• Authors:
    • Murray, B. C.
    • McCarl, B. A.
    • Kim, M. -K.
  • Source: Ecological Economics
  • Volume: 64
  • Issue: 4
  • Year: 2008
  • Summary: One major concern regarding land-based carbon sequestration involves the issue of permanence. Sequestration may not last forever and may either be released in the future or require expenditures to maintain the practices that keep it sequestered. In this paper, we investigate the differential value of offsets in the face of impermanent characteristics by forming a price discount that equalizes the effective price per ton between a “perfect offset” and one possessing some with impermanent characteristics. We find this discount to be a function of the future needs to replace offsets (in the face of lease expiration quantity or volatilization upon activities such as timber harvest) and the magnitude of any needed maintenance costs. We investigate the magnitude of the discounts under alternative agricultural tillage and forest management cases. In those studies, we find that permanence discounts in the range of 50% are not uncommon. This means that in the market place an impermanent sequestration offset may only receive payments amounting to 50% of the market carbon price. Furthermore, we find that in the face of escalating carbon prices that offsets may prove to be worthless.
  • Authors:
    • Hepperly, P.
    • LaSalle, T. J.
  • Year: 2008
  • Authors:
    • Plowden, Y.
    • Benham, E. C.
    • Franks, E. C.
    • Salon, P. R.
    • Dell, C. J.
  • Source: Journal of Soil and Water Conservation
  • Volume: 63
  • Issue: 3
  • Year: 2008
  • Summary: No-till (NT) crop production is expected to sequester soil C, but little data is available for dairy forage systems. Our objective was to quantify impacts of NT and rye (Secale cereale L.) cover crops on soil C and N pools and associated soil properties on Pennsylvania dairies. Samples were collected from seven fields following corn harvest. The NT fields had approximately 50% more C and N in particulate and mineral-associated pools in the upper 5 cm (2 in) compared to conventional tillage, but C and N accumulations below 5 cm were similar. This suggests a C sequestration rate of ~0.5 Mg ha-1 y-1 (~0.2 tn ac-1 yr-1) in the 8 to 13 years NT has been used. Soil aggregate stability and cation exchange capacity were proportional to C pool sizes. Rye cover crops had no clear impact. Findings show that expected increases in C sequestration and soil quality with NT can be achieved in dairy forage systems.
  • Authors:
    • Hofman, G.
    • Gabriels, D.
    • De Neve, S.
    • Vandenbruwane, J.
    • Van den Bossche, A.
    • D'Haene, K.
  • Source: Biology and Fertility of Soils
  • Volume: 45
  • Issue: 2
  • Year: 2008
  • Summary: The effect of reduced tillage (RT) on nitrous oxide (N2O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N2O emission of soils taken in September 2005 varied from 50 to 1,095 mu g N kg(-1) dry soil. The N2O emissions of soils from the RT fields taken in September 2005 were statistically (P 0.05) higher or comparable than the N2O emissions from their respective CT soil. The N2O emission of soils taken in February 2006 varied from 0 to 233 mu g N kg(-1) dry soil. The N2O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N2O emissions from their respective CT soil. A positive and significant Pearson correlation of the N2O-N emissions with nitrate nitrogen (NO3--N) content in the soil was found (P 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO3- -N content of the soil and reduced N2O emissions from RT soils.
  • Authors:
    • Wallander, R.
    • Lemke, R. L.
    • Miller, P. R.
    • Engel, R. E.
    • Dusenbury, M. P.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 2
  • Year: 2008
  • Summary: Field measurements of N2O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N2O emission-time profiles for cropping systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N2O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha-1 available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N2O emissions were modest in contrast to reports from more humid regions. Greatest N2O flux activity occurred following urea-N fertilization (10-wk) and during freeze-thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N2O emissions during the post-N fertilization period, while denitrification was more important during freeze-thaw cycles. Cumulative -yr N2O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha-1) than wheat-fallow (CT and NT) (0.48 kg N ha-1), and wheat-pea (0.71 kg N ha-1) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha-1). Tillage did not affect N2O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%).
  • Authors:
    • Lal, R.
    • Elder, J. W.
  • Source: Soil & Tillage Research
  • Volume: 98
  • Issue: 1
  • Year: 2008
  • Summary: As in other drained, intensively cultivated Histosols of the world, soil subsidence is a growing concern of vegetable farmers in the muck crops region of North Central, Ohio. Subsidence in organic soils is caused primarily by aerobic degradation of soil organic matter (SOM), which in turn makes available large quantities of once bound C and N. Upon drainage and cultivation, soil C and N dynamics shift drastically. Organic soils transition from CO2 and organic N sinks, to persistent sources, whereas CH4 uptake capacity increases. Therefore, this study was conducted to assess the short-term (within the first year) impact of conversion of intensively tilled organic soils to no-till management. The specific objectives of this study were to: (i) compare soil moisture content, soil temperature, and greenhouse gas (GHG) emission rates from moldboard/disking (MB), no-till (NT), and bare (B) treatments in cultivated organic soils, and (ii) estimate the rate of subsidence associated with these tillage practices. Over the year, soil moisture content (SMC) was significantly higher in MB (0.90 kg kg-1) than B (0.84 kg kg-1) treatments; however NT (0.87 kg kg-1) was not significantly different from either MB or B treatments. Mean annual temperatures at 5 cm depth were significantly higher in B (16.9 °C) compared to MB (16.2 °C) and NT (15.9 °C) treatments The CO2 emissions were not significantly different among treatments, while N2O emissions were significantly higher from MB (96.9 kg N2O-N ha-1 yr-1) than NT (35.8 kg N2O-N ha-1 yr-1) plots. Both CH4 uptake and CH4 emission exhibited low annual flux in all treatments.