Nitrogen fertilizer and herbicide transport from tile drained fields

Offsite transport of N fertilizers and pesticides through subterranean drai nage pipes (tiles) has been linked to surface water contamination in the U. S. Corn Belt. This study was conducted from water years 1995 to 1997 to eva luate N export From two tile systems (Tiles a and B) in adjacent Gelds [in seed corn-soybean rotation (Zea mays L.-Glycine nax (L,) Merr.)] in respons e to timing and form of N application In addition, during the 1997 water ye ar; concentrations of two herbicides were determined on grab samples to rel ate bile herbicide losses with field application rates. During the 1995 and 1996 water years, Tile A exported approximately 20% more N per unit area t han Tile B; however, during the 1997 water year. Tile A exported nearly 70% more N, This result was partly caused by the leaching of 142 kg of NH4+-N following a winter application of (NH4)(2)SO4 fertilizer in the drainage ar ea of Tile A. The fertilizer was applied on top of 10 cm of snow, and withi n 4 d, a series of afternoon melting events began. We hypothesize that incr eased tile now rates mere caused by rapid infiltration of melt water throug h partially frozen soil (Drummer silty clay loam, fine-silty, mixed mesic T ypic Haplaquolls) that allowed the NH4+ ion to bypass the soil matrix (conc , reached 278 mg NH4+-N L-1). The incidence of elevated concentrations of N fertilizer and herbicides in tiles during high now events following agrich emical application indicated rapid water transport via preferential Oo uc p aths, thereby limiting the contact of these solutes with the sop.