Influence of no-till and a winter rye cover crop on nitrate losses from tile-drained row-crop agriculture in Iowa.

Artificial subsurface drainage is necessary to maintain agricultural production in the soils and climate of north-central Iowa. However, it can result in adverse environmental impacts, because it intercepts and diverts some water and soluble NO -N directly to streams. We investigated the impact of no-till and a winter rye cover crop (Secale cereale L.) on seasonal and annual NO -N concentration and loading in leachate from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. The eight treatments are chisel plow (CT), chisel plow with winter cereal rye (CTr), no-till (NT), and no-till with winter cereal rye (NTr), with "-C" indicating corn and "-S" indicating soybeans. Plots with artificial subsurface drainage were monitored for water quality from 2011 to 2015. The NT and CTr treatments consistently decreased NO -N loss on the seasonal and annual scales compared with CT. Compared with NT, NTr did not reduce NO -N loading nor concentration in leachate, probably because of low NO leaching potential from NT combined with low rye cover crop biomass throughout the study with NT. The 5-yr average annual NO -N concentrations were: 16.9 mg L with CT-S, 16.7 mg L with CT-C, 12.6 mg L with NT-S, 12.0 mg L with CTr-S, 11.8 mg L with CTr-C, 11.4 mg L with NTr-S and NTr-C, and 11.1 mg L with NT-C. Overall, both no-till and a cover crop showed potential for improving N management for water quality.