Spatial variability of soil properties complicates the understanding of water and solute transport at the field scale. This study evaluated the impact of land use, soil surface roughness, and rainfall characteristics on water transport and Br- leaching under field conditions by means of a new experimental design employing scale-dependent treatment distribution. On a transect with two land use systems, i.e., cropland and grassland, rainfall intensity and the time delay between Br- application and subsequent rainfall were arranged in a periodically repetitive pattern at two different scales. Both scales were distinct from the scale of surface roughness as described by elevation variance. Nests of tensiometers and suction probes were installed at 1-m intervals along the transect to monitor matric potentials and Br- concentrations at different depths, respectively. After rainfall simulation, soil samples were collected at every 0.5 m horizontal distance in 10 cm vertical increments down to 1 m depth for Br- analysis. Soil Br- concentration was more evenly distributed with soil depth and leached deeper in grassland than cropland, owing to vertically continuous macropores that supported preferential flow. Frequency-domain analysis and autoregressive state-space approach revealed that the dominant factors controlling Br- leaching varied with depth. In shallow layers, land use was the main driving force for Br- distribution. Beyond that, the spatial pattern of Br- was mostly affected by rainfall characteristics. Below 40 cm, the horizontal distribution of Br- was dominated by soil texture and to a smaller extent by rainfall intensity. Bromide concentrations obtained from soil solution samples that were collected through suction probes showed similar results with respect to the influence of rainfall intensity. The spatial variation scale of temporal matric potential change varied with both time and depth, corresponding to different boundary condition scales. Matric potential change in some cases, reflected the impact of soil properties other than the boundary conditions investigated, such as hydraulic conductivity, contributing to the scale-variant behavior of Br- leaching. These findings suggest the applicability of scale-dependent treatment distribution in designing field experiments and also hold important implications for agricultural management and hydrological modelling.

Rapid and deep transport of solutes in soils can potentially pollute groundwater resources. Field estimates of solute leaching depth based on randomized sampling provide extremely variable field average estimates that confound the treatment effects of the leaching study with the high spatial variation of soil hydraulic properties. The purpose of this study was to investigate the spatial scale of variation of solute (Bromide) leaching depth, and apply this scale of variation to study the leaching depth of Bromide as a function of a sinusoidal application of transport causing factors, i.e., rainfall amount, intensity and application time delay. Solute leaching depth varied over different spatial scales. The deepest leaching was observed on plots where the Br center of mass ranged from 19-30 cm depth. Deep leaching occurred with large quantities of low intensity precipitations (5.5 to 6 cm/day) and short time delays (≤ 17 hours), respectively. The hydraulic gradient presented cyclic variation at 8 m wavelength across the 10-30cm depth compartment. Spectral analysis indicated that spatial variation of the leaching depth was mainly affected by precipitation amount and intensity and only a small portion of the leaching depth variation was caused by time delay. Cross-spectral analysis identified common cyclic variation between the Br leaching depth and precipitation amount, intensity and time delay over 32, 32 and 8 m wavelengths, respectively. Simulated Br concentration over depth and horizontal distance and soil water matric potential ψm were in good agreement with experimental observations, the latter revealing a satisfactory Br and water mass balance.