most important factors of water erosion. The objective of this study was to determine rainfall erosivity and the return period of rainfall in the Coastal Plains region, near Aracruz, a town in the state of Espírito Santo, Brazil, based on available data. Rainfall erosivity was calculated based on historic rainfall data, collected from January 1998 to July 2004 at 5 min intervals, by automatic weather stations of the Aracruz Cellulose S.A company. A linear regression with individual rainfall and erosivity data was fit to obtain an equation that allowed data extrapolation to calculate individual erosivity for a 30-year period. Based on this data the annual average rainfall erosivity in Aracruz was 8,536 MJ mm ha -1 h -1 yr -1 . Of the total annual rainfall erosivity 85 % was observed in the most critical period October to March. Annual erosive rains accounted for 38 % of the events causing erosion, although the runoff volume represented 88 % of the total. The annual average rainfall erosivity return period was estimated to be 3.4 years.Index terms: kinetic energy, R-factor, USLE, recurrence interval, probability of occurrence.(

EUPS) é um importante instrumento na predição das perdas de solo e no planejamento do controle da erosão hídrica. A EUPS foi desenvolvida nos Estados Unidos, por Wischmeier & Smith (1965, 1978, e tem sido utilizada em vários países. A EUPS, segundo Wischmeier & Smith (1978), é composta pelos seguintes fatores: perda de solo (fator A -expresso em Mg ha -1 ano -1 ); erosividade da chuva (fator R -expresso em MJ mm ha -1 h -1 ano -1 ); erodibilidade do solo (fator K -expresso em ha Mg h ha -1 MJ -1 mm -1 ); fator topográfico (fator LS -adimensional), que considera a declividade (D -expresso em %) e o comprimento de rampa do solo (L -expresso em m); índice de ABSTRACT RESUMOcobertura vegetal (fator C -adimensional); e práticas conservacionistas (fator P -adimensional), sendo que, em muitos casos, o fator C pode ser determinado em associação com o fator P (CP). Na EUPS, a erodibilidade consiste no fator responsável pela susceptibilidade do solo à erosão hídrica, sendo condicionada, basicamente, por atributos mineralógicos, químicos, morfológicos, físicos e biológicos do solo (Dumas 1965, Wischmeier & Mannering 1969, El-Swaify & Dangler 1977. A erodibilidade representa o efeito dos processos que regulam a infiltração da água no solo, a desagregação pelo impacto da gota de chuva e a resistência ao transporte pelo fluxo superficial, os quais são responsáveis pelo comportamento do solo, em relação aos processos erosivos (Lal 1988). O valor de erodibilidade é mui-1. Trabalho recebido em abr./2010 e aceito para publicação em ago./2011 (n° registro: PAT 9604/

Soil and water losses caused by water erosion represent a risk of environmental damage and loss of soil productivity, with economic, social and environmental consequences. Plant cover is an important ally against water erosion, together with the knowledge of rainfall characteristics. Thus, this study aimed to evaluate the soil and water losses and to determine rainfall patterns in two homogeneous eucalyptus plantations; one in Yellow Argisol, located in Teixeira de Freitas, and another in Humiluvic Spodosol, located in Caravelas, both in the Extreme South of the state of Bahia. Erosion plots were installed, and consisted of three treatments: bare soil, eucalyptus, and native forest. Rainfall data was obtained from an automatic gauging station, with 10 minute registration interval for erosivity (erosivity index EI 30 ) and rainfall pattern analyses. Higher soil losses were observed in Yellow Argisol, and the advanced rainfall pattern was predominant. Eucalyptus minimum tillage was efficient in reducing soil and water losses by water erosion.

A aplicação de fósforo em solos brasileiros é uma prática frequente e tal operação pode afetar alguns atributos do solo. Assim, com o objetivo de avaliar os efeitos da fosfatagem na estabilidade de agregados e nas perdas de solo por erosão de um Latossolo Vermelho Acriférrico típico de Lavras (MG), foram aplicados, em duas parcelas de 72 m 2 , o equivalente a 450 kg ha -1 de P 2 O 5 a lanço mais 180 kg ha -1 de P 2 O 5 em linhas. A estabilidade de agregados foi determinada por ultra-som para classes de 7,93 a 4,76; 4,76 a 2,00; 2,00 a 1,00; 1,00 a 0,50; 0,50 a 0,25 e < 0,25 mm, e por peneiramento úmido para a fração de 7,93 a 4,76 mm. Também foi estimada a perda de solo por erosão com uso do sistema de pinos. A fosfatagem reduziu significativamente a estabilidade de agregados por peneiramento a úmido e por ultrasom para agregados maiores que 1 mm e aumentou as perdas de solo em 2,85 vezes. Agregados maiores que 2 mm apresentaram estabilidade 2,83 vezes menor com fosfatagem, o que pareceu influenciar as perdas de solo. A fosfatagem reduziu o ponto de efeito salino nulo e aumentou a densidade de cargas negativas, o que explicou os resultados obtidos. Palavras-chave: Erosão do solo, agregação, ultra-som, fosfatagem AbstractPhosphorus application in Brazilian soils is a common practice and such operation may affect some soil properties. Thus, with the objective of measuring the effect of the phosphate fertilization on aggregate stability and soil loss by erosion of a typic Acriferric Red Latosol from Lavras (MG), soil plots were fertilized with the equivalent to 450 kg ha -1 of P 2 O 5 , broadcasted, and 180 kg ha -1 of P 2 O 5 applied over lines, in two plots of 72 m 2 . Aggregate stability was measured by sonication at different sizes of aggregates: 7.93 to 4.76; 4.76 to 2.00; 2.00 to 1.00; 1.00 to 0.50; 0.50 to 0.25 and <0.25 mm. Wet sieving was also performed to estimate aggregate stability at the fraction of 7.93 to 4.76 mm. The amount of erosion was measured using a grid of pins on soil surface. Phosphate fertilization significantly reduced aggregate stability by wet sieving and ultrasonic for larger aggregates than 1 mm, and increased the erosion in 2.85 times. Aggregates larger than 2 mm showed stability 2.83 times lower with phosphate, which could influence soil loss. The phosphate fertilization reduced the zero point of salt effect, and increased the negative charges density,

Soil and water losses caused by water erosion represent a risk of environmental damage and loss of soil productivity, with economic, social and environmental consequences. Plant cover is an important ally against water erosion, together with the knowledge of rainfall characteristics. Thus, this study aimed to evaluate the soil and water losses and to determine rainfall patterns in two homogeneous eucalyptus plantations; one in Yellow Argisol, located in Teixeira de Freitas, and another in Humiluvic Spodosol, located in Caravelas, both in the Extreme South of the state of Bahia. Erosion plots were installed, and consisted of three treatments: bare soil, eucalyptus, and native forest. Rainfall data was obtained from an automatic gauging station, with 10 minute registration interval for erosivity (erosivity index EI 30 ) and rainfall pattern analyses. Higher soil losses were observed in Yellow Argisol, and the advanced rainfall pattern was predominant. Eucalyptus minimum tillage was efficient in reducing soil and water losses by water erosion.