Saturday, 15 July 2006

Effectiveness of Cropping on Runoff and Soil Losses on Diverse Environmental Settings in Brazil.

Sonia C. F. Dechen1, Isabella C. DeMaria1, Jerry A. Ngailo2, Orlando M. Castro1, and Sidney R. Vieira1. (1) Instituto Agronômico, Avenida Barão de Itapura, 1.481 (Botafogo), CEP 13020-902 Campinas, São Paulo, Brazil, (2) Ministry of Agriculture and Food, Agricultural Research Institute Mlingano, National Soil Service, P.O. Box 5088, Tanga, Tanzania

The effect of four different treatments on surface runoff and soil loss, their seasonal distribution and temporal variations in three contrasting locations were examined using runoff-erosion plots (4 m x 25 m long) for a six year period in Sao Paulo State, Brazil. Bare fallow, and three crops (soybeans, maize and sunflower) were planted to evaluate their effectiveness in runoff and soil loss control. In this study, data has consistently revealed that runoff and soil loss was reduced over 60% simply by planting a crop to ensure the soils were well protected when erosive rainstorms were the most destructive. The runoff and soil losses generated were highest in sunflower and maize, but least from soybean plots. Cropping practices played a major role in seasonal distribution of runoff and soil loss. Under bare fallow, approximately 90% of runoff and 79% of soil loss occurred during the non-cropping season. There was variation in the rainfall and erosivity factor the three locations for but was consistently highest during December to April months each year, which coincided with the period during which runoff and soil losses were also highest. The data from three sites have clearly elucidated that runoff and soil loss can be minimized by crop management that produces a protective vegetative cover on soils, reducing damage to the top soil. One of the most important conclusions of this a study is that in all environments, it is necessary to select and manage crop types that provide sufficient cover on the soil. These do not only provide enough residues during the time of the year when the soils are the most vulnerable to both runoff and soil loss, but also the rooting systems favor soil strength. Seasonal variations in the two parameters must be considered when designing or using event-based models to predict runoff and soil losses.

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