• Authors:
    • Levesque, G.
    • Prevost, D.
    • Chantigny, M. H.
    • Belanger, G.
    • Angers, D. A.
    • Rochette, P.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 2
  • Year: 2004
  • Summary: There is considerable uncertainty relative to the emissions of N2O from legume crops. A study was initiated to quantify N2O fluxes from soils cropped to alfalfa (Medicago sativa L.) and soybean (Glycine max L.), and to improve our understanding of soil and climatic factors controlling N2O emissions from these crops. Measurements were made on three soils cropped to alfalfa, soybean, or timothy (Phleum pratense L.), a perennial grass used as a control. In situ soil-surface N2O emissions (FN2O) were measured 47 times during the 2001 and 2002 growing seasons. Soil water, NH4-N, NO3-N, and N2O contents, and soil temperature were also determined to explain the variation in gas fluxes. Emissions of N2O were small under the grass where very low soil mineral N content probably limited denitrification and N2O production. Soil mineral N contents under legumes were up to 10 times greater than under timothy. However, soil mineral N contents and FN2O were not closely related, thus suggesting that the soil mineral N pool alone was a poor indicator of the intensity of N2O production processes. Higher FN2O were measured under legume than under timothy in only 6 out of 10 field comparisons (site-years). Moreover, the emissions associated with alfalfa (0.67-1.45 kg N ha-1) and soybean (0.46-3.08 kg N ha-1) production were smaller than those predicted using the emission coefficient proposed for the national inventory of greenhouse gases (alfalfa = 1.60-5.21 kg N ha-1; soybean = 2.76-4.97 kg N ha-1). We conclude that the use of the current emission coefficient may overestimate the N2O emissions associated with soybean and alfalfa production in eastern Canada.
  • Authors:
    • Paustian, K.
    • Mosier, A. R.
    • Conant, R. T.
    • Breidt, F. J.
    • Ogle, S. M.
    • Six, J.
  • Source: Global Change Biology
  • Volume: 10
  • Issue: 2
  • Year: 2004
  • Summary: No-tillage (NT) management has been promoted as a practice capable of offsetting greenhouse gas (GHG) emissions because of its ability to sequester carbon in soils. However, true mitigation is only possible if the overall impact of NT adoption reduces the net global warming potential (GWP) determined by fluxes of the three major biogenic GHGs (i.e. CO2, N2O, and CH4). We compiled all available data of soil-derived GHG emission comparisons between conventional tilled (CT) and NT systems for humid and dry temperate climates. Newly converted NT systems increase GWP relative to CT practices, in both humid and dry climate regimes, and longer-term adoption (>10 years) only significantly reduces GWP in humid climates. Mean cumulative GWP over a 20-year period is also reduced under continuous NT in dry areas, but with a high degree of uncertainty. Emissions of N2O drive much of the trend in net GWP, suggesting improved nitrogen management is essential to realize the full benefit from carbon storage in the soil for purposes of global warming mitigation. Our results indicate a strong time dependency in the GHG mitigation potential of NT agriculture, demonstrating that GHG mitigation by adoption of NT is much more variable and complex than previously considered, and policy plans to reduce global warming through this land management practice need further scrutiny to ensure success.
  • Authors:
    • McConkey, B.
    • Zhang, Z.
    • Goddard, T. W.
    • Lemke, R. L.
    • Izaurralde, R. C.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 4
  • Year: 2004
  • Summary: Nitrous oxide fluxes from soils are inherently variable in time and space. An improved understanding of this variability is needed to make accurate estimates of N2O fluxes at a regional scale. The objectives of this work were to (i) characterize the influence of soil-landscape combinations and N application rates on N2O emissions and to (ii) determine the contribution of these influences on the estimation of N2Oemissions at the field scale.We used static chambers and gas chromatography methods to measure N2O fluxes and collected ancillary data (mineral N, water soluble C, soil water content, soil temperature) in Canada at Mundare (AB) in the aspen parkland ecoregion and at Swift Current (SK) in the short-grass prairie eco-region. At Mundare, measurements were taken in 1995 and 1996 by landscape position and land use.At Swift Current, data were collected in 1999 and 2000 by landscape position and N rate. At Mundare, landscape position affected N2O emissions but the pattern varied seasonally. During a 46-d period in summer 1995, a flux of 430 g N2O-N ha-1 measured in a backslope was greater than the 60 g N2O-N ha-1 measured on average in shoulder and depressional areas. The flux pattern changed during a 43-d spring thaw of 1996 when fluxes from depressional areas were greatest (1710 g N2O-N ha-1). Nitrous oxide emissions from natural areas were small. The emission pattern during summer 1996 was similar to that of 1995 but the fluxes were an order of magnitude larger. At Swift Current, N2O fluxes in summer 1999 were affected by topography and N rate. Fluxes were greatest in depressional areas receiving N at 110 kg ha-1 (3140 g N2O-N ha-1). Use of the area fraction occupied by each landscape position to calculate N2O flux increased the estimates of N2O fluxes at the field scale in five out of six cases. Further research of N2O fluxes in variable landscapes should help elucidate factors controlling N2O fluxes from pedon to field scale and thus translate into improved flux estimates at regional scales.
  • Authors:
    • Lal, R.
    • Jacinthe, P. A.
  • Source: Soil Science
  • Volume: 169
  • Issue: 4
  • Year: 2004
  • Summary: Information regarding the impact of soil surface condition on soil-atmosphere exchange of gases is limited. In this study, fluxes and soil air concentrations of CO2, CH4, and N2O were monitored for 17 months at three central Ohio sites, including a bare (vegetation-free) soil, a mulch (covered with decomposed and fresh straw) site, and a 68-year-old deciduous forest (litter and canopy cover). Fertilizer was not applied to any of the sites. Relationships between daily fluxes of CO2 and soil temperature were described by linear and exponential functions. At the bare site, CO2 emission reached a maximum at 25°C, beyond which there was apparent insensitivity of soil respiration to temperature. Annual fluxes of CO2 and N2O from the bare, mulch, and forest sites (3.2, 4.9, and 4.6 Mg CO2-C ha-1 and 1.1, 1.3, and 1.4 kg N2O-N ha-1, respectively) were not significantly different. The bare and mulch sites were net CH4 emitters, but the forest was significantly different as a net CH4 sink (-2.2 kg CH4- C ha-1 y-1) with daily uptake averaging -0.92 and -0.63 mg CH4-C m-2 during dry and wet periods, respectively. Increased soil air concentrations of CO2 and N2O in the 10-20-cm soil depth coincided with higher emission rates. A generally similar trend was observed at the bare and mulch sites with respect to CH4. However, at the forest site, increased CH4 concentration in the upper soil layers was accompanied by increased uptake (-3.5 mg CH4-C m-2 d-1) in the summer but a net and short-lived emission (+0.5 mg CH4-C m-2 d-1) during spring thaw. N2O emission followed rainfall distribution, and the largest N2O pulses consistently followed termination of dry periods by rainfall events. Our conclusion is that wet-dry cycles are a more important controller of N2O emission from unfertilized soils than either temperature or soil cover.
  • Authors:
    • Dale, B. E.
    • Kim, S.
  • Source: Biomass and Bioenergy
  • Volume: 26
  • Issue: 4
  • Year: 2004
  • Summary: The global annual potential bioethanol production from the major crops, corn, barley, oat, rice, wheat, sorghum, and sugar cane, is estimated. To avoid conflicts between human food use and industrial use of crops, only the wasted crop, which is defined as crop lost in distribution, is considered as feedstock. Lignocellulosic biomass such as crop residues and sugar cane bagasse are included in feedstock for producing bioethanol as well. There are about 73:9 Tg of dry wasted crops in the world that could potentially produce 49:1 GL year-1 of bioethanol. About 1:5 Pg year-1 of dry lignocellulosic biomass from these seven crops is also available for conversion to bioethanol. Lignocellulosic biomass could produce up to 442 GL year-1 of bioethanol. Thus, the total potential bioethanol production from crop residues and wasted crops is 491 GL year-1, about 16 times higher than the current world ethanol production. The potential bioethanol production could replace 353 GL of gasoline (32% of the global gasoline consumption) when bioethanol is used in E85 fuel for a midsize passenger vehicle. Furthermore, lignin-rich fermentation residue, which is the coproduct of bioethanol made from crop residues and sugar cane bagasse, can potentially generate both 458 TWh of electricity (about 3.6% of world electricity production) and 2:6EJ of steam. Asia is the largest potential producer of bioethanol from crop residues and wasted crops, and could produce up to 291 GL year -1 of bioethanol. Rice straw, wheat straw, and corn stover are the most favorable bioethanol feedstocks in Asia. The next highest potential region is Europe (69:2 GL ofbioethanol), in which most bioethanol comes from wheat straw. Corn stover is the main feedstock in North America, from which about 38:4 GL year -1 of bioethanol can potentially be produced. Globally rice straw can produce 205 GL of bioethanol, which is the largest amount from single biomass feedstock. The next highest potential feedstock is wheat straw, which can produce 104 GL of bioethanol. This paper is intended to give some perspective on the size ofthe bioethanol feedstock resource, globally and by region, and to summarize relevant data that we believe others will 0nd useful, for example, those who are interested in producing biobased products such as lactic acid, rather than ethanol, from crops and wastes. The paper does not attempt to indicate how much, if any, of this waste material could actually be converted to bioethanol.
  • Authors:
    • Zhao, J.
    • Kling, C. L.
    • Kurkalova, L. A.
  • Source: Environmental Management
  • Volume: 33
  • Issue: 4
  • Year: 2004
  • Summary: This study empirically estimates the multiple benefits of a subsidy policy that would offer payments to farmers in return for the adoption of conservation tillage, and compares the outcomes of alternative targeting designs for such a policy. The least-cost incentive payment policy schemes are simulated for the State of Iowa by using the data for roughly 12,000 National Resource Inventory (NRI) points. We use an economic conservation tillage adoption model to evaluate the costs of adoption and a physical process simulation model (EPIC) to estimate the environmental benefits due to adoption at each of the NRI points.Two targeting options are considered. We assess the costs and environmental consequences of a practice-based policy instrument (which maximizes the acres of land in conservation tillage, regardless of its level of environmental benefits) and contrast it to a performance based instrument (which yields the highest amount of environmental benefits per dollar spent). Carbon sequestration in agricultural soils, reduction of soil erosion by wind and water, and the reduction in nitrogen runoff are considered as possible targets for the performance-based instruments. We find that the practice-based instrument provides high proportions of the four benefits relative to the policies that target the benefits directly, especially at the higher policy budget levels. Similarly, we estimate that targeting one of the four benefits individually provides high percentages of the other benefits as compared with the amounts of the benefits obtainable if they were targeted directly.
  • Authors:
    • Isla, R.
    • Ellsworth, J. W.
    • Blackmer, A. M.
    • Kyveryga, P. M.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 2
  • Year: 2004
  • Summary: Soil temperature at the time of application has been the primary factor used to predict rates of nitrification and assess the risks associated with losses of N applied in the fall as anhydrous ammonia in the Corn Belt. We report studies assessing the importance of soil pH as a factor affecting nitrification rates and losses of this N before corn (Zea Mays L.) begins rapid growth in June. Data were collected in a series of field studies conducted during 4 yr. Anhydrous ammonia was applied in the fall after soils had cooled to 7.5. Significant relationships between soil pH and percentage nitrification were observed each year. Means of measurements made in mid-April (when planting begins) indicated 89% nitrification of fertilizer N in soils having pH > 7.5 and 39% nitrification of this N in soils having pH < 6.0. The finding that soil pH influenced when nitrification occurred helps to explain why the effects of nitrification inhibitors have been variable in this region. Significant relationships between soil pH and recovery of fertilizer N as exchangeable NH4+ and NO3- were observed in years with above-average rainfall before samples were collected in April. The effects of soil pH on nitrification, therefore, influenced the amounts of NO3- lost by denitrification or leaching during spring rainfall. The observed effects of pH on nitrification rates suggest that economic and environmental benefits of delaying application of fertilizer N may be greater in higher-pH soils than in lower-pH soils.
  • Authors:
    • Wienhold, B. J.
    • Tanaka, D. L.
    • Liebig, M. A.
  • Source: Soil & Tillage Research
  • Volume: 78
  • Issue: 2
  • Year: 2004
  • Summary: The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA1: fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0-7.5, 7.5-15, and 15-30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop-fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mgha-1), particulate organic matter C (POM-C) (by 4.98Mgha-1), potentially mineralizable N (PMN) (by 32.4 kg ha-1), and microbial biomass C (by 586 kg ha-1), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h-1) relative to the crop-fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha-1 for PMN; 792 kg ha-1 for microbial biomass C) as compared with sequences with fallow (SW-S-F and SW-F) (Average = 15.9 kg ha-1 for PMN; 577 kg ha-1 for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.
  • Authors:
    • Lewis, D. T.
    • Reedy, T. E.
    • Martens, D. A.
  • Source: Global Change Biology
  • Volume: 10
  • Issue: 1
  • Year: 2004
  • Summary: Conversion of former agricultural land to grassland and forest ecosystems is a suggested option for mitigation of increased atmospheric CO2. A Sharpsburg prairie loess soil (fine, smectitic, mesic Typic Argiudoll) provided treatments to study the impact of long-term land use on soil organic carbon (SOC) content and composition for a 130-year-old cropped, pasture and forest comparison. The forest and pasture land use significantly retained more SOC, 46% and 25%, respectively, compared with cropped land use, and forest land use increased soil C content by 29% compared with the pasture. Organic C retained in the soils was a function of the soil N content (r=0.98, P<0.001) and the soil carbohydrate (CH) concentration (r=0.96, P<0.001). Statistical analyses found that soil aggregation processes increased as organic C content increased in the forest and pasture soils, but not in the cropped soil. SOC was composed of similar percentages of CHs (49%, 42% and 51%), amino acids (22%, 15% and 18%), lipids (2.3%, 2.3% and 2.9%) and unidentified C (21%, 29% and 27%), but differed for phenolic acids (PAs) (5.7%, 11.6% and 1.0%) for the pasture, forest and cropped soils, respectively. The results suggested that the majority of the surface soil C sequestered in the long-term pasture and forest soils was identified as C of plant origin through the use of CH and PA biomarkers, although the increase in amino sugar concentration of microbial origin indicates a greater increase in microbial inputs in the three subsoils. The practice of permanent pastures and afforestation of agricultural land showed long-term potential for potential mitigation of atmospheric CO2.
  • Authors:
    • Paustian, K.
    • Capalbo, S. M.
    • Antle, J. M.
    • Mooney, S.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: A large body of research suggests that US crop-land soils can also sequester significant amounts of C and are a promising source of C credits. This paper presents a framework for assessing the transactions costs associated with per-hectare and per-credit contract types and addresses the potential magnitude of transactions costs associated with measuring soil C credits under a per-credit contract within the dry-land crop region of Montana, USA. In the empirical analysis, we estimate the total measurement costs for soil C credits and investigate how changes in contract (and region) size as well as increases in C credit variability affect total measurement costs. The empirical analyses suggest that increasing the size of the contract and aggregating credits over a larger number of producers can lower measurement costs associated with the per-credit contract, even in the face of increasing C variability. Thus contracts for large quantities of soil credits increase the likelihood that the per-credit contract remains more efficient than the per-hectare contract. However, these empirical results reflect the specific data and conditions present within the case study region. The theoretical expectation is that sample size and measurement costs can either increase or decrease as the population to be sampled increases. Thus the measurement costs associated with a per-credit contract could respond differently from this analysis across the spatial extent of the US.