• Authors:
    • Lal, R.
    • Jarecki, M. K.
  • Source: Soil Science
  • Volume: 171
  • Issue: 3
  • Year: 2006
  • Summary: Accelerating soil erosion, leading to loss of the surface soil, is a common occurrence in croplands on undulating terrain. Yet the impact of erosion and reclamation measure on emission of greenhouse gases (GHG) is not known. Three predominant GHG emitted from cropland are as follows: carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). The most abundant GHG is CO2, but N2O and CH4 are also important, with global warming potentials (GWP) of 297 and 23, respectively. The objectives of this study were to evaluate the effect of imitated soil erosion on gaseous emission, to determine the effects of application of wheat (Triticum aestivum) residue mulch and swine manure and soybean (Glycine max) residue compost as soil-restorative measures on fluxes of CO2, N2O, and CH4 from uncropped, undisturbed, and desurfaced plots, and to determine relations between GHG fluxes and air and soil temperature, precipitation, and soil-moisture regimes. The microplot (2 X 2 m) experiment was established in 2002 on a Crosby silt loam (fine mixed Aeric Ochraqudalf ) near South Charleston, Ohio. The experimental design included two soils: undisturbed and desurfaced soil in which the top 0-cm to 20-cm layer was mechanically removed to simulate severe soil erosion. There were three cover treatments: bare soil, wheat mulch at the rate of 8 Mg dry matter ha-1 y-1, and compost made from swine manure and soybean residues at the rate of 20 Mg dry matter ha-1 y-1. All plots received mineral fertilizer at the rate of 100 kg N ha-1. Desurfacing decreased soil moisture, increased temperature, decreased daily and annual CO2 fluxes (1.05 vs. 1.59 g CO2-C m-2 d-1), and increased N2O fluxes (3.58 vs. 1.81 mg N2O-N m-2 d-1). Daily CO2 and annual fluxes were higher from compost than mulch plots. The lowest daily CO2 flux was measured from bare plots. The daily N2O fluxes significantly increased after compost application but were more significantly affected by rainfall events. CH4 fluxes were characterized by a high variability; however, more uptake was observed in compost (-0.41 kg ha-1 y-1) than in mulch (0.60 kg ha-1 y-1) and bare plots (2.75 kg ha-1 y-1). Daily CO2 fluxes were positively correlated with soil (r = 0.82) and air temperatures (r = 0.84) and negatively correlated with soil-moisture content (r = -0.53). Daily N2O fluxes were highly correlated with precipitation (r = 0.88). Fluxes of CO2 and N2O were mutually correlated (r = 0.56), but CH4 fluxes were not correlated with temperature, moisture, precipitation, or fluxes of other GHG. Computed GWP was higher in compost-covered plots than in mulched and bare plots. Estimation of fluxes of GHG indicates that N2O accounts for 13% to 28% and CH4 for -0.5% to 5% of the total emission. Therefore, a completed assessment of flux of GHG must be based on measurement of all three gases (i.e., CO2, N2O, and CH4).
  • Authors:
    • Wilhelm, W. W.
    • Archer, D.
    • Allmaras, R. R.
    • Reicosky, D. C.
    • Johnson, J. M. F.
  • Source: Journal of Soil and Water Conservation
  • Volume: 61
  • Issue: 4
  • Year: 2006
  • Summary: SUMMARY: We still need an answer to the critical question: ˜How much crop biomass is needed to protect and maintain the soil resource, and correspondingly, how much can be harvested as renewable fuel? Through photosynthesis and the processes of growth and translocation, plants use solar energy to transform carbon dioxide and water into grain and biomass.The latter is useful for nurturing the soil biology, maintaining soil properties important in soil quality, and also as a bioenergy feedstock. A practical compromise is needed for crop biomass to function effectively in the competing roles of soil conservation and renewable energy production. Economics and government policy will drive development of biomass for biofuel industries. However, we cannot afford to overlook the potential costs associated with wide-scale removal of crop residues from the land.These costs may not be readily apparent in the short term and economic impacts are not easily quantified. Thus far, farmers are not compensated based on the ecosystem services provided by agricultural watersheds. We suggest a cautious approach to harvesting crop biomass for energy until science-based research provides answers and guidance to the critical questions of how much,when, and where to harvest crop biomass. Research is needed to provide land managers, the biomass industry, and action agencies with sound, scientifically based, field-tested guidelines for sustainable production and harvest of crop residues. This need is especially critical in light of the current economic pressures to find alternative energy sources and the short time-frame set by DOE for domestic renewable fuels to become a significant contributor to the nation's energy and product supply. As the biomass energy industry develops, we strongly encourage soil and energy conservation to achieve sustainable energy security.
  • Authors:
    • Jung, Y. S.
    • Meek, D. W.
    • Cambardella, C. A.
    • Jaynes, D. B.
    • Parkin, T. B.
    • Kaspar, T. C.
  • Source: Soil Science Society of America Journal
  • Volume: 70
  • Issue: 4
  • Year: 2006
  • Summary: Winter cover crops have the potential to increase soil organic C in the corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation in the upper Midwest. Management effects on soil C, however, are often difficult to measure because of the spatial variation of soil C across the landscape. The objective of this study was to determine the effect of oat (Avena sativa L.), rye (Secale cereale L.), and a mixture of oat and rye used as winter cover crops following soybean on soil C levels over 3 yr and both phases of a corn-soybean rotation using terrain attributes as covariates to account for the spatial variability in soil C. A field experiment was initiated in 1996 with cover crop treatments, both phases of a corn-soybean rotation, and a controlled-traffic no-till system. Oat, rye, and oat-rye mixture cover crop treatments were overseeded into the soybean phase of the rotation in late August each year. Cover crop treatments were not planted into or after the corn phase of the rotation. Soil C concentration was measured on 450 samples taken across both rotation phases in a 7.62-m grid pattern in the late spring of 2000, 2001, and 2002. Slope, relative elevation, and wetness index (WI) were used as covariates in the analysis of variance to remove 77% of the variation of soil C caused by landscape driven patterns of soil C. Soil C concentrations were 0.0023 g C g soil -1 higher in 2001 and 0.0016 g C g soil-1 higher in 2002 than in 2000. The main effects of cover crops were not significant, but the interaction of cover crops and rotation phase was significant. The rye cover crop treatment had 0.0010 g C g soil-1 higher soil C concentration than the no-cover- crop control in the soybean phase of the rotation, which included cover crops, but had 0.0016 g C g soil -1 lower C concentrations than the control in the corn phase of the rotation, which did not have cover crops. Using terrain covariates allowed us to remove most of the spatial variability of soil C, but oat and rye cover crops planted every other year after soybean did not increase soil C concentrations averaged over years and rotation phases.
  • Authors:
    • Bullock, D. G.
    • Hao, X.
    • Robertson, G. P.
    • Kravchenko, A. N.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 6
  • Year: 2006
  • Summary: Lack of information about the spatial variability of soil C in different management systems limits accurate extrapolation of C sequestration findings to large scales. The objectives of this study were to: (i) describe and quantify variability of total C in three management systems, chisel-plow (CT) and no-till (NT) with conventional chemical inputs and a chisel-plow organic management practice with cover crops (CT-cover) 15 yr after conversion from conventional management; (ii) assess the strengths of spatial correlation in the three studied systems; and (iii) evaluate contributions of topography and texture to the overall total C variability and its spatial components. The data were collected at 12 60 by 60 m plots at the Long Term Ecological Research site, Kellogg Biological Station, MI. The data consisted of elevation measurements taken on a 2 by 5 m grid and a total of 1160 measurements of total C, sand, silt, and clay contents taken from the 0- to 5-cm depth. Overall variability of total C in NT was more than four times greater than in CT, and in CT-cover the variability was more than two times greater than CT. Spatial correlation of total C was the strongest in NT, followed by CT-cover, and then by CT. Stronger spatial structures in NT and CT-cover were found to form in response to topographical and texture gradients. Effects of texture were largely associated with topographical effects; however, even when topography was controlled for, texture still substantially contributed to explaining total C variability.
  • Authors:
    • Smucker, A. J. M.
    • Snap, S. S.
    • Robertson, G. P.
    • Kravchenko, A. N.
  • Source: Agronomy Journal
  • Volume: 98
  • Issue: 3
  • Year: 2006
  • Summary: Changes in soil C as a result of changes in management are relatively slow, and several years of experimentation are needed before differences in management practices can be detected using traditional statistical procedures such as randomized complete block design (RCBD). Using spatial analyses (SA) that take into account spatial variability between plots has a potential for faster and more efficient detection of soil C differences. We hypothesize that for variables with strong spatial continuity, such as total soil C, accurate spatial variability assessment can be obtained even in relatively small experiments. Thus, SA can significantly improve the statistical efficiency of even these experiments. The objective of this study is to test this hypothesis by comparing performances of RCBD analysis and SA for simulated small-sized experiments where soil C is the response variable. Total soil C data collected from 11 field sites at the Long-Term Ecological Research (LTER) experiment in Michigan were used as an input for simulated experiments. Performance of SA depended on the strength of spatial correlation in soil C and was found to be related to topographical diversity of the experimental sites. In the sites with more diverse topography and stronger spatial correlation of soil C the SA produced lower standard errors for treatment means than those of the RCBD analysis (8 out of 11 sites). In two sites with the flattest topography and weak spatial correlation, SA did not have advantages over RCBD.
  • Authors:
    • Rolston, D. E.
    • van Kessel, C.
    • King, A. P.
    • Six, J.
    • Lee, J.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Issue: 3
  • Year: 2006
  • Summary: There is a lack of understanding of how associations among soil properties and management-induced changes control the variability of greenhouse gas (GHG) emissions from soil. We performed a laboratory investigation to quantify relationships between GHG emissions and soil indicators in an irrigated agricultural field under standard tillage (ST) and a field recently converted (2 yr) to no-tillage (NT). Soil cores (15-cm depth) were incubated at 25{degrees}C at field moisture content and 75% water holding capacity. Principal component analysis (PCA) identified that most of the variation of the measured soil properties was related to differences in soil C and N and soil water conditions under ST, but soil texture and bulk density under NT. This trend became more apparent after irrigation. However, principal component regression (PCR) suggested that soil physical properties or total C and N were less important in controlling GHG emissions across tillage systems. The CO2 flux was more strongly determined by microbial biomass under ST and inorganic N content under NT than soil physical properties. Similarly, N2O and CH4 fluxes were predominantly controlled by NO3- content and labile C and N availability in both ST and NT soils at field moisture content, and NH4+ content after irrigation. Our study indicates that the field-scale variability of GHG emissions is controlled primarily by biochemical parameters rather than physical parameters. Differences in the availability and type of C and N sources for microbial activity as affected by tillage and irrigation develop different levels and combinations of field-scale controls on GHG emissions.
  • Authors:
    • Zentner, R.
    • Campbell, C. A.
    • Zhong, Z.
    • Lemke, R. L.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 6
  • Year: 2006
  • Summary: The atmospheric buildup of greenhouse gases (GHGs) is a serious environmental issue. Globally, agricultural activities are an important source of anthropogenic GHGs, contributing [~]20% of the annual atmospheric increase. Management choices largely determine if agricultural soils will be a source, a sink, or will be neutral with respect to GHG net flux. The proportion of agricultural land that is seeded to pulse crops in the Northern Great Plains (NGP) region of North America has been increasing rapidly over the past decade. Introducing pulses into cereal-based cropping systems could influence the net GHG balance of those systems because pulse crops are thought to stimulate soil-emitted N2O, have different pesticide and fertilizer requirements, and the quality and quantity of their residues vary substantially compared with cereal crops. In this paper we briefly review the available literature, and discuss the potential impact of pulse crops on the net flux of CO2, N2O, and CH4 from soils, and the CO2 emissions associated with energy inputs for cropping systems in the NGP. We also calculate net GHG balances for two example sites. Estimating the final GHG outcome of introducing pulses into cereal-based cropping systems is still uncertain, but current information suggests that replacing a cereal with a pulse crop will likely result in no change or a small but positive net GHG benefit (lower emissions to the atmosphere) for crop rotations in the NGP region.
  • Authors:
    • Zhang, F. S.
    • Halvorson, A. D.
    • Mosier, A. R.
    • Liu, X. J.
  • Source: Plant and Soil
  • Volume: 280
  • Issue: 1-2
  • Year: 2006
  • Summary: To evaluate the impact of N placement depth and no-till (NT) practice on the emissions of NO, N2O, CH4 and CO2 from soils, we conducted two N placement experiments in a long-term tillage experiment site in northeastern Colorado in 2004. Trace gas flux measurements were made 2-3 times per week, in zero-N fertilizer plots that were cropped continuously to corn (Zea mays L.) under conventional-till (CT) and NT. Three N placement depths, replicated four times (5, 10 and 15 cm in Exp. 1 and 0, 5 and 10 cm in Exp. 2, respectively) were used. Liquid urea-ammonium nitrate (UAN, 224 kg N ha)1) was injected to the desired depth in the CT- or NT-soils in each experiment. Mean flux rates of NO, N2O, CH4 and CO2 ranged from 3.9 to 5.2 lg N m)2 h)1, 60.5 to 92.4 lg N m)2 h)1, )0.8 to 0.5 lg C m)2 h)1, and 42.1 to 81.7 mg C m)2 h)1 in both experiments, respectively. Deep N placement (10 and 15 cm) resulted in lower NO and N2O emissions compared with shallow N placement (0 and 5 cm) while CH4 and CO2 emissions were not affected by N placement in either experiment. Compared with N placement at 5 cm, for instance, averaged N2O emissions from N placement at 10 cm were reduced by more than 50% in both experiments. Generally, NT decreased NO emission and CH4 oxidation but increased N2O emissions compared with CT irrespective of N placement depths. Total net global warming potential (GWP) for N2O, CH4 and CO2 was reduced by deep N placement only in Exp. 1 but was increased by NT in both experiments. The study results suggest that deep N placement (e.g., 10 cm) will be an effective option for reducing N oxide emissions and GWP from both fertilized CT- and NT-soils.
  • Authors:
    • Paustian, K.
    • Lokupitiya, E.
  • Source: Journal of Environmental Quality
  • Volume: 35
  • Year: 2006
  • Summary: Parties to the United Nations Framework Convention on Climate Change (UNFCCC) are required to submit national greenhouse gas (GHG) inventories, together with information on methods used in estimating their emissions. Currently agricultural activities contribute a significant portion (approximately 20%) of global anthropogenic GHG emissions, and agricultural soils have been identified as one of the main GHG source categories within the agricultural sector. However, compared to many other GHG sources, inventory methods for soils are relatively more complex and have been implemented only to varying degrees among member countries. This review summarizes and evaluates the methods used by Annex 1 countries in estimating CO2 and N2O emissions in agricultural soils. While most countries utilize the Intergovernmental Panel on Climate Change (IPCC) default methodology, several Annex 1 countries are developing more advanced methods that are tailored for specific country circumstances. Based on the latest national inventory reporting, about 56% of the Annex 1 countries use IPCC Tier 1 methods, about 26% use Tier 2 methods, and about 18% do not estimate or report N2O emissions from agricultural soils. More than 65% of the countries do not report CO2 emissions from the cultivation of mineral soils, organic soils, or liming, and only a handful of countries have used country-specific, Tier 3 methods. Tier 3 methods usually involve process-based models and detailed, geographically specific activity data. Such methods can provide more robust, accurate estimates of emissions and removals but require greater diligence in documentation, transparency, and uncertainty assessment to ensure comparability between countries. Availability of detailed, spatially explicit activity data is a major constraint to implementing higher tiered methods in many countries.
  • Authors:
    • Perez, A.
    • Ali, M.
    • Pollack, S.
    • Lucier, G.
  • Year: 2006
  • Summary: The U.S. fruit and vegetable industry accounts for nearly a third of U.S. crop cash receipts and a fifth of U.S. agricultural exports. A variety of challenges face this complex and diverse industry in both domestic and international markets, ranging from immigration reform and its effect on labor availability to international competitiveness. The national debate on diet and health frequently focuses on the nutritional role of fruit and vegetables, and a continued emphasis on the benefits of eating produce may provide opportunities to the industry. In the domestic market, Americans are eating more fruit and vegetables than they did 20 years ago, but consumption remains below recommended levels. In terms of per capita consumption expressed on a fresh-weight basis, the top five vegetables are potatoes, tomatoes, lettuce, sweet corn, and onions while the top five fruit include oranges, grapes (including wine grapes), apples, bananas, and pineapples. The industry also faces a variety of trade-related issues, including competition with imports. During 2002-04, imports accounted for 21 percent of domestic consumption of all fresh and processed fruit and vegetables, up from 16 percent during 1992-94.