Characteristics of Preferential Flow Paths and Their Impact on Nitrate Nitrogen Transport on Agricultural Land

Abstract

Preferential flow is important for solute transport in soil. This study aims to investigate distribution characteristics of preferential flow paths in agricultural land and to determine the effects of preferential flow on nitrate nitrogen transport. Dye tracer experiments were conducted on two farmland plots in Changping County, Beijing. Two undisturbed soil columns (with preferential flow) and two packed soil columns (without preferential flow) were used to determine the influence of preferential flow on nitrate nitrogen transport. The results showed greater nitrate nitrogen movement with a relatively higher velocity in the undisturbed soil columns, which is on average 2.31 times of that in the packed soil column. The breakthrough time of undisturbed soil columns was 12 h with 43% reduction compared with that of the packed soil columns. The preferential transport of NO3¯ in the undisturbed soil columns accounted for 43.83% of the total flux and resulted in a 97.60% accumulative leached mass for NO3¯ of the total mass. These results indicated that the preferential flow with a limited total flux ratio could lead to a large proportion of NO3¯ transport. Tailing phenomenon was observed and found to be a unique feature in the preferential flow’s breakthrough curve. Tailing might be caused by discrepancies between the preferential flow, matrix flow, and penetration rate during infiltration.