Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/1999
Publication Date: 12/29/2000
Interpretive Summary: Field experiments were conducted at the Willsboro Research farm of Cornell University, Ithaca, New York, to determine the impact of preferential flow on the transport of agricultural chemicals. Prior to this investigation, it has been assumed that pesticides, having a strong affinity for the soil, would exhibit reduced mobilities relative to mobile non-adsorbed chemicals. .Unfortunately, the impact of preferential flow, a common field-scale transport process, on the relative movement of mobile and adsorbed chemicals is unknown. Bromide was used to mimic the transport behavior of nitrate (non-adsorbing chemicals) while rhodamine WT was used to mimic pesticide transport (adsorbing chemicals). A tile drain monitoring facility (depth 0.9 m) was used so that the mass of each chemical applied could be accurately determined. The results show that both non-adsorbing and adsorbing tracers, which were co-applied, arrived at the tile drain at the same time. This indicates that the water dynamics of preferential flow paths dominate the initial phase of contaminant transport regardless of the affinity of the applied chemicals to the soil matrix.
Technical Abstract: Field experiments were conducted by using a tile drain monitoring facility to determine the impact of preferential flow on the transport of adsorbing and non-adsorbing tracers at the Willsboro Research Farm of Cornell University. Simulated rainfall with 7.5 mm h**-1 intensity and 7.5 h duration was applied to a 18 x 65 m no-till plot. After 72 min of irrigation, a pulse of bromide and rhodamine WT was uniformly applied through irrigation and, four hours later, a second pulse of chloride and rhodamine WT was applied. The breakthrough of these tracers were measured by sampling the tile buried at 0.9 m. The same experiments were repeated in an adjacent conventional-till plot, except the rainfall intensity was reduced to 5 mm h**-1 to minimize surface runoff. The results showed that both the non-adsorbing and the adsorbing tracers applied in the same pulse arrived at the tile line at the same time and their breakthrough curves peaked at the same time. This suggested that water dynamics of preferentia flow paths dominated the initial phase of the contaminant transport, regardless of the retardation properties of contaminants.