Accuracy and variability of runoff sampling methods
Alessandro Samuel-Rosa[1*], Jean Michel Moura-Bueno, Ricardo Simão Diniz Dalmolin
 Universidade Tecnológica Federal do Paraná -- Prolongamento da Rua Cerejeira, s/n -- 85892-000 -- Santa Helena, PR -- Brasil.
 Universidade Federal de Pelotas -- Campus Universitário, s/n -- 96010-610 -- Capão do Leão, RS -- Brasil.
 Universidade Federal de Santa Maria -- Av. Roraima 1000, Prédio 42, Sala 3309 -- 97105-900 -- Santa Maria, RS -- Brasil.
* Corresponding author <firstname.lastname@example.org>
The method used to obtain runoff samples in soil erosion monitoring studies is an important source of data variability. In this study, we evaluated the manual sampling method used in Brazil. We present as an alternative the prototype of a sample splitter for suspensions with high concentration of total solids. Using soil material with 583 g kg^-1^ of sand and 89 g kg^-1^ of clay, the manual method and the sample splitter were tested for their ability to produce representative samples of 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 using the manual method, with a variation of the same magnitude (CV between 20 and 45%). The splitter was efficient in producing samples representative of the suspension -- even without altering the particle size distribution of the total solids. Both absolute percentage errors (|<5%|) and the variation between replicates (CV <3%) were small. The problems with the manual method are due to the inefficient homogenization that facilitates the differential sedimentation of the particles of different sizes. If these problems are also found in other studies, then the prototype that we developed is a reasonable alternative.
Keywords: Erosion monitoring, Soil loss, Sandy soil, Sample splitter, Uncertainty.
Manuscript submitted to Scientia Agricola on 24-Apr-2019 and recommended for publication -- after two revision rounds -- on 06-Oct-2019 under the title "Replacing the (inefficient) manual runoff sampling method used in Brazil – a prototype sample splitter".