Soil profile distributions of water and solutes following frequent high water inputs

Investigation of factors affecting leaching patterns under tilled and no-till soils are important for successful modelling of solute leaching. There can be various other factors that may offset an anticipated tillage effect on solute leaching. A study was conducted in a Donnelly silty loam (fine-loamy, mixed frigid Typic Cryoboralf) at Dawson Creek, British Columbia, Canada, to investigate how a reactive chemical (FD&C blue#1 dye) and a conservative tracer (bromide, Br−) would leach in a no-till (NT) soil compared to a tilled (T), when high volume of water are provided discretely, at short time intervals. Three plots of 1.5 m × 1.5 m were prepared in each NT and T soil for flood irrigation. The chemicals were applied by spray using a knapsack sprayer. Soil cores were extracted from a maximum depth of 1.25 m using a truck mounted hydraulic soil sampler at 5, 19, and 55 days (S1, S2, and S3, respectively) after irrigating different amounts of water. These soil cores, sub-sampled at different depths, were analysed for water content, Br− and dye concentrations. The analyses indicated that Br− and dye moved in distinctive patterns in the two tillage systems. After irrigating with a total of 240 mm of ponded water in three applications over a period of 10 days, the centre of mass of the travel depth profiles for Br− was 0.15 m in the NT and 0.26 m in the T plots; for the dye, 0.27 m in the NT and 0.17 m in the T plots. At soil core sampling times S1, S2, and S3, the average mass recovered for Br− was 82%, 39%, and 27% in the NT and 78%, 50%, and 45% in the T plots. For the dye, mass recovery rates of 78%, 58%, and 22% were observed in the NT and 92%, 79% and 25% in the T plots. The increasing mass loss of Br− observed with increasing net water inputs in the two tillage systems was more likely due to a lateral loss with water than due to a leaching below sampling depth. The increasing mass loss of dye over time in the two tillage systems was more likely due to a high rate of degradation than to a loss through a lateral or vertical flow.