Manual Sampling and Tank Size Effects on the Calibration Curve of Plot Sediment Storage Tanks

In many experimental soil erosion plots, runoff is collected and carried by a conveyance system to a sequence ofstorage tanks. If the soil loss is measured by collecting, after mixing, samples of the stored suspension, then a calibration curvebetween the actual mean concentration (C) and the measured concentration (Cm) in the storage tank occurs. The aim of thisarticle was to evaluate experimentally the factors affecting the relationship between C and Cm. For a sandy loam soil, thereplicated measurements of Cm (20 samples) for two values of the actual concentration (C = 5 and 25 g/L) showed that thevariability of the measurements of Cm is low and confirmed the reliability of a calibration curve obtained by a single seriesof runs. Results from experiments carried out with a clay soil to compare the calibration curves obtained by four field workerssuggested that the maximum uncertainty in the soil loss measurement due to the choice of the calibration curve should notexceed 100% of the true value. Moreover, the slope of the calibration curve was independent of both the water level in thetank and the field worker. Finally, a comparison among the calibration curves of a prototype tank and some model tanks wascarried out for both a sandy loam and a clay soil in order to establish a scaled-up relationship among tanks of different size.Soil-specific and theoretically based scaled-up relationships were deduced.