• Authors:
    • Cue, R. I.
    • Rochette, P.
    • Gregorich, E. G.
    • Whalen, J. K.
    • Sey, B. K.
  • Source: Soil Science Society of America Journal
  • Volume: 72
  • Issue: 4
  • Year: 2008
  • Summary: Agricultural practices affect the production and emission of CO2 and N2O from soil. The purpose of this 2-yr field study was to determine the effects of tillage (conventionally tilled [CT] and no-till [NT]) and fertilizer source (composted cattle manure and inorganic N-P-K fertilizer) on the CO2 and N2O content in soil profiles under corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The mean CO2 and N2O gas contents (i.e., mass of gas per unit soil volume) in the soil profile were determined periodically during two field seasons by sampling the soil atmosphere using plastic tubes installed at three depths (10, 20, and 30 cm) within the crop row. The soil CO2 content was greater in CT than NT soil and in manure-amended than inorganically fertilized plots during 1 yr of the study. The soil N2O content was not affected by tillage practices or fertilizer sources. A significant autocorrelation between sampling dates in both years suggested that the CO2 and N2O contents in the soil profile were not erratic or random, but temporally dependent on site-specific factors. The peak CO2 and N2O levels were measured within 50 d after seeding, probably because soil moisture conditions slowed diffusive gas flux but were favorable for microbial activity. Fluctuations in soil CO2 and N2O contents were not related to the seasonal variation in soil temperature. At most sampling dates, there was a significant (P < 0.05) positive correlation between the CO2 and N2O content in the soil profile, suggesting similarity in the rate of gas accumulation and diffusive flux for CO2 and N2O in soils. The CO2 and N2O content in the soil profile appeared to be controlled more by soil moisture than soil temperature or agricultural practices.
  • Authors:
    • Li, C.
    • Drury, C. F.
    • Rochette, P.
    • Desjardins, R. L.
    • Grant, B. B.
    • Smith, W. N.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: Process-based models play an important role in the estimation of soil N2O emissions from regions with contrasting soil and climatic conditions. A study was performed to evaluate the ability of two process-based models, DAYCENT and DNDC, to estimate N2O emissions, soil nitrate- and ammonium-N levels, as well as soil temperature and water content. The measurement sites included a maize crop fertilized with pig slurry (Quebec) and a wheat-maize-soybean rotation as part of a tillage-fertilizer experiment (Ontario). At the Quebec site, both models accurately simulated soil temperature with an average relative error (ARE) ranging from 0 to 2%. The models underpredicted soil temperature at the Ontario site with ARE from -5 to -7% for DNDC and from -5 to -13% for DAYCENT. Both models underestimated soil water content particularly during the growing season. The DNDC model accurately predicted average seasonal N2O emissions across treatments at both sites whereas the DAYCENT model underpredicted N2O emissions by 32 to 58% for all treatments excluding the fertilizer treatment at the Quebec site. Both models had difficulty in simulating the timing of individual emission events. The hydrology and nitrogen transformation routines need to be improved in both models before further enhancements are made to the trace gas routines.
  • Authors:
    • Trostle, R.
  • Source: USDA, Economic Research Service
  • Year: 2008
  • Summary: This 2008 report, from the USDA's Economic Research Service, discusses factors contributing to the recent increase in food commodity prices.
  • Authors:
    • Diamant, A.
    • Knipping, E.
  • Source: Handout for US EPA Integrated Nitrogen Committee
  • Year: 2008
  • Authors:
    • McLaughlin, N. B.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: t is well established that nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural land are influenced by the type of crop grown, the form and amount of nitrogen (N) applied, and the soil and climatic conditions under which the crop is grown. Crop rotation adds another dimension that is often overlooked, however, as the crop residue being decomposed and supplying soluble carbon to soil biota is usually from a different crop than the crop that is currently growing. Hence, the objective of this study was to compare the influence of both the crop grown and the residues from the preceding crop on N2O and CO2 emissions from soil. In particular, N2O and CO2 emissions from monoculture cropping of corn, soybean and winter wheat were compared with 2-yr and 3-yr crop rotations (corn-soybean or corn-soybean-winter wheat). Each phase of the rotation was measured each year. Averaged over three growing seasons (from April to October), annual N2O emissions were about 3.1 to 5.1 times greater in monoculture corn (2.62 kg N ha-1 ) compared with either monoculture soybean (0.84 kg N ha-1) or monoculture winter wheat (0.51 kg N ha-1). This was due in part to the higher inorganic N levels in the soil resulting from the higher N application rate with corn (170 kg N ha-1) than winter wheat (83 kg N ha-1) or soybean (no N applied). Further, the previous crop also influenced the extent of N2O emissions in the current crop year. When corn followed corn, the average N2O emissions (2.62 kg N ha1 ) were about twice as high as when corn followed soybean (1.34 kg N ha-1) and about 60% greater than when corn followed winter wheat (1.64 kg N ha-1). Monoculture winter wheat had about 45% greater CO2 emissions than monoculture corn or 51% greater emissions than monoculture soybean. In the corn phase, CO2 emissions were greater when the previous crop was winter wheat (5.03 t C ha-1) than when it was soybean (4.20 t C ha-1) or corn (3.91 t C ha-1). Hence, N2O and CO2 emissions from agricultural fields are influenced by both the current crop and the previous crop, and this should be accounted for in both estimates and forecasts of the emissions of these important greenhouse gases.
  • Authors:
    • Worth, D.
    • Desjardins, R. L.
    • Verge´, X. P. C.
    • Dyer, J. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 5
  • Year: 2008
  • Summary: Estimates of the efficiency of mitigation measures on reducing greenhouse gas (GHG) emissions from the agricultural sector are required. In this paper, recently calculated dairy GHG emissions for 2001 were extrapolated back to 1981 for census years using an index. The index was verified by comparing it with estimates based on the Intergovernmental Panel on Climate Change (IPCC) methodology for 1991. The index agreed with the IPCC estimates within 1% for methane and 4% for nitrous oxide on a national scale with no region having a difference of more than 5% for methane. For nitrous oxide, all regions were within 10%, except British Columbia, where the index was 19% too high. The index indicates that GHG emissions from primary milk production within the Canadian dairy industry have decreased by about 49% since 1981, mainly due to a 57% reduction in the dairy cow population during that period. The GHG emissions per kilogram of milk decreased by 35%, that is from 1.22 kg CO2eq kg-1 milk to 0.91 kg CO2eq kg-1 milk. Because this study took into account the energy-related CO2 emissions from all the major farm inputs (fertilizer and fossil fuel), there was little risk of hidden GHG emissions in the emission intensity calculation. This study demonstrates that where lack of input data restricts historical application of simulation models, a semi-empirical index approach can yield valuable results. Key words: Greenhouse gas, dairy industry, index, intensity indicator
  • Authors:
    • Min, D. H.
    • Thelen, K. D.
    • Fronning, B. E.
  • Source: Agronomy Journal
  • Volume: 100
  • Issue: 6
  • Year: 2008
  • Summary: The emerging cellulosic-based ethanol industry will likely use corn (Zea mays L.) stover as a feedstock source. Growers wishing to maintain, or increase soil C levels for agronomic and environmental benefit will need to use C amendments such as manure, compost, or cover crops, to replace C removed with the corn stover. The objective of this research was to determine the effect of cover crops, manure, and compost on short-term C sequestration rates and net global warming potential (GWP) in a corn-soybean [Glycine max (L.) Merr.] rotation with complete corn stover removal. Field experiments consisting of a corn-soybean-corn rotation with whole-plant corn harvest, were conducted near East Lansing, MI over a 3-yr period beginning in the fall of 2001. Carbon amendments were: compost, manure, and a winter cereal rye (Secale cereale L.) cover crop. Compost and manure amendments raised soil C levels in the 0 to 5 and 0 to 25 cm soil profile but not in the 5 to 25 cm soil profile over the relatively short-term duration of the study. Total soil organic C (SOC) (kg ha-1) in the 0 to 25 cm profile increased by 41 and 25% for the compost and manure treatments, respectively, and decreased by 3% for the untreated check. Compost and manure soil amendments resulted in a net GWP of -1811 and -1060 g CO2 m-2 yr-1, respectively, compared to 12 g CO2 m-2 yr-1 for untreated.
  • Authors:
    • Chan, C.
    • McKim, U. F.
    • St-Georges, P.
    • Rochette, P.
    • Gregorich, E. G.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Year: 2008
  • Summary: The ways in which agricultural soils are managed influence the production and emission of nitrous oxide (N2O). A field study was undertaken in 2003, 2004, and 2005 to quantify and evaluate N2O emission from tilled and no-till soils under corn (Zea mays L.) and soybeans (Glycine max L. Merr.) in Ontario. Overall, N2O emission was lowest in 2003, the driest and coolest of the 3 yr. In 2004, the significantly larger annual N2O emission from no-till soils and soils under corn was attributed to an episode of very high N2O emission following the application of fertilizer during a period of wet weather. That the N loss by N2O emission occurred only in no-till soils and was large and long-lasting (~4 wk) confirms the strong effect that management has in reducing fertilizer N losses. In 2005, tilled soils had significantly larger N2O emission than no-till soils, most of which was emitted before the end of June. Because the tilled soils were better aerated, nitrification was likely the primary process contributing to the larger emission. Relatively low N2O emission from soybeans suggests biological N fixation does not appear to contribute substantially to the annual N2O emission. Further study of methods to reduce N2O emission in agricultural systems should focus on improving N use efficiency within a particular tillage system rather than looking to differences between tillage systems.
  • Authors:
    • Barfoot, P.
    • Brookes, G.
  • Year: 2008
  • Authors:
    • Raper, R. L.
    • Wood, C. W.
    • Reeves, D. W.
    • Shaw, J. N.
    • Franzluebbers, A. J.
    • Causarano, H. J.
  • Source: Soil Science Society of America Journal
  • Volume: 72
  • Issue: 1
  • Year: 2008
  • Summary: Quantification of the impact of long-term agricultural land use on soil organic C (SOC) is important to farmers and policyrnakers, but few studies have characterized land use and management effects on SOC across physiographic regions. We measured the distribution and total stock of SOC to a depth of 20 cm under conventional tillage (CvT), conservation tillage (CsT), and pasture in 87 production fields from the Southern Piedmont and Coastal Plain Major Land Resource Areas. Across locations, SOC at a depth of 0 to 20 cm was: pasture (38.9 Mg ha(-1)) > CsT (27.9 Mg ha(-1)) > CvT (22.2 Mg ha(-1)) (P <= 0.02). Variation in SOC was explained by management (41.6%), surface horizon clay content (5.2%), and mean annual temperature (1.0%). Higher clay content and cooler temperature contributed to higher SOC. Management affected SOC primarily at the soil surface (0-5 cm). All SOC fractions (i.e., total SOC, particulate organic C, soil microbial biomass C, and potential C mineralization) were strongly correlated across a diversity of soils and management systems (r = 0.85-0.96). The stratification ratio (concentration at the soil surface/concentration at a lower depth) of SOC fractions differed among management systems (P <= 0.0001), and was 4.2 to 6.1 under pastures, 2.6 to 4.7 under CsT and 1.4 to 2.4 under CvT; these results agree with a threshold value of 2 to distinguish historically degraded soils with improved soil conditions from degraded soils. This on-farm survey of SOC complements experimental data and shows that pastures and conservation tillage will lead to significant SOC sequestration throughout the region, resulting in improved soil quality and potential to mitigate CO2 emissions.