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winter rye (Secale cereale l.) cover crop (rcc) has potential to reduce no 3 -n loss from corn (Zea mays l.) and soybean [Glycine max (l.) Merr.] fields. However, rcc effects on annual crop productivity and corn optimal n fertilization requirement are unclear. the objectives were to evaluate corn and soybean yield response to rcc and corn optimal n rate. treatments were no-rcc and rcc with six fertilizer n rates (0-225 kg n ha -1 ) applied to corn in a no-till corn-soybean (cs) rotation at four iowa sites in 2009 through 2011. the rcc biomass and n uptake was low, with a maximum of 1280 kg dry matter (dM) ha -1 and 26 kg n ha -1 , respectively. in the no-n control, the rcc reduced soil profile no 3 -n by 15 kg n ha -1 only at time of rcc control before corn planting. corn canopy sensing, plant height, and plant population indicated more n stress, reduced plant stand, and slower growth with rcc. the rcc reduced corn grain yield by 6% at the economic optimum n rate (eonr). the eonr was the same with no-rcc and rcc, but plant n uptake efficiency (Pue) was reduced at low n rates with rcc, but not above the eonr. soybean yield was not affected by rcc. results indicate n fertilization rate should be the same with or without rcc. improvement in rcc systems and management could make rcc a more viable practice within notill corn and soybean production.Abbreviations: CS, corn-soybean; DM, dry matter; EONR, economic optimum nitrogen rate; NDVI, normalized difference vegetative index; NUE, nitrogen use efficiency; PAN, plant available nitrogen; PUE, plant nitrogen uptake efficiency; RCC, rye cover crop; SOM, soil organic matter; YEONR, yield at economic optimum nitrogen rate. E nvironmental concerns related to crop N fertilization is an ongoing issue (USEPA, 2007), including reducing N in surface waters related to hypoxia in coastal surface waters Kladivko et al., 2014). Nitrogen application rate to corn is an important factor in regard to cropping system profitability and NO 3 loss. Applying only the optimal N rate will not stop NO 3 loss, nor necessarily achieve the drinking water standard (Lawlor et al., 2007). Successful development of agricultural systems that benefit water quality have to be more inclusive of several agricultural practices, rather than only N rate or timing (Hatfield et al., 2009). Therefore, additional in-field practices are needed to reduce NO 3 losses (Sainju and Singh, 2008).Nitrate losses in tile drainage water from corn production systems can range from 7 to 68 kg N ha -1 yr -1 (Lawlor et al., 2007), and with most values ranging from 29 to 56 kg N ha -1 yr -1 (Sawyer and Randall, 2008). Cover crops have shown potential for uptake of residual N from fertilizers or inorganic N released from degrading soil organic matter (SOM) in the period between annual crops (Strock et al., 2004;Tonitto et al.,

We evaluated the impacts of natural wetlands and various land uses on stream nitrogen concentration in two grassland-dominated catchments in eastern Hokkaido, Japan. Analyzing land use types in drainage basins, measuring denitrification potential of its soil, and water sampling in all seasons of 2003 were performed. Results showed a highly significant positive correlation between the concentration of stream NO3-N and the proportion of upland area in drainage basins in both catchments. The regression slope, which we assumed to reflect the impact on water quality, was 24% lower for the Akkeshi catchment (0.012 +/- 0.001) than for the Shibetsu catchment (0.016 +/- 0.001). In the Akkeshi catchment, there was a significant negative correlation between the proportion of wetlands in the drainage basins and stream NO3-N concentration. Stream dissolved organic nitrogen (DON) and carbon (DOC) concentrations were significantly higher in the Akkeshi catchment. Upland and urban land uses were strongly linked to increases in in-stream N concentrations in both catchments, whereas wetlands and forests tended to mitigate water quality degradation. The denitrification potential of the soils was highest in wetlands, medium in riparian forests, and lowest in grasslands; and was significant in wetlands and riparian forests in the Akkeshi catchment. The solubility of soil organic carbon (SOC) and soil moisture tended to determine the denitrification potential. These results indicate that the water environment within the catchments, which influences denitrification potential and soil organic matter content, could have caused the difference in stream water quality between the two catchments.