Content area
Full text
Improving field-crop use of fertilizer nitrogen is essential for protecting water quality and increasing crop yields. The objective of this study was to determine the effectiveness of controlled tile drainage (CD) and controlled tile drainage with subsurface irrigation (CDS) for mitigating off-field nitrate losses and enhancing crop yields. The CD and CDS systems were compared on a clay loam soil to traditional unrestricted tile drainage (UTD) under a corn (Zea Mays L.)-soybean (Glycine Max. (L.) Merr.) rotation at two nitrogen (N) fertilization rates (N1: 150 kg N ha^sup -1^ applied to corn, no N applied to soybean; N2: 200 kg N ha^sup -1^ applied to corn, 50 kg N ha^sup -1^ applied to soybean). The N concentrations in tile flow events with the UTD treatment exceeded the provisional long-term aquatic life limit (LT-ALL) for freshwater (4.7 mg N L^sup -1^) 72% of the time at the N1 rate and 78% at the N2 rate, whereas only 24% of tile flow events at N1 and 40% at N2 exceeded the LT-ALL for the CDS treatment. Exceedances in N concentration for surface runoff and tile drainage were greater during the growing season than the non-growing season. At the N1 rate, CD and CDS reduced average annual N losses via tile drainage by 44 and 66%, respectively, relative to UTD. At the N2 rate, the average annual decreases in N loss were 31 and 68%, respectively. Crop yields from CDS were increased by an average of 2.8% relative to UTD at the N2 rate but were reduced by an average of 6.5% at the N1 rate. Hence, CD and CDS were effective for reducing average nitrate losses in tile drainage, but CDS increased average crop yields only when additional N fertilizer was applied.
Abbreviations: CD, controlled tile drainage; CDS, controlled tile drainage with subsurface irrigation; FWM, flow-weighted mean; LT-ALL, long-term aquatic life limit; UTD, unrestricted tile drainage.
SUBSURFACE tile drains in humid temperate regions are installed to remove excess soil water from agricultural fields so that crop productivity is not unduly compromised by poor soil aeration or untimely agronomic operations. Tile drains also remove excess soil water during the non-cropping season, however, and nitrate leaching losses via tile drainage during the non-cropping period can impair surface and...