The method used to sample the runoff collected from soil erosion plots can be a significant source of error. In this study, we performed a laboratory experiment to evaluate the efficiency of the runoff sampling method most commonly used in Brazil. It is based on the manual homogenization and sampling of the collected runoff. Using soil material with 583 g kg-1 of sand and 89 g kg-1 of clay, the manual sampling method was tested for its ability to produce representative samples of artificial suspensions with a concentration of 2, 10 and 50 g L-1 of total solids. An underestimation of 30 % or more of the concentration of total solids was observed, with a variation of the same magnitude (CV between 20 and 45 %). We then developed a prototype sample splitter to replace the manual sampling method and tested it using the same artificial suspensions. The splitter was efficient in producing samples representative of the artificial suspensions, even without altering the particle size distribution of the total solids. Both absolute percentage errors (|< 5 %|) and the variation between five replicates (CV < 3 %) were small. The problems with the manual method are due to the inefficient homogenization that facilitates the differential sedimentation of particles of different sizes. If these problems are also found in other areas, then the prototype that we developed is a reasonable alternative.
Somos gratos ao Dr. Pablo Miguel (Universidade Federal de Pelotas – UFPel) que participou da aquisição de dados. Somos gratos a dois revisores anônimos pelos comentários úteis sobre a versão original do manuscrito, bem como pelos comentários críticos de outros três revisores anônimos em uma versão anterior do manuscrito. A pesquisa para este artigo foi financiada pela Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) e pelo Conselho Nacional Brasileiro de Desenvolvimento Científico e Tecnológico (CNPq).