Now showing 1 - 5 of 5
  • Publication
    Soil-Atmosphere Exchange of NH3 and NOx in Differently Managed Vegetation Types of Southern Germany
    Ammonia (NH3) and Nitrogen Oxides (NOx = NO + NO2) emissions from soils and vegetation, and their subsequent deposition are key factors in global Nitrogen (N) cycling and have important functions in atmospheric and ecosystem degradation processes. To better understand their contribution, NH3 and NOx gases were simultaneously measured from differently managed vegetation types using a dynamic-chamber method. Biomass and N yields were higher from unfertilized clover-grass than fertilized oilseed radish. Summer cuts of clover-grass resulted in 137% higher biomass and 2.7-3.7% N concentrations than autumn cuts. Mulching reduced the re-growth and biomass production in clover-grass by 16% compared to cutting. The relative loss of NH3 through mulching was higher from the clover-grass (2.18%) than in the oilseed radish (0.08%). The total NH3 release over the four cuts of the clover-grass was 0.58% of the N removed. The influence of biomass-N, either mulched or cut, on the total NOx emission was temporary, resulted in net deposition (0.02-0.15% of the added/removed biomass-N). The ecosystems acted as sources for NH3, with the rate being weakly related to the added biomass-N, air temperature and humidity (R2 = 0.58, p<0.07), and sinks for NOx, with the rate influenced significantly by sunshine hours, precipitation and amount of biomass-N added (R2 = 0.87, p<0.001). We conclude that cutting clover-grass multiple times could be a good option to reduce the emissions of reactive N species and increase fodder yields with moderate N. Additionally, clover-grass could be superior for soil conservation measures over oilseed radish. Results imply further studies on the annual exchanges of gaseous N between the ecosystems and the atmosphere through long-term measurements.
  • Publication
    Evidence of aerobic and anaerobic methane oxidation coupled to denitrification in agricultural soils
    Agricultural soils may act as either a source or a sink for atmospheric methane (CH4) depending on soil type, aeration, water regimes, nutrient availability and environmental variables. The interaction between CH4 and nitrogen (N) has been identified as one of the major gaps in the global carbon (C) and N cycles. Methane is being considered as a low-cost electron donor for coexisting denitrifiers and the denitrification process may be coupled to either aerobic CH4 oxidation involving direct nitrate/nitrite reduction (partial denitrification), or anaerobic relating predominantly to nitrite/nitric oxide reduction (complete denitrification). It is evidenced from isotopic studies that CH4 production and oxidation could take place simultaneously in agricultural soils at water content above field capacity, linking to the presence of anaerobic microsites and aerobic-anaerobic interface. This results in either aerobic or anaerobic CH4 oxidation coupled to the highest N2O emissions, demonstrating a close relationship between CH4 oxidation and denitrification (partial) processes. Besides the involvement of a microbial consortium in the interactive process, recent advancement with microbiological techniques prove the occurrence of the coupled process by combining aerobic methanotrophs and denitrifiers, as well as oxidization of ammonium and metabolic by-products, releasing N2O as a terminal product. However, the apparent anaerobic phenomenon lacks known genes for dinitrogen (N2) production, but subsequent isotopic labelling reveals that methanotrophs could bypass the denitrification intermediate N2O to produce N2 and oxygen that oxidizes CH4. Further investigations using both advanced molecular microbiology and isotope tracing techniques are necessary to elucidate the nature of the processes, better understand the mechanisms in agricultural soils and develop biotechnological solutions to the issues concerning particularly to climate change.
  • Publication
    Turnover of Chicken Manure in Some Upland Soils of Asia: Agricultural and Environmental Perspectives
    Recycling of organic manure/waste is an important global issue to improve soil productivity for sustaining agricultural production as well as to preserve the environment. In Asia, rearing of poultry especially chicken is becoming one of the key industrial sectors and the wastes from clean-out operations may contribute largely to plant nutrients. Thus, some recent research works on the use of chicken manure (CM) in the uplands of tropical Asia are reviewed. Relative loss of the added CM-C was averaged 83% during a 90-day incubation and in-situ retention of labile organic-C was poor in 2 years, signifying long-term episodes to sequestrate its inherent low C. Ammonification of the added CM was rapid during 1-2 weeks followed by oxidation of NH4+. The high pH of CM remarkably influenced nitrification either after a lag phase or immediately after application, ensuing NO3- leaching to occur under favourable conditions. Net mineralization/ nitrification was greater with CM than with other wider C/N ratio organic residues. CM-N recovery was relatively low, indicating immobilization and other N loss processes. Likewise, a large N2O loss of added CM-N with or without other N sources under field (0.99%) and laboratory (6.66%) conditions was observed, along with presumable NH3 volatilization. Composted CM/litter could reduce the loss by limiting the transformation of organic N. Application of CM (fresh/composted) either alone or with inorganic fertilizers demonstrated crop yield benefits and reduced the use of the latter as well as a noticeable residual effect to the succeeding crops. Results suggest that strategic but agro-economically viable composting might have great advantages in synchronizing CM-N release with plant uptake and in reducing appreciable amounts of labile C and gaseous N loss under upland conditions and thus, in minimizing environmental risk.
  • Publication
    Strategic Management of Grazing Grassland Systems to Maintain and Increase Organic Carbon in Soils
    Understanding management-induced C sequestration potential in soils under agriculture, forestry, and other land use systems and their quantification to offset increasing greenhouse gases are of global concern. This chapter reviews management-induced changes in C storage in soils of grazing grassland systems, their impacts on ecosystem functions, and their adaptability and needs of protection across socio-economic and cultural settings. In general, improved management of grassland/pasture such as manuring/slurry application, liming and rotational grazing, and low to medium livestock units could sequester C more than under high intensity grazing conditions. Converting cultivated land to pasture, restoration of degraded land, and maximizing pasture phases in mixed-cropping, pasture with mixed-livestock, integrated forestry-pasturage of livestock (silvopastoral) and crop-forestry-pasturage of livestock (agro-silvopastoral) systems could also maintain and enhance soil organic C density (SOCρ). In areas receiving low precipitation and having high erodibility, grazing exclusion might restore degraded grasslands and increase SOCρ. Yet, optimizing C sequestration rates, sowing of more productive grass varieties, judicial inorganic and organic fertilization, rotational grazing, and other climate-resilient approaches could improve overall farm productivity and profitability and attain sustainability in livestock farming systems.
  • Publication
    Assessing the sensitivity of fertilizer types and soil variables on nitrous oxide emissions in permanent grasslands using the DNDC model
    The adoption and use of improved methodologies including models that reflect more robust emissions accounting procedures and the identification of specific mitigation options for agricultural greenhouse gases are a global concern. In Ireland, country-specific N2O emission factors (EFs) are constrained primarily by short-term measurements and limited coverage of regulating factors. Simulation of N2O emissions from grassland silage plots managed for 42 years with different slurry treatments was performed using the DeNitrification-DeComposition (DNDC95) model. The objective was to assess the long-term impact of management practices on N2O fluxes and EFs, and the sensitivity of the outputs to key inorganic and organic fertilizer management and soil variables. The DNDC performed well for urea, cattle slurry and pig slurry applied at variable rates, delivering EFs on-average of 0.35±0.02, 1.80±0.28 and 1.53±0.41%, respectively. Variation in the derived-EFs could be explained by differences in nitrogen inputs (49%), rainfall (16%) and temperature (10%) and are close to national estimates. Sensitivity analysis of the model demonstrated that N2O EFs were higher with ammonium sulphate compared to CAN and urea fertilizers, and with urea-N at higher rates. The replacement of slurry either after the second or third silage cut by urea decreased EFs significantly. There was a strong correlation with the sensitivity of N2O EFs to soil texture, bulk density, pH and organic carbon (R2=0.96-0.99). The resulting-EFs ranged from 0.28 to 0.41% for urea, 1.12 to 2.07% for cattle slurry, and 1.05 to 1.65% for pig slurry, and the corresponding values on-average were 0.35±0.02, 1.74±0.17 and 1.39±0.12%. These findings show that DNDC95, although requiring more improvement, could provide an accurate representation of the effect of soils, climate and management practices on N2O fluxes and subsequent estimates of disaggregated EFs.