Influência do preparo do solo e de plantas de cobertura na erosão hídrica de um Argissolo Vermelho-Amarelo

Abstract

The soil erosion is a serious environment degradation factor and it is correlated with various characteristics, such as soil erodibility, rain erosivity, and amount of soil cover. This study was developed in order to evaluate the effect of different kind of soil tillage and soil plant coverage in the losses of water and soil caused by hydric erosion in a Yellow-Red Ultisol. Also, to evaluate two types of images classificators applied to determinate the degree of soil covering, resulting from the plant shading of the soil surface. The experiment was conducted in an area of Embrapa Agrobiologia experimental field, located at Seropédica municipality, Rio de Janeiro State, Brazil, between 24 December, 2004 and 25 May, 2005. Five plots with 22m per 3.5m were installed in a back-slope position, with a 0.09 m m-1 slope. Each plot received one treatment, they were: Conventional soil tillage in level and Mucuna Cinza (Mucuna pruriens) sowing Mucuna; Conventional soil tillage in level and sowing in level of Crotalária (Crotalaria juncea) Crotalária; Conventional soil tillage in level and sowing in level of Maize (Zea mays) Milho em Nível; Conventional soil tillage following the direction of the slope, down slope, and Maize sowing in the same way Milho Morro a Baixo; and Conventional soil tillage down slope, without soil cover Solo Exposto. The soil coverage level was measured using digital photographs taken perpendicularly to the soil surface, at 15, 23, 29, 33, 41, 44, 51, 56, 62, 68, 72, 76, 81 e 83 days after sowing. It was monitored the decomposition of crops residues, from cutting of aerial parts of crops, placed in the soil surface. Data from water and soil losses, and decomposition ratio of residues, were adjusted using mathematics models, according to the better correlation. Both methods applied to evaluate the digital images classification, to determinate the soil cover levels, were considered adequate, with global exactness superior to 0.9. The biggest soil cover levels were from the treatments Crotalária and Mucuna. The decomposition of crop residues from Crotalaria and Mucuna treatments decreased exponentially according to the exposing time; while the crop residues from Milho em Nível and Milho Morro a Baixo decreased exponentially and linearly, with exposing time. The soil tillage down slope, associated to Maize sowing in the same direction, contributed to the highest soil and water losses, while the crotalaria sowing in level was responsible for the smallest soil and water losses. Key words: Soil cover rate. Soil and water loss. Soil tillage.