• Authors:
    • Ahuja, L. R.
    • Westfall, D. G.
    • Peterson, G. A.
    • Sherrod, L. A.
  • Source: Soil Science Society of America Journal
  • Volume: 67
  • Issue: 5
  • Year: 2003
  • Summary: Soil organic C (SOC) has decreased under cultivated wheat (Triticum aestivum)-fallow (WF) in the central Great Plains.We evaluated the effect of no-till systems of WF, wheat-corn (Zea Mays)-fallow (WCF), wheat-corn-millet (Panicum miliaceum)-fallow, continuous cropping (CC) without monoculture, and perennial grass (G) on SOC and total N (TN) levels after 12 yr at three eastern Colorado locations. Locations have long-term precipitation averages of 420 mm but increase in potential evapotranspiration (PET) going from north to south. Within each PET location, cropping systems were imposed across a topographic sequence of summit, sideslope, and toeslope. Cropping intensity, slope position, and PET gradient (location) independently impacted SOC and TN to a 5-cm soil depth. Continuous cropping had 35 and 17% more SOC and TN, respectively, than the WF system. Cropping intensity still impacted SOC and TN when summed to 10 cm with CC > than WF. Soil organic C and TN 20% in the CC system compared with WF in the 0- to 10-cm depth. The greatest impact was found in the 0- to 2.5-cm layer, and decreased with depth. Soil organic C and TN levels at the high PET site were 50% less than at the low and medium PET sites, and toeslope soils were 30% greater than summit and sideslopes. Annualized stover biomass explained 80% of the variation in SOC and TN in the 0- to 10-cm soil profile. Cropping systems that eliminate summer fallowing are maximizing the amount of SOC and TN sequestered.
  • Authors:
    • Paustian, K.
    • Eve, M.
    • Sperow, M.
  • Source: Climatic Change
  • Volume: 57
  • Issue: 3
  • Year: 2003
  • Summary: Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO2 increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (1012g) C yr-1, over present rates of 17 Tg C yr-1 (estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129 Mha) would increase soil C sequestration by 47 Tg C yr-1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about 37 Tg C yr-1. Elimination of summer fallow practices and conversion of highly erodible cropland to perennial grass cover could sequester around 20 and 28 Tg C yr-1, respectively. The soil C sequestration potential from including a winter cover crop on annual cropping systems was estimated at 40 Tg C yr-1. All rates were estimated for a fifteen-year projection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr-1) represents about 5% of 1999 total U.S. CO2 emissions or nearly double estimated CO2 emissions from agricultural production (43 Tg C yr-1). For purposes of stabilizing or reducing CO2 emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions (2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.
  • Authors:
    • Angers, D. A.
    • Gregorich, E. G.
    • VandenBygaart, A. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 83
  • Issue: 4
  • Year: 2003
  • Summary: To fulfill commitments under the Kyoto Protocol, Canada is required to provide verifiable estimates and uncertainties for soil organic carbon (SOC) stocks, and for changes in those stocks over time. Estimates and uncertainties for agricultural soils can be derived from long-term studies that have measured differences in SOC between different management practices. We compiled published data from long-term studies in Canada to assess the effect of agricultural management on SOC. A total of 62 studies were compiled, in which the difference in SOC was determined for conversion from native land to cropland, and for different tillage, crop rotation and fertilizer management practices. There was a loss of 24 ± 6% of the SOC after native land was converted to agricultural land. No-till (NT) increased the storage of SOC in western Canada by 2.9 ± 1.3 Mg ha–1; however, in eastern Canada conversion to NT did not increase SOC. In general, the potential to store SOC when NT was adopted decreased with increasing background levels of SOC. Using no-tillage, reducing summer fallow, including hay in rotation with wheat (Triticum aestivum L.), plowing green manures into the soil, and applying N and organic fertilizers were the practices that tended to show the most consistent increases in SOC storage. By relating treatment SOC levels to those in the control treatments, SOC stock change factors and their levels of uncertainty were derived for use in empirical models, such as the United Nations Intergovernmental Panel on Climate Change (IPCC) Guidelines model for C stock changes. However, we must be careful when attempting to extrapolate research plot data to farmers fields since the history of soil and crop management has a significant influence on existing and future SOC stocks.
  • Authors:
    • Morgan, J. A.
    • Pendall, E.
    • Mosier, A. R.
  • Source: Atmospheric Chemistry and Physics
  • Volume: 3
  • Issue: 5
  • Year: 2003
  • Summary: An open-top-chamber (OTC) CO2 enrichment (approximately 720 mmol mol-1) study was conducted in the Colorado shortgrass steppe from April 1997 through October 2001. Aboveground plant biomass increased under elevated CO2 and soil moisture content was typically higher than under ambient CO2 conditions. Fluxes of CH4, CO2, NOx and N2O, measured weekly year round were not significantly altered by CO2 enrichment over the 55 month period of observation. During early summer of 2002, following the removal of the open-top-chambers from the CO2 enrichment sites in October 2001, we conducted a short term study to determine if soil microbial processes were altered in soils that had been exposed to double ambient CO2 concentrations during the growing season for the past five years. Microplots were established within each experimental site and 10mm of water or 10mm of water containing the equivalent of 10 g m-2 of ammonium nitrate-N was applied to the soil surface. Fluxes of CO2, CH4, NOx and N2O fluxes within control (unchambered), ambient CO2 and elevated CO2 OTC soils were measured at one to three day intervals for the next month. With water addition alone, CO2 and NO emission did not differ between ambient and elevated CO2 soils, while CH4 uptake rates were higher and N2O fluxes lower in elevated CO2 soils. Adding water and mineral N resulted in increased CO2 emissions, increased CH4 uptake and decreased NO emissions in elevated CO2 soils. The N addition study confirmed previous observations that soil respiration is enhanced under elevated CO2 and N immobilization is increased, thereby decreasing NO emission.
  • Authors:
    • Pu, X. P.
    • Kang, M. Y.
    • Hu, Z. Z.
    • Long, R. J.
    • Dong, S. K.
  • Source: Grass and Forage Science
  • Volume: 58
  • Issue: 3
  • Year: 2003
  • Summary: Abstract The productivity and nutritive value of some cultivated perennial grasses, Bromus inermis (B), Elymus sibricus (S), E. nutans (N), Agropyron cristatum (A), Poa crymophila (P) and mixtures B + N, S + A, B + S + A, S + B + N, N + S + A, B + S + N + A, B + N + A + P, B + S +A + P and S + N + A + P, in the alpine region of the Tibetan Plateau were investigated. Elymus nutans and E. sibricus and the mixtures, B + S + N + A, B + S +A + P and S + N + A + P, were most productive with yields of dry matter (DM) of between 11 000 and 14 000 kg-1 of biomass annually in the second harvest year. Acid-detergent fibre (ADF) concentrations increased (P < 0·05), and crude protein (CP) concentrations and in sacco DM degradability values decreased (P < 0·05) with the maturity of the cultivated grasses. Swards, based on these species and mixtures, have the potential to be the main choices for cultivation in the Tibetan Plateau because they produce more nutrients than other grass species and mixtures. Late August (flowering stage of dominant grasses) is the optimum time for harvesting as the yield of rumen-degradable CP is highest that of DM relatively high and the DM degradability is satisfactory.
  • Authors:
    • Saliendra, N. Z.
    • Johnson, D. A.
    • Gilmanov, T. G.
  • Source: Basic and Applied Ecology
  • Volume: 4
  • Issue: 2
  • Year: 2003
  • Summary: The sagebrush-steppe ecosystem covers more than 36 million ha and could play an important role in the global carbon cycle; however, quantitative estimates of CO2 fluxes on these extensive ecosystems are not available. The Bowen ratio/energy balance technique (BREB) was used to continuously monitor CO2 fluxes during the 1996 to 1999 growing seasons at a sagebrush-steppe site near Dubois, Idaho, USA. The daytime and night-time CO2 fluxes were modeled to provide estimates of occasionally missing or aberrant data points so that daily (24-h) integrals across the entire growing season could be quantified. Depending on the particular time of the season, daytime fluxes were best described by a rectangular hyberbolic, nonrectangular hyperbolic, or hysteresis-type functions that included radiation, relative humidity, and soil temperature. Night-time CO2 fluxes exhibited greater variability than daytime fluxes and were not closely correlated with any single meteorological characteristic. Night-time fluxes were predicted using a nonlinear parameter identification technique that estimated values of daytime respiration, which were significantly correlated with night-time fluxes. For the four growing seasons of our study, the integrated seasonal fluxes ranged from 284 to 1,103 g CO2 m-2 with an overall average of 635 g CO2 m-2. Respiratory losses during the non-growing season were estimated to be about 1.5 g CO2 m-2 day-1 or a total of 270 g CO2 m-2. This gives an annual net positive flux (carbon sequestration) estimate of 365 g CO2 m-2 (or 1.0 t C ha-1). These results suggest that the combination of BREB measurements and modeling techniques can be used to provide estimates of CO2 fluxes on important rangeland ecosystems.
  • Authors:
    • Vigil,M. F.
    • Nielsen,D. C.
    • Benjamin,J. G.
  • Source: Geoderma
  • Volume: 116
  • Issue: 1-2
  • Year: 2003
  • Summary: Soil management decisions often are aimed at improving or maintaining the soil in a productive condition. Several indicators have been used to denote changes in the soil by various management practices, but changes in bulk density is the most commonly reported factor. Bulk density, in and of itself, gives little insight on the underlying soil environment that affects plant growth. We investigated using the Least Limiting Water Range (LLWR) to evaluate changes in the soil caused by soil management. The LLWR combines limitations to root growth caused by water holding capacity, soil strength and soil aeration into a single number that can be used to determine soil physical improvement or degradation. The LLWR appeared to be a good indicator of plant productivity when the full potential of water holding capacity on available water can be realized, such as with wheat (Triticum aestivum, L.) grown in a no-till system when the wheat followed a fallow period. A regression of wheat yield to LLWR gave an r(2) of 0.76. The LLWR was a poorer indicator of plant productivity when conditions such as low total water availability limited the expression of the potential soil status on crop production. Dryland corn (Zea mays, L.) yields were more poorly correlated with LLWR (r(2)=0.18), indicating that, under dryland conditions, in-season factors relating to water infiltration may be more important to corn production than water holding capacity. An improved method to evaluate in-season soil environmental dynamics was made by using Water Stress Day (WSD). The WSD was calculated by summing the differences of actual water contents in the field from the limits identified by the LLWR during the growing season. A regression of irrigated corn yield with LLWR as the soil indicator of the soil environment resulted in an r(2) of 0.002. A regression of the same yield data with WSD as the indicator of the soil environment resulted in an r(2) of 0.60. We concluded that the LLWR can be a useful measure of management effects on soil potential productivity. Soil management practices that maximize the LLWR can maximize the potential of a soil for crop production. Knowledge of the LLWR for a soil can help the farm manager optimize growing conditions by helping schedule irrigation and for making tillage decisions. The WSD, calculated from the LLWR and in-season water dynamics, allows us to evaluate changes in the soil caused by differing soil management practices and identify critical periods of stress on the plant that can reduce production.
  • Authors:
    • Yang, H.
    • Walters, D. T.
    • Dobermann, A.
    • Cassman, K. G.
  • Source: Annual Review of Environment and Resources
  • Volume: 28
  • Issue: 1
  • Year: 2003
  • Summary: Agriculture is a resource-intensive enterprise. The manner in which food production systems utilize resources has a large influence on environmental quality. To evaluate prospects for conserving natural resources while meeting increased demand for cereals, we interpret recent trends and future trajectories in crop yields, land and nitrogen fertilizer use, carbon sequestration, and greenhouse gas emissions to identify key issues and challenges. Based on this assessment, we conclude that avoiding expansion of cultivation into natural ecosystems, increased nitrogen use efficiency, and improved soil quality are pivotal components of a sustainable agriculture that meets human needs and protects natural resources. To achieve this outcome will depend on raising the yield potential and closing existing yield gaps of the major cereal crops to avoid yield stagnation in some of the world's most productive systems. Recent trends suggest, however, that increasing crop yield potential is a formidable scientific challenge that has proven to be an elusive goal.
  • Authors:
    • McDonald, C.
    • Stevenson, F.
    • Zentner, R.
    • McConkey, B.
    • Miller, P.
    • Gan, Y.
  • Source: Agronomy Journal
  • Volume: 95
  • Issue: 2
  • Year: 2003
  • Summary: Crops grown in previous years impact the amounts of residual soil water and nutrients available for subsequent plant growth. Appropriate sequences allow efficient use of the available soil resources by the crop to increase yields at a system's level. This study was conducted to determine whether the grain yield and grain crude protein concentration (GCPC) of durum wheat ( Triticum turgidum L.) were related to crops grown in the previous 2 yr. Durum was grown following pulses [chickpea ( Cicer arietinum L.), lentil ( Lens culinaris Medik.), and dry pea ( Pisum sativum L.)], oilseed [mustard ( Brassica juncea L.) or canola ( B. napus L.)], and spring wheat ( Triticum aestivum L.) in southwest Saskatchewan from 1996 to 2000. Durum increased grain yields by 7% and GCPC by 11% when grown after pulse crops rather than after spring wheat. Durum after oilseeds increased grain yield by 5% and GCPC by 6%. Pulse and oilseed crops grown for the previous 2 yr increased durum grain yield 15% and GCPC 18% compared with continuous wheat systems. Fall residual soil NO 3-N and available soil water accounted for 3 to 28% of the increased durum yield in two of five site-years, whereas those two factors accounted for 12 to 24% of the increased GCPC in three of five site-years. Durum grain yield was negatively related to GCPC. The relationship was stronger when durum was preceded by oilseeds compared with pulses. Broadleaf crops in no-till cropping systems provide significant rotational benefits to durum wheat in the semiarid northern Great Plains.
  • Authors:
    • Shanahan, J. F.
    • Wienhold, B. J.
    • Mortensen, D. A.
    • Johnson, C. K.
    • Doran, J. W.
  • Source: Agronomy Journal
  • Volume: 95
  • Issue: 2
  • Year: 2003
  • Summary: Site-specific management (SSM) can potentially improve both economic and ecological outcomes in agriculture. Effective SSM requires strong and temporally consistent relationships among identified management zones; underlying soil physical, chemical, and biological parameters; and crop yields. In the central Great Plains, a 250-ha dryland experiment was mapped for apparent electrical conductivity (EC a). Eight fields were individually partitioned into four management zones based on equal ranges of deep (EC DP) and shallow (EC SH) EC a (approximately 0-30 and 0-90 cm depths, respectively). Previous experiments documented negative correlations between ECSH and soil properties indicative of productivity. The objectives of this study were to examine EC SH and EC DP relationships with 2 yr of winter wheat ( Triticum aestivum L.) and corn ( Zea mays L.) yields and to consider the potential applications of EC a-based management zones for SSM in a semiarid cropping system. Within-zone wheat yield means were negatively correlated with EC SH ( r=-0.97 to -0.99) and positively correlated with EC DP ( r=0.79-0.97). Within-zone corn yield means showed no consistent relationship with EC SH but positive correlation with EC DP ( r=0.81-0.97). Equal-range and unsupervised classification methods were compared for EC SH; within-zone yield variances declined slightly (0-5%) with the unsupervised approach. Yield response curves relating maximum wheat yields and EC SH revealed a boundary line of maximum yield that decreased with increasing EC SH. In this semiarid system, EC SH-based management zones can be used in SSM of wheat for: (i) soil sampling to assess residual nutrients and soil attributes affecting herbicide efficacy, (ii) yield goal determination, and (iii) prescription maps for metering inputs.