N Losses in Tile Drainage
C. Kent Keller
In the semi-arid Palouse region, many lower-landscape positions have been tile drained to enhance crop yield. At Cook Agronomy Farm from 2000-2004 we monitored the discharge of a tile drain and a nearby profile of soil water for nitrate concentration ([NO3]), electrical conductivity level (EC), and water content to develop a conceptual framework describing soil nitrate occurrence and loss via subsurface pathways. Tile-drain baseflow [NO3] was consistently 4 mg-N L-1 and baseflow EC was 200 - 300 µS cm-1. Each year sudden synoptic increases in tile-drain discharge and [NO3] occurred in early winter following approximately 150 mm of fall precipitation, which saturated the soil and mobilized high-[NO3] soil water throughout the profile. The greatest tile-drain [NO3] (20-30 mg-N L-1) occurred approximately contemporaneous with greatest tile-drain discharges. The EC decrease each year (to about 100 µS cm-1) during high discharge, a dilution effect, lagged approximately one month behind the first appearance of high [NO3] and was consistent with advective transport of low-EC water from the shallow profile under saturated conditions. Water-budget considerations and temporal [NO3] patterns suggest that these processes deliver water to the tile drain from both lower- and upper-slope positions, the latter via lateral flow during the high-flow season. Management practices that reduce the fall reservoir of soil nitrate might be effective in reducing N loading to streams and shallow groundwater in this region.
A tile-drained catchment at the Cook Agronomy Farm. Elevations are masl, contour interval is 2.5 m. NW-SE-running crop-rotation sections are delineated by light double lines. Drain line position is approximate. Bulls-eye symbol indicates location of drain outlet with nearby time domain reflectometry and soil water sampling instrumentation, installed via a backhoed trench.
Data for the four-year study period. a) Event and cumulative daily precipitation by water year (Oct-Sept). Vertical arrows indicate time of cumulation of 150 mm of fall precipitation (pptn). Co-incident onset of high-flow season is evident in the discharge hydrograph for a 660-ha catchment (grayscale) containing the Cook Farm. b) Tile drain (TD) discharge rate and 48-h mean soil volumetric water content at selected depths; c) Tile drain nitrate concentration and nitrate-corrected electrical conductivity (EC), with solid vertical bars showing times of 150-mm precipitation accumulation from panel a.
Heading using the h3tag
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.