Corn (Zea mays L.) residue removal at high rates can result in negative impacts to soil ecosystem services. The use of cover crops could be a potential strategy to ameliorate any adverse effects of residue removal while allowing greater removal levels. Hence, the objective of this study was to determine changes in water erosion potential, soil organic C (SOC) and total N concentration, and crop yields under early-and lateterminated cover crop (CC) combined with five levels of corn residue removal after 3 years on rainfed and irrigated no-till continuous corn in Nebraska. Treatments were no CC, early-and late-terminated winter rye (Secale cereale L.) CC, and 0, 25, 50, 75, and 100% corn residue removal rates. Complete residue removal reduced mean weight diameter (MWD) of water-stable aggregates (5 cm depth) by 29% compared to no removal at the rainfed site only, suggesting increased water erosion risk at rainfed sites. Late-terminated CC significantly increased MWD of water-stable aggregates by 27 to 37% at both sites compared to no CC, but earlyterminated CC had no effect. The increased MWD with late-terminated CC suggests that CC when terminated late can offset residue removal-induced risks of water erosion. Residue removal and CC did not affect SOC and total soil N concentration. Particulate organic matter increased with lateterminated CC at the irrigated site compared to no CC. Complete residue removal increased irrigated grain yield by 9% in 1 year relative to no Ruis et al. in Bioenergy Res 2017 Can Cover Crop Use 2 removal. Late-terminated CC had no effect on corn yield except in 1 year when yield was 8% lower relative to no CC due to low precipitation at corn establishment. Overall, late-terminated CC ameliorates residue removalinduced increases in water erosion potential and could allow greater levels of removal without reducing corn yields in most years, in the short term, under the conditions of this study.

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Much of the previous evaluation of active crop canopy sensors for in-season assessment of crop N status has occurred in environments without water stress. Th e impact of concurrent water and N stress on the use of active crop canopy sensors for in-season N management is unknown. Th e objective of this study was to evaluate the performance of various spectral indices for sensing N status of corn (Zea mays L.), where spectral variability might be confounded by water-induced variations in crop refl ectance. Th e study was conducted in 2009 and 2010 with experimental treatments of irrigation level (100 and 70% evapotranspiration [ET]), previous crop {corn-corn or soybean [Glycine max (L.) Merr.]-corn} and N fertilizer rate (0, 75, 150, and 225 kg N ha -1 ). Crop canopy refl ectance was measured from V11 to R4 stage using two active sensors-a two band (880 and 590 nm) and a three band (760, 720, and 670 nm). Among the indices, the vegetation index described by near infrared minus red edge divided by near infrared minus red (DATT) and Meris terrestrial chlorophyll index (MTCI) were the least aff ected by water stress, with good ability to diff erentiate N rate with both previous crops. Th e chlorophyll index using amber band (CI), normalized diff erence vegetation index using red edge band (NDVI_RE) and the normalized vegetationi using the red band (NDVI_Red) showed more variation due to water supply, and had only moderate ability to diff erentiate N rates. ).Abbreviations: ACS, active crop canopy sensors; CC, irrigated corn aft er corn; CI, chlorophyll index vegetation index using amber and near infrared; CIRE, chlorophyll index vegetation index using red edge and near infrared; CS, irrigated corn aft er soybean; DATT, vegetation index calculated using near infrared, red edge, and red bands published by Datt (1999); ET, evapotranspiration; MTCI, Meris terrestrial chlorophyll index; NDVI_RE, normalized diff erence vegetation index using the red edge band; NDVI_Red, normalized diff erence vegetation index using the red band; NIR, near infrared; NSI, nitrogen suffi ciency index.

Core Ideas Polymer coated N fertilizer was effective in improving crop yields. Chemical inhibitors used in the study was not effective in reducing environmental N losses. Varieties of available different chemical inhibitors may act differently and need to be compared and contrasted. Nitrogen fertilizer modifications such as coating or chemical additives are designed to either slow or inhibit N transformation, thereby to improve grain yield (GY) and reduce N losses. Effectiveness of these specialized products depend on various factors including climate. This field trial compared effects of various fertilizer modifications in irrigated corn (Zea mays L.) in loamy sand in Nebraska. Urea–ammonia–nitrate (UAN), UAN with 30% methylene–urea (UAN–MU), split‐applied UAN‐MU (UAN–MU–SP) and polymer‐coated urea (PCU) were evaluated in 2009. In 2010 and 2011, UAN with nitrapyrin (UAN–IN) and nutrisphere (UAN‐NS) and PCU were evaluated. The PCU treatment consistently improved GY compared to other N treatments in all 3 yr irrespective of inter‐annual climatic variations. In 2009, a dry year, UAN–MU and UAN were not different but UAN–MU–SP increased GY, grain and total N uptake (GNU, TNU) compared to UAN and UAN–MU. In dry (2009) and wet (2011) years, residual N did not differ by N rate while it was the greatest in the highest N rate in 2010, a normal year. The UAN–IN and UAN–NS improved GY, GNU, and TNU compared to UAN in 2010. These treatments performed as well or better than UAN, even when the UAN rate was higher. In 2011 that had high potential for N leaching, UAN–IN and UAN–NS did not increase GY compared to UAN. In extreme weather conditions, chemical additives failed to improve performance of UAN, when N was all applied after corn emergence.

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