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WQFS Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in West Lafayette, Indiana Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2 O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring or fall. Soybean (SC) rotated with CS and restored prairie grass (RP) were also included. The CO2 fluxes correlated (P≤0.001) with soil temperature (ρ: 0.74) and accumulated rainfall 120 h before sampling (ρ: 0.53); N2O fluxes correlated with soil temperature (ρ: 0.34). Seasonal CO2–C emissions were not different across treatments (4.4 Mg ha−1 yr−1) but differed between years. Manured soils were net seasonal CH4–C emitters (0.159–0.329 kg ha−1 yr−1), whereas CSUAN and CCUAN Treatments significantly influenced seasonal N2O–N emissions (P< 0.001) and ranged from <1.0 kg ha−1yr−1in RP and SC to between 3 and 5 kg ha−1yr−1in CC (fall application) and CSUAN and >8 kg ha−1yr−1in CC (spring application); differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn–soybean rotation, and restoration of prairies may diminish N2O emissions and hence contribute to global warming mitigation.
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NVND Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Sidney, Montana Management practices, such as irrigation, tillage, cropping system, and N fertilization, may influence soil greenhouse gas (GHG) emissions. We quantified the effects of irrigation, tillage, crop rotation, and N fertilization on soil CO2, N2O, and CH4 emissions from March to November, 2008 to 2011 in a Lihen sandy loam in western North Dakota. Treatments were two irrigation practices (irrigated and non-irrigated) and five cropping systems (conventional-tilled malt barley [Hordeum vulgaris L.] with N fertilizer [CTBFN], conventional-tilled malt barley with no N fertilizer [CTBON], no-tilled malt barley-pea [Pisum sativum L.] with N fertilizer [NTB-PN], no-tilled malt barley with N fertilizer [NTBFN], and no-tilled malt barley with no N fertilizer [NTBON]). The GHG fluxes varied with date of sampling while peaking immediately after precipitation, irrigation, and/or N fertilization events during increased soil temperature. Both CO2 and N2O fluxes were greater in CTBFN under the irrigated condition but CH4 uptake was greater in NTB-PN under the non-irrigated condition than in other treatments. While tillage and N fertilization increased CO2 and N2O fluxes by 8 to 30%, N fertilization and monocropping reduced CH4 uptake by 39 to 40%. The NTB-PN, regardless of irrigation, might mitigate GHG emissions by reducing CO2 and N2O emissions and increasing CH4 uptake relative to other treatments. To account for global warming potential for such a practice, information on productions associated with CO2 emissions along with N2O and CH4 fluxes are needed.
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Irrigation Residue Removal Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network and Resilient Economic Agricultural Practices in Lincoln, Nebraska USDA-ARS REAP Study (Ithaca, NE) - NEMEIRR Sustainable intensification of high-yielding production systems may help meet increasing demands for food, fuel, and fiber worldwide. Specifically, corn stover is being removed by producers for livestock purposes, and stover is also targeted as a primary 2nd generation biofuel feedstock. The NEMEIRR experimental objectives are to quantify how stover removal (no removal, moderate removal, high removal) and tillage management (no-till, disk) affect crop yields, soil organic carbon, soil greenhouse gas emissions, and other soil responses (microbial community structure, function; soil health). This experiment is conducted in a fully irrigated continuous corn system in the western Corn Belt, and soil and plant measurements have been taken since study establishment in 2001. By: V.L. Jin (1 Sep 2016). (41 9 43.3 N. 96 14 41.4 W; 349 m asl). Thc soil is Tomck silt loam (a fine, smectitic. mesic Pachic Argiudoll) and Filbert silt loam (a fine, smectitie. mesie Verne Argialboll). Long-term (1981-2010) mean annual precipitation is 74 cm and tempera¬ture is 9.8°C The study has been in continuous corn since 2000. Thc experimental design is a randomized complete block with factorial treatments arranged in split plots. The whole-plot factor is tillage treatment (NT or CT) and the subplot factor is none (0%). medium (•35%). and high (40%) stover removal calcu¬lated on a mass basis. Nitrogen fertilizer was applied at 202 kg N ha-I yr I in 2001. 2002. 2004. 2007. 2008. 2009, and 2010.190 kg N hi t yr-I in 2003. and 168 kg N ha 1 yr- I in 2005 and 2006. Treatments (tillage) and subplot treatments (residue re¬moval levels) were randomly assigned in a factorial arrangement to whole-plot experimental units (9 by 45.6 m) and subplots within the whole plots (9 by 15.2 m) in six blocks. The previous crop for the entire area in 2000 was corn under rainfcd conditions. Before 2000. the study site was historically cropped with corn, soybean [Glycinc max (L.) Merr.). oat (Arena JoIliM L.), and alfalfa (Maid-ago saliva L). In the spring of 2001, residue was removed from the medium and high stover removal treatments using a flail chopper. The entire study was then disked to remove ridges formed during the previous crop year. In each successive year of the study, only the disk treatment area was tilled to a depth of 15 to 20 cm. usually in the spring before plant¬ing. Irrigation was conducted with a solid set sprinkler system in 2001, then supplemental water applications from 2002 to 2010 were made using a linear-move irrigation system. Irrigation treat¬ments were applied when deemed necessary, with annual rates averaging 12.5 ± 7.0 cm from 2001-2010 (Table I). Glyphosatc-tolerant corn hybrids adapted to eastern Nebraska have been used throughout the study. Corn was plant¬ed with a six-row planter in 76-cm rows at a rate *174.000 viable seeds ha 1, typically during the first week of May. Weed control was accomplished using glyphosate EN-(phosphonomethyl)gly¬eine] and atrazine (6.chloro-N-ethyl-AP-(1-methylethyl)-1.3.5- triazine-2.4-diamine) applications along with in-season cultiva.
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Nitrogen Source Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Fort Collins, Colorado 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-effi ciency N fertilizers with emissions from conventional dry granular urea in irrigated cropping systems. These emissions were monitored from several irrigated cropping systems receiving N fertilizer rates ranging from 0-246 kg/ha from years 2007-2008 with intermediate rates of 157 kg/ha applied to the barley crop in corn-barley rotation and 56 kg/ha applied to the dry bens in the corn-dry bean rotation. 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). Nitrous oxide fluxes were measured during ten growing seasons using static, vented chambers and a gas chromatograph analyzer. This work shows that the use of no-till and enhanced-effi ciency N fertilizers can potentially reduce N2O emissions from irrigated systems.
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Nitrogen Source Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Mandan, North Dakota Use of dietary amendments to reduce nitrogen (N) in excreta represents a possible strategy to decrease greenhouse gas (GHG) emissions from livestock. In this regard, ingestion of small amounts of condensed quebracho tannin has been found to reduce N concentration in livestock urine. In this study, we sought to quantify the effects of tannin-affected cattle urine, normal cattle urine, and NH4NO3 in solution on greenhouse gas flux. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) flux was measured using static chamber methodology from the three N treatments and a no application control over a six-week period in a mixed grass prairie in west-central North Dakota, USA. Over the course of the study, average CO2 emission was greatest from normal urine (335 ± 8 mg C m-2 hr-1) and least from the control (229 ± 19 mg C m-2 hr-1), with intermediate fluxes for the tannin urine and NH4NO3 treatments (290 ± 27 and 286 ± 54 mg C m-2 hr-1, respectively). Methane uptake was prevalent throughout the study, as soil conditions were predominantly warm and dry. Uptake of CH4 was greatest within the control (-30 ± 2 µg C m-2 hr-1) and least in the tannin urine treatment (-12 ± 4 µg C m-2 hr-1). Uptake of CH4 was over 40% less within the tannin urine treatment as compared to normal urine, and may have been repressed by the capacity of tannin to bind monooxygenases responsible for CH4 oxidation. Average N2O emission from NH4NO3 solution was more than twice that of all other treatments. Though the tannin urine treatment possessed 34% less N than normal cattle urine, cumulative N2O emission between the treatments did not differ. Results from this study suggest the use of condensed quebracho tannin as a dietary amendment for livestock does not yield GHG mitigation benefits in the short-term.
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Poultry Litter Study for Agricultural Antibiotic Resistance in Bowling Green, Kentucky Poultry litter (PL) is a by-product of broiler production. Most PL is land applied. Land-applied PL is a valuable nutrient source for crop production but can also be a route of environmental contamination with manure-borne bacteria. The objective of this study was to characterize the fate of pathogens, fecal indicator bacteria (FIB), and bacteria containing antibiotic resistance genes (ARGs) after application of PL to soils under conventional till or no-till management. This 2-yr study was conducted in accordance with normal agricultural practices, and microbial populations were quantified using a combination of culture and quantitative, real-time polymerase chain reaction analysis. Initial concentrations of Campylobacter jejuni in PL were 5.4 ± 3.2 × 106 cells g-1 PL; Salmonella sp. was not detected in the PL but was enriched periodically from PL-amended soils. Escherichia coli was detected in PL (1.5 ± 1.3 × 102 culturable or 1.5 ± 0.3 × 107 genes g-1) but was rarely detected in field soils, whereas enterococci (1.5 ± 0.5 × 108 cells g-1 PL) were detected throughout the study. These results suggest that enterococci may be better FIB for field-applied PL. Concentrations of ARGs for sulfonamide, streptomycin, and tetracycline resistance increased up to 3.0 orders of magnitude after PL application and remained above background for up to 148 d. These data provide new knowledge about important microbial FIB, pathogens, and ARGs associated with PL application under realistic field-based conditions.
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Corn-Switchgrass Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network and Resilient Economic Agricultural Practices in Lincoln, Nebraska Lincoln NE Corn-Switchgrass Experiment USDA-ARS REAP Study (Ithaca, NE) - NEMEIRR Sustainable intensification of high-yielding production systems may help meet increasing demands for food, fuel, and fiber worldwide. Specifically, corn stover is being removed by producers for livestock purposes, and stover is also targeted as a primary 2nd generation biofuel feedstock. The NEMEIRR experimental objectives are to quantify how stover removal (no removal, moderate removal, high removal) and tillage management (no-till, disk) affect crop yields, soil organic carbon, soil greenhouse gas emissions, and other soil responses (microbial community structure, function; soil health). This experiment is conducted in a fully irrigated continuous corn system in the western Corn Belt, and soil and plant measurements have been taken since study establishment in 2001. By: V.L. Jin (1 Sep 2016). marginal or idle cropland in the USA alone [In Approxi-mately 40% of USA maize (Zea map L) grain production is used for fuel ethanol production and the non-grain biomass or stover remaining after grain harvest has been proposed as a significant cellulosic feedstock for advance biofue Is production [18,191. No-till or minimum-till farming practices have increased in the USA because of their con-servation benefits and reduced production costs (201. Infor-mation on the effect of maize stover removal under no-till management on soil C from long-term Arles has not been available to date [211. Most of the research on SOC in agricultural production systems focused on C in the 0 to 30 cm depth 122-271. A few studies in which soil sampling has been conducted at greater depths indicate that !reduc-tion agriculture affects soil C deeper in the soil profile 128,291. We initiated a replicated, long-term, non-irrigated soil C sequestration study in 1998 in eastern Nebraska. USA. to evaluate the effects of N fertilizer and harvest management treatments on SOC for switchgrass managed far biomass production and for a no-till maze production system with and without stover removal. It is the longest on-going C sequestration study on these crops grown for bioenergy. Our hypotheses were that N knilization and harvest manage-ment practices affect soil C sequestration in both no-till maize and switchgrass biomass production systems and that these changes occur deeper than 30 cm in the soil profile. Herein, we report the changes in SOC that occurred during the period from 1998 to 3007. Materials and Methods Experiment Field. The field used in the study was similar to the marginally productive fields expected to be used for switchgrare biomass production anti is in the western part of the main maize production area of the USA. it is located on the University of Nebraska's Agricultural Research and Development Center (ARDC), Ithaca. Nebraska, USA (latitude 41.151, longitude 96.401 which is 50 km west of Omaha, NE. The field has Yutan silty clay loam (fine-silty, mixed, supaactive, mesic Mollie I 11,h:daft) and Tomek silt loam (fine, smectit ic, mesic Pachic Argiudoll ) soils. The ranges in the surface three depths of the Yutan soil for water 01 and kw CEC were 6.2 to 6.8 and 26 to 32 emotes kg r,respectively. The corresponding range in the surface three depths of the Tomek soil were water p11 values of 6.1 to 7.0 and a CEC range of from 24.4 to 32.3 moles kg-I. It is one of the least productive fields of the ARDC and is typical of marginally productive cropland fields Out might be used for switchgrass production for bier energy. The field used in the study was previously in sorghum (Sorghwn bicolor (L) Moench) in 1996 and in soybeans (Gipine mar (L) Merr.) in 1997. Experimental Design The study is a randomized (r-3) complete block split-split plot experimental design. Large rots were used so that field scale equipment could be used. Main plot lengths are the width of the field (ISO m) and are 18 m wide. Main plot treatments were two cultivars of switchgrass, Trailblazer and Cave-in-Rock, and no-till maize. The maize hybrid used was a commercial glyphosate (Roundupt? tolerant hybrid adapted to the region. The experiment was established in 1998 with the planting of the switchgrass plots. In 1998, plots designated for the no-till maize treatments were planted to glyphosate tolerant soybeans and grown using no-till management. No-till maize production began in 1999. Main plots were subdivided into three subplots which were used for N fertility treatments. Subplots are 30 m long x18 m wide and are separated by 15 m wide alleys. Nitrogen (N) fertilizer rates were randomly assigned to the subplots within species main plots. No fertilizer was applied during the establishment year for the switchgrass. In 1999, N fenilizer treatments were NI -0, 1¦2 - 80, N3-180, and N4-240 kg N he'. From 2000 on. they were NI -0, N2-60, N3-120, and N4-180 kg N he'. Fertilizer rates were reduced for 2000 and thereafter because of the 1999 resuhs on maize and the summarization of previous fertility re-search on switchgrass [34 Rates on the switchgrass were NI, N2, and N3. Rates used on no-till maize were N2, N3, and N4. Ammonium nitrate fertilizer was broadcast with a bulk spreader throughout the duration of the study. The 0 N-rate for switchgrass was used as a low input treatment only for switchgrass. In 2001. the switchgrass and corn subplots were split lengthwise into 9 m wide sub-subplots for harvest treatments. Switchgrass Management Switchgrass plots were seeded directly into the soybean stubble from the previous year using a no-till drill with a planting rate of 6.7 kg he' (pure live seed basis). A re-emergence application of 2 kg hat atrazine [Aaoex 4 Lit: 6-chloro-N-erhyl-Isr-(1-methylethyl)-1, 3. 5-triazine-2, 4- di amine' was applied for weed control. There were no other management inputs the establishment year. The 60 and 120 kg N ha-I rates represent the low to high rates recom-mended switchtoass grown for bioenergy [301 with the 0 rate representative or a no-input system. A previous study [301 showed that switchgrass harvested after a killing frost had significantly less N in the biomass than switchgrass harvested at anthesis indicating N was being recycled to the roots of switchgrass late in the growing season. Begin-ning in 2001. harvest treatments were applied to the sib-subplots within switchgrass cultivar N-fertility subplots to determine if harvest date might affect SOC. One harvest treatment (H I) was a mid-August harvest and the other (le) was a harvest in October or November, following a killing frost. Plots were harvested only once a year. A 4.6)(0.9 m (4.2 m2) area was harvested in each subplot with a flail-type plot harvester in 1998 and the following April, all remaining biomass from the previous year was removed with a field harvester prior to spring green-up. In 1999 and thereafter, switchgrass yield harvests weir made with flail harvesters and associated weighing equipment by harvesting a 0.9 to 1.8 m wide swath (varied with harvester used) the full 30 m length of the plots. At time of harvest, subsamples were collected from each sub-subplot, weighed for moisture con-tent, dried at 50°C for 48 h. and reweighed to determine dry matter content Yields were adjusted to a dry weight basis. The C concentration of the switchgrass samples was deter-mined using near infrared spectrometer (NIRS) procedures and calibrations 1311. A field flail harvester was used to remove all remaining biomass from the plots immediately following the yield harvests using the same harvest height of 10 cm. Maize Management Maize seed was planted directly into soybean stubble of the previous year in 1999 with a no-till drill and the maize plots of the previous year thereafter. The maize was gown in 0.76 m wide rows. The N rates that were used represent the low-to-high rates for maize grown under rarofed conditions in the region. Nitrogen fertilizer was applied using the same equipment as for switchgass plots. Glyphosate herbicide was applied after the maize had emerged and was about 40 cm in height. No other management inputs were applied until grain harvest Aboveground samples (one row 4.4 m long) were collected soon after physiological maturity in each N rate subplot and later from each sub-subplot for total biomass yields. Ears were removed and stalks were then cut at ground level, chopped and weighed. A representative subsample was collected, dried and weighed for gravimetric moisttre determination to calculate stover dry matter pro-duction. Ears were dried and weighed, added to the calcu-lated stover weight to obtain total biomass yields on a dry weight basis. Maize grain yields were determined with a plot combine equipped with a weighing unit, subsamples were collected for moisture determination, and yields were adjusted to oven dry weight basis. Because of the emerging interest in using maize stover for biomass energy, in 2001 stover harvest treatments were applied to the sro-subplots. The harvest treatments were no residue harvested (11 1 ) and approximately 50 % of the stover remaining after grain harvest (112). Stover was harvested from the 112 treatments after grain harvest using the flail forage harvesters that were used to harvest switchgass plots. Harvested stover yields were determined by harvesting the stover from two non-border rows of each sub-subplot its entire 30 m length with a plot-flail harvester. The remaining rows were harvested with a field scale flail harvester set at the same 10 cm height as the plot harvester. All stover weights were con-vetted to a dry-weight basis (50°C oven for 48 h). Maize grain and stover samples were analyzed for total C by dry combustion 1321. Soil Sampling and Analysis Baseline soil samples were obtained in July 1998 and plots were thereafter re-sampled at approximately 3-year intervals in May 2001. April 2004, and in May 2007. The initial sampling location was in the center of each subplot. Subse-quent soil samples were offset a fixed distance from each subplot or sub-subplot center to prevent re-sampling of a previous sampling site from which soil had been removed. Sample collection was done using the procedures described by Follett et al. [331. In brief, the plant material was re-moved from the soil surface and then, using a flat-bladed shovel. undercutting and removing the soil from the 0-5. 5 -10, and 10-30 an depths. Samples were also collected from the 30-60. 60-90. 90-120. and 120-150 cm depths at the July 1998 and May 2007 sampling dates using a hydraulic probe. Soil bulk densities were determined using the USDA-NRCS National Soils Laboratory methods (34J. The stan-dardized procedure (Soil Survey Laboratory method 3B1) to measure bulk density requires collection of field occurring fabric (clods), coating them with Saran F-310 in the field (NRCS 2004; Soil Survey Laboratory method 311), transport to the laboratory, and desorption to 33 kPa (1/3 bar). After reaching equilibrium, the clod is weighed in air to measure mass and in water to measure its volume, and next dried at 110°C (230°F) with its mass and volume again determined. A correction is made fir mass and volume of rock fragments and the plastic coating with the BD value reported for < mm (0.079in) soil fabric. Once samples Were collected they were sieved through a 2 mm sieve and < mm plant material picked from the soil. air dried (room temperature), subsampled, mechanically ground to pass through a 0.2-mm sieve, and the robsamples were stored in sealed glass containers with screw type lids All soils were checked for carborstes and in the very few casts where carbonates existed they were removed prior to analyses for organic C using accepted procedures [35,36J. All analyses were on an oven dry weight (55°C). The methodology is such that both the isotopic C analyses and the analyses for the total SOC are date at the same time for the same sample.
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Farming Systems Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Morris, Minnesota Tillage is decreasing globally due to recognized benefits of fuel savings and improved soil health in the absence of disturbance. However, a perceived inability to control weeds effectively and economically hinders no-till adoption in organic production systems in the Upper Midwest, USA. A strip-tillage (ST) strategy was explored as an intermediate approach to reducing fuel use and soil disturbance, and still controlling weeds. An 8-year comparison was made between two tillage approaches, one primarily using ST the other using a combination of conventional plow, disk and chisel tillage [conventional tillage (CT)]. Additionally, two rotation schemes were explored within each tillage system: a 2-year rotation (2y) of corn (Zea mays L.), and soybean (Glycine max [L.] Merr.) with a winter rye (Secale cereale L.) cover crop; and a 4-year rotation (4y) of corn, soybean, spring wheat (Triticum aestivum L.) underseeded with alfalfa (Medicago sativa L.), and a second year of alfalfa. These treatments resulted in comparison of four main management systems CT-2y, CT-4y, ST-2y and ST-4y, which also were managed under fertilized and non-fertilized conditions. Yields, whole system productivity (evaluated with potential gross returns), and weed seed densities (first 4 years) were measured. Across years, yields of corn, soybean and wheat were greater by 34% or more under CT than ST but alfalfa yields were the same. Within tillage strategies, corn yields were the same in 2y and 4y rotations, but soybean yields, only under ST, were 29% lower in the fertilized 4y than 2 yr rotation. In the ST-4y system yields of corn and soybean were the same in fertilized and non-fertilized treatments. Over the entire rotation, system productivity was highest in the fertilized CT-2y system, but the same among fertilized ST-4y, and non-fertilized ST-2y, ST-4y, and CT-4y systems. Over the first 4 years, total weed seed density increased comparatively more under ST than CT, and was negatively correlated to corn yields in fertilized CT systems and soybean yields in the fertilized ST-2y system. These results indicated ST compromised productivity, in part due to insufficient weed control, but also due to reduced nutrient availability. ST and diverse rotations may yet be viable options given that overall productivity of fertilized ST-2y and CT-4y systems was within 70% of that in the fertilized CT-2y system. Closing the yield gap between ST and CT would benefit from future research focused on organic weed and nutrient management, particularly for corn.
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Biofuel Residue Removal Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network and Resilient Economic Agricultural Practices in Morris, Minnesota The Biofuel Residue Removal experiment was established at Swan Lake Research farm near Morris MN in 2005. It consists of 3 separate experimental sites, one for each of three tillages—Chisel Plow, No Tillage established in 1995 and No Tillage established in 2005. Four residue removal treatments with 4 replicates were established in a corn/soybean rotation where each phase of the rotation was present each year. Each replicate has 8 plots, 4 removal treatments times 2 crops. Residue removal treatments are no removal, half removal, complete removal, and 75 % removal which was changed to cob removal in 2008. The 3 experiments have a total of 96 plots—3 tillages x 4 removal rates x 2 crops x 4 replicates. Greenhouse gas fluxes were measured from spring of 2008 through planting in 2011 in the no and complete removal plots. Root and above ground samples were taken at 75% silk (corn) or R6 (soybean) for plots where greenhouse gasses were measured. Soil samples to 1 meter were taken in 2005 and 2010. Veronica Acosta-Martinez from Lubbock TX measured enzymes and FAME from samples taken in 2008. POM was measured in 2005 and 2009. Erosivity was measured using a rotary sieve in 2011, 2012, and 2013. Corn biomass was sampled at physiological maturity and divided into above ear shank, below ear shank, and cob. It was analyzed for C and N and microwave digested for ICP analysis.
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Fort Ellis Research and Extension Center Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Sidney, Montana Sheep (Ovis aries L.) grazing is an inexpensive method of weed control in dryland cropping systems but little is known about its effect on net greenhouse gas (GHG) emissions. We evaluated the effect of sheep grazing compared to herbicide application for weed control on GHG (CO2, N2O, and CH4) emissions from May to October, 2010 and 2011, net global warming potential (GWP), and greenhouse gas intensity (GHGI) in a silt loam under dryland cropping systems in western Montana. Treatments were two fallow management practices (sheep grazing [GRAZ] and herbicide application [CHEM]) and three cropping sequences (continuous alfalfa [Medicago sativa L.] [CA], continuous spring wheat [Triticum aestivum L.] [CSW], and spring wheat-pea [Pisum sativum L.] /barley [Hordeum vulgaris L.] hay-fallow [W-P/B-F]). Gas samples were collected at 3 to 14 d intervals with a vented, static chamber. Regardless of treatments, GHG fluxes peaked immediately following substantial precipitation (>12 mm) and/or N fertilization mostly from May to August. Total CO2 flux from May to October was greater in GRAZ with CA, but total N2O flux was greater in CHEM and GRAZ with CSW than in other treatments. Total CH4 flux was greater in CA than in W-P/B-F. Net GWP and GHGI were greater in GRAZ with W-P/B-F than in most other treatments. Greater CH4 flux due to increased enteric fermentation as a result of longer duration of grazing during fallow, followed by reduced crop residue returned to the soil and/or C sequestration rate, probably increased net GHG flux in GRAZ with W-P/B-F. Sheep grazing on cropping sequence containing fallow may not reduce net GHG emissions compared to herbicide application for weed control on continuous crops.