• Authors:
    • Robertson, G. P.
    • Kravchenko, A. N.
    • Basso, B.
    • Senthilkumar, S.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 6
  • Year: 2009
  • Summary: Temporal changes in soil C content vary as a result of complex interactions among different factors including climate, baseline soil C levels, soil texture, and agricultural management practices. The study objectives were: to estimate the changes in soil total C contents that occurred in the past 18 to 21 yr in soils under agricultural management and in never-tilled grassland in southwest Michigan; to explore the relationships between these changes and soil properties, such as baseline C levels and soil texture; and to simulate C changes using a system approach model (SALUS). The data were collected from two long-term experiments established in 1986 and 1988. Georeferenced samples were collected from both experiments before establishment and then were resampled in 2006 and 2007. The studied agricultural treatments included the conventional chisel-plow and no-till management systems with and without N fertilization and the organic chisel-plow management with cover crops. Total C was either lost in the conventional chisel-plowed systems or was only maintained at the 1980s levels by the conservation management systems. The largest loss in the agricultural treatments was 4.5 Mg ha(-1) total C observed in the chisel-plow system without N fertilization. A loss of 17.3 Mg ha(-1) occurred in the virgin grassland sod. Changes in C content tended to be negatively related to baseline C levels. Under no-till, changes in C were positively related to silt + clay contents. The SALUS predictions of soil C changes were in excellent agreement with the observed data for most of the agricultural treatments and for the virgin soil.
  • Authors:
    • Robertson, G. P.
    • Kravchenko, A. N.
    • Senthilkumar, S.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 6
  • Year: 2009
  • Summary: Topography is one of the major factors affecting sod C and N contents at the field/landscape level. However, topographical effects are likely to differ in magnitude in different agricultural systems. The objective of this study was to examine the interactions between topography and management systems on Soil C and N. The study was conducted at the Kellogg Biological Station Long-Term Ecological Research (LTER) site in southwest Michigan. The studied treatments were chisel-plow (CT) and no-till (NT) with conventional chemical inputs and a chisel-plow organic management system with winter leguminous cover crops (CT-cover). At the 0- to 5-cm depth in both upperslope and valley positions total C and N contents of NT management were the highest followed by CT-cover and then CT At 0- to 15-, 20- to 30-, and 30- to 40-cm depths, treatment effects varied depending on the landscape position. There were no differences among the treatments in upperslopes, while in the valleys total C and N tended to be the highest in NT and CT-cover followed by CT. The results indicated the importance of accounting for interaction between topography and management practices when assessing C sequestration across landscapes with varying topography. Total C stocks at the 0- to 30-cm depths were around 35,32, and 27 MgC ha(-1) soil (+/- 2 MgC ha(-1) standard error) in CT-cover, NT and CT respectively, across upperslopes and valleys. Overall, CT-cover was found to be as efficient in maintaining C and N content as no-till with conventional chemical inputs. Power analysis for C and N stocks at the 0- to 40-cm depth revealed that because of high variability in total C and N stocks at greater depths, the 10 to 30 samples per treatment available in this study were inadequate to detect differences in C and N stocks if the differences were < 26 MgC ha(-1).
  • Authors:
    • Fixen, P. E.
    • Jensen, T. L.
    • Bruulsema, T. W.
    • Snyder, C. S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 133
  • Issue: 3-4
  • Year: 2009
  • Summary: Fertilizer nitrogen (N) use is expanding globally to satisfy food, fiber, and fuel demands of a growing world population. Fertilizer consumers are being asked to improve N use efficiency through better management in their fields, to protect water resources and to minimize greenhouse gas (GHG) emissions, while sustaining soil resources and providing a healthy economy. A review of the available science on the effects of N source, rate, timing, and placement, in combination with other cropping and tillage practices, on GHG emissions was conducted. Implementation of intensive crop management practices, using principles of ecological intensification to enhance efficient and effective nutrient uptake while achieving high yields, was identified as a principal way to achieve reductions in GHG emissions while meeting production demands. Many studies identified through the review involved measurements of GHG emissions over several weeks to a few months, which greatly limit the ability to accurately determine system-level management effects on net global warming potential. The current science indicates: (I) appropriate fertilizer N use helps increase biomass production necessary to help restore and maintain soil organic carbon (SOC) levels; (2) best management practices (BMPs) for fertilizer N play a large role in minimizing residual soil nitrate, which helps lower the risk of increased nitrous oxide (N2O) emissions; (3) tillage practices that reduce soil disturbance and maintain crop residue on the soil surface can increase SOC levels, but usually only if crop productivity is maintained or increased; (4) differences among fertilizer N sources in N2O emissions depend on site- and weather-specific conditions; and (5) intensive crop management systems do not necessarily increase GHG emissions per unit of crop or food production; they can help spare natural areas from conversion to cropland and allow conversion of selected lands to forests for GHG mitigation, while supplying the world's need for food, fiber, and biofuel. Transfer of the information to fertilizer dealers, crop advisers, farmers, and agricultural and environmental authorities should lead to increased implementation of fertilizer BMPs, and help to reduce confusion over the role of fertilizer N on cropping system emissions of GHGs. Gaps in scientific understanding were identified and will require the collaborative attention of agronomists, soil scientists, ecologists, and environmental authorities in serving the immediate and long-term interests of the human population. (C) 2009 Elsevier B.V. All rights reserved.
  • Authors:
    • USDA
  • Year: 2009
  • Authors:
    • Jarecki, M. K.
    • Lal, R.
    • Ussiri, D. A. N.
  • Source: Soil & Tillage Research
  • Volume: 104
  • Issue: 2
  • Year: 2009
  • Summary: Nitrous oxide (N2O) and methane (CH4) emitted by anthropogenic activities have been linked to the observed and predicted climate change. Conservation tillage practices such as no-tillage (NT) have potential to increase C sequestration in agricultural soils but patterns of N2O and CH4 emissions associated with NT practices are variable. Thus, the objective of this study was to evaluate the effects of tillage practices on N2O and CH4 emissions in long-term continuous corn (Zea mays) plots. The study was conducted on continuous corn experimental plots established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. The experimental design consisted of NT, chisel till (CT) and moldboard plow till (MT) treatments arranged in a randomized block design with four replications. The N2O and CH4 fluxes were measured for 1-year at 2-week intervals during growing season and at 4-week intervals during the off season. Long-term NT practice significantly decreased soil bulk density (rho(b)) and increased total N concentration of the 0-15 cm layer compared to MT and CT. Generally, NT treatment contained higher soil moisture contents and lower soil temperatures in the surface soil than CT and MT during summer, spring and autumn. Average daily fluxes and annual N2O emissions were more in MT (0.67 mg m(-2) d(-1) and 1.82 kg N ha(-1) year(-1)) and CT (0.74 mg m(-2) d(-1) and 1.96 kg N ha(-1) year(-1)) than NT (0.29 mg m(-2) d(-1) and 0.94 kg N ha(-1) year(-1)). On average, NT was a sink for CH4, oxidizing 0.32 kg CH4-C ha(-1) year(-1), while MT and CT were sources of CH4 emitting 2.76 and 2.27 kg CH4-C ha(-1) year(-1), respectively. Lower N2O emission and increased CH4 oxidation in the NT practice are attributed to decrease in surface rho(b), suggesting increased gaseous exchange. The N2O flux was strongly correlated with precipitation, air and soil temperatures, but not with gravimetric moisture content. Data from this study suggested that adoption of long-term NT under continuous corn cropping system in the U.S. Corn Belt region may reduce GWP associated with N2O and CH4 emissions by approximately 50% compared to MT and CT management.
  • Authors:
    • VandenBygaart, A. J.
  • Source: Soil Science Society of America Journal
  • Volume: 73
  • Issue: 4
  • Year: 2009
  • Summary: Comments on "Regional study of no-till effects on carbon sequestration in the Midwestern United States"
  • Authors:
    • Worth, D.
    • Desjardins, R. L.
    • Dyer, J. A.
    • Vergé, X. P. C.
  • Source: The Journal of Applied Poultry Research
  • Volume: 18
  • Issue: 2
  • Year: 2009
  • Summary: As people become more aware of the environmental footprint of different foods, consumers may modify their diets to reduce the impact of their diets on the environment. For this to occur, it is necessary to know the impact that individual food types have on the environment. This publication presents the greenhouse gas (GHG) emissions as well as the GHG emission intensity associated with various types of poultry production in Canada for the census years 1981 to 2006. Greenhouse gas emissions were calculated using the methodology from the Intergovernmental Panel on Climate Change adjusted for conditions in Canada. Direct emissions of CH4, N2O, and CO2 from birds, their facilities, and the avian crop complex, corresponding to the area used to grow the crops that feed Canadian poultry, were estimated using poultry diet surveys. Between 1981 and 2006, because of the strong growth of broiler production, GHG emissions from the poultry industry increased by 40%. The main GHG was N2O, representing approximately 57% of the total emissions. Fossil fuel CO2 accounted for approximately 38%, whereas CH4 accounted for 5%. In western Canada, GHG emission intensities decreased owing to a reduction in the consumption of fossil fuels associated with the adoption of reduced- and no-tillage cropping systems, whereas in eastern Canada, the reduction was due to lower N2O emissions. The emissions of all 3 GHG from turkeys decreased because of the more rapid turnover of a marketable product (shortened life span) in later census years. Compared with other Canadian meat protein commodities in 2001, poultry emitted only 47% as much GHG per unit of live weight as pork and only 10% as much GHG per unit of live weight as beef.
  • Authors:
    • Institute for the Study of Earth, Oceans and Space
  • Year: 2009
  • Summary: The DNDC model is a process-base model of carbon (C) and nitrogen (N) biogeochemistry in agricultural ecosystems. This document describes how to use the PC Windows versions of the DNDC model for predicting crop yield, C sequestration, nitrate leaching loss, and emissions of C and N gases in agroecosystems. Part I provides a brief description of the model structure with relevant scientific basis. Part II describes how to install the model. Part III and IV demonstrate how to conduct simulations with the site and regional versions of DNDC, respectively. Part V provides basic information for uncertainty analysis with DNDC. Part VI contains six case studies demonstrating the input procedures for simulating crop yield, soil C dynamics, nitrate leaching loss, and trace gas emissions. A list of relevant publications is included in Part VII. These publications provide more information about the scientific background and applications of DNDC far beyond this User's Guide. DNDC9.3 can run in two modes: site or regional. By selecting the mode, the users will open a corresponding interface to manage their input information for the modeled site or region.
  • Authors:
    • Six, J.
    • van Kessel, C.
    • Fonte, S. J.
    • Kong, A. Y. Y.
  • Source: Soil & Tillage Research
  • Volume: 104
  • Issue: 2
  • Year: 2009
  • Summary: Few studies address nutrient cycling during the transition period (e.g., 1-4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N2O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize-tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced N-15-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 mu m), microaggregates (53-250 mu m) and silt-and-clay (<53 mu m). We found a cropping system effect on soil N-new (i.e., N derived from N-15-fertilizer or - N-15-cover crop), with 173 kg N-new ha(-1) in the conventional system compared to 71.6 and 69.2 kg N-new ha(-1) in the low-input and organic systems, respectively. In the conventional system, more N-new was found in the microaggregate and silt-and-clay fractions, whereas, the N-new of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-N-new than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-N-new was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N2O emissions (39.5 g (NO)-O-2-N ha(-1) day(-1)) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha(-1)) produced intermediate N2O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N2O emissions, and N availability. (C) 2009 Elsevier B.V. All rights reserved.
  • Authors:
    • Lal, R.
  • Source: Soil & Tillage Research
  • Volume: 102
  • Issue: 2
  • Year: 2009
  • Summary: Global energy demand of 424 EJ year-1 in 2000 is increasing at the rate of 2.2% year-1. There is a strong need to increase biofuel production because of the rising energy costs and the risks of global warming caused by fossil fuel combustion. Biofuels, being C-neutral and renewable energy sources, are an important alternative to fossil fuels. Therefore, identification of viable sources of biofuel feedstock is a high priority. Harvesting lignocellulosic crop residues, especially of cereal crops, is being considered by industry as one of the sources of biofuel feedstocks. Annual production of lignocellulosic residues of cereals is estimated at 367 million Mg year-1 (75% of the total) for the U.S., and 2800 million Mg year-1 (74.6% of the total) for the world. The energy value of the residue is 16 × 106 BTU Mg-1. However, harvesting crop residues would have strong adverse impact on soil quality. Returning crop residues to soil as amendments is essential to: (a) recycling plant nutrients (20-60 kg of N, P, K, Ca per Mg of crop residues) amounting to 118 million Mg of N, P, K in residues produced annually in the world (83.5% of world's fertilizer consumption), (b) sequestering soil C at the rate of 100-1000 kg C ha-1 year-1 depending on soil type and climate with a total potential of 0.6-1.2 Pg C year-1 in world soils, (c) improving soil structure, water retention and transmission properties, (d) enhancing activity and species diversity of soil fauna, (e) improving water infiltration rate, (f) controlling water runoff and minimizing risks of erosion by water and wind, (g) conserving water in the root zone, and (h) sustaining agronomic productivity by decreasing losses and increasing use efficiency of inputs. Thus, harvesting crop residues as biofuel feedstock would jeopardize soil and water resources which are already under great stress. Biofuel feedstock must be produced through biofuel plantations established on specifically identified soils which do not compete with those dedicated to food crop production. Biofuel plantations, comprising of warm season grasses (e.g., switch grass), short rotation woody perennials (e.g., poplar) and herbaceous species (e.g., miscanthus) must be established on agriculturally surplus/marginal soils or degraded/desertified soils. Plantations established on such soils would restore degraded ecosystems, enhance soil/terrestrial C pool, improve water resources and produce biofuel feedstocks.