Elemar Antonino Cassol

Erosividade, coeficiente de chuva, padrões e período de retorno das chuvas de Quaraí, RS

The planning of agricultural and civil engineering activities must be based on knowledge of rainfall erosion potential. For Quarai, RS, Brazil, the rainfall erosivity and its relationship with precipitation and rainfall coefficient, rainfall patterns and rainfall return period were determined. Daily rainfall data from the 1966-2003 period were used. For each erosive rainfall the segments of the rainfall chart with the same intensity were separated and the data recorded in a worksheet. The mean precipitation and rainfall patterns were estimated, as well as the monthly and annual erosivity by the EI30 index (International System of Units), using the software Chuveros. The rainfall coefficient was calculated. Pearson correlations and linear regressions between the erosivity index EI30 and the mean annual precipitation and rainfall coefficient (Rc) were performed. The rainfall maximum intensity was calculated by the method of extreme distribution type I for different rainfall durations (1/6, 1/3, 1/2, 1, 2, 4, 8, 12, 24 and 48 h) and rainfall return periods (2, 5, 10, 20, 50 and 100 years). Equations were adjusted that relate the maximum intensity and rainfall duration to all return periods, by the method of simple linear regression, and the rainfall characteristics related in a graph. The mean annual values of EI30 (R factor of USLE) determined for Quarai, RS, Brazil, was 9,292 MJ mm ha-1 h -1 year-1. The following equations were obtained: EI30 = -754.37 + 13.50 p (r2 = 0.85) and EI30 = -47.35 + 82.72 Rc (r2 = 0.84). In relation to the total precipitation studied, 44 % of the number of rainfalls and 90 % of the volume were erosive. Of the total rainfalls evaluated, 44 % of the number and 90 % of the volume were erosive. Of the total erosive rainfall events, 51 % had an advanced, 25 % had an intermediate, and 24 % had a delayed hydrological pattern. Of the total volume of erosive rainfalls, 57 % showed and advanced pattern, 25 % intermediate, and 18 % a delayed pattern.

Erosão em entressulcos sob diferentes tipos de preparo e manejo do solo

(3) Resumo – A validacao de uso de modelos de predicao da erosao hidrica do solo baseados em processos fisicos fundamentais necessita de informacoes sobre os valores de seus parâmetros obtidos em condicoes locais. Este trabalho foi realizado no campo em um Argissolo Vermelho distrofico tipico, com o objetivo de avaliar a erosao hidrica em entressulcos sem preparo do solo (com residuos culturais na superficie), com preparo convencional com solo descoberto (sem residuos) e com preparo convencional com residuos incorporados. O esquema experimental baseou-se nos estudos realizados para a determinacao da erodibilidade do solo em relacao ao modelo WEPP (Water Erosion Prediction Project). Foi aplicada chuva simulada com intensidade planejada de 60 mm h -1 , durante 70 minutos, e coletadas amostras da enxurrada das parcelas em entressulcos. A perda de solo em entressulcos foi significativamente menor no tratamento sem preparo do solo em relacao aos tratamentos submetidos ao preparo convencional. As taxas de erosao e perda de agua em entressulcos foram crescentes com o tempo de chuva ate atingir um ponto de valor maximo, apos o qual decresceram, com excecao do tratamento sem preparo do solo, cujas taxas foram crescentes em todo o periodo de aplicacao da chuva. O valor da erodibilidade do solo em entressulcos e de Ki = 2,83x10 6 kg s m -4 . Termos para indexacao: erodibilidade do solo em entressulcos, predicao da erosao, erosao hidrica do solo, cultivo convencional. Interrill soil erosion under different tillage and management systems

Escoamento superficial e desagregação do solo em entressulcos em solo franco-argilo-arenoso com resíduos vegetais

Soil surface cover with crop residue modifies surface flow characteristics, generated by excess rainfall, and soil detachment and sediment transport resulting from the erosion process. The objective of this study was to evaluate the hydraulic conditions, detachment and flow resistance on interrill erosion on soil covered with residue. The experiment was conducted in the laboratory, on a Hapludult soil at a slope of 0.10 m m -1 , under simulated rainfall and soil surface covered with soybean residue at the rates of 0, 0.05, 0.1, 0.2, 0.4, and 0.8 kg m -2 . The increase in soil surface cover (SC) with residue, caused an increase in water flow depth and hydraulic roughness, and a decrease in the mean flow velocity, due to an increase in the viscous forces from the physical interference of residue on runoff, thus contributing to a reduction in interrill soil detachment rate (Di). The Di was 5.35x10 -4 kg m -2 s -1 for bare soil and was reduced to 1.50x10 -5 kg m -2 s -1 for soil with 100% of surface cover. The Laflens and the potential models were adequate to estimate the coefficient of soil coverage by residue in direct contact with soil as a function of the soil surface cover.

PERDAS DE NUTRIENTES POR EROSÃO EM DIFERENTES MÉTODOS DE MELHORAMENTO DE PASTAGEM NATIVA NO RIO GRANDE DO SUL

Growth stagnation on native grassland during the winter season has stimulated the introduction of winter species in order to increase forage offer for animals in the State of Rio Grande do Sul, Brazil. To determine the nutrient losses by erosion as affected by different methods of native grassland improvement, an experiment was carried out at the Agronomic Experimental Station of the Federal University of Rio Grande do Sul, in Eldorado do Sul. A mixture of the winter forage species black oat, Italian ryegrass and arrowleaf clover was introduced on a Paleudult soil under long time native grassland use. Experimental plots of 3,5 by 11,0 m at 0.107 m m-1 of average slope were submitted to simulated rainfall of 64 mm h-1 average intensity and 75 minutes of duration in three different runs: 55 days after soil tillage and sowing; 125 days after soil tillage and sowing (right after the first grazing); and 175 days after soil tillage and sowing (right after the second grazing). The experimental design was completely randomized with five treatments for the introduction of winter species: Zero tillage (Control), No-tillage, Disking; Sub-soiling, and Conventional tillage. During each rainfall, runoff samples were collected every 15 minutes, and the available phosphorus, calcium, magnesium and potassium nutrient concentrations were determined by the extraction method of ionic exchange resin. There was a difference between the rain application runs and the treatments in relation to the nutrient concentrations and losses in the runoff. Highest losses occurred in the first run. In general, highest nutrient losses occurred in the Control treatment and lowest in Conventional tillage. These nutrient losses were not directly related with soil and water losses, but determined by soil surface conditions as well as fertilizer and lime application methods.

Relações da erosão em entressulcos com o tipo e com a quantidade de resíduo vegetal na superfície do solo

Crop residue in direct contact with the soil surface is very effective in dissipating the energy of raindrop impact on soil, being also a physical barrier against interrill overland flow. The presence of these residues may strongly affect the interrill soil erosion process. A study was carried out with the objective of evaluating the relationship between interrill erosion and amounts of crop residue in direct contact with soil surface and to verify the differences in this relationship for corn and wheat residues. An experiment was conducted at the Forest and Soil Conservation Research Center of FEPAGRO, in Santa Maria, RS, on a Paleudult sandy loam soil. Experimental interrill plots of 0.50 x 0.75 m, with the largest dimension parallel to the direction of land slope of 0.17 m m-1, were arranged in 4 completely random blocks. Residues of corn and wheat chopped in pieces of about 7.5 cm were distributed over the plots on freshly tilled soil, at amounts of 0.00, 0.05, 0.10, 0.20, 0.40 and 0.80 kg m-2. Simulated rainfall was applied at a mean intensity of 67 mm h-1, during 90 minutes. There was a significant variation of interrill soil and water losses with the time of rainfall and with amount of crop residues. However, there was no variation with the type of residue. The relationship between interrill soil loss and amount of residue in direct contact with soil surface fitted well to an exponential equation. This exponential model is recommended to estimate the subfactor interrill soil cover by residues in direct contact with the surface, because it is easy to use and obtain measurements.

Relação entre a erodibilidade em entressulcos e estabilidade dos agregados

A erodibilidade do solo e uma caracteristica utilizada nos planejamentos conservacionistas, especialmente, quando areas agricolas sao utilizadas intensivamente. As praticas de conservacao devem ser mais intensas em solos com erodibilidade alta do que em areas com erodibilidade baixa. Como a determinacao da erodibilidade do solo e dificil de ser realizada no campo, avaliou-se a relacao entre os indices de expressao de estabilidade dos agregados e a erodibilidade do solo em entressulcos, utilizando amostras de solos do Rio Grande do Sul com propriedades quimicas, fisicas e mineralogicas diferentes. Foram medidas em laboratorio a estabilidade dos agregados e a erodibilidade do solo em entressulcos, servindo-se de chuva simulada. Os coeficientes de determinacao (R2) entre diferentes indices de estabilidade dos agregados e a erodibilidade do solo em entressulcos foram significativos (p < 0,01), indicando que esses indices foram adequados para predizer a erodibilidade do solo em entressulcos. Alguns indices que usam o diâmetro medio ponderado para expressar a estabilidade dos agregados tambem foram significativos (p < 0,05). A estabilidade dos agregados mostrou-se adequada para estimar a suscetibilidade dos solos a erosao hidrica em entressulcos.

Estimativa da erodibilidade em entressulcos de latossolos do Rio Grande do Sul

Models of soil water erosion prediction and estimation are generally based on a series of parameters, normally determined by applying simulated rainfall in the field or laboratory. The use of simpler, faster and cheaper parameters such as texture, content and oxide type and aggregate water stability may contribute to facilitate the estimation of the factor interrill soil erodibility (Ki). The purpose of this study was: i) to determine the interrill soil erodibility of three Brazilian Oxisols; ii) evaluate the use of soil sand and clay contents in the prediction of interrill soil erodibility, as in the WEPP model; iii) verify the correlation among some soil properties and the interrill soil erodibility factor. The interrill soil erosion rates were determined in laboratory, using three Oxisols with different clay content of the State of Rio Grande do Sul, Brazil, under a mean intensity of simulated rainfall of 88 mm h-1, applied during 180 min on bare soil, using experimental interrill plots of 0.36 m2 at a slope of 0.09 m m-1 and an initial water tension of 6 kPa. The susceptibility of soils with high clay and Fe oxide contents and higher water aggregate stability to interrill erosion was lower. The experimentally determined values of interrill soil erodibility (Ki factor) varied from 0.76 x 106 kg s m-4 to 1.48 x106 kg s m-4 for the studied Oxisols. The aggregate water stability index was highly correlated with the interrill soil erodibility factor (r= -0.90**). The use of soil sand and clay contents, as suggested by the WEPP model, did not prove adequate to estimate the interrill soil erodibility (Ki factor). The variation in clay and Fe oxide contents explained 97 % (p<0.01) of the interrill soil erodibility variation.

RESIDUAL EFFECT OF SOIL TILLAGE ON WATER EROSION FROM A TYPIC PALEUDALF UNDER LONG-TERM NO- TILLAGE AND CROPPING SYSTEMS (1)

Soil erosion is one of the chief causes of agricultural land degradation. Practices of conservation agriculture, such as no-tillage and cover crops, are the key strategies of soil erosion control. In a long-term experiment on a Typic Paleudalf, we evaluated the temporal changes of soil loss and water runoff rates promoted by the transition from conventional to no-tillage systems in the treatments: bare soil (BS); grassland (GL); winter fallow (WF); intercrop maize and velvet bean (M+VB); intercrop maize and jack bean (M+JB); forage radish as winter cover crop (FR); and winter cover crop consortium ryegrass - common vetch (RG+CV). Intensive soil tillage induced higher soil losses and water runoff rates; these effects persisted for up to three years after the adoption of no-tillage. The planting of cover crops resulted in a faster decrease of soil and water loss rates in the first years after conversion from conventional to no-tillage than to winter fallow. The association of no-tillage with cover crops promoted progressive soil stabilization; after three years, soil losses were similar and water runoff was lower than from grassland soil. In the treatments of cropping systems with cover crops, soil losses were reduced by 99.7 and 66.7 %, compared to bare soil and winter fallow, while the water losses were reduced by 96.8 and 71.8 % in relation to the same treatments, respectively.

Infiltração de água e perdas de água e solo por erosão influenciadas por diferentes métodos de melhoramento da pastagem nativa gaúcha

A paralisacao do crescimento da pastagem nativa no periodo do inverno na regiao Sul do Brasil tem incentivado tecnicas de melhoramento das pastagens. Com o objetivo de estudar a infiltracao de agua no solo e as perdas de solo e agua por erosao influenciadas por metodos de melhoramento da pastagem nativa, realizou-se um estudo em area da Estacao Experimental Agronomica da UFRGS, no municipio de Eldorado do Sul (RS), em um Podzolico Vermelho-Amarelo submetido ao uso prolongado com pastagem nativa, no qual se fez a introducao de uma mistura das especies hibernais: aveia preta (Avena strigosa ), azevem (Lolium multiflorum ) e trevo vesiculoso (Trifolium vesiculosum). O delineamento experimental foi completamente casualizado e com cinco tratamentos que diferiram quanto a maneira de introducao das novas especies: testemunha (a lanco), gradagem, plantio direto, convencional e subsolagem. As parcelas tinham a dimensao de 3,5 x 11,0 m e uma declividade aproximada de 0,107 m m-1. Aplicaram-se chuvas simuladas de 64 mm h-1, durante 75 min, em tres epocas: (a) aos 55 dias do preparo do solo e semeadura, logo apos o primeiro pastejo, (b) aos 125 dias do preparo do solo e semeadura, e (c) logo apos o segundo pastejo, aos 175 dias do preparo do solo e semeadura. Entre as chuvas simuladas, realizou-se um pastejo por dois dias. A subsolagem apresentou a maior taxa constante de infiltracao e a menor taxa constante de enxurrada. As perdas de solo foram pequenas nas tres epocas avaliadas. As maiores perdas de agua ocorreram na testemunha e as menores na subsolagem, indicando ter sido este ultimo tratamento efetivo em quebrar camadas compactadas subsuperficiais.

Fatores relacionados à suscetibilidade da erosão em entressulcos sob condições de uso e manejo do solo

This study evaluated factors related to the suscetibility to the interrill soil erosion in an Entisol subjected to different degrees of soil use and management. The experiment was carried out under laboratory conditions using samples collected from tobacco fields and disturbed soil placed in erosion pans measuring (0.23 m2) with a slope of 0.09 m m-1. The experimental design was in randomized blocks. Simulated rainfall intensity of 100 mm h-1 was applied to the following treatments: (I) conventionally tilled soil; (II) no-till soil; and (III) native forest soil. Total kinetic energy (rainfall and runoff) to soil loss, average rate of detachment, and aggregate stability indexes were used to assess susceptibility to interrill erosion. Results show that the factors related with the susceptibility to interrill erosion are associated not just to the characteristics and properties that confer cohesivity to soil, but also to those factors that affect runoff hydraulics and therefore the sediment transport phase as well.