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Identifying the most profitable crop rotation for an area is a continuous research challenge. The objective of this study was to evaluate 2‐, 3‐, and 4‐yr limited irrigation corn (Zea maysL.)‐based crop rotations for grain yield, available soil water, crop water productivity, and profitability in comparison with 1 yr continuous corn (CC). A field study was conducted from 2001 through 2010 on a deep silt loam soil near Tribune, KS. The study consisted of four crop rotations, that is, CC, corn–winter wheat (Triticum aestivumL.) (C–W), corn–winter wheat–grain sorghum (Sorghum bicolorL.) (C–W–Gs), and corn–winter wheat–grain–sorghum–soybean [Glycine max(L.) Merr.] (C–W–Gs–Sb) with irrigation limited to 254 mm annually. Grain yield of corn from the CC rotation was significantly lower, on average by 2.5 Mg ha−1, than corn yield from the other three rotations mainly due to difference in irrigation level. However, the mean yield of CC over one cycle of rotation [∼10.2 Mg (ha rotation‐cycle)−1] was significantly greater than mean corn equivalent grain yield of the other three rotations over one cycle of each rotation. Seasonal soil water usage from upper depths of the soil profile was significantly greater for CC. In this study, average crop water productivity [16.6 kg (mm ha)−1] and profitability of the CC rotation were also greater than in the other rotations. In selecting profitable rotations, producers should consider crop yield potential and value in addition to resilience. Core IdeasThis research compares four corn‐based rotations from yield, resource use, and impact on environment which are crucial to cropping decision and consultingSecond it addresses an area of limited water irrigation condition in which research outputs are rare. Dryland and irrigated conditions are relatively well covered, but cropping decision when there is resource which is more than dryland but less than full irrigation is not well addressed. This research result contributes to that.Third, this research is based on long‐term data that address yield of major crops (corn, wheat, sorghum, and soybean) and water use of these crops at every 30 cm of rooting depth. This information will continuously be used by researchers looking for such a data for modeling and other purposes. This research compares four corn‐based rotations from yield, resource use, and impact on environment which are crucial to cropping decision and consulting Second it addresses an area of limited water irrigation condition in which research outputs are rare. Dryland and irrigated conditions are relatively well covered, but cropping decision when there is resource which is more than dryland but less than full irrigation is not well addressed. This research result contributes to that. Third, this research is based on long‐term data that address yield of major crops (corn, wheat, sorghum, and soybean) and water use of these crops at every 30 cm of rooting depth. This information will continuously be used by researchers looking for such a data for modeling and other purposes.

Dairy manure is often applied to cropped soils as a substitute for inorganic N fertilizers, but the impacts of manure on soil trace gas fluxes, yields, and soil N are uncertain in the semiarid western United States. Soil carbon dioxide (CO2–C), methane (CH4–C), nitrous oxide (N2O–N), and ammonia (NH3–N) emissions were monitored using surface chambers from five N treatments: (i) partially composted solid dairy manure (DM) (412 kg N ha−1), (ii) DM + AgrotainPlus (DM+AP), (iii) enhanced efficiency N fertilizer (SuperU [SU]) (179 kg N ha−1), (iv) urea (179 kg N ha−1), and (v) check (no N applied), to determine their effect on growing season (GS) and nongrowing season emissions from a tilled clay loam soil under irrigated, continuous corn production for 3 yr. SuperU and AgrotainPlus contain urease and nitrification inhibitors. Averaged over years, GS soil CO2–C emissions were greater for DM and DM+AP than for urea, SU, and check treatments due to the large amount of C added with the manure; CH4–C emissions did not vary among N treatments; and N2O–N emissions decreased in the order urea = DM = DM+AP > SU > check. AgrotainPlus added to the DM did not reduce N2O–N emissions compared with DM. Cumulative NH3–N emissions after manure application decreased in the order urea > SU > check, with no significant differences between SU, DM, and DM+AP. Dairy manure provided slow‐release N with nitrate intensities lower than urea and N2O–N emissions similar to urea. These results highlight the importance of best‐management practices such as immediate irrigation after N application and use of urease and nitrification inhibitors to minimize N losses. Nitrification inhibitor mixed with manure did not reduce N2O emissions.Dairy manure provided a slow‐release N with nitrate intensities lower than urea.Delayed irrigation can increase ammonia losses from urea and affect subsequent N2O emissions.Urea formulated with nitrification inhibitor can reduce N2O emissions.

Manure can substitute for inorganic N fertilizers and can mitigate potential soil deterioration under irrigated corn (Zea maysL.) silage production, but the impact on yields, soil C and N have not been thoroughly studied in the semiarid western United States. Five N source treatments (dairy manure [DM, 412 kg N ha−1], DM + AgrotainPlus [DM+AP], SuperU [SU, 179 kg N ha−1], urea [179 kg N ha−1], and control [no N applied]) were studied (3 yr) to determine effects on silage and grain yields, N uptake, and changes in soil properties (soil organic carbon [SOC], total soil nitrogen [TSN], nitrate‐nitrogen [NO3–N], and soil test phosphorus [STP]) in an irrigated, conventionally‐ tilled clay loam soil under continuous corn silage production. Silage, grain, and stover yields and N uptake were greater with N application than control, with no difference between DM, DM+AP, urea, and SU. Fall soil NO3–N was greater with N application than control (0–90‐cm depth), but lower with DM than for SU (0–180‐cm depth). Soil test P was seven times greater with DM than with inorganic P after 3 yr. The SOC and TSN were strongly related to root and DM inputs, increasing with DM application but decreasing or remaining constant for SU, urea, and control treatments. Dairy manure is a valuable source of C, N, and P for irrigated tilled corn silage production with minimal NO3–N leaching or excessive soil P after 3 yr and can ameliorate residue removal and tillage impacts.

Corn (Zea maysL.) stover removal can increase yields under no‐till (NT) in climates where cold spring soil temperatures delay emergence and plant growth. The study objective was to evaluate partial stover removal (PR) effects on irrigated NT corn grain and stover yields, N uptake, and changes in soil organic carbon (SOC) and total soil nitrogen (TSN) compared to full stover retained (FR) under three N treatments on a clay loam soil. Stover removal (average 66%) increased early spring soil temperatures and enhanced early plant development compared to FR. Grain and stover yields increased with increasing N rate, as did plant N and C uptake, but varied with stover treatment. Averaged over N rate, grain yields were greater with PR than FR, but stover yields were lower with PR than FR. The C/N ratio of stover declined with increasing N rate. Nitrogen fertilization did not significantly influence SOC and TSN stocks after 7 yr. Averaged over N rates, PR removal decreased SOC 2.4 Mg SOC ha−1, but FR increased SOC 6.8 Mg SOC ha−1in 0‐ to 30‐cm soil depth. TSN stocks increased significantly with FR (1176 kg N ha−1) but not with PR (70 kg N ha−1). These results suggest that continued, long‐term residue removal will negate any initial yield benefits from more rapid early spring plant development. Partial stover removal as a cellulosic feedstock at the levels we used for ethanol production would negatively impact soil quality under irrigated, NT corn production in Colorado.

Nitrogen rate studies were conducted under furrow‐irrigated corn (Zea maysL.) production on a silty clay soil to compare granular urea with polymer‐coated urea (PCU) and stabilized urea (SU, contains urease and nitrification inhibitors) effects on corn yields, plant N uptake, and N use efficiency. Polymer‐coated urea had a yield advantage over urea 2 (continuous corn) of 3 yr at N rates below maximum yield, which resulted in greater economic returns with PCU (4–14%) at N rates from 168 to 280 kg N ha−1. The SU fertilizer had no yield or economic advantage over urea. Grain and stover yields and N uptake increased with increasing N rate for all N sources. Expressing grain yields from all N sources as a linear‐plateau function of N rate showed that yields were maximized at 14.3 Mg ha−1at an N rate of 254 kg N ha−1or available N level (soil NO3–N plus fertilizer N) of 295 kg N ha−1. Nitrogen recovery efficiency (RE) tended not to vary with N rate, with no differences between SU and urea but greater RE (19%) with PCU than urea under continuous corn. Fertilizer N use efficiency did not vary with N rate but was greater for PCU (36%) than for urea (32%) under continuous corn. In contrast to SU, PCU provided grain yield and potential economic advantages over urea under continuous corn production at N rates below those needed with urea for maximum grain yield.

Enhanced‐efficiency N fertilizers (EENFs) have potential for mitigating N2O emissions from N‐fertilized cropping systems. Stabilized EENFs contain nitrification and/or urease inhibitors. Slow‐release EENFs contain N components that are slowly released with variable release rates. Controlled‐release EENFs release N at more predictable rates. The effectiveness of several EENFs in reducing soil N2O emissions from a clay loam soil under irrigated, corn (Zea maysL.)‐based production systems in Colorado (2002–2012) was investigated. A controlled‐release, polymer‐coated urea, ESN, reduced N2O emissions by 42% compared with urea and 14% compared with urea–NH4NO3solution (UAN) in no‐till and strip‐till environments, but had no effect in a conventional tillage environment. A stabilized urea source, SuperU, reduced N2O emissions by 46% compared with urea and 21% compared with UAN. A stabilized UAN source, UAN + AgrotainPlus, reduced N2O emissions by 61% compared with urea and 41% compared with UAN alone. A slow‐release UAN source, UAN + Nfusion, reduced N2O emissions by 57% compared with urea and 28% compared with UAN. Urea–NH4NO3reduced N2O emissions by 35% compared with urea. A linear increase in N2O emissions with increasing N rate was observed for untreated urea and UAN. Developers of management protocols to reduce N2O emissions from irrigated cropping systems in semiarid areas can use this information to estimate reductions in N2O emissions when EENFs are used. Policymakers can use this information to help determine financial credits needed to encourage producers to use these technologies in their crop production systems.

Conventional tillage (CT) with high N rates and irrigation is used more frequently than no‐till (NT) for growing continuous corn (Zea maysL.) in the central Great Plains of the United States. The objective of this study was to evaluate soil organic C (SOC) stocks throughout the soil profile as well as the potential for maintaining or sequestering SOC within the soil profile (0– 120 cm) under irrigated, continuous corn as affected by NT and CT and three N rates. Isotopic δ13C techniques provided information about the fate of C added to soil by corn (C4–C) and of residual C3–C from cool‐season plants grown before this study. Relative contributions of C4–C and C3–C to SOC stocks after 8 yr were determined. Retention of C4–C from corn was measured under NT and CT. Nitrogen fertilization slowed losses of C3–C and improved retention of C4–C. No‐till was superior to CT in maintaining SOC. Deep soil sampling to 120 cm and the use of stable C isotope techniques allowed evaluation of changes in SOC stocks during the 8‐yr period. Change in SOC under NT vs. CT resulted from greater loss of C3–C stocks under CT throughout the soil profile. Irrigated corn has a low potential to sequester SOC in the central Great Plains, especially under CT. The results of this study indicate that stability of the soil organic matter and its perceived “recalcitrance” is altered by environmental and biological controls.

Limited information is available on how N fertilizer placement affects soil nitrous oxide (N2O) emissions under irrigated conditions in the semiarid western United States. Our objective was to compare surface banding near corn row and broadcasting of three N sources (urea, polymer‐coated urea [PCU], and stabilized urea [SU] containing urease and nitrification inhibitors) on N2O emissions from a clay loam soil under sprinkler‐irrigated continuous corn production. The N fertilizers were applied at a rate of 202 kg N ha−1to strip‐till (2010 and 2011) and no‐till (2011) corn at crop emergence, with ∼19 mm irrigation water applied the next day. Band‐applied N had a 1.46‐fold greater N2O emission than broadcast N averaged over N sources and three studies. Soil N2O–N emissions from urea were 1.48‐ and 1.74‐fold greater than from PCU and SU, respectively, when averaged over N placement and studies. The N placement × source interaction was not significant. Averaged across studies, grain yield and N uptake did not vary with N placement, whereas grain yields were greater for SU than PCU but were not different from urea. Nitrous oxide emissions per unit of N applied, per unit of grain yield, and per unit N uptake were 59, 49, and 47% greater, respectively, with banded than with broadcast N fertilizer. These studies show that N placement and N source selection are important manageable factors that can affect N2O emissions and need to be considered when developing N2O mitigation practices in irrigated cropping systems in the semiarid western United States.

Ammonia (NH3) volatilization is one of the main pathways of N loss from agricultural cropping systems. This study evaluated the NH3–N loss from four urea‐based N sources (urea, urea–ammonium nitrate [UAN], SuperU, and ESN [polymer‐coated urea]) surface band applied at a rate of 200 kg N ha−1to irrigated, strip‐till corn production systems for 2 yr using semi‐static chambers (semi‐open and open) to measure NH3–N loss. The efficiency of the semi‐static chambers in estimating NH3–N loss under field conditions was determined using 15N labeled urea applied at rates of 50, 100, and 200 kg N ha−1. Both chamber types had similar NH3–N recoveries and calibration factors. Immediate irrigation with 16 to 19 mm of water 1 d after N fertilization probably limited NH3–N volatilization from surface‐applied N fertilizers to a range of 0.1 to 4.0% of total N applied. SuperU, which contains a urease inhibitor, had the lowest level of NH3–N loss when compared to the other N sources. Analyzed across years, estimated NH3–N losses for the N sources were in the order: ESN = UAN > urea > SuperU. Both years the results showed that measurement time may need to be increased to evaluate NH3–N volatilization from polymer‐coated urea N sources such as ESN. The open‐chamber method was a viable, low cost method for estimating NH3–N loss from small field plot N studies.

Limited irrigation management practices are being used in the Central Great Plains to conserve water by optimizing crop water use efficiency. Limited irrigation may reduce total crop biomass production and amount of crop residue returned to the soil. Crop residue production within four no‐till (NT) crop rotations [continuous corn (Zea maysL.) (CC); corn–winter wheat (Triticum aestivumL.) (CW); corn–winter wheat–grain sorghum (Sorghum bicolorL. Moench) (CWS); corn–winter wheat–grain sorghum–soybean [Glycine max(L.) Merr.] (CWSSb)] was measured and changes in soil organic carbon (SOC) and total soil nitrogen (TSN) stocks were monitored for 10 yr. Crop residue yields varied with crop being produced and with rotation, as did residue N and C returned to the soil. The C/N ratio of the residue varied with crop. The SOC and TSN pools increased with time in all rotations. The rate of gain in SOC and TSN mass for each rotation was 717, 477, 335, and 270 kg SOC ha−1yr−1and 114, 92, 87, and 84 kg TSN ha−1yr−1for the CC, CW, CWS, and CWSSb rotations, respectively, in the 0 ‐ to 30.5‐cm soil depth. The rate of change in SOC and TSN mass was lowest with CWSSb (8.7 Mg residue ha−1yr−1) and highest with CC (12.0 Mg residue ha−1yr−1). Approximately 6.8 to 7.6 Mg residue ha−1yr−1would be needed to maintain SOC stocks under limited irrigation.

A nitrogen (N) source comparison study was conducted to further evaluate the effects of inorganic N source and placement on growing‐season and non‐crop period soil nitrous oxide (N2O). Commercially available controlled‐release N fertilizers were evaluated for their potential to reduce N2O emissions from a clay loam soil compared with conventionally used granular urea and urea‐ammonium nitrate (UAN) fertilizers in an irrigated no‐till (NT) corn (Zea maysL.) production system. Controlled‐release N fertilizers evaluated were: a polymer‐coated urea (ESN), stabilized urea (SuperU), and UAN+AgrotainPlus (SuperU and AgrotainPlus contain nitrification and urease inhibitors). Each N source was surface band applied (202 kg N ha−1) near the corn row at emergence and watered into the soil the next day. Subsurface banded ESN (ESNssb) and check (no N applied) treatments were included. Nitrous oxide fluxes were measured during two growing seasons and after harvest using static, vented chambers. All N sources had significantly lower growing‐season N2O emissions than granular urea (0.7% of applied N), with UAN+AgrotainPlus (0.2% of applied N) and ESN (0.3% of applied N) having lower emissions than UAN (0.4% of applied N). Similar trends were observed when expressing N2O emissions on a grain yield and N uptake basis. Corn grain yields were not different among N sources but were greater than the check. Selection of N fertilizer source can be a mitigation practice for reducing N2O emissions in NT, irrigated corn in semiarid areas. In our study, UAN+AgrotainPlus consistently had the lowest level of N2O emissions with no yield loss.

Nitrogen (N) application to crops generally results in increased nitrous oxide (N2O) emissions. Commercially available, enhanced‐efficiency N fertilizers were evaluated for their potential to reduce N2O emissions from a clay loam soil compared with conventionally used granular urea and urea‐ammonium nitrate (UAN) fertilizers in an irrigated strip‐till (ST) corn (Zea maysL.) production system. Enhanced‐efficiency N fertilizers evaluated were a controlled‐release, polymer‐coated urea (ESN), stabilized urea, and UAN products containing nitrification and urease inhibitors (SuperU and UAN+AgrotainPlus), and UAN containing a slow‐release N source (Nfusion). Each N source was surface‐band applied (202 kg N ha−1) at corn emergence and watered into the soil the next day. A subsurface‐band ESN treatment was included. Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. All N sources had significantly lower growing season N2O emissions than granular urea, with UAN+AgrotainPlus and UAN+Nfusion having lower emissions than UAN. Similar trends were observed when expressing N2O emissions on a grain yield and N uptake basis. Loss of N2O–N per kilogram of N applied was <0.8% for all N sources. Corn grain yields were not different among N sources but greater than treatments with no N applied. Selection of N fertilizer source can be a mitigation practice for reducing N2O emissions in strip‐till, irrigated corn in semiarid areas.

Converting to no‐till (NT) production can affect N requirements for optimizing corn (Zea maysL.) yields while enhancing soil organic carbon (SOC) and N levels. Nitrogen fertilization impacts on irrigated, NT continuous‐corn grain, stalk, cob, and stover yields, stover C and N uptake, and C/N ratios were evaluated for 11 yr on a clay loam soil. Changes in SOC and total soil nitrogen (TSN) were also monitored. Grain, stalk, cob, and stover yields increased with increasing N rate, as did N and C uptake. The C/N ratio of stalk residue declined with increasing N rate, but cob C/N ratio was not affected, with an average stover C/N ratio of 68 at the highest N rate. Nitrogen fertilization increased SOC and TSN levels with average SOC and TSN mass rate gains with N application of 0.388, 0.321, and 0.160 Mg SOC ha−1yr−1and 0.063, 0.091, and 0.140 Mg TSN ha−1yr−1in the 0‐ to 7.6‐, 0‐ to 15.2‐, and 0‐ to 30.4‐cm soil depths, respectively. The SOC and TSN mass rate changes were lower without N application. Increases in TSN appeared to be more rapid than SOC, resulting in a decline in the soil C/N ratio with time. Under irrigated, NT continuous corn production, N fertilization optimized grain and residue yields, with the enhanced benefit of increased SOC and TSN levels in the semiarid central Great Plains. Removal of cobs or partial stover residue as a cellulosic feedstock for ethanol production appears possible without negative effects on soil quality under irrigated, NT corn production.

Conventional plow tillage (CT) is a common soil management practice under irrigated continuous corn (Zea maysL.) in the semiarid central Great Plains that requires a relatively high N fertilizer rate to optimize grain yield and economic returns. This study investigated how four rates of N input (0, 67, 101, and 224 kg N ha−1) under irrigated CT management affects aboveground corn production, stover characteristics, and crop biomass. We also examined soil quality parameters under these treatments, including total soil carbon (TSC) and soil particulate organic matter (POM), soil organic carbon (SOC) and total soil nitrogen (TSN) stocks in the 0‐ to 7.6‐, 0‐ to 15.2‐, and 0‐ to 30.4‐cm soil depths of a clay loam soil. Nitrogen fertilization significantly increased corn grain, stalks, cob and stover yields as well as C and N content of the biomass. The C/N ratios of stalks and stover decreased with increasing N rate, but cob C/N ratios did not change. Increasing N rate increased TSN concentration in 0‐ to 7.6‐ and 7.6‐ to 15.2‐cm depths and decreased C/N ratio in all soil layers between 1999 and 2008. We found no significant change in SOC and POM‐C stocks under increasing N fertilizer addition after 10 yr of irrigated, CT continuous corn despite higher stover yields, and the stover C and N returned to the soil after harvest with increasing N rate. The lack of increased SOC storage with increasing residue C inputs suggests that decomposition processes controlled the SOC stocks.

Nitrogen fertilization is essential for optimizing crop yields; however, it may potentially increase nitrous oxide (N2O) emissions. The study objective was to assess the ability of commercially available enhanced‐efficiency N fertilizers to reduce N2O emissions following their application in comparison with conventional dry granular urea and liquid urea‐ammonium nitrate (UAN) fertilizers in an irrigated no‐till (NT) corn (Zea maysL.) production system. Four enhanced‐efficiency fertilizers were evaluated: two polymer‐coated urea products (ESN and Duration III) and two fertilizers containing nitrification and urease inhibitors (SuperU and UAN+AgrotainPlus). Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. Enhanced‐efficiency fertilizers significantly reduced growing‐season N2O‐N emissions in comparison with urea, including UAN. SuperU and UAN+AgrotainPlus had significantly lower N2O‐N emissions than UAN. Compared with urea, SuperU reduced N2O‐N emissions 48%, ESN 34%, Duration III 31%, UAN 27%, and UAN+AgrotainPlus 53% averaged over 2 yr. Compared with UAN, UAN+AgrotainPlus reduced N2O emissions 35% and SuperU 29% averaged over 2 yr. The N2O‐N loss as a percentage of N applied was 0.3% for urea, with all other N sources having significantly lower losses. Grain production was not reduced by the use of alternative N sources. This work shows that enhanced‐efficiency N fertilizers can potentially reduce N2O‐N emissions without affecting yields from irrigated NT corn systems in the semiarid central Great Plains.

Crop biomass has been proposed as a source stock for bioethanol production. Levels of crop residue removal must be determined to prevent degradation of soil physical and chemical properties resulting from soil organic carbon (SOC) loss. Carbon inputs from crop residues and an estimate of inputs from roots and rhizodeposition (Creturn) were calculated and compared with changes in SOC after seven cropping seasons at Akron, CO. Tillage treatments included a chisel plow (CP) and a no‐till (NT) treatment. A crop rotation alternating grasses and broadleaf crops was compared with continuous corn (Zea maysL.). Irrigation treatments included water application to meet evapotranspiration demand or application only during the reproductive stage of each crop. Total Creturnvaried from 25 Mg ha−1for the delayed irrigation, crop rotation plots to 63 Mg ha−1for the fully irrigated, continuous corn plots. The change in SOC in the surface 30 cm of soil varied from −0.8 Mg SOC ha−1for the rotation plots to a gain of 2.8 Mg ha−1for the continuous corn plots after 7 yr. Correlating crop residue input with change in SOC showed that about 4.6 Mg ha−1yr−1Creturnis needed to maintain SOC levels for NT cropping systems and an average of 7.4 Mg ha−1yr−1Creturnis needed to maintain SOC levels under chisel tillage. Continuous corn was the only system that consistently provided sufficient crop residue to maintain SOC levels. Residue removal for off‐farm use should consider only amounts that can be harvested without decreasing SOC levels.

Recent soil and crop management technologies have potential for mitigating greenhouse gas emissions; however, these management strategies must be profitable if they are to be adopted by producers. The economic feasibility of reducing net greenhouse gas emissions in irrigated cropping systems was evaluated for 5 yr on a Fort Collins clay loam soil (a fine‐loamy, mixed, superactive, mesic Aridic Haplustalf). Cropping systems included conventional tillage continuous corn (Zea maysL.) (CT‐CC), no‐till continuous corn (NT‐CC), and no‐till corn–bean (NT‐CB) including 1 yr soybean [Glycine max(L.) Merr.] and 1 yr dry bean (Phaseolus vulgarisL.). The study included six N fertilization rates ranging from 0 to 246 kg ha−1Results showed highest average net returns for NT‐CB, exceeding net returns for NT‐CC and CT‐CC by US$182 and US$228 ha−1, respectively, at economically optimum N fertilizer rates. Net global warming potential (GWP) generally increased with increasing N fertilizer rate with the exception of NT‐CC, where net GWP initially declined and then increased at higher N rates. Combining economic and net GWP measurements showed that producers have an economic incentive to switch from CT‐CC to NT‐CB, increasing annual average net returns by US$228 ha−1while reducing annual net GWP by 929 kg CO2equivalents ha−1The greatest GWP reductions (1463 kg CO2equivalents ha−1) could be achieved by switching from CT‐CC to NT‐CC while also increasing net returns, but the presence of a more profitable NT‐CB alternative means NT‐CC is unlikely to be chosen without additional economic incentives.

Nitrogen fertilization is essential for optimizing crop yields; however, it increases N2O emissions. The study objective was to compare N2O emissions resulting from application of commercially available enhanced‐efficiency N fertilizers with emissions from conventional dry granular urea in irrigated cropping systems. Nitrous oxide emissions were monitored from corn (Zea maysL.) based rotations receiving fertilizer rates of 246 kg N ha−1when in corn, 56 kg N ha−1when in dry bean (Phaseolus vulgarisL.), and 157 kg N ha−1when in barley (Hordeum vulgareL. ssp. vulgare). Cropping systems included conventional‐till continuous corn (CT‐CC), no‐till continuous corn (NT‐CC), no‐till corn–dry bean (NT‐CDb), and no‐till corn–barley (NT‐CB). In the NT‐CC and CT‐CC systems, a controlled‐release, polymer‐coated urea (ESN) and dry granular urea were compared. In the NT‐CDb and NT‐CB rotations, a stabilized urea source (SuperU) was compared with urea. Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. Cumulative growing season N2O emissions from urea and ESN application were not different under CT‐CC, but ESN reduced N2O emissions 49% compared with urea under NT‐CC. Compared with urea, SuperU reduced N2O emissions by 27% in dry bean and 54% in corn in the NT‐CDb rotation and by 19% in barley and 51% in corn in the NT‐CB rotation. This work shows that the use of no‐till and enhanced‐efficiency N fertilizers can potentially reduce N2O emissions from irrigated systems.

Long‐term effects of tillage intensity, N fertilization, and crop rotation on carbon dioxide (CO2) and methane (CH4) flux from semiarid irrigated soils are poorly understood. We evaluated effects of: (i) tillage intensity [no‐till (NT) and conventional moldboard plow tillage (CT)] in a continuous corn rotation; (ii) N fertilization levels [0–246 kg N ha−1for corn (Zea maysL.); 0 and 56 kg N ha−1for dry bean (Phaseolus vulgarisL.); 0 and 112 kg N ha−1for barley (Hordeum distichonL.)]; and (iii) crop rotation under NT soil management [corn‐barley (NT‐CB); continuous corn (NT‐CC); corn‐dry bean (NT‐CDb)] on CO2and CH4flux from a clay loam soil. Carbon dioxide and CH4fluxes were monitored one to three times per week using vented nonsteady state closed chambers. No‐till reduced (14%) growing season (154 d) cumulative CO2emissions relative to CT (NT: 2.08 Mg CO2–C ha−1; CT: 2.41 Mg CO2–C ha−1), while N fertilization had no effect. Significantly lower (18%) growing season CO2fluxes were found in NT‐CDb than NT‐CC and NT‐CB (11.4, 13.2 and 13.9 kg CO2–C ha−1d−1respectively). Growing season CH4emissions were higher in NT (20.2 g CH4ha−1) than in CT (1.2 g CH4ha−1). Nitrogen fertilization and cropping rotation did not affect CH4flux. Implementation of NT for 7 yr with no N fertilization was not adequate for restoring the CH4oxidation capacity of this clay loam soil relative to CT plowed and fertilized soil.

Escalating fossil fuel cost and concern over global climate change have accelerated interest in cellulosic feedstocks, such as corn (Zea maysL.) cobs, for liquid fuel production. Little information is available about this plant organ. We compiled and summarized available cob data from several recent field studies in the Central Great Plains. Data were collected from two locations in Colorado and two in Texas that had multiple N fertilizer treatments, varying tillage systems, and different growing seasons. Cob:grain yield ratio, cob:ear ratio, cob:stover ratio, and cob N and C uptake were determined for each site. Cob yield generally increased with increasing N rate. At the high N rates, cob yield ranged from 1.44 to 2.2 Mg ha−1. Cob:stover ratio ranged from 0.14 to 0.25 at high N fertilizer levels. The N concentration varied little among N levels at any location, varying more among locations and year, ranging from 2.52 to 5.19 g kg−1. Nitrogen uptake at the highest N‐levels ranged from 4.65 to 8.37 kg ha−1. The relationship between final grain yield at 155 g kg−1water content and oven‐dried cob yield was linear (r2= 0.75) such that cob yield increased 0.096 Mg ha−1for each Mg ha−1increase in grain yield. This study provides basic information on cob yield and quality for agronomists, and examples are discussed on how the data could be useful for determining the feasibility of harvesting corn cobs as a cellulosic feedstock.

Conversion of irrigated cropland from conventional tillage (CT) to no-till (NT) could have several environmental benefits including reduced erosion potential, reduction of greenhouse gas emissions, and conservation of water. However NT must be economically viable if it is to be adopted. Costs of production and economic returns were evaluated for an irrigated, continuous corn (Zea maysL.) system under CT and NT over 6 yr on a clay loam soil in northern Colorado. Yield responses to N fertilization were included to determine economic optimum fertilization rates under each tillage system. Corn grain yields at economic optimum N fertilizer rates were 1.1 to 1.4 Mg ha-1lower for NT than for CT. However, net returns were $46 to 74 ha-1higher for NT than for CT due to reductions in operating costs of $57 to 114 ha-1and reductions in machinery ownership costs of $87 to 90 ha-1. Operating cost savings were realized largely due to fuel and labor reductions of 75% and 71 to 72%, respectively, and in spite of higher N fertilizer requirements of 16 to 55 kg ha-1for NT compared to CT. No-till, irrigated, continuous corn appears to be an economically viable option for replacing CT production systems in the central Great Plains, especially when combined with the environmental benefits of the NT system.

Onion (Allium cepaL.) is a high cash value crop with a very shallow root system that is frequently irrigated and fertilized with high N rates to maximize yield. Converting from furrow-irrigated to drip-irrigated onion production may reduce N fertilizer needs, water inputs, and NO3–N leaching potential. Onion growth and N uptake, fresh yield, and residual soil NO3–N were determined under drip and furrow irrigation on a clay loam soil with N fertilizer rates from 0 to 224 kg N ha-1. Onions were sampled bi-weekly from 25 May to 30 August in 2005 and 2006 from each treatment. In 2005, 72% less water was applied with the drip system compared with furrow system, and 57% less in 2006. Onion yields were significantly greater with the drip system. Total marketable fresh onion yield increased with increasing N rate in 2005 only. The drip system had more colossal and jumbo sized onions and less medium sized onions than the furrow system. Biomass production and N accumulation accelerated in mid-June each year with an average total N accumulation (leaves + bulbs) of 121 kg N ha-1at final harvest. Irrigation water use efficiency (IWUE) and N use efficiency (NUE) were higher with the drip system than with the furrow system. Residual soil NO3–N levels were greater in the drip-irrigated treatments after onion harvest in 2005 than in the furrow-irrigated treatments, but soil NO3–N levels were similar after harvest in 2006. Adjusted gross economic returns (less the cost of N, water, and drip system) were greater with drip irrigation than with furrow irrigation. This study demonstrates that fresh onion yields, potential economic returns, IWUE, and NUE can be improved in Colorado by using drip irrigation for onion production rather than furrow irrigation.

We evaluated the effects of irrigated crop management practices on nitrous oxide (N2O) emissions from soil. Emissions were monitored from several irrigated cropping systems receiving N fertilizer rates ranging from 0 to 246 kg N ha−1during the 2005 and 2006 growing seasons. Cropping systems included conventional‐till (CT) continuous corn (Zea maysL.), no‐till (NT) continuous corn, NT corn–dry bean (Phaseolus vulgarisL.) (NT‐CDb), and NT corn–barley (Hordeum distichonL.) (NT‐CB). In 2005, half the N was subsurface band applied as urea‐ammonium nitrate (UAN) at planting to all corn plots, with the rest of the N applied surface broadcast as a polymer‐coated urea (PCU) in mid‐June. The entire N rate was applied as UAN at barley and dry bean planting in the NT‐CB and NT‐CDb plots in 2005. All plots were in corn in 2006, with PCU being applied at half the N rate at corn emergence and a second N application as dry urea in mid‐June followed by irrigation, both banded on the soil surface in the corn row. Nitrous oxide fluxes were measured during the growing season using static, vented chambers (1–3 times wk−1) and a gas chromatograph analyzer. Linear increases in N2O emissions were observed with increasing N‐fertilizer rate, but emission amounts varied with growing season. Growing season N2O emissions were greater from the NT‐CDb system during the corn phase of the rotation than from the other cropping systems. Crop rotation and N rate had more effect than tillage system on N2O emissions. Nitrous oxide emissions from N application ranged from 0.30 to 0.75% of N applied. Spikes in N2O emissions after N fertilizer application were greater with UAN and urea than with PCU fertilizer. The PCU showed potential for reducing N2O emissions from irrigated cropping systems.

Converting irrigated, conventional‐till (CT) systems to no‐till (NT) production systems can potentially reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions. Nitrogen fertilization effects on irrigated corn (Zea maysL.) and malting barley (Hordeum distichonL.) yields in a corn‐barley rotation were evaluated for 6 yr on a clay loam soil to determine the viability of using a NT system and N needs for optimum crop yield. Six N treatments were established with N rates varying from 0 to 224 kg N ha−1for corn and 0 to 112 kg N ha−1for barley. Corn and barley grain yields were significantly increased by N fertilization each of 3 yr in the rotation. Three year average corn grain yields were near maximum with an available N (AN) (soil + fertilizer + irrigation water N) level of 274 kg N ha−1Barley yields increased linearly with increasing N rate with grain protein content near 130 kg protein Mg−1grain at the highest N rate. Nitrogen use efficiency (NUE) by corn and barley, based on grain N removal, decreased with increasing AN level and ranged from 204 to 39 and 68 to 31 kg grain kg−1AN for the low and high N treatments for corn and barley, respectively. Total plant N uptake required to produce one Mg grain at near maximum yield in this study averaged 21 kg N for corn and 27 kg N for barley. Corn and barley residue production increased with increasing N rate. Irrigated, NT corn yields obtained in this corn‐barley rotation were acceptable (>10 Mg ha−1) for northern Colorado; however, barley yields did not meet our expected yield goal of 5.4 Mg ha−1with the N rates used in this study, but grain protein was near maximum for malting barley. An irrigated, NT corn‐barley production system appears to be feasible in northern Colorado.

Irrigated, no‐till (NT) production systems can potentially reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with conventional till (CT) systems. Including a legume in the rotation may also reduce N fertilizer requirements. Nitrogen fertilization (6 N rates) effects on irrigated, corn (Zea maysL.) and soybean [Glycine max(L.) Merr.] yields in a corn–soybean rotation were evaluated for 5 yr on a clay loam soil to determine the viability of an irrigated NT system and N needs for optimum crop yield. Corn grain yields were significantly increased by N fertilization each of 3 yr in the rotation, but soybean grain yields (2 yr) did not respond to N fertilization, averaging 2.79 Mg ha−1. Three year average corn grain yields were near maximum with an available N (AN) (soil + fertilizer + irrigation water N) level of 257 kg N ha−1. Nitrogen use efficiency (NUE) by corn and soybean, based on grain N removal, decreased with increasing AN level and ranged from 155 to 46 and 88 to 18 kg grain kg−1. AN for the low and high N treatments for corn and soybean, respectively. Estimated total N required to produce one Mg grain at maximum yield averaged 20 kg N for corn and 54 kg N for soybean. Corn residue increased with increasing N rate, but soybean residue was constant across N rates. Excellent irrigated, NT corn yields were obtained in this corn–soybean rotation for northern Colorado, but soybean yields were only marginally acceptable. Short soybean plant height (30–40 cm) and shattering made combine harvest difficult resulting in significant grain loss. Improved soybean cultivars are needed for this area to make a corn–soybean rotation a viable production system.

The impact of management on global warming potential (GWP), crop production, and greenhouse gas intensity (GHGI) in irrigated agriculture is not well documented. A no‐till (NT) cropping systems study initiated in 1999 to evaluate soil organic carbon (SOC) sequestration potential in irrigated agriculture was used in this study to make trace gas flux measurements for 3 yr to facilitate a complete greenhouse gas accounting of GWP and GHGI. Fluxes of CO2, CH4, and N2O were measured using static, vented chambers, one to three times per week, year round, from April 2002 through October 2004 within conventional‐till continuous corn (CT‐CC) and NT continuous corn (NT‐CC) plots and in NT corn–soybean rotation (NT‐CB) plots. Nitrogen fertilizer rates ranged from 0 to 224 kg N ha−1Methane fluxes were small and did not differ between tillage systems. Nitrous oxide fluxes increased linearly with increasing N fertilizer rate each year, but emission rates varied with years. Carbon dioxide efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. The CT soils were smaller net sinks for GWP than NT soils. The determinant for the net GWP relationship was a balance between soil respiration and N2O emissions. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when appropriate crop production levels are achieved, net CO2emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer.

A no‐till (NT) production system has potential to reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with a conventional till (CT) system. Nitrogen fertilization (four to six N rates) and tillage system (CT and NT) effects on irrigated, continuous corn (Zea maysL.) yields were evaluated for 5 yr on a clay loam soil to determine the viability of the NT system and N needs for optimum yield. Corn in both NT and CT systems responded similarly to available N supply. Grain yields were significantly increased by N fertilization in both tillage systems, with a 16% higher average maximum yield in the CT than in the NT system. Grain yields were near maximum with an available N (soil + fertilizer N) level of 276 and 268 kg N ha−1in the CT and NT systems, respectively. Nitrogen fertilizer use efficiency (NFUE) averaged 43% over N rates and years for both systems. Total N required to produce 1 Mg of grain at maximum yield averaged 19 and 20 kg N Mg−1grain for the CT and NT systems, respectively. Corn residue increased with increasing N rate with no difference in residue production between tillage systems. The lower grain yield with NT probably resulted from the slow early spring development and delayed tasseling compared with the CT system as a result of cooler spring soil temperatures in the NT system. No‐till, irrigated, continuous corn production has potential for replacing CT systems in the central Great Plains area, but with reduced yield potential. Current N fertilizer recommendations for CT corn based on yield goal may need to be modified for NT to account for the lower yield potential and slightly higher N requirement.

High levels of residual NO3–N are present in the soils of the Arkansas River Valley in Colorado where alfalfa (Medicago sativaL.), grains, fruits, and vegetable crops are produced. This study evaluated the use of continuous corn (Zea maysL.) to reduce residual N levels in a furrow‐irrigated, silty clay soil. Fertilizer N needed to maintain optimum corn yields following watermelon [Citrullus lanatus(Thunb.) Matsum. and Nakai], and its impacts on NO3–N leaching potential were also evaluated. Treatments evaluated from 2000 through 2003 included two N sources (urea and Polyon) and six fertilizer N rates. Corn grain yields were not significantly increased by N fertilization the first year following watermelon but increased with increasing residual soil NO3–N levels the second year without additional N fertilization and increased by N fertilization in the third and fourth years. Nitrogen source did not significantly affect corn grain yields, residual soil NO3–N, or N fertilizer use efficiency (NFUE). Nitrogen use efficiency generally decreased with increasing level of available N. Average NFUE based on grain N removal over 4 yr was 55% at the lowest fertilizer N rate and 30% at the highest N rate. Excluding the first corn crop, grain yields and gross economic returns less N costs were maximized with about 265 and 258 kg ha−1of available N (soil plus fertilizer N), respectively. Soil residual NO3–N levels declined following the second, third, and fourth corn crops. Reducing N application rates (based on credits for residual soil NO3–N and previous crop) to the first corn crop produced in rotation with fruit or vegetable crops in the Arkansas River Valley will improve profitability and reduce root zone residual soil NO3–N levels and NO3–N leaching potential. Continuous corn production for 2 to 3 yr with conservative N fertilization rates can reduce residual soil NO3–N levels in the Arkansas River Valley.

The Root Zone Water Quality Model (RZWQM) is a comprehensive agricultural system model with the capacity to predict crop–environmental response to varying soil and crop management systems. Our objective was to evaluate RZWQM for its ability to simulate a 2‐yr winter wheat (Triticum aestivumL.)–fallow (WF) rotation and a more complex wheat–corn (Zea maysL.)–fallow (WCF) rotation under tilled and no‐till (NT) conditions on a Weld silt loam soil in semi‐arid northeastern Colorado. Measured data from all phases of both rotations were compared with simulated values using root mean square error (RMSE) values to quantify the agreement. Soil water in different layers, total soil profile (180 cm) water contents, and grain yield were accurately predicted with RMSEs ranging between 0.055 and 0.061 m3m−3, 4.6 and 7.1 cm, and 244 and 867 kg ha−1, respectively. Leaf area index (LAI), evapotranspiration, and biomass predictions were less accurate with RMSEs between 0.7 and 1.6 cm2, 5.5 and 9.7 cm, and 1027 and 2714 kg ha−1, respectively. Greater soil water and crop yield measured for NT compared with conventional tillage (CT) were simulated reasonably well. Predicted soil organic C was greater in the surface 0.10 m for NT compared with CT after 11 yr. Although the crop growth component of RZWQM needs improvement, especially with regard to LAI, we conclude the model has potential for simulating alternative crop rotations in the central Great Plains. One potential application for RZWQM in this region may be to predict viable cropping opportunities for evolving conservation programs such as the Conservation Security Program (CSP).

There are concerns that restored grasslands currently under the Conservation Reserve Program (CRP) will experience increased soil erosion when they are returned to crop production. Our objective was to compare runoff, erosion, and erodibility on CRP land converted to annual hay production (permanent hayed, PH) and crop production under conventional‐till (preplant disk tillage, CT) and no‐till (NT) management. Erosion study was conducted in central North Dakota on Typic Argiustoll soil 6 yr after the CRP land had been converted to hay production and crop production with a spring wheat (Triticum aestivumL.) –winter wheat–dry pea (Pisum sativumL.) rotation. Runoff volumes and soil loss (by alum precipitation of sediment) were measured on 1.5 by 5 m bordered plots on 4% slope under a rainfall simulator delivering 1‐ to 3‐h rains at 50 or 75 mm h−1, followed by three rains of 20 min or less at rates from 25 to 125 mm h−1Erodibility was calculated from ratios and regressions of soil loss rates versus runoff rates measured at relative steady state. Runoff rates from 50 and 75 mm h−1rains for CT, NT, and PH averaged 9, 12, and 21 mm h−1, respectively, and supported soil loss rates of 20, 7, and 8 g m−2h−1Erodibility of undisturbed CT, NT, and PH was 1.65, 0.29, and 0.28 g m−2mm−1, respectively, showing NT did not differ from PH and that CT management increased erodibility six‐fold above PH. Thorough disk tillage increased erodibility three‐fold over CT, 15‐fold over NT, and nine‐fold over PH. Complete, nondisturbing residue removal increased erodibility less than tillage, from 1.2 times for CT to 2.5 times for NT. Chemically weeded NT exhibited the same low erodibility as the grassland PH treatment under the conditions of study—4% land slope, above average precipitation, and a residue‐productive crop rotation. However, erodibility of tilled NT was significantly higher than that of tilled PH, showing the higher inherent stability of grassland surface soil with its perennial plant root structures.

No‐till (NT) production systems, especially winter wheat (Triticum aestivumL.)‐summer crop‐fallow, have increased in the central Great Plains, but few N fertility studies have been conducted with these systems. Therefore, winter wheat (W) response to N fertilization in two NT dryland crop rotations, wheat‐corn (Zea maysL.)‐fallow (WCF) and wheat‐sorghum (Sorghum bicolorL.)‐fallow (WSF), on a Platner loam (fine, smectitic, mesic Aridic Paleustoll) was evaluated for 9 yr. Five N rates, 0, 28, 56, 84, and 112 kg N ha−1, were applied to each rotation crop. Wheat biomass and grain yield response to N fertilization varied with year but not with crop rotation, increasing with N application each year, with maximum yields being obtained with 84 kg N ha−1over all years. Based on grain N removal, N fertilizer use efficiency (NFUE) varied with N rate and year, averaging 86, 69, 56, and 46% for the 28, 56, 84, and 112 kg ha−1N rates, respectively. Grain protein increased with increasing N rate. Precipitation use efficiency (PUE) increased with N addition, leveling off above 56 kg N ha−1. A soil plus fertilizer N level of 124 to 156 kg N ha−1was sufficient to optimize winter wheat yields in most years in both rotations. Application of more than 84 kg N ha−1on this Platner loam soil, with a gravel layer below 120 cm soil depth, would more than likely increase the amount of NO3‐N available for leaching and ground water contamination. Wheat growers in the central Great Plains need to apply N to optimize dryland wheat yields and improve grain quality, but need to avoid over‐fertilization with N to minimize NO3‐N leaching potential.

Annualized yields with more intensive cropping (IC) systems tend to be greater than those of spring wheat–fallow (SW–F); however, little economic comparison information is available. The long‐term (12 yr) effects of tillage system and N fertilization on the economic returns from two dryland cropping systems in North Dakota were evaluated. An IC rotation [spring wheat (Triticum aestivumL.)–winter wheat (T. aestivumL.)–sunflower (Helianthus annuusL.)] and a SW–F rotation were studied. Tillage systems included conventional till (CT), minimum till (MT), and no‐till (NT). Nitrogen rates were 34, 67, and 101 kg N ha−1for the IC system and 0, 22, and 45 kg N ha−1for the SW–F system. Annual precipitation ranged from 206 to 655 mm, averaging 422 mm over 12 yr. The IC system generated higher profits than the SW–F system, but the IC profits were more variable. Within the IC system, MT generated higher profits than corresponding N treatments under CT and NT, but MT profits were more variable. Of the N rates evaluated, the largest N rates generated the largest profits. The dryland IC system with MT and NT was more profitable than the best SW–F system using CT for this location. Stochastic dominance analyses revealed that the SW–F system and IC system CT treatments were economically inefficient when compared with the IC system with MT and NT.