• Authors:
    • Herrick, J. E.
    • Janzen, H. H.
    • Schuman, G. E.
  • Source: Environmental Pollution
  • Volume: 116
  • Issue: 3
  • Year: 2002
  • Summary: The USA has about 336 Mha of grazing lands of which rangelands account for 48%. Changes in rangeland soil C can occur in response to a wide range of management and environmental factors. Grazing, fire, and fertilization have been shown to affect soil C storage in rangelands, as has converting marginal croplands into grasslands. Carbon losses due to soil erosion can influence soil C storage on rangelands both by reducing soil productivity in source areas and potentially increasing it in depositional areas, and by redistributing the C to areas where soil organic matter mineralization rates are different. Proper grazing management has been estimated to increase soil C storage on US rangelands from 0.1 to 0.3 Mg C ha-1 year-1 and new grasslands have been shown to store as much as 0.6 Mg C ha-1 year-1. Grazing lands are estimated to contain 10-30% of the world's soil organic carbon. Given the size of the C pool in grazing lands we need to better understand the current and potential effects of management on soil C storage.
  • Authors:
    • Albrecht, A.
    • Sa, J. C. D.
    • Ogle, S. M.
    • Denef, K.
    • Feller, C.
    • Six, J.
  • Source: Agronomie
  • Volume: 22
  • Issue: 7
  • Year: 2002
  • Summary: The long-term stabilization of soil organic matter (SOM) in tropical and temperate regions is mediated by soil biota (e. g. fungi, bacteria, roots and earthworms), soil structure (e. g. aggregation) and their interactions. On average, soil C turnover was twice as fast in tropical compared with temperate regions, but no major differences were observed in SOM quality between the two regions. Probably due to the soil mineralogy dominated by 1:1 clay minerals and oxides in tropical regions, we found a higher aggregate stability, but a lower correlation between C contents and aggregate stability in tropical soils. In addition, a smaller amount of C associated with clay and silt particles was observed in tropical versus temperate soils. In both tropical and temperate soils, a general increase in C levels (approximate to 325 +/- 113 kg C.ha(-1).yr(-1)) was observed under no-tillage compared with conventional tillage. On average, in temperate soils under no-tillage, compared with conventional tillage, CH4 uptake (approximate to0.42 +/- 0.10 kg C-CH4.ha(-1) yr(-1)) increased and N2O emissions increased (approximate to 1.95 +/- 0.45 kg N-N2O.ha(-1).yr(-1)). These increased N2O emissions lead to a negative global warming potential when expressed on a CO2 equivalent basis.
  • Authors:
    • Williams, S.
    • Schuler, J.
    • Lamm, D.
    • Killian, K.
    • Elliott, T.
    • Easter, M.
    • Cipra, J.
    • Bluhm, G.
    • Paustian, K.
    • Brenner, J.
    • Smith, P.
  • Year: 2002
  • Summary: Land managers have long known the importance of soil organic matter in maintaining the productivity and sustainability of agricultural land. More recently, interest has developed in the potential for using agricultural soils to sequester C and mitigate increasing atmospheric carbon-dioxide by adopting practices that increase standing stocks of carbon in soil organic matter and vegetation. Practices that increase the amount of CO2 taken up by plants (through photosynthesis), which then enter the soil as plant residues, tend to increase soil C stocks. Likewise, management practices that reduce the rate of decay or turnover of organic matter in soils will also tend to increase carbon stocks.
  • Authors:
    • Peters, M.
    • Paustian, K.
    • House, R. M.
    • Sperow, M.
  • Source: Agricultural Practices and Policies for Carbon Sequestration in Soil
  • Year: 2002
  • Authors:
    • Stroup, W. W.
  • Source: Journal of Agricultural, Biological, and Environmental Statistics
  • Volume: 7
  • Issue: 4
  • Year: 2002
  • Summary: Spatial variability among experimental units is known to exist in many designed experiments. Agronomic field trials are a particularly well-known example, but there are others. Historically, spatial variability has been dealt with in one of two ways: either though design, by blocking to account for spatial effects, or though analysis, by nearest neighbor adjustment. More recently, mixed models with spatial covariance structures such as those used in geostatistics have been proposed. These mixed model procedures have tempted some to conclude-to the dismay of many consulting statisticians-that design principles may be bypassed, since spatial covariance models can recover any lost information. Although design principles clearly should not be ignored, spatial procedures do raise questions. Are traditional notions of appropriate design affected? If so, how? How do spatial effects mixed models compare to conventional analysis of variance used in conjunction with blocked designs? This article presents mixed model methods to assess power and precision of proposed designs in the presence of spatial variability and to compare competing design and analysis strategies. The main conclusion is that, if anything, spatial models reinforce the need for sound design principles, particularly the use of incomplete block designs.
  • Authors:
    • U.S. EPA
    • U.S. EPA
  • Year: 2002
  • Authors:
    • Leary, M.
    • Roberti, D. A.
    • Medina, J.
    • Eaton, D.
    • Paparian, M.
    • Jones, S. R.
    • Moulton-Patterson, L.
  • Year: 2002
  • Summary: from exec summary: "This project sought to quantify the effect of compost feedstocks (green waste and poultry manure), compost maturity, and soil texture on vegetable crops. All of the field work was conducted in cooperation with commercial vegetable growers in Santa Cruz, Santa Clara, and San Benito Counties. Initially, the intent was to work equally with conventionally and organically farmed crops. However, in the end, the majority of the field trials occurred on conventional farms. Efforts to match similar crops to trials performed on different soil textures (conventional and organic) were largely unsuccessful due to the inevitable complications inherent in on-farm studies."
  • Authors:
    • Kimble, J. M.
    • Lal, R.
    • Jacinthe, P. A.
  • Source: Soil & Tillage Research
  • Volume: 67
  • Year: 2002
  • Summary: Enhancement of soil organic carbon (SOC) stocks through mulching has been proposed, and although this practice can alter several soil properties, its impact on the temporal variability of carbon dioxide (CO2) emission from soils has not been widely investigated. To that end, we monitored CO2 fluxes from a central Ohio Luvisol (fine, mixed, mesic Aeric Ochraqualf) amended with wheat (Triticum aestivum L.) straw applied at rates of 0 (M0), 8 (M8) and 16 (M16)Mgdry matter ha1 per year and supplemented with fertilizer (244 kg per year) or without. The experimental design was a randomized complete block design with three replications. The intensity of CO2 emission was higher in the late winter (mean: 2.79 g 2 per day) and summer seasons (2.45 gCO2- 2 per day) and lowest in the autumn (1.34 gCO2- 2 per day). While no significant effect of N fertilization on CO2 emission was detected, soil mulching had a significant effect on the seasonal variation of CO2 fluxes. The percentage of annual CO2 emitted during the winter and spring was similar across treatments (17-22%); however, 43% of the annual CO2 loss in the M0 plots occurred during the summer as opposed to 26% in the mulch treatments. A close relationship (F = 0.47X +4.45, R2 = 0.97,P <0.001) was found between annual CO2 flux (F, MgCO2-C ha 1) and residue-C input (X,MgCh 1). Litter and undecomposed residue amounted to 0.32 and 0.67MgC ha 1 per year in the M8 and M16 plots, respectively. After 4 years of straw application, SOC stocks (0-10 cm) were 19.6, 25.6 and 26.5MgCh1 in the M0, M8 and M16 treatments, respectively. The results show that soil mulching has beneficial effect on SOC sequestration and strongly influence the temporal pattern of CO2 emission from soils.
  • Authors:
    • Jellum, E. J.
    • Kuo, S.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 3
  • Year: 2002
  • Summary: Removing cover crop top growth in the spring for forage or to prevent incorporation problems is one management option. The effects of this residue management on soil quality and productivity need to be determined. This study, conducted from 1994 to 1998 at Puyallup, WA, determined effects of various winter cover crops and residue management on soil N availability, soil C and N, and corn (Zea mays L.) yield. Included in the study were monocultures of rye (Secale cereale L.), ryegrass (Lolium multiflorum Lam), and vetch (Vicia villosa Roth subsp. villosa) and biculture of vetch and rye or ryegrass. Each year, the cover crops were seeded in the fall and incorporated into, or removed from, the soil in the spring. Average top-growth biomass was higher for the bicultures than for the monocultures. Total N accumulation was generally greatest under vetch, followed by the bicultures, and lowest for the monocultured rye or ryegrass. Whereas removing top growth of monocultured vetch or bicultures depressed presidedress soil NO3-N (Ni), the effect was generally not found for monocultured rye or ryegrass. Corn yields were affected by amounts of Ni and N fertilizer applied (r2 > 0.789), irrespective of cover crop species and residue management. Removing top growth of the cover crops limited residue C input and reduced soil organic C and N after 5 yr. Soil organic C and N accumulation, as well as increasing soil C sequestration to reduce CO2 release into atmosphere, should be considered when deciding which residue management option to choose.
  • Authors:
    • Kimble, J.
    • Follett, R. F.
    • Reeves, V. B.
    • Reeves, J. B.
    • McCarty, G. W.
  • Source: Soil Science Society of America Journal
  • Volume: 66
  • Issue: 2
  • Year: 2002
  • Summary: The ability to inventory soil C on landscapes is limited by the ability to rapidly measure soil C. Diffuse reflectance spectroscopic analysis in the near-infrared (NIR, 400-2500 nm) and mid-infrared (MIR, 2500-25 000 nm) regions provides means for measurement of soil C. To assess the utility of spectroscopy for soil C analysis, we compared the ability to obtain information from these spectral regions to quantify total, organic, and inorganic C in samples representing 14 soil series collected over a large region in the west central United States. The soils temperature regimes ranged from thermic to frigid and the soil moisture regimes from udic to aridic. The soils ranged considerably in organic (0.23-98 g C kg-1) and inorganic C content (0.0-65.4 g CO3-C kg-1). These soil samples were analyzed with and without an acid treatment for removal of CO3. Both spectral regions contained substantial information on organic and inorganic C in soils studied and MIR analysis substantially outperformed NIR. The superior performance of the MIR region likely reflects higher quality of information for soil C in this region. The spectral signature of inorganic C was very strong relative to soil organic C. The presence of CO3- reduced ability to quantify organic C using MIR as indicated by improved ability to measure organic C in acidified soil samples. The ability of MIR spectroscopy to quantify C in diverse soils collected over a large geographic region indicated that regional calibrations are feasible.