No abstract

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 NO3–N directly to streams. We investigated the impact of no‐till and a winter rye cover crop (Secale cereale L.) on seasonal and annual NO3–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 NO3–N loss on the seasonal and annual scales compared with CT. Compared with NT, NTr did not reduce NO3–N loading nor concentration in leachate, probably because of low NO3 leaching potential from NT combined with low rye cover crop biomass throughout the study with NT. The 5‐yr average annual NO3–N concentrations were: 16.9 mg L−1 with CT‐S, 16.7 mg L−1 with CT‐C, 12.6 mg L−1 with NT‐S, 12.0 mg L−1 with CTr‐S, 11.8 mg L−1 with CTr‐C, 11.4 mg L−1 with NTr‐S and NTr‐C, and 11.1 mg L−1 with NT‐C. Overall, both no‐till and a cover crop showed potential for improving N management for water quality.

No abstract

Subsurface drainage improves row crop production but also short circuits nitrate-nitrogen (NO 3-N) pathways in the soil with significant losses to surface waters. The objective of this study was to evaluate the effect of shallow, controlled, conventional, and undrained drainage treatments on depth to water table, drainage volume and NO 3-N loads, soil water content and storage in the soil profile, and crop yields. This research was conducted at the Iowa State University Southeast Research Farm near Crawfordsville, Iowa, from 2007 to 2015. We report on years five through nine here. The site consisted of eight large field plots with each of the four drainage treatments replicated twice. One-half of each plot was planted with corn (Zea mays L.) and the other half with soybeans (Glycine max [L.] Merr.). The corn and soybean halves were rotated every year in accordance with a typical corn-soybean rotation. The undrained treatment had a shallower water table than the other treatments and had a significantly higher number of days during the growing season when the water table was within 30 cm (12 in) of the ground surface than the other treatments. However, there was no difference in soil water contents in the top 80 cm (31.5 in) of the soil profile during the growing season between drainage treatments. Over the five-year study, controlled and shallow drainage reduced annual subsurface flows by 60% and 58%, respectively, while also reducing NO 3-N loads by 61% and 49%, respectively, as compared to the conventional drainage design. Crop yields were similar along the drainage designs but significantly lower in the undrained treatment. This study highlights the effectiveness of shallow and controlled drainage to reduce NO 3-N loads.

No abstract