• Authors:
    • Abney, T. S.
    • Vyn, T. J.
    • Stott, D. E.
    • Gal, A.
    • Omonode, R. A.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 2
  • Year: 2006
  • Summary: For various reasons, North American crop farmers are more likely to practice limited-duration no-till than continuous no-till (NT). Little is known about effects of short-term no-till (ST-NT) on organic C and total N relative to NT and conventional-till systems. A field experiment was initiated in 1980 to study the effects of NT, chisel plow (CP), and moldboard plow in continuous corn (CC; Zeamays L.) and soybean (Glycinemax. L.)-corn (SC) rotations on dark prairie soil. In 1996, the moldboard treatments were split into a ST-NT subplot and an intermittently chisel-plowed (STI-CP) subplot that was chiseled only before corn. In 2003, soil samples were taken incrementally to the 1.0-m depth from NT, CP, ST-NT, and STI-CP plots. Soil C and N accumulation was unaffected by rotation system at any depth interval. Tillage treatments significantly affected soil C and N concentrations only in the upper 50 cm. On an equivalent soil mass basis, C storage to 1.0 m after 24 yr totaled 151 Mg ha21 in continuous NT, but just 108 Mg ha21 in continuous CP. Short-term no-till and STI-CP systems resulted in 26 and 21 Mg ha21, respectively, more soil C than CP. Total N storage was similar for NT and ST-NT systems, but was significantly lower (4 Mg ha21 less) with CP. Our results suggest that the combination of moldboard plowing (17 yr) followed by short-term (6-7 yr) no-till or intermittent chisel was generally superior to continuous chisel plowing (24 yr) in soil C and N contents.
  • Authors:
    • Kaspar, T. C.
    • Parkin, T. B.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 4
  • Year: 2006
  • Summary: Soil N2O emissions from three corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems in central Iowa were measured from the spring of 2003 through February 2005. The three managements systems evaluated were full-width tillage (fall chisel plow, spring disk), no-till, and no-till with a rye (Secale cereale L. Rymin') winter cover crop. Four replicate plots of each treatment were established within each crop of the rotation and both crops were present in each of the two growing seasons. Nitrous oxide fluxes were measured weekly during the periods of April through October, biweekly during March and November, and monthly in December, January, and February. Two polyvinyl chloride rings (30-cm diameter) were installed in each plot (in and between plant rows) and were used to support soil chambers during the gas flux measurements. Flux measurements were performed by placing vented chambers on the rings and collecting gas samples 0, 15, 30, and 45 min following chamber deployment. Nitrous oxide fluxes were computed from the change in N2O concentration with time, after accounting for diffusional constraints. We observed no significant tillage or cover crop effects on N2O flux in either year. In 2003 mean N2O fluxes were 2.7, 2.2, and 2.3 kg N2O-N ha-1 yr-1 from the soybean plots under chisel plow, no-till, and no-till + cover crop, respectively. Emissions from the chisel plow, no-till, and no-till + cover crop plots planted to corn averaged 10.2, 7.9, and 7.6 kg N2O-N ha-1 yr-1, respectively. In 2004 fluxes from both crops were higher than in 2003, but fluxes did not differ among the management systems. Fluxes from the corn plots were significantly higher than from the soybean plots in both years. Comparison of our results with estimates calculated using the Intergovernmental Panel on Climate Change default emission factor of 0.0125 indicate that the estimated fluxes underestimate measured emissions by a factor of 3 at our sites.
  • Authors:
    • Boyles, S. B.
    • Nelson, R. G.
    • Rice, C. W.
    • Williams, J. R.
    • Pendell, D. L.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 4
  • Year: 2006
  • Summary: This study examined the economic potential of no-tillage versus conventional tillage to sequester soil carbon by using two rates of commercial N fertilizer or beef cattle manure for continuous corn (Zea mays L.) production. Yields, input rates, field operations, and prices from an experiment were used to simulate a distribution of net returns for eight production systems. Carbon release values from direct, embodied, and feedstock energies were estimated for each system, and were used with soil carbon sequestration rates from soil tests to determine the amount of net carbon sequestered by each system. The values of carbon credits that provide an incentive for managers to adopt production systems that sequester carbon at greater rates were derived. No-till systems had greater annual soil carbon gains, net carbon gains, and net returns than conventional tillage systems. Systems that used beef cattle manure had greater soil carbon gains and net carbon gains, but lower net returns, than systems that used commercial N fertilizer. Carbon credits would be needed to encourage the use of manure-fertilized cropping systems.
  • Authors:
    • Kimble, J. M.
    • McCarty, G. W.
    • Follett, R. F.
    • Reeves, J. B.
  • Source: Communications in Soil Science and Plant Analysis
  • Volume: 37
  • Issue: 15-20
  • Year: 2006
  • Summary: The objective of this study was to compare mid-infrared (MIR) an near-infrared (NIR) spectroscopy (MIRS and NIRS, respectively) not only to measure soil carbon content, but also to measure key soil organic C (SOC) fractions and the delta13C in a highly diverse set of soils while also assessing the feasibility of establishing regional diffuse reflectance calibrations for these fractions. Two hundred and thirty-seven soil samples were collected from 14 sites in 10 western states (CO, IA, MN, MO, MT, ND, NE, NM, OK, TX). Two subsets of these were examined for a variety of C measures by conventional assays and NIRS and MIRS. Biomass C and N, soil inorganic C (SIC), SOC, total C, identifiable plant material (IPM) (20x magnifying glass), the ratio of SOC to the silt+clay content, and total N were available for 185 samples. Mineral-associated C fraction, delta13C of the mineral associated C, delta13C of SOC, percentage C in the mineral-associated C fraction, particulate organic matter, and percentage C in the particulate organic matter were available for 114 samples. NIR spectra (64 co-added scans) from 400 to 2498 nm (10-nm resolution with data collected every 2 nm) were obtained using a rotating sample cup and an NIRSystems model 6500 scanning monochromator. MIR diffuse reflectance spectra from 4000 to 400 cm-1 (2500 to 25,000 nm) were obtained on non-KBr diluted samples using a custom-made sample transport and a Digilab FTS-60 Fourier transform spectrometer (4-cm-1 resolution with 64 co-added scans). Partial least squares regression was used with a one-out cross validation to develop calibrations for the various analytes using NIR and MIR spectra. Results demonstrated that accurate calibrations for a wide variety of soil C measures, including measures of delta13C, are feasible using MIR spectra. Similar efforts using NIR spectra indicated that although NIR spectrometers may be capable of scanning larger amounts of samples, the results are generally not as good as achieved using MIR spectra.
  • Authors:
    • Parrish, D. J.
    • Ebinger, M. H.
    • Lal, R.
    • Sartori, F.
  • Source: Critical Reviews in Plant Sciences
  • Volume: 25
  • Issue: 5
  • Year: 2006
  • Summary: Energy crops are fast-growing species whose biomass yields are dedicated to the production of more immediately usable energy forms, such as liquid fuels or electricity. Biomass-based energy sources can offset, or displace, some amount of fossil-fuel use. Energy derived from biomass provides 2 to 3% of the energy used in the U.S.A.; but, with the exception of corn-(Zea mays L.)-to-ethanol, very little energy is currently derived from dedicated energy crops. In addition to the fossil-fuel offset, energy cropping might also mitigate an accentuated greenhouse gas effect by causing a net sequestration of atmospheric C into soil organic C (SOC). Energy plantations of short-rotation woody crops (SRWC) or herbaceous crops (HC) can potentially be managed to favor SOC sequestration. This review is focused primarily on the potential to mitigate atmospheric CO2 emissions by fostering SOC sequestration in energy cropping systems deployed across the landscape in the United States. We know that land use affects the dynamics of the SOC pool, but data about spatial and temporal variability in the SOC pool under SRWC and HC are scanty due to lack of well-designed, long-term studies. The conventional methods of studying SOC fluxes involve paired-plot designs and chronosequences, but isotopic techniques may also be feasible in understanding temporal changes in SOC. The rate of accumulation of SOC depends on land-use history, soil type, vegetation type, harvesting cycle, and other management practices. The SOC pool tends to be enhanced more under deep-rooted grasses, N-fixers, and deciduous species. Carbon sequestration into recalcitrant forms in the SOC pool can be enhanced with some management practices (e.g., conservation tillage, fertilization, irrigation); but those practices can carry a fossil-C cost. Reported rates of SOC sequestration range from 0 to 1.6 Mg C ha(-1) yr(-1) under SRWC and 0 to 3 Mg C ha(-1) yr(-1) under HC. Production of 5 EJ of electricity from energy crops-a perhaps reasonable scenario for the U.S.A.-would require about 60 Mha. That amount of land is potentially available for conversion to energy plantations in the U.S.A. The land so managed could mitigate C emissions (through fossil C not emitted and SOC sequestered) by about 5.4 Mg C ha(-1) yr(-1). On 60 Mha, that would represent 324 Tg C yr(-1)-a 20% reduction from current fossil-fuel CO2 emissions. Advances in productivity of fast-growing SRWC and HC species suggest that deployment of energy cropping systems could be an effective strategy to reduce climate-altering effects of anthropogenic CO2 emissions and to meet global policy commitments.
  • Authors:
    • Angers, D. A.
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 86
  • Issue: 3
  • Year: 2006
  • Summary: In response to Kyoto Protocol commitments, countries can elect agricultural carbon sinks to offset emissions from other sectors, but they need to verify soil organic carbon (SOC) stock change. We summarize issues we see as barriers to obtaining accurate measures of SOC change, including: soil depth, bulk density and equivalent soil mass, representation of landscape components, experimental design, and the equilibrium status of the SOC. If the entire plow depth is not considered, rates of SOC storage under conservation compared with conventional tillage can be overstated. Bulk density must be measured to report SOC stock on an area basis. More critical still is the need to report SOC stock on an equivalent mass basis to normalize the effects of management on bulk deisity. Most experiments comparing SOC under differing management have been conducted in small, flat research plots. Although results obtained from these long-term experiments have been useful to develop and validate SOC prediction models, they do not adequately consider landscape effects. Traditional agronomic experimental designs can be inefficient for assessing small changes in SOC stock within large spatial variability. Sampling designs are suggested to improve statistical power and sensitivity in detecting changes in SOC stocks over short time periods.
  • Authors:
    • Varvel, G. E.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 2
  • Year: 2006
  • Summary: Sequestration and storage of carbon (C) by agricultural soils has been cited as one potential part of the solution to soil degradation and global climate change. However, C sequestration in soils is a slow and dynamic process. The objective of this study was to evaluate the effects of crop rotation and N fertilizer management on soil organic C (SOC) levels at several points in time during 18 yr of a long-term study in the Western Corn Belt. Seven cropping systems (three monoculture, two 2-yr, and two 4-yr rotations) with three levels of N fertilizer were compared. Soil samples were taken in the spring in 1984, 1992, 1998, and 2002 to a depth of 30 cm in 0- to 7.5-, 7.5- to 15-, and 15- to 30-cm increments. No differences were obtained in SOC levels in 1984 at the beginning of the study. After 8 yr, rotation significantly increased SOC 449 kg ha-1 across all cropping systems. From 1992 to 2002, SOC levels in the 0- to 7.5-cm depth decreased by 516 kg ha-1 across all cropping systems. Soil organic C levels in the 7.5- to 15-cm depths in 1992 and 2002 demonstrated similar rotation effects to those in the surface 0- to 7.5-cm, being not significantly affected from 1984 to 1992 but being significantly decreased from 1992 to 2002 (568 kg SOC ha-1 across all cropping systems). Many of the SOC gains in the surface 30 cm measured during the first 8 yr of the study were lost during the next 10 yr in all but the 4-yr cropping systems after 18 yr. The loss of SOC in this latter period occurred when depth of tillage was increased by using a tandem disk with larger-diameter disks. These results demonstrate that more than one point-in-time measurement from long-term experiments is necessary to monitor SOC changes when several management variables, such as cropping system and N fertilizer, are being used. They also indicate that apparent small changes in cultural practices, such as in depth of tillage in this experiment, can significantly change SOC dynamics in the soil. Subtle changes in cultural practices (e.g., tillage depth) can have significant long-term results, but long-term experiments are required to quantify their impact under variable climatic conditions.
  • Authors:
    • Spokas, K. A.
    • Dolan, M. S.
    • Baker, J. M.
    • Venterea, R. T.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 5
  • Year: 2006
  • Summary: Few studies have examined the impacts of rotational tillage regimes on soil carbon (C) and nitrogen (N). We measured the C and N content of soils managed under corn (Zea mays L.)-soybean (Glycine max L.) rotation following 10 and 15 yr of treatments. A conventional tillage (CT) regime employing moldboard and chisel plowing in alternate years was compared with both continuous no-till (NT) and biennial tillage (BT), which employed chisel plowing before soybean only. While masses of C and N in the upper 0.3 m under both BT and NT were higher than CT, only the BT treatment differed from CT when the entire sampled depth (0.6 m) was considered. Decreased C inputs, as indicated by reduced grain yields, may have limited C storage in the NT system. Thus, while more C was apparently retained under NT per unit of C input, some tillage appears necessary in this climate and cropping system to maximize C storage. Soil carbon dioxide (CO2) fluxes under NT were greater than CT during a drier than normal year, suggesting that C storage may also be partly constrained under NT due to wetter conditions that promote increased soil respiration. Increased temperature sensitivity of soil respiration with increasing soil moisture was also observed. These findings indicate that long-term biennial chisel plowing for corn-soybean in the upper mid-west USA can enhance C storage, reduce tillage-related fuel costs, and maintain yields compared with more intensive annual tillage.
  • Authors:
    • Hegymegi, P.
    • Gal, A.
    • Smith, D. R.
    • Omonode, R.A.
    • Vyn, T. J.
  • Source: 17th Triennial Conference of the International Soil Tillage Research Organisation (ISTRO)Conference Proceedings
  • Year: 2006
  • Summary: Few researchers have assessed the possibly interacting effects of long-term tillage and rotation practices on organic carbon (OC) sequestration in soil to depths well beyond the maximum depth of tillage operations while also studying carbon dioxide (CO2) emissions from the soil surface of those same experiments. This study was conducted from 2003 to 2005 on tillage and rotation experiments initiated 30 yrs ago in West-Central Indiana on a dark prairie soil with silty clay loam texture.. Our objectives were to determine how tillage systems such as moldboard plow (MP), chisel (CP), and no-till affected OC retention and surface soil CO2 emissions. These tillage systems were investigated in continuous corn and corn-soybean rotations. Soil OC distribution was determined from soil cores in multiple increments to a 1.0 m depth in late 2003 and early 2004. Gas fluxes from the soil surface were measured at weekly or biweekly intervals for up to 14 weeks in the corn growing seasons of 2004 and 2005. The increase in soil OC with no-till relative to moldboard plow averaged just 8 t/ha (or 5% on an equivalent mass basis) in both rotations. Rotation systems had little impact on OC; continuous corn was not superior to the soybean-corn rotation in either no-till or moldboard plow systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC, relative to no-till, in the 30-50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Growing season CO2 emissions were significantly affected by rotation but not by tillage treatments. . CO2 emission was higher under continuous corn than with corn following soybean. Our results suggest that conclusions about soil OC gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken much deeper than the deepest depth of direct soil disturbance by tillage implements. After 3 decades of consistent tillage and crop rotation management, tillage system impacts on overall soil OC retention and seasonal CO2 emissions were less than expected. Continuous corn did not store more soil OC than rotation corn, perhaps because continuous corn emitted more CO2 from the soil surface than corn- soybean rotation systems.
  • Authors:
    • Jakas, M. C. Q.
    • Rosenberg, N. J.
    • McGill, W. B.
    • Williams, J. R.
    • Izaurralde, R. C.
  • Source: Ecological Modelling
  • Volume: 192
  • Issue: 3-4
  • Year: 2006
  • Summary: Soil carbon sequestration (SCS) has emerged as a technology with significant potential to help stabilize atmospheric CO2 concentrations and thus reduce the threat of global warming. Methods and models are needed to evaluate and recommend SCS practices based on their effects on carbon dynamics and environmental quality. Environment Policy Integrated Climate (EPIC) is a widely used and tested model for simulating many agroecosystem processes including plant growth, crop yield, tillage, wind and water erosion, runoff, soil density, and leaching. Here we describe new C and N modules developed in EPIC built on concepts from the Century model to connect the simulation of soil C dynamics to crop management, tillage methods, and erosion processes. The added C and N routines interact directly with soil moisture, temperature, erosion, tillage, soil density, leaching, and translocation functions in EPIC. Equations were also added to describe the effects of soil texture on soil C stabilization. Lignin concentration is modeled as a sigmoidal function of plant age. EPIC was tested against data from a conservation reserve program (CRP) 6-year experiment at five sites in three U.S. Great Plains states and a 61-year long-term agronomic experiment near Breton, Canada. Mean square deviations (MSD) calculated for CRP sites were less than 0.01 (kg C m(-2))(2), except for one site where it reached 0.025 (kg C m(-2))(2). MSD values in the 61-year experiment ranged between 0.047 and 0.077 (kg C m(-2))(2). The version of the EPIC model presented and tested here contains the necessary algorithms to simulate SCS and improve understanding of the interactions among soil erosion, C dynamics, and tillage. A strength of the model as tested is its ability to explain the variability in crop production, C inputs and SOC and N cycling over a wide range of soil, cropping and climatic conditions over periods from 6 to 61 years. For example, at the Breton site over 61 years, EPIC accounted for 69% of the variability in grain yields, 89% of the variability in C inputs and 91% of the variability in SOC content in the top 15 cm. Continued development is needed in understanding why it overpredicts at low SOC and underpredicts at high SOC. Possibilities now exist to connect the C and N cycling parts of EPIC to algorithms to describe denitrification as driven by C metabolism and oxygen availability. (c) 2005 Elsevier B.V. All rights reserved.