PREFERENTIAL TRANSPORT OF BROMIDE IN UNDISTURBED CORES UNDER DIFFERENT IRRIGATION METHODS

Bromide (Br-) column leaching studies were conducted to estimate solut e velocities and magnitude of preferential flow (ratio of solute to pi ston flow velocities) under pending and high intensity sprinkler metho ds. Twenty undisturbed Portneuf silt loam soil cores (250 mm x 300 mm) were collected at spatially distributed locations in a 0.81-ha corn f ield. The samples were divided into two sets of 10, and Br- leaching s tudies were conducted under pending and high intensity sprinkler metho ds. Analysis of the breakthrough curves (BTCs) indicated that preferen tial flow occurred under both methods in all of the samples. The peak and median solute velocities were 29-311% and 20-60%, respectively, la rger than corresponding piston flow velocities. Though the solute velo cities were larger under the pending method due to larger input flux v alues, the average magnitude of the preferential flow was similar betw een the two methods. The mobile-immobile model predicted the BTCs bett er than the convection-dispersion model, with an average mobile percen tage of 75 to 80. For the Portneuf silt-loam soil and given test condi tions, the assumption of peak solute arrival to a given depth based on piston flow is not valid because of large differences between the pea k and piston flow velocities. The large variabilities measured for pea k solute velocity under both methods indicate the importance of repeat ed field measurements for determination of both magnitude and level of uncertainty.