In studies of erosion, runoff, and infiltration, high soil variability may demand many replicate measurements and rapid, inexpensive methodology. We developed a drop‐forming rainfall simulator in which flow through long, coiled capillary drip tubes is controlled by an adjustable Mariotte‐type bubbling tube. These rain simulators are inexpensive, rugged, simple to operate, easily transported, and require minimal maintenance. Responses to pressure head and water temperature changes were determined for two simulators using tap water. Flow response to pressure head changes corresponded closely to that predicted by Poiseuille's Law. Response to increasing water temperatures was somewhat less than predicted, due to formation of bubbles in the capillary tubes. Simulators incorporating long, coiled capillary tubes can provide combinations of low flow rates and large drop sizes, or a desired range of flow rates when appropriate drip tube diameters, lengths, and numbers of tubes per unit area are combined.

Soil hydraulic properties have numerous sources of variability related to spatial, temporal, and management‐related processes. Soil type is considered to be the dominant source of variability, and parameterization is typically based on soil survey databases. This study evaluated the relative significance of other sources of variability: spatial and temporal at multiple scales, and management‐related factors. Identical field experiments were conducted for 3 yr at two sites in New York on clay loam and silt loam soils, and at two sites in Maryland on silt loam and sandy loam soils, all involving replicated plots with plow‐till and no‐till treatments. Infiltrability was determined from 2054 measurements using permeameters, and Campbell's a and b parameters were determined based on water‐retention data from 875 soil cores. Variance component analysis showed that differences among the sites were the most important source of variability for a (coefficient of variation, CV = 44%) and b (CV = 23%). Tillage practices were the most important source of variability for infiltrability (CV = 10%). For all properties, temporal variability was more significant than field‐scale spatial variability. Temporal and tillage effects were more significant for the medium‐ and fine‐textured soils, and correlated to initial soil water conditions. The parameterization of soil hydraulic properties solely based on soil type may not be appropriate for agricultural lands since soil‐management factors are more significant. For infiltrability, temporal factors also need to be explicitly recognized. Sampling procedures should give adequate recognition to soil‐management and temporal processes as significant sources of variability to avoid biased results.

Tillage most affects the large pore spaces, including macropores, which dominate percolation through field soils. Rain events are expected to promote post‐tillage changes in pore geometry. Pore‐geometric influences on macropore transport were examined under multiple rains, in a Kingsbury clay soil under no‐till (NT) and plow‐till (PT). Four replicate pairs of large undisturbed sample columns were installed on grid wick iysimeters comprising 5 × 5 grids of 36‐cm2 cells. Five simulated rains having mean depths and intensifies of 40 mm and 38 mm h−1, respectively, were applied, separated by intervals of 4, 8, 9, and 50 d, using a constant‐head drop‐forming rainfall simulator. Atrazine [6‐chloro‐N2‐ethyl‐N4‐isopropyl‐1,3,5‐triazine‐2,4‐diamine] and a Br− tracer were applied 24 and 1 h, respectively, before the first rain. Persistence of spatial percolation patterns was quantified by inter‐event correlation coefficients of the cell‐scale water outflows. Outflow was significantly greater in NT than in PT, averaging 75 and 54% of applied rain, respectively, but Br− export did not differ significantly between them. Spatial outflow patterns changed between events in both tillage treatments and were more variable in NT. Distributions of cell‐scale cumulative change in outflow proportion were unimodal and symmetric. Percolation in NT occurred as bypass flow through direct pathways, relative to PT pathways characterized by mixing. Transport variability due to temporal variability of functional macropore flowpaths may account for some solute tailing in field soils.

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