• Authors:
    • Smith, R. F.
    • Koike, S. T.
    • Yokota, R.
    • Murphree, L.
    • Jackson, L. E.
    • Smukler, S. M.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 126
  • Issue: 3-4
  • Year: 2008
  • Summary: Studying the management strategies suited to large-scale organic production, particularly during the mandated 3-year transition period from conventional management, is a unique research challenge. Organic production traditionally relies on small, diverse plantings and complex management responses to cope with soil fertility and pest pressures, so research should represent decision-making options of an organic grower at the farm scale. This study analyzes crop, soil, pest and management changes during the organic transition period on two ranches (40 and 47 ha) in the Salinas Valley, California in cooperation with a large conventional vegetable producer, Tanimura and Antle, Inc. Permanent transects were established across the two ranches at the onset of adoption of organic practices, and soil and plants were sampled at harvest of almost all crops, while all management operations were recorded by the co-operator. The similar to 10 ha blocks were divided into many small plantings, and 17 different cash crop and cover crop species were planted during the transition period. Management inputs consisted of a range of organic fertilizers and amendments, sprinkler and drip irrigation, cultivation and hand-hoeing, and several types of organic pesticides. Results from the 3-year period followed these general trends: increase in soil biological indicators (microbial biomass and arbuscular mycorrhizae), low soil nitrate pools, adequate crop nutrients, minor disease and weed problems, and sporadic mild insect damage. Multivariate statistical analyses indicated that some crops and cultivars consistently produced higher yields than others, relative to the maximum yield for a given crop. Multi-factor contingency tables showed clear differences in insect and disease damage between crop taxa. Although Tanimura and Antle, Inc. used some of the principles of organic farming (e.g., crop diversity, crop rotation, and organic matter (OM) management), they also relied on substitution-based management, such as fertigation with soluble nutrients, initially heavy applications of organic pesticides, and use of inputs derived from off-farm sources. Their initial production of a large number of crop taxa in small plantings at staggered intervals proved to be an effective strategy for avoiding risks from low yields or crop failure and allowed them to move towards a smaller number of select, successful crops towards the end of the transition. This study demonstrates the feasibility of large-scale producers to transition to organic practices in a manner that was conducive to both production goals and environmental quality, i.e., increased soil C pools, low soil nitrate, and absence of synthetic pesticides. (C) 2008 Elsevier B.V. All rights reserved.
  • Authors:
    • Snyder, C. S.
  • Year: 2008
  • Summary: The discussion and guides that follow are oriented toward the central U.S. Corn Belt, but are relevant to other cropping systems with similar crop geographies. They are provided to assist in fertilizer nitrogen (N) management decisions that will help lessen the impact of fertilizer N use on greenhouse gas (GHG) emissions and help mitigate the global warming potential (GWP) - expressed as CO2 equivalent. The three GHGs of interest to agriculture are: nitrous oxide (N2O), methane (CH4), and CO2. The GWP of CH4 is 23 times greater and the GWP of N2O is 296 times greater than that of CO2. Because fertilizer N use may be associated with N2O emissions, and because the GWP of N2O is so much greater than CO2, fertilizer N BMPs to reduce N2O emissions are emphasized in this practical guide. For example, fertilizer N BMPs which help minimize excess nitrate (NO3 -) in the soil during warm, wet, or waterlogged conditions can result in lowered risks for N2O emission.
  • Authors:
    • Belina, K. M.
    • Steenwerth, K.
  • Source: Applied Soil Ecology
  • Volume: 40
  • Issue: 2
  • Year: 2008
  • Summary: Impacts of soil tillage and cover crops on soil carbon (C) dynamics and microbiological function were investigated in a vineyard grown in California's mediterranean climate. We (1) compared soil organic matter (SOM), C dynamics and microbiological activity of two cover crops [Trios 102 (Triticale x Triosecale) ('Trios'), Merced Rye (Secale cereale) ('Rye')] with cultivation ('Cultivation') and (2) evaluated seasonal effects of soil temperature, water content, and precipitation on soil C dynamics (0-15 cm depth). From treatments established in November 2001, soils were sampled every 2-3 weeks from November 2005 to November 2006. Gravimetric water content (GWC) reflected winter and spring rainfall. Soil temperature did not differ among treatments, reflecting typical seasonal patterns. Few differences in C dynamics between cover crops existed, but microbial biomass C (MBC), dissolved organic C (DOC), and carbon dioxide (CO2) efflux in 'Trios' and 'Rye' were consistently 1.5-4-fold greater than 'Cultivation'. Cover crops were more effective at adding soil C than 'Cultivation'. Seasonal patterns in DOC, and CO2 efflux reflected changes in soil water content, but MBC displayed no temporal response. Decreases in DOC and potential microbial respiration (RESPmic) (i.e., microbially available C) also corresponded to or were preceded by increases in CO2 efflux, suggesting that DOC provided C for microbial respiration. Despite similar MBC, DOC, RESPmic, annual CO2 efflux and aboveground C content between the two cover crops, greater aboveground net primary productivity and SOM in 'Trios' indicated that 'Trios' provided more soil C than 'Rye'.
  • Authors:
    • Snyder, K.
    • Sims, P. L.
    • Schuman, G. E.
    • Saliendra, N. Z.
    • Morgan, J. A.
    • Mielnick, P.
    • Mayeux, H.
    • Johnson, D. A.
    • Haferkamp, M.
    • Gilmanov, T. G.
    • Frank, A. B.
    • Emmerich, W.
    • Dugas, W.
    • Bradford, J. A.
    • Angell, R.
    • Svejcar, T.
  • Source: Rangeland Ecology & Management
  • Volume: 61
  • Issue: 5
  • Year: 2008
  • Summary: Rangelands account for almost half of the earth's land surface and may play an important role in the global carbon (C) cycle. We Studied net ecosystem exchange (NEE) of C on eight North American rangeland sites over a 6-yr period. Management practices and disturbance regimes can influence NEE; for consistency, we compared ungrazed and undisturbed rangelands including four Great Plains sites from Texas to North Dakota, two Southwestern hot desert sites in New Mexico and Arizona, and two Northwestern sagebrush steppe sites in Idaho and Oregon. We used the Bowen ratio-energy balance system for continuous measurements of energy, water vapor, and carbon dioxide (CO2) fluxes at each study site during the measurement period (1996 to 2001 for most sites). Data were processed and screened using standardized procedures, which facilitated across-location comparisons. Although almost any site could be either a sink or source for C depending on yearly weather patterns, five of the eight native rangelands typically were sinks for atmospheric CO2 during the study period. Both sagebrush steppe sites were sinks and three of four Great Plains grasslands were sinks, but the two Southwest hot desert sites were sources of C on an annual basis. Most rangelands were characterized by short periods of high C uptake (2 mo to 3 mo) and long periods of C balance or small respiratory losses of C. Weather patterns during the measurement period strongly influenced conclusions about NEE on any given rangeland site. Droughts tended to limit periods of high C uptake and thus cause even the most productive sites to become sources of C on an annual basis. Our results show that native rangelands are a potentially important terrestrial sink for atmospheric CO2, and maintaining the period of active C uptake will be critical if we are to manage rangelands for C sequestration.
  • Authors:
    • Trostle, R.
  • Source: USDA, Economic Research Service
  • Year: 2008
  • Summary: This 2008 report, from the USDA's Economic Research Service, discusses factors contributing to the recent increase in food commodity prices.
  • Authors:
    • U.S. EPA
  • Year: 2008
  • Summary: The United States Environmental Protection Agency (EPA) prepares the oficial U.S. Inventory of Greenhouse Gas Emissions and Sinks to comply with existing commitments under the United Nations Framework Convention on Climate Change (UNFCCC).
  • Authors:
    • Hyberg, S.
    • Iovanna, R.
    • Feather, C.
    • Barbarika, A.
  • Year: 2008
  • Authors:
    • Skiles, S.
    • Wirth, J.
    • Ogle, S.
    • Del Grosso, S.
  • Source: Technical Bulletin 1921
  • Year: 2008
  • Summary: Emissions of the three most important long-lived greenhouse gases (GHG) have increased measurably over the past two centuries. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations in the atmosphere have increased by approximately 35%, 155%, and 18%, respectively, since 1750. In the U.S., agriculture accounted for close to 7% of total GHG emissions (7260 Tg CO2 eq.) in 2005. Livestock, poultry, and crop production contributed a total of 481 Tg CO2 eq. to the atmosphere in 2005. This total includes an offset from agricultural soil carbon sequestration of roughly 32 Tg CO2 eq. The primary agricultural sources are N2O emissions from cropped and grazed soils (263 Tg CO2 eq.), CH4 emissions from enteric fermentation (112 Tg CO2 eq.), and CH4 emissions from managed livestock waste (41 Tg CO2 eq.). Forests in the United States contributed a net reduction in atmospheric GHG of approximately 787 Tg CO2 eq. in 2005, which offset total U.S. GHG emissions by approximately 11%. In aggregate, the U.S. agricultural sector (including GHG sources for crop, poultry, and livestock production and GHG removal from the atmosphere via sinks for in) was estimated to be a net sink of 306 Tg CO2 eq. in 2005.
  • Authors:
    • Vives, C. A.
    • Szogi, A. A.
    • Vanotti, M. B.
  • Source: Waste Management
  • Volume: 28
  • Issue: 4
  • Year: 2008
  • Summary: Trading of greenhouse gas (GHG) emission reductions is an attractive approach to help producers implement cleaner treatment technologies to replace current anaerobic lagoons. Our objectives were to estimate greenhouse gas (GHG) emission reductions from implementation of aerobic technology in USA swine farms. Emission reductions were calculated using the approved United Nations framework convention on climate change (UNFCCC) methodology in conjunction with monitoring information collected during full-scale demonstration of the new treatment system in a 4360-head swine operation in North Carolina (USA). Emission sources for the project and baseline manure management system were methane (CH4) emissions from the decomposition of manure under anaerobic conditions and nitrous oxide (N2O) emissions during storage and handling of manure in the manure management system. Emission reductions resulted from the difference between total project and baseline emissions. The project activity included an on-farm wastewater treatment system consisting of liquid-solid separation, treatment of the separated liquid using aerobic biological N removal, chemical disinfection and soluble P removal using lime. The project activity was completed with a centralized facility that used aerobic composting to process the separated solids. Replacement of the lagoon technology with the cleaner aerobic technology reduced GHG emissions 96.9%, from 4972 tonnes of carbon dioxide equivalents (CO2-eq) to 153 tonnes CO2-eq/year. Total net emission reductions by the project activity in the 4360-head finishing operation were 4776.6 tonnes CO2-eq per year or 1.10 tonnes CO2-eq/head per year. The dollar value from implementation of this project in this swine farm was US$19,106/year using current Chicago Climate Exchange trading values of US$4/t CO2. This translates into a direct economic benefit to the producer of US$1.75 per finished pig. Thus, GHG emission reductions and credits can help compensate for the higher installation cost of cleaner aerobic technologies and facilitate producer adoption of environmentally superior technologies to replace current anaerobic lagoons in the USA. Published by Elsevier Ltd.
  • Authors:
    • Stanenas, Adam J.
    • Venterea, Rodney T.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 4
  • Year: 2008
  • Summary: The impact of no-till (NT) and other reduced tillage (RT) practices on soil to atmosphere fluxes of nitrous oxide (N2O) are difficult to predict, and there is limited information regarding strategies for minimizing fluxes from RT systems. We measured vertical distributions of key microbial, chemical, and physical properties in soils from a long-term tillage experiment and used these data as inputs to a process-based model that accounts for N2O production, consumption, and gaseous diffusion. The results demonstrate how differences among tillage systems in the stratification of microbial enzyme activity chemical reactivity, and other properties can control NO fluxes. Under nitrification-dominated conditions, simulated N2O emissions in the presence of nitrite (NO2-) were 2 to 10 times higher in NT soil compared to soil under conventional tillage (CT). Under denitrification-dominated conditions in the presence of nitrate (NO3-), higher bulk density and water content under NT promoted higher denitrification rates than CT. These effects were partially offset by higher soluble organic carbon and/or temperature and lower N2O reduction rates under CT. The NT/CT ratio of N2O fluxes increased as NO2- or NO3- was placed closer to the surface. The highest NT/CT ratios of N2O flux (> 30:1) were predicted for near-surface NO3- placement, while NT/CT ratios < 1 were predicted for NO3- placement below 15 cm. These results suggest that N2O fluxes from RT systems can be minimized by subsurface fertilizer placement and by using a chemical form of fertilizer that does not promote substantial NO2- accumulation.