SEDIMENT YIELS FROM SECONDARY FOREST ROADS ON Pinus taeda COMMERCIAL PLANTATION IN SOUTHERN BRAZIL HIGHLAND.
CARLA M. CAMARGO CORR╩A1, RENATO A. DEDECEK2, and JORGE R. MALINOVSKI1. (1) FOREST SCIENCE DEPT. - FEDERAL UNIVERSITY OF PARAN┴, Rua Lothario Meisner, 3400 - CAMPUS III, Curitiba, Brazil, (2) EMBRAPA CNPFlorestas, Caixa Postal 319, Colombo, Brazil
Forest roads can cause as much erosion as agricultural areas when there are no conservation and maintenance measures. This work aimed to evaluate, during the period of one year, the losses of sediments from roads in Pinus taeda commercial plantation located on the northern plateau of the state of Santa Catarina, in South Brazil. The treatments evaluated were: secondary roads on a clayey and on a loamy soil, with and without conservation measures by the company, which consisted water bars associated with water retention boxes located at 50 meter intervals, presence or absence of primary coating, associated with differentiated relief and soil conditions, right after the harvest of wood. Soil losses from secondary roads, measuring 100 m length and 6 m wide, were collected at lower end using a Coshocton wheel device and stored in plastic buckets. Samples of the runoff were collected every fifteen days to separate sediment and water. Sediments were analyzed for nutrients and texture determination. Annual rainfall was 1454 mm on a clayey soil area and 1496 mm on a loamy soil area, resulting on values of rainfall erosivity of 1098 MJ mm ha-1 h-1 and 992 MJ mm ha -1 h -1, respectively. The sediments originating from forest roads on both soil textures showed higher nutrient concentration when produced in roads without conservation measures. Except for organic carbon and potassium, that showed higher concentration in sediments from road with conservation measure. Soil losses from roads on clayey soil, gentle relief and with conservation measures were 1.44 t km -1 and without conservation measures, 2.40 t km -1. And from roads located on a loamy soil with 12 to 15 % slope, soil losses were equal to 4.07 t km -1 with conservation measures and 5.24 t km -1 without conservation measures. Considering in the clayey soil area that the road density was 23.82 m ha-1, total soil losses could reach 0.034 t ha-1 and 0.057 t ha-1 with and without conservation measure, respectively. In a sandy soil area that the road density was 24.31 m ha-1, producing soil losses equal to 0.099 t ha-1 and 0.127 t ha-1 with and without conservation measure. Conservation measures adopted on roads in clayey soil areas reduced sediment yield in around 40 %, while on sandy soil areas this reduction was around 22 %.
Key words: water erosion, primary coating roads, water bars