No-till Continuous Corn Research Articles

Cover crop performance under a changing climate in continuous corn system over Nebraska.

Fall-planted cover crop (CC) within a continuous corn (Zea mays L.) system offers potential agroecosystem benefits, including mitigating the impacts of increased temperature and variability in precipitation patterns. A long-term simulation using the Decision Support System for Agrotechnology Transfer model was made to assess the effects of cereal rye (Secale cereale L.) on no-till continuous corn yield and soil properties under historical (1991-2020) and projected climate (2041-2070) in eastern Nebraska. Local weather data during the historical period were used, while climate change projections were based on the Canadian Earth System Model 2 dynamically downscaled using the Canadian Centre for Climate Modelling and Analysis Regional Climate Model 4 under two representative concentration pathways (RCP), namely, RCP4.5 and RCP8.5. Simulations results indicated that CC impacts on corn yield were nonsignificant under historical and climate change conditions. Climate change created favorable conditions for CC growth, resulting in an increase in biomass. CC reduced N leaching under climate change scenarios compared to an average reduction of 60% (7kg ha- 1 ) during the historical period. CC resulted in a 6% (27mm) reduction in total water in soil profile (140cm) and 22% (27mm) reduction in plant available water compared to no cover crop during historical period. CC reduced cumulative seasonal surface runoff/soil evaporation and increased the rate of soil organic carbon buildup. This research provides valuable information on how changes in climate can impact the performance of cereal rye CC in continuous corn production and should be scaled to wider locations and CC species.

Did cover crop or animal manure ameliorate corn residue removal effects on soil mechanical properties after 10 years?

Crop residue removal may negatively affect soil mechanical properties, which are key components of soil quality. To evaluate potential long-term effects, we assessed the 10-yr impact of corn (Zea mays L.) residue removal (59 % of non-grain biomass annually) on surface soil mechanical properties (0–20 cm). We also evaluated whether adding carbon (C) amendments, such as using a winter rye (Secale cereale L.) cover crop or surface-applying cattle manure (24 Mg ha−1 biannually) can ameliorate the effects of crop residue removal. This long-term study was under irrigated no-till continuous corn on a silt loam soil in south-central Nebraska, USA. Measurements included soil penetration resistance, field bulk density, aggregate strength, Atterberg limits (liquid limit, plastic limit, and plasticity index), Proctor maximum bulk density, and the water content at which the Proctor maximum bulk density (critical water content) occurs. Reduction in soil organic carbon (SOC) concentration explained most of the changes in soil mechanical properties. Long-term corn residue removal increased penetration resistance (+40 %) for the 0–20 cm depth, and reduced aggregate strength (−44 %), plasticity index (−22 %), and critical water content (−13 %) in the 0–5 cm depth. Residue removal also reduced field bulk density (−5%), liquid limit (−12 %), and plastic limit (−10 %) in the 0–10 cm depth, but increased Proctor maximum bulk density (+8 %) in the 0–5 cm depth. Winter rye cover crop reduced field bulk density (−5%, 0–15 cm depth) and increased penetration resistance (+52 %, 0–20 cm depth). Surface-applied manure amendments increased the near-surface soil liquid limit (+8 %) and plastic limit (+8 %) in the 0–5 cm depth. Given the high rate of residue removal used in this experiment, our findings support that excessive corn residue removal over the long-term (∼10 years) negatively affects near-surface soil mechanical properties, but that use of winter rye cover crop or surface-applied manure can minimally to partially ameliorate these effects.

Measured and simulated effects of residue removal and amelioration practices in no-till irrigated corn (Zea mays L.)

Reducing nitrous oxide (N2O) emissions to the atmosphere is expected to provide substantial climate mitigation benefits. Herein, we measured soil N2O emission and crop yield responses in a nine-year, no-till continuous corn system under contrasting management practices including irrigation (full; deficit), corn stover retention (100 % retention; maximum mechanical removal), and cover crop use (winter cereal rye, Secale cereale L.; no cover crop). Field-measured data were used to construct a structural equation model (SEMobs) to explore the causal effects of management on soil N2O emissions. We also used the Root Zone Water Quality Model 2 (RZWQM2) to simulate management effects on soil N2O emission. Structural equation modeling was used for the field-measured data (SEMobs) and the RZWQM2 simulated data (SEMsim) to quantify management relationships with soil and determine whether relationships observed in field data were captured by RZWQM2 simulations. Our experimental field results showed that stover removal decreased annual N2O emissions compared to stover retention, only for deficit irrigated soil (2.83 ± 1.31 vs. 4.49 ± 3.65 kg N ha−1 y−1) and that deficit irrigation decreased annual N2O emissions compared to full irrigation, only for soil with cover crops (3.31 ± 3.19 vs. 4.11 ± 3.80 kg N ha−1 y−1). The SEMobs and SEMsim results showed similar direction and magnitude of relationships between daily soil N2O emissions and various management and environmental drivers. Our study improved the mechanistic understanding for the effects of agricultural management on soil N2O emissions and can help reduce N2O emissions from agricultural systems.

Temporal Change of Soil Carbon on a Long-Term Experimental Site with Variable Crop Rotations and Tillage Systems

The impacts of tillage practices and crop rotations are fundamental factors influencing changes in the soil carbon, and thus the sustainability of agricultural systems. The objective of this study was to compare soil carbon status and temporal changes in topsoil from different 4 year rotations and tillage treatments (i.e., no-till and conventional tillage). Rotation systems were primarily corn and soy-based and included cereal and alfalfa phases along with red clover cover crops. In 2018, soil samples were collected from a silty-loam topsoil (0–15 cm) from the 36 year long-term experiment site in southern Ontario, Canada. Total carbon (TC) contents of each sample were determined in the laboratory using combustion methods and comparisons were made between treatments using current and archived samples (i.e., 20 year and 9 year change, respectively) for selected crop rotations. Overall, TC concentrations were significantly higher for no-till compared with conventional tillage practices, regardless of the crop rotations employed. With regard to crop rotation, the highest TC concentrations were recorded in corn–corn–oats–barley (CCOB) rotations with red clover cover crop in both cereal phases. TC contents were, in descending order, found in corn–corn–alfalfa–alfalfa (CCAA), corn–corn–soybean–winter wheat (CCSW) with 1 year of seeded red clover, and corn–corn–corn–corn (CCCC). The lowest TC concentrations were observed in the corn–corn–soybean–soybean (CCSS) and corn–corn–oats–barley (CCOB) rotations without use of cover crops, and corn–corn–soybean–winter wheat (CCSW). We found that (i) crop rotation varieties that include two consecutive years of soybean had consistently lower TC concentrations compared with the remaining rotations; (ii) TC for all the investigated plots (no-till and/or tilled) increased over the 9 year and 20 year period; (iii) the no-tilled CCOB rotation with 2 years of cover crop showed the highest increase of TC content over the 20 year change period time; and (iv) interestingly, the no-till continuous corn (CCCC) rotation had higher TC than the soybean–soybean–corn–corn (SSCC) and corn–corn–soybean–winter wheat (CCSW). We concluded that conservation tillage (i.e., no-till) and incorporation of a cover crop into crop rotations had a positive effect in the accumulation of TC topsoil concentrations and could be suitable management practices to promote soil fertility and sustainability in our agricultural soils.

Microbial trade-off in soil organic carbon storage in a no-till continuous corn agroecosystem

Recent perspective has highlighted the microbial importance of interplay between catabolic breakdown and anabolic synthesis in influencing soil organic carbon (SOC) dynamics and persistence. However, studies on these contrasting activities remain rare, despite value to global discussions on economic and ecologically sustainable ecosystem management. Here we investigate microbial response in a no-till farm in Northeast China after an 8-year manipulation of plant residue returns of varying quantity including control (0%, NT0), low (33%, NT33), medium (67%, NT67) and high (100%, NT100). Topsoil amino sugar biomarker analysis indicated microbial necromass contributed to SOC formation in NT33 and NT67, while the contribution was minimal in NT100. Sequencing data analyses along with subsoil SOC indicated increased microbial degradation of existing SOC upon mulch quantity gradient. We found that a low level (33%) of the previous year's stover return was an optimized trade-off for topsoil (0–5 cm) carbon storage and off-field economic demand for material. This study demonstrates the non-linear relationship between carbon inputs and SOC content, and suggests the importance of the trade-off effects between microbial catabolism and anabolism.

Dedicated Bioenergy Crops and Water Erosion.

Information on the water quality impact of perennial warm-season grasses (WSGs) when grown in marginal lands as dedicated energy crops is limited. We studied how WSGs affected runoff, sediment, and nutrient losses and related near-surface soil properties to those of no-till corn ( L.) on an eroded soil in southwestern Iowa and a center pivot corner in east-central Nebraska. The experiment at the eroded soil was established in 2012, and treatments included 'Liberty' switchgrass ( L.) and no-till continuous corn. The experiment at the pivot corner was established in 2013 with 'Liberty' switchgrass, 'Shawnee' switchgrass, low-diversity grass mixture, and corn. We simulated rainfall at 63.5 ± 2.8 mm h for 1 h to portray 5-yr return periods and measured water erosion in spring 2017. Time to runoff start and runoff depth did not differ between WSGs and corn. On the eroded soil, sediment and nutrient losses did not differ between treatments. At the pivot corner, sediment (0.71 vs. 0.15 Mg ha) and PO-P (0.037 vs. 0.006 kg ha) losses were five times higher in corn than in WSGs. Near-surface soil properties did not differ on the eroded soil, but at the pivot corner, wet aggregate stability was four times higher and residue cover was 34% higher in WSGs than in corn. Water-stable aggregates were negatively correlated with NO-N and PO-P losses. Overall, WSGs can improve water quality in marginally productive croplands, but their effectiveness appears to be site specific.

Legacy effects of land use on soil nitrous oxide emissions in annual crop and perennial grassland ecosystems

Land use conversions into and out of agriculture may influence soil-atmosphere greenhouse gas fluxes for many years. We tested the legacy effects of land use on cumulative soil nitrous oxide (N2 O) fluxes for 5yr following conversion of 22-yr-old Conservation Reserve Program (CRP) grasslands and conventionally tilled agricultural fields (AGR) to continuous no-till corn, switchgrass, and restored prairie. An unconverted CRP field served as a reference. We assessed the labile soil C pool of the upper 10cm in 2009 (the conversion year) and in 2014 using short-term soil incubations. We also measured insitu soil N2 O fluxes biweekly from 2009 through 2014 using static chambers except when soils were frozen. The labile C pool was approximately twofold higher in soils previously in CRP than in those formerly in tilled cropland. Five-year cumulative soil N2 O emissions were approximately threefold higher in the corn system on former CRP than on former cropland despite similar fertilization rates (~184kg N·ha-1 ·yr-1 ). The lower cumulative emissions from corn on former cropland were similar to emissions from switchgrass that was fertilized less (~57kg N·ha-1 ·yr-1 ), regardless of former land use, and lowest emissions were observed from the unfertilized restored prairie and reference systems. Findings support the hypothesis that soil labile carbon levels modulate the response of soil N2 O emissions to nitrogen inputs, with soils higher in labile carbon but otherwise similar, in this case reflecting land use history, responding more strongly to added nitrogen.

Ecosystem carbon exchange on conversion of Conservation Reserve Program grasslands to annual and perennial cropping systems

Land use changes into and out of agricultural production may substantially influence ecosystem carbon (C) balance for many years. We examined ecosystem C balances for eight years after the conversion of 22 year-old Conservation Reserve Program (CRP) grasslands and formerly tilled agricultural fields (AGR) to annual (continuous no-till corn) and perennial (switchgrass and restored prairie) cropland. An unconverted CRP field (CRP-Ref) was maintained as a historical reference. Ecosystem C balance was assessed using adjusted net ecosystem carbon exchange (NEEadj) calculated by adding C removed in harvested biomass to NEE measured using eddy covariance method. The cumulative NEEadj of the corn and perennial systems on former CRP fields showed that these systems were a net C source to the atmosphere over the 8-year period while on former AGR fields, the perennial systems were net C sinks and the corn system near-neutral. The CRP-Ref was near neutral until a drought year when it became a net source. The corn system on the CRP field will likely reach a new lower soil C equilibrium at least 14 years after conversion but will never regain the C lost upon conversion under current no-till management with residue partially removed. On the other hand, the perennial systems could fully regain in ∼14 years the C lost following conversion. The cumulative NEEadj of the corn systems exhibited a higher C emission than did the perennial systems within the same land use histories, reflecting the dominant role of crop type and management in agricultural ecosystem C balance. Results suggest that converting croplands to grasslands results in immediate C gains whereas converting grasslands to croplands results in permanent (no-till corn with partial residue removal) or temporary (perennial herbaceous crops) net C loss to the atmosphere. This has a significant implications for global climate change mitigation where biomass production from annual and perennial crops is promoted to avoid fossil-fuel C emissions (biofuel) or to remove CO2 from the atmosphere (bioenergy C capture and storage).

Early accumulation of active fraction soil carbon in newly established cellulosic biofuel systems

We examined relative changes in soil C pools shortly after the establishment of six perennial and two annual bioenergy cropping systems that differed in diversity (monoculture vs. polyculture). Perennial systems included two monocultures (switchgrass, Panicum virgatum; and miscanthus, Miscanthus×giganteus) and four polycultures including hybrid poplar (Populus sp.)+herbaceous understory; mixed native grasses, successional vegetation, and restored prairie. Two annual systems included no-till continuous corn (Zea mays) and rotational corn (corn-soybean (Glycine max)-canola (Brassica napus)). Each crop was planted in a full factorial design at both a moderate fertility Alfisol and a high fertility Mollisol site. Relative differences in active, slow, and passive C pools in surface soils, where C changes are most likely to be detected early, were evaluated with 322-day laboratory incubations followed by acid hydrolysis to infer different pools from exponential decay curves. Five years post-establishment, active C pools under perennial polycultures at the Alfisol site were up to twice those under annual and perennial monocultures, and followed the order hybrid poplars (696±216μgCg−1 soil, n=5 replicate blocks)≈native grasses (656±155)≈restored prairie (638±44)>early successional (500±54)≫continuous corn (237±68)≈rotational corn (180±n.a.). Active C pools in perennial monocultures were similar to those in continuous corn: switchgrass (274±29)≈miscanthus (299±9). In contrast, differences in active C pools among crops at the more fertile Mollisol site were not detectable except for greater pools in the restored prairie and rotational corn systems. At both sites, slow and passive C pools differed little among systems except that slow pools were greater in the poplar system. That diversity rather than perenniality itself led to greater active C pools suggests that polycultures might be used to accelerate soil C accumulation in bioenergy and other perennial cropping systems.

Can Cover Crop Use Allow Increased Levels of Corn Residue Removal for Biofuel in Irrigated and Rainfed Systems?

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 late-terminated 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 early-terminated 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 late-terminated CC at the irrigated site compared to no CC. Complete residue removal increased irrigated grain yield by 9% in 1 year relative to no 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 removal-induced 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.

Bioenergy cropping systems that incorporate native grasses stimulate growth of plant-associated soil microbes in the absence of nitrogen fertilization

The choice of crops and their management can strongly influence soil microbial communities and their processes. We used lipid biomarker profiling to characterize how soil microbial composition of five potential bioenergy cropping systems diverged from a common baseline five years after they were established. The cropping systems we studied included an annual system (continuous no-till corn) and four perennial crops (switchgrass, miscanthus, hybrid poplar, and restored prairie). Partial- and no-stover removal were compared for the corn system, while N-additions were compared to unfertilized plots for the perennial cropping systems. Arbuscular mycorrhizal fungi (AMF) and Gram-negative biomass was higher in unfertilized perennial grass systems, especially in switchgrass and prairie. Gram-positive bacterial biomass decreased in all systems relative to baseline values in surface soils (0–10cm), but not subsurface soils (10–25cm). Overall microbial composition was similar between the two soil depths. Our findings demonstrate the capacity of unfertilized perennial cropping systems to recreate microbial composition found in undisturbed soil environments and indicate how strongly agroecosystem management decisions such as N addition and plant community composition can influence soil microbial assemblages.

Transition to second generation cellulosic biofuel production systems reveals limited negative impacts on the soil microbial community structure.

Currently we lack knowledge on how the soil microbial community responds to the transition from traditional grain production to cellulosic feedstock production systems with residue removal for biofuel production. Implementation of second-generation biofuel production systems could create a challenge in meeting the goal of providing cellulose biomass if the processes impact soil's function as part of ecosystem services. Our goal was to assess the transition period as we move from a grain harvest system with residue return into biomass production systems with both residue and grain removal. The existing traditional systems were continuous corn (CC) and corn–soybean rotations (corn–soybean–corn (R1) or soybean–corn–soybean (R2)). The biomass production systems include a previously established mixed tall grass prairie dominated by big bluestem (Andropogon gerardii; PR) where the above ground biomass is now harvested when it had been previously burned, corn–soybean rotations transitioned to residue recovery based on: Miscanthus×giganteus (MS), dual-purpose sorghum (Sorghum bicolor; SG), upland switchgrass (Panicum virgatum; c.v. Shawnee; SW) and a tilled continuous corn changed to continuous no-till corn (Zea mays; CR) with the residue removed. Over a three-year transition period, biological indicators of soil health included microbial biomass and community structure profile using phospholipid fatty acid (PLFA) biochemical markers, and an assessment of the saprotrophic fungal diversity using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction amplified ITS rRNA genetic marker. Over the course of the transition, bacterial biomass dominated soils in the annual systems of CC, R1, R2, CR and SG, and the perennial system of MS. While fungal biomass dominated soils under PR. Fungal PLFA signatures and ITS-DGGE profiles demonstrated similarity between PR and the transitioned SW system, and to a lesser extent SG. In contrast, MS did not statistically alter the microbial biomass, community structure or fungal diversity away from patterns observed in the corn–soybean system. Our findings support microbial community stability and resilience as we found no negative impacts in any of the biomass recovery systems (PR, MS, SG, SW and CR) relative to the traditional systems (CC, R1 and R2), as indicated by measures of soil health. We did find that the selection of the plant types used in the biomass system could have a significant impact on the structure of both bacterial and fungal communities. With respect to soil health indicators including the fungal community, our findings suggest the dual-purpose SG system provides an encouraging alternative to continuous maize when considering plant biomass production. The selection of this dedicated perennial biomass system offers an avenue to enhance indicators of soil health and associated ecosystem services while supporting the bioenergy economy.

Can Cover Crop and Manure Maintain Soil Properties After Stover Removal from Irrigated No‐Till Corn?

Addition of cover crops and animal manure following corn (Zea mays L.) stover removal for expanded uses may mitigate negative soil property effects of stover removal. We studied the short-term (3 yr) cumulative impacts of stover removal with and without winter rye (Secale cereale L.) cover crop or animal manure application on near-surface (0- to 5-cm depth) soil properties under irrigated no-till continuous corn on a Hastings silt loam (fine, smectitic, mesic Udic Argiustolls) (<3% slope) near Clay Center, NE. Treatments were irrigation levels (full and deficit), amelioration practices (none, cover crop, or animal manure), stover removal (no removal or maximum removal), and N fertilization (125 or 200 kg N ha⁻¹). Data collected after 3 yr indicate that stover removal (63%) reduced geometric mean diameter of dry aggregates 93%, increased erodible fraction sixfold, and reduced aggregate stability 32% compared with plots without stover removal. Stover removal from plots with cover crop or manure reduced dry aggregate size and stability and increased erodible fraction compared with plots without removal and amelioration practices, indicating that amelioration practices did not offset stover removal effects. Stover removal reduced wet aggregate stability and soil organic C (SOC) concentration in the 0- to 2.5-cm depth, but cover crop or manure mitigated these small reductions. Stover removal did not change water infiltration rates and had small effects on particulate organic matter (POM). Overall, in the short term, cover crop or manure may not provide sufficient protection from raindrop impact and wetting and drying cycles to maintain soil structure, resulting in increased susceptibility to wind erosion. Use of these amelioration practices, however, may offset changes in surface layer wet aggregate stability and SOC after high rates of stover removal in this region.

Does inorganic nitrogen fertilization improve soil aggregation? Insights from two long-term tillage experiments.

The relationship between inorganic fertilization and soil aggregation is not well understood. We studied cumulative nitrogen (N) fertilization impacts on aggregation, soil organic C (SOC), pH, and their relationships under irrigated and rainfed experiments in Nebraska after 27 and 28 yr, respectively. The dominant soil series were Crete silt loam at the irrigated site, and Coleridge silty clay loam at the rainfed site. We studied irrigated continuous corn ( L.) in chisel plow (CP) and ridge till (RidgeT) receiving 0, 75, 150, and 300 kg N ha yr and rainfed continuous corn and corn-soybean [ (L.) Merr.] in moldboard plow (MP), reduced till (RT), and no-till (NT) with corn receiving 0, 80, and 160 kg N ha yr. Fertilization altered soil aggregation in all tillage systems under continuous corn. Mean weight diameter of water-stable aggregates (MWDA) increased in the upper 7.5-cm depth in NT but decreased in the 7.5- to 60-cm depth by 1.5 times with N application. Fertilization reduced pH but had little or no effect on SOC. Both MWDA and pH ( = 0.47***) decreased under irrigated corn, particularly in the 7.5- to 30-cm depth. No-till and RT had two to five times greater near-surface MWDA than MP. Continuous corn had greater MWDA than corn-soybean in the upper 30-cm depth except in MP. Long-term N fertilization improves near-surface soil aggregation in NT continuous corn but reduces aggregation in the subsoil. Results also suggest that, if fertilizers are applied at rates of about 80 kg N ha, deterioration of soil aggregation would be minimal.

Curve numbers for long-term no-till corn and agricultural practices with high watershed infiltration

The Curve Number (CN) method is an engineering and land management tool for estimating surface runoff from rainstorms. We investigated CN under continuous long-term no-till corn (<i>Zea mays</i> L.; watershed WS191) and compared it with other potentially high infiltration agricultural practices using data from three experimental watersheds (average area = 0.74 ha [1.83 ac]) at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio. Practices compared were wheat (<i>Triticum aestivum</i> L.) and first- and second-year meadow as part of a 4-year corn–wheat–meadow–meadow rotation (CWMM), continuous meadow, and continuous no-till corn, mulch-tilled corn, and conventionally tilled corn (i.e., moldboard plow). Double-mass curves of runoff for no-till and permanent meadow documented the significant and immediate reduction in runoff from the no-till management. Runoff was generated at a rate of 4.9 mm y⁻¹ (0.19 in yr⁻¹) during the no-till period compared with permanent pasture at 44 mm y⁻¹ (1.73 in yr⁻¹) (no-till was 11% of the meadow rate). The asymptotic CN (CNi) for the 48-year record of continuous no-till corn practice at WS191 decreased substantially to 66.3 (−24.3 CN units) from the period of conventional corn in rotation on the same site. The Natural Resources Conservation Service handbook value for no-till CN was 16 CN units larger at 82. The larger than expected reduction in CN was probably due the presence of a thriving earthworm population and numerous earthworm-created macropores that enhance infiltration. The CN for the mulch-tilled corn culture treatment (74.6) was lower than conventional corn (90.6 largest) by 16 CN units. CN was surprisingly high (77.4) for a watershed in continuous meadow, which was similar to mulch-tilled corn. The wheat years in rotation also had some of the smallest CN values (63.7), suggesting a smaller CN for a practice similar to that used in organic agriculture today. Continuous no-till corn had a slightly larger CN (66.3) than meadow (61.9) in the CWMM rotation, suggesting that simple grass establishment can be as effective as long-term no-till to reduce runoff. CN of approximately 60 was the lowest found. The results are applicable for areas of similar terrain, management practices, geology, soils, subsoil permeability, and climate of the NAEW watersheds. Differences between handbook and measured CN suggest that local values are more representative than handbook values.

Greenhouse Gas Mitigation Economics for Irrigated Cropping Systems in Northeastern Colorado

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 mays L.) (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 vulgaris L.). The study included six N fertilization rates ranging from 0 to 246 kg ha−1 Results 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−1 while reducing annual net GWP by 929 kg CO2 equivalents ha−1 The greatest GWP reductions (1463 kg CO2 equivalents 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.

Tillage and Inorganic Nitrogen Source Effects on Nitrous Oxide Emissions from Irrigated Cropping Systems

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 mays L.) based rotations receiving fertilizer rates of 246 kg N ha−1 when in corn, 56 kg N ha−1 when in dry bean (Phaseolus vulgaris L.), and 157 kg N ha−1 when in barley (Hordeum vulgare L. 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.

Stabilization of organic carbon in chemically separated pools in no-till and meadow soils in Northern Appalachia

Land use and soil management affects soil organic carbon (SOC) pools, chemical composition of stabilized SOC fractions, and the depth distribution. No-till production of corn ( Zea mays L.) is a recommended management practice that reduces soil losses and increases SOC concentration, but the scientific knowledge of the mechanisms of C sequestration and protection is scanty. Therefore, the objective of this research was to compare the SOC pool, C pool in fine roots, and chemically separated C fractions with depth in three pedons from the same soil series: (i) meadow converted from no-till corn in 1988 (Meadow), (ii) continuous no-till corn since 1970 (NT); and (iii) continuous no-till corn with beef cattle manure since 1964 (NTm) at the North Appalachian Experimental Watershed near Coshocton, Ohio. The SOC pool (Mg ha − 1 ) from 0–69 cm was the highest in NTm (76.2) and progressively smaller in NT (49.3) and Meadow (46.6) pedons. The SOC concentrations and pool sharply decreased with depth, but were always more in NTm than NT soil. Fine root C pool (Mg ha − 1 ) was much larger in the pedon with perennial vegetation (Meadow, 1.28) than in those under corn (NT, 0.21; NTm, 0.09). The pool of chemically separated C fractions and their depth distribution varied depending on the separation technique. The amounts of C preferentially bound to soil minerals in 0–69 cm depth were comparable among pedons, as indicated by treatment with HF to release mineral-bound SOC. The NTm pedon had a larger pool of recalcitrant non-hydrolyzable C (58.4 Mg ha − 1 ), as indicated by HCl treatment. The Meadow pedon stored the smallest pool (3.4 Mg ha − 1 ) of oxidisable C, as was indicated by treatment with disodium peroxodisulfate (Na 2S 2O 8). The relationship between chemically separated C fractions and turnover time of SOC at depth, however, warrants further studies. Nevertheless, the results indicate that no-till corn with added manure has a high potential for C sequestration by increasing the size of the SOC pool in the subsurface horizons.

Net Global Warming Potential and Greenhouse Gas Intensity in Irrigated Cropping Systems in Northeastern Colorado

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(-1). Methane 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 CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer.

STOCK AND DISTRIBUTION OF TOTAL AND CORN-DERIVED SOIL ORGANIC CARBON IN AGGREGATE AND PRIMARY PARTICLE FRACTIONS FOR DIFFERENT LAND USE AND SOIL MANAGEMENT PRACTICES

Land use, soil management, and cropping systems affect stock, distribution, and residence time of soil organic carbon (SOC). Therefore, SOC stock and its depth distribution and association with primary and secondary particles were assessed in long-term experiments at the North Appalachian Experimental Watersheds near Coshocton, Ohio, through δ13C techniques. These measurements were made for five land use and soil management treatments: (1) secondary forest, (2) meadow converted from no-till (NT) corn since 1988, (3) continuous NT corn since 1970, (4) continuous NT corn-soybean in rotation with ryegrass since 1984, and (5) conventional plow till (PT) corn since 1984. Soil samples to 70-cm depth were obtained in 2002 in all treatments. Significant differences in soil properties were observed among land use treatments for 0 to 5-cm depth. The SOC concentration (g C kg−1 of soil) in the 0 to 5-cm layer was 44.0 in forest, 24.0 in meadow, 26.1 in NT corn, 19.5 in NT corn-soybean, and 11.1 in PT corn. The fraction of total C in corn residue converted to SOC was 11.9% for NT corn, 10.6% for NT corn-soybean, and 8.3% for PT corn. The proportion of SOC derived from corn residue was 96% for NT corn in the 0 to 5-cm layer, and it decreased gradually with depth and was 50% in PT corn. The mean SOC sequestration rate on conversion from PT to NT was 280 kg C ha−1 y−1. The SOC concentration decreased with reduction in aggregate size, and macro-aggregates contained 15 to 35% more SOC concentration than microaggregates. In comparison with forest, the magnitude of SOC depletion in the 0 to 30-cm layer was 15.5 Mg C/ha (24.0%) in meadow, 12.7 Mg C/ha (19.8%) in NT corn, 17.3 Mg C/ha (26.8%) in NT corn-soybean, and 23.3 Mg C/ha (35.1%) in PT corn. The SOC had a long turnover time when located deeper in the subsoil. Additional research is needed to understand association of SOC with particle and aggregate size fractions and temporal changes and depth-distribution with regard to land use and soil management.