- Authors:
- Source: United States Department of Energy
- Volume: 6450-010P
- Year: 2006
- 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:
- 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.
- Authors:
- Deregibus, V. A.
- Bartoloni, N.
- Rodriguez, A. M.
- Jacobo, E. J.
- Source: Rangeland Ecology & Management
- Volume: 59
- Issue: 3
- Year: 2006
- Summary: We evaluated the adequacy of rotational grazing to improve rangeland condition in the Flooding Pampa region, eastern Argentina, comparing the floristic composition dynamic of the 2 main plant communities under rotational and continuous grazing over a study period of 4 years (1993-1996). The experiment was conducted in commercial farms located in 4 sites of the Flooding Pampa region. In each site, a couple of farms, one managed under rotational grazing (implemented in 1989) and an adjacent one managed under continuous grazing at a similar stocking rate (1 AU(.)ha(-1)), constituted the replications of the experiment. Basal cover of species, litter, and bare soil were monitored in midslope and lowland grassland communities on each farm. Total plant basal cover in midslope and in lowland communities remained unchanged over the whole experimental period under both grazing methods. Under rotational grazing, litter cover was higher in both communities while the amount of bare soil showed a significant reduction in lowlands and a tendency to be lower in midslope. Basal cover of legumes, C-3 annual and C-3 perennial grasses was higher, while cover of C-4 prostrate grasses was lower under rotational grazing in the midslope community. In the lowland community, rotational grazing effects were evident only in the drier years, when higher cover of hydrophytic grasses and legumes and lower cover of forbs occurred. Plant species diversity did not change in response to grazing. In conclusion, rotational grazing promoted functional groups composed of high forage value species and reduced bare soil through the accumulation of litter. These changes indicate an improvement in rangeland condition and in carrying capacity. As the stocking rate was approximately 60% higher than the average stocking rate of the Flooding Pampa region, we believe that productivity and sustainability may be compatible by replacing continuous with rotational grazing.
