• 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:
    • 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:
    • Gassman, P. W.
    • Kling, C. L.
    • Feng, H.
  • Source: Choices
  • Year: 2004
  • Summary: Capturing and storing carbon in biomass and soils in the agriculture and forest sector has gained widespread acceptance as a potential greenhouse gas mitigation strategy. Scientists increasingly understand the mechanisms by which various land-use practices can sequester carbon. Such practices include the introduction of cover crops on fallow land, the conversion of conventional tillage to conservation tillage, and the retirement of land from active production to a grass cover or trees. However, the policy design for implementing carbon sequestration activities is still being developed, and significant uncertainties remain concerning the cost effectiveness of carbon sequestration relative to other climate-change mitigation strategies.
  • Authors:
    • Stuedemann, J. A.
    • Wilkinson, S. R.
    • Franzluebbers, A. J.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 5
  • Year: 2004
  • Summary: Productivity, quality, and persistence of 'Coastal' bermudagrass [Cynodon dactylon (L.) Pers.] pastures are affected by fertilization, but possible interactions with defoliation regime including animal grazing are not fully known. We evaluated three sources of fertilization with equivalent N rates [inorganic, crimson clover (Trifolium incarnatum L.) cover crop plus inorganic, and chicken (Gallus gallus) broiler litter] factorially arranged with four defoliation regimes [unharvested, cattle (Bos taurus) grazing to maintain high (4.5 +/- 1.6 Mg ha(-1)) and low (2.5 +/- 1.1 Mg ha(-1)) forage mass, and hayed monthly] on estimated forage dry matter production, forage and surface residue C/N ratio, and ground cover of pastures on a Typic Kanhapludult in Georgia during 5 yr. Mean annual forage dry matter production was 7.5 +/- 0.7 Mg ha(-1) with hay harvest but declined (1.3 Mg ha(-1) yr(-1)) significantly with time as a result of lower precipitation. With grazing, estimated production was 8.3 +/- 1.0 Mg ha(-1) and did not change with time, suggesting that grazing cattle sustained forage productivity by recycling nutrients and creating better surface soil conditions. Coastal bermudagrass as a percentage of ground cover (initially 81%) declined 5 +/- 2% yr(-1) with unharvested and grazing to maintain low forage mass, declined 3 +/- 1% yr(-1) with haying, and remained unchanged (-1 +/- 1% yr(-1)) with grazing to maintain high forage mass. Pastures with high forage mass were more productive than with low forage mass (9.2 +/- 1.6 vs. 7.5 +/- 1.1 Mg ha(-1)) from a forage sustainability perspective, primarily by avoiding encroachment of undesirable plant species.
  • Authors:
    • Cooper, R. J.
    • Carroll, J. P.
    • Cederbaum, S. B.
  • Source: Conservation Biology
  • Volume: 18
  • Issue: 5
  • Year: 2004
  • Summary: Among the major agricultural crops in the southeastern United States, cotton (Gossypium hirsutum L.) generally provides the least suitable habitat for most early successional songbirds. Newer cropping approaches, such as use of conservation tillage and stripcover cropping, offer hope for improving the ecological value of cotton fields. We examined the effects of clover stripcover cropping with conservation tillage versus conventionally grown cotton with either conventional or conservation tillage on avian and arthropod species composition and field use in east-central Georgia. Stripcover fields had higher bird densities and biomass and higher relative abundance of arthropods than both conservation tillage and conventional fields. During migration and breeding periods, total bird densities on stripcover fields were 2-6 times and 7-20 times greater than on conservation and conventional fields, respectively. Abundance and biomass for epigeal arthropods were also greatest on stripcover fields during much of the breeding season. Although the clover treatment attracted the highest avian and arthropod densities, conservation fields still provided more wildlife and agronomic benefits than conventional management. Our findings suggest that both conservation tillage and stripcropping systems will improve conditions for birds in cotton, with stripcropped fields providing superior habitat. The reduction of inputs possible with the clover system could allow farmers to lower costs associated with conventional cotton production by $282-317/ha. This reduction of input, coupled with similar or possibly increased yield over conventional systems makes stripcover cropping not only a good choice for reducing negative impacts on wildlife and surrounding ecosystems, but also an economically desirable one.
  • Authors:
    • Paustian, K.
    • Six, J.
    • Conant, R. T.
  • Source: Biology and Fertility of Soils
  • Volume: 40
  • Issue: 3
  • Year: 2004
  • Summary: Since land use change can have significant impacts on regional biogeochemistry, we investigated how conversion of forest and cultivation to pasture impact soil C and N cycling. In addition to examining total soil C, we isolated soil physiochemical C fractions in order to understand the mechanisms by which soil C is sequestered or lost. Total soil C did not change significantly over time following conversion from forest, though coarse (250-2,000 [micro]m) particulate organic matter C increased by a factor of 6 immediately after conversion. Aggregate mean weight diameter was reduced by about 50% after conversion, but values were like those under forest after 8 years under pasture. Samples collected from a long-term pasture that was converted from annual cultivation more than 50 years ago revealed that some soil physical properties negatively impacted by cultivation were very slow to recover. Finally, our results indicate that soil macroaggregates turn over more rapidly under pasture than under forest and are less efficient at stabilizing soil C, whereas microaggregates from pasture soils stabilize a larger concentration of C than forest microaggregates. Since conversion from forest to pasture has a minimal impact on total soil C content in the Piedmont region of Virginia, United States, a simple C stock accounting system could use the same base soil C stock value for either type of land use. However, since the effects of forest to pasture conversion are a function of grassland management following conversion, assessments of C sequestration rates require activity data on the extent of various grassland management practices.
  • Authors:
    • Perfect, E.
    • Herbeck, J.
    • Murdock, L.
    • Grove, J. H.
    • Dí­az-Zorita, M.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 6
  • Year: 2004
  • Summary: The development of well-structured soils is a goal for achieving sustainable and productive agricultural systems. Nevertheless, the maintenance of soil structure in continuous no-till (NT) soils has sometimes been thought to induce soil conditions that are detrimental to crop yields. The objectives of this research were to characterize the effects of periodic tillage disruption in otherwise NT systems on soil properties and the yields of winter wheat (Triticum aestivum L.), double-cropped soybean [Glycine max (L.) Merr.], and maize (Zea mays L.) in rotation and to determine if soil structural changes occurring in tilled soils are independent of changes in other soil properties. A field experiment was established in 1992 on a Huntington silt loam soil (Fluventic Hapludoll) at the University of Kentucky Research and Education Center in Princeton (KY) under a NT crop sequence with two seedbed preparation methods for winter wheat, (a) NT or (b) chisel plus disk tillage (Till). In fall 2000, similar soil chemical properties were observed between disrupted and continuous NT systems over the 0- to 20-cm layer. The geometric mean diameter of dry fragments and the soil water content retained between 0.0003 and 0.03 MPa water potential was greater in NT soils than in soils tilled for winter wheat. Tillage for winter wheat enhanced winter wheat yields (4.2% increase), mostly under low-yielding conditions, but it resulted in a reduction of subsequent summer crop yields (i.e., 3.7% for soybean and 7.0% for maize). The yields obtained in our study translate to an economic benefit for the continuous NT system. Net returns per hectare were estimated to be $73 higher for the winter wheat/double-crop soybean-maize rotation under NT than under Till treatments. The differences in maize yields between NT and tilled treatments were attributed to a better water supply in NT soil due to the maintenance of a larger number of mesopores and a great hydraulic conductivity. In the absence of significant changes in other physicochemical properties, periodic tillage appears to disrupt soil structure, which negatively affects crop productivity.
  • Authors:
    • Lowenberg-DeBoer, J.
    • Bongiovanni, R.
    • Anselin, L.
  • Source: American Journal of Agricultural Economics
  • Volume: 86
  • Issue: 3
  • Year: 2004
  • Summary: The objective of this study is to determine the potential for using spatial econometric analysis of combine yield monitor data to estimate the site-specific crop response functions. The specific case study is for site-specific nitrogen (N) application to corn production in Argentina. Spatial structure of the yield data is modeled with landscape variables, spatially autoregressive error and groupwise heteroskedasticity. Results suggest that N response differs by landscape position, and that site-specific application may be modestly profitable. Profitability depends on the model specification used, with all spatial models consistently indicating profitability, whereas the nonspatial models do not.
  • Authors:
    • Spurlock, S.
    • Heatherly, L.
    • Reddy, K.
  • Source: Agronomy Journal
  • Volume: 96
  • Issue: 3
  • Year: 2004
  • Summary: Management inputs that maximize economic return from the early plantings of soyabean ( Glycine max) in the midsouthern USA have not been evaluated fully. The objective was to compare perennial weed control in and yields and economic returns from plantings of maturity group (MG) IV and V soyabean cultivars grown in the field (Mississippi, USA) under different weed management systems (WMS) following shallow (ST) and deep (DT) fall tillage. Adjacent experiments were conducted near Stoneville, Mississippi. Weed management systems were (i) glyphosate ( N-(phosphonomethyl)glycine)-resistant (GR) cultivars with preemergent (PRE) nonglyphosate herbicides followed by postemergent (POST) glyphosate; (ii) GR cultivars with POST glyphosate; (iii) non-GR cultivars with PRE plus POST nonglyphosate herbicides; and (iv) non-GR cultivars with POST nonglyphosate herbicides. Control of perennial redvine ( Brunnichia ovata) declined in the ST environment when non-GR cultivars were used, but this did not result in a yield decline. Control of perennial johnsongrass ( Sorghum halepense) at the end of the study period averaged 93% when GR cultivars were used regardless of tillage treatment, and this was associated with lower yield. Use of PRE+POST vs. POST-only weed management sometimes resulted in lower profits regardless of fall tillage treatment. The fall tillage treatment * WMS interaction was not significant for yield or net return, which indicates that use of DT for perennial weed management is not economical.
  • Authors:
    • Rogers, H.
    • Runion, G.
    • Torbert, H.
    • Prior, S.
  • Source: Environmental Management
  • Volume: 33
  • Issue: Supplement 1
  • Year: 2004
  • Summary: Elevated atmospheric CO 2 concentration can increase biomass production and alter tissue composition. Shifts in both quantity and quality of crop residue may alter carbon (C) and nitrogen (N) dynamics and management considerations in future CO 2-enriched agroecosystems. This study was conducted to determine decomposition rates of the legume soybean [ Glycine max (L.) Merr.] and nonlegume grain sorghum [ Sorghum bicolor (L.) Moench.] residue produced under two levels of atmospheric CO 2 (ambient and twice ambient) on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults) in Auburn, Alabama, USA, managed using no-till practices. At maturity, harvested plants were separated into component parts for dry weight determination and tissue analysis. Mass, C, and N losses from residues were determined using the mesh bag method. Biomass production was significantly greater for soybean compared to sorghum and for elevated versus ambient CO 2-grown plants. The CO 2 level had little affect on the C/N ratio of residue (probably because the tissue used was senesced). Elevated CO 2 concentration did not affect percent residue recovery; however, greater biomass production observed under elevated CO 2 resulted in more residue and C remaining after overwintering. The higher total N content of soybean residue, particularly when grown under elevated CO 2, indicated more N may be available to a following crop with lower N inputs required. Results suggest that in a high CO 2 environment, greater amounts of residue may increase soil C and ground cover, which may enhance soil water storage, improve soil physical properties, and reduce erosion losses.