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.

Impact of rye on soil temperature

In the U.S. Midwest, nitrate in subsurface tile drainage from corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] systems is detrimental to water quality at local and national scales. The objective of this replicated plot study in northwest Iowa, performed in 2015–2020, was to investigate the influence of nitrogen (N) fertilizer timing on crop production and NO3 load in subsurface (tile) drainage discharge. Four treatments applied to corn included fall anhydrous ammonia with a nitrification inhibitor (F), spring anhydrous ammonia (S), split‐banded urea at planting and mid‐vegetative growth (SS), and no N fertilizer (0N). Across crops and years, NO3–N concentration in subsurface drainage discharge was the same at 11.7 mg L–1 for F and S applied anhydrous ammonia (AA). The NO3–N concentration was statistically lower with SS urea (10 mg L–1) than F and S, and 0N was lower than SS at 8.3 mg L–1. Average annual NO3–N loads were not different between any treatments due to plot variability in drainage discharge. Corn responded to N application, with overall mean yield the same for F, S, and SS. There were no agronomic or water quality benefits for applying AA in spring compared with fall, where the F included a nitrification inhibitor and was applied to cold soils. Split‐applied urea had a small positive water quality impact but no crop yield enhancement. This study shows that there were improvements to NO3–N concentration in subsurface drainage discharge, but more nutrient reduction practices are needed than fertilizer N management alone to reduce nitrate load to surface water systems.

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ABSTRACT. Nutrient reduction strategies were developed and are being implemented across