Abstract
AbstractA 49‐d field experiment monitoring water and solute movement through a structured sandy loam is reported. Two field plots, each 15 by 30 m2 in area were instrumented with a 3 by 6 grid of small lysimeters containing undisturbed soil. Each lysimeter was weighed before and after irrigation and had effluent concentrations and drainage volumes recovered periodically. At the beginning of the experiment a pulse of KBr was added to the field and lysimeters with a mechanical lawn spreader and was leached into the soil with three water irrigations per week. Each plot received the same amount of water per irrigation but at intensities of 5.5 and 9.5 mm/h. Effluent breakthrough curves were constructed for each lysimeter. Substantial indication of preferential flow through part of the wetted pore space was observed in each lysimeter and the average breakthrough curves reflected substantial bypass. A statistical analysis of the drainage concentrations as a function of time showed the two fieldwide breakthrough curves to be identical. This not only showed that no intensity effect was apparent for solute movement on these plots but also indicated that the plot areas were large enough to incorporate all of the field scale variability within them. A calculation of solute flux from each lysimeter showed no correlation between instantaneous drainage and instantaneous solute concentration. As a consequence, we were able to show that the traditional method of estimating field scale solute flux as the product of average drainage and average concentration was adequate to describe solute leaching below the fields. Thirty‐six soil cores were taken in the two plots at the conclusion of the experiment. The average concentration depth patterns were similar for the two treatments and showed evidence of movement to at least 1.2 m during the lifetime of the experiment, implying that preferential flow continued to occur to greater depths.
Published Version
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