Nitrogen transport via surface and subsurface flow in an agricultural field

Abstract

Nitrogen in runoff waters and in soil was monitored in a clay field, in southern Finland. Subsurface drainage accounted for 51% of the total runoff (439 mm) and 79% of the total N losses (30 kg ha -1 ) in June 1994-December 1996. Nitrate nitrogen (NO 3 -N) formed 32-96% of the total N load. NO 3 -N in the subsurface drainage water rapidly increased from 2 to 60 mg l -1 after the sequence of fertilization and rainfalls. NO 3 -N in the soil water indicated prominent preferential flow from the top layer into the tile drains. Total N in the runoff waters remained below 5 mg l -1 during the snowmelt and below 10 mg l -1 in the autumn. In these seasons, the determining factor in N transport was the high water volumes of surface runoff and subsurface drainage. The preferential flow paths are likely caused by both macropores and the backfilled trenches above the tile drains.