Field Evaluation of Passive Capillary Samplers

Abstract

Soil solution samplers have certain inadequacies that limit their range of possible applications. Passive capillary samplers (PCAPS), which apply suction to the soil pore water via a hanging water column in a fiberglass wick, have shown promising results in preliminary experiments in regard to collection efficiency of water and Br tracers. The objectives of this study were to evaluate PCAPS with respect to (i) effect of installation procedure and operational characteristics; and (ii) ability to estimate the soil‐water and solute flux. We installed 32 PCAPS and 32 ceramic suction cup samplers at a depth of 1.2 m in an undisturbed silt loam soil. For the first year, water flux, NO3‐N and Br concentrations in the part of the PCAPS closest (0.3 m) to the refilled trench were 15, 14, and 34% less, respectively, than in the part farthest (0.9 m) away from the refilled trench. This was attributed to installation procedure, since the bias ceased for the second year. Soil‐water flux measurements of PCAPS underestimated those determined by a water balance by 20 to 34%. Some of the discrepancy is thought to be due to the lack of accounting for runoff, which was observed but not quantified. The recovery of a Br tracer was low with an average of 29%, ranging from 5 to 77%, which was attributed to lateral water movement due to prominent lateral stratification. To estimate the mean Br concentration with a 30% bound at the 0.05 confidence level on this 1‐ha field site, 25 PCAPS and 37 suction cup samplers are necessary. Sampling a more evenly distributed solute such as residual fertilizer NO3 requires only eight PCAPS for this level of confidence.

Spatial and temporal variations in percolation fluxes in a tropical Andosol influenced by banana cropping patterns

“…1). This can be explained by suction lysimeter induced lateral heterogeneity in the soil water potentials resulting in percolation flux convergence in the soil layer over WL (Holder et al, 1991) and flux divergence over GL (Brandi-Dohrn et al, 1996). The overpercolation in WL can also be explained by the possibility that the mesh samplers were of unsuitable size, as mentioned by various authors (Knutson and Selker, 1994;Lacas et al, 2004).…”

“…Their main weaknesses are related to the disturbance created when they are installed in the soil and to the possible differences in flow intensities and flow lines between the natural and sampled soil due to the imposed water potential condition. Among them, the zero-tension lysimeters (Boll et al, 1991;Goyne et al, 2000;Zhu et al, 2002) and the suction lysimeters (Boll et al, 1992;Brandi-Dohrn et al, 1996;Brye et al, 1999;Kosugi and Katsuyama, 2004) must be distinguished. The former sets the interface between the soil and the lysimeter at the atmospheric pressure and collects drainage water only when the soil above the interface becomes saturated.…”

Micro‐Trench Experiments on Interflow and Lateral Pesticide Transport in a Sloped Soil in Northern Thailand

“…The wick had a filament diameter of 0.7 μm, a filament tortuosity of 0.79, a porosity of 0.90, a bulk density of 0.25 g cm −3 , a diameter of 1.45 cm (Knutson and Selker, 1994), and a hydraulic conductivity of 10 −2 cm s −1 (Holder et al, 1991). Numerous studies have shown that capillary wick samplers are suitable to collect soil water and solutes (BrandiDohrn et al, 1996; Goyne et al, 2000; Louie et al, 2000). Holder et al (1991) found that adsorption of inorganic ions and selected organic chemicals to this wick material was very small.…”

Water and Bromide Recovery in Wick and Pan Lysimeters under Conventional and Zero Tillage

“…Bromide (Br) concentration for the pan lysimeter was greater near the center of the pan, whereas Br concentration for the wick lysimeter appeared to be randomly distributed spatially. Wick lysimeters have been shown to increase collection efficiency compared to pan lysimeters (Boll et al 1991;Brandi-Dohrn et al 1996) because the wick exerts tension on the soil above the wick lysimeter, collecting water from the soil matrix that might otherwise be diverted around a pan lysimeter. The collection efficiency for two wick lysimeters in a 1-month experiment by Boll et al (1991) was 103% of water and 65% of Br compared to 25% and 7% for water and Br, respectively, for a pan lysimeter.…”