Impact of Long‐Term Tillage Systems for Continuous Corn on Nitrate Leaching to Tile Drainage

Abstract

Information is lacking on the long‐term impact of tillage systems on NO 3 losses to surface and groundwater. An 11‐yr (1982–1992) study was conducted to assess NO 3 losses to subsurface, tile drainage for corn ( Zea mays L.) grown with continuous conventional tillage (CT) and no tillage (NT) on a poorly drained Webster clay loam soil (fine‐loamy, mixed, mesic Typic Haplaquoll) at Waseca, MN. Nitrogen was applied at an annual application rate of 200 kg ha −1 . Mean annual subsurface drain flow during the 11‐yr period was 35 mm higher for NT (315 ram) compared with CT (280 mm). Flow‐weighted nitrate‐nitrogen (NO 3 ‐N) concentrations increased dramatically in the wet years (1990 and 1991) following the dry period of 1987 to 1989. Flow‐weighted NO 3 ‐N concentrations during the 11‐yr period averaged 13.4 and 12.0 mg L −1 for CT and NT, respectively. Although subsurface drain flow was 12% higher with NT, NO 3 ‐N losses were about 5% higher with CT mainly due to higher NO 3 ‐N concentrations with CT in the last 2 yr. Corn grain yields and N removal were significantly higher in 6 out of 11 yr with CT compared with NT with no difference between tillage systems in the other 5 yr. Grain yields averaged 8.6 Mg ha −1 with CT and 7.3 Mg ha −1 with NT during the 11‐yr period. Multiple regression equations showed that annual flow‐weighted NO 3 ‐N concentration is best predicted from residual soil NO 3 in the 0‐ to 1.2‐m profile and spring rainfall while NO 3 ‐N flux can be predicted well from May and June rainfall. Results from this long‐term study indicate that on this poorly drained soil, CT had a positive effect on corn grain yield and N removal compared with NT, but tillage systems had minimal impact on NO 3 losses to subsurface drain flow. Higher drain flow with NT does not necessarily result in higher NO 3 ‐N fluxes lost via subsurface drainage.