Chloride leaching in two Ontario soils: Measurement and prediction using HYDRUS-1D

Deterministic numerical modelling can often be used to complement and extend field results, and to provide extra insight into the mechanisms of water and solute movement within the profile of agricultural soils. Chloride leaching and near-surface soil water content in a Guelph loam and a Maryhill loam cropped to corn (Zea mays L.) were measured over a 12-mo period (October 2007 to September 2008) and simulated using the HYDRUS-1D numerical model (version 4.12). Field measurements and prediction indicated that over 70% of the applied chloride (Cl) was lost to deep drainage (below 80 cm depth) during the winter months (November 2007 to April 2008) in both soils. Normalized root mean square error (NRMSE) values for HYDRUS-1D estimates of near-surface (0- to 30-cm depth interval) soil water content over the growing season (April to September, 2008) were 28% for Guelph loam and 42% for Maryhill loam. The NRMSE value for estimated versus measured Cl mass remaining in the soil profile (0-80 cm depth interval) over the winter months was 17% for both soils. It was concluded that the HYDRUS- 1D model can provide reasonable predictions of near-surface soil water content and profile leaching losses of tracer solutes. Further work is required, however, to determine if the predictive ability of HYDRUS-1D might be improved by incorporating the effects of freeze-thaw cycles on soil hydraulic properties and solute leaching. Further study is also required to establish the model's ability to simulate the leaching behaviour of reactive solutes, such as nitrate, in agricultural soils.