81. Nitrous oxide emissions from wetland soil amended with inorganic and organic fertilizers

• Authors:
  • Wuta, M.
  • Nyamangara, J.
  • Masaka, J.
• Source: Archives of Agronomy and Soil Science
• Volume: 60
• Issue: 10
• Year: 2014
• Summary: Agricultural soils are a primary source of anthropogenic trace gas emissions, and the subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. A field experiment was carried out in an ephemeral wetland in central Zimbabwe in order to determine the effect of cattle manure (1.36%N) and mineral N fertilizer (ammonium nitrate, 34.5%N) application on N2O fluxes from soil. Combined applications of 0kgN fertilizer+0Mg cattle manure ha(-1) (control), 100kgN fertilizer+15Mg manure ha(-1) and 200kgN fertilizer+30Mg manure ha(-1) constituted the three treatments arranged in a randomized complete block design with four replications. Tomato and rape crops were grown in rotation over a period of two seasons. Emissions of N2O were sampled using the static chamber technique. Increasing N fertilizer and manure application rates from low to high rates increased the N2O fluxes by 37-106%. When low and high rates were applied to the tomato and rape crops, 0.51%, 0.40%, and 0.93%, 0.64% of applied N was lost as N2O, respectively. This implies that rape production has a greater N2O emitting potential than the production of tomatoes in wetlands.

82. Influence of mechanical loading on static and dynamic CO2 efflux on differently textured and managed Luvisols

• Authors:
  • Peth, S.
  • Mordhorst, A.
  • Horn, R.
• Source: Geoderma
• Volume: 219
• Issue: May
• Year: 2014
• Summary: Mechanical disturbance of soil structure is commonly related to altered physical changes in pore systems, which control CO2 effluxes e.g. by changes in gas transport properties and in microbial activity. Soil compaction mostly leads to reduced CO2 fluxes. In contrast, structured soils can also release physically entrapped CO2 or give access to protected carbon sources inside aggregates due to aggregate breakdown by disruptive forces. In this study it was investigated how far arable soil management affects structure- and compaction-related CO2-releases using incubation experiments and CO2 gas analysis under standard matric potentials (-6 kPa). CO2 efflux was analyzed before, during and after mechanical loading using the alkali trap method (static efflux) and a gas flow compaction device (GaFloCoD, dynamic efflux). Intact soil cores (236 and 471 cm(3)) were collected from a Stagnic Luvisol with loamy sand (conservation and conventional tillage systems) and a Haplic Luvisol with clayey silt (under different fodder crops) from the topsoil (10-15 cm) and subsoil (35-45 cm). Mechanical stability was reflected by the pre-compression stress value (P-c) and by the tensile strength of aggregates (12-20 mm). Changes in pore systems were described by air conductivity as well as air capacity and total porosity. While CO2-releases varied highly during the compaction process (GaFloCoD) for different stress magnitudes, soil depths and management systems, basal respiration rates were generally reduced after mechanical loading by almost half of the initial rates irrespective of soil management. For both methods (dynamic and static efflux) restriction in gas transport functionality was proved to have major influence on inhibition of CO2 efflux due to mechanical loading. GaFloCoD experiments demonstrated that decreases in CO2 efflux were linked to structural degradation of pore systems by exceeding internal soil strength (P-c). Otherwise, re-equilibrating matric potentials to 6 kPa and re-incubating offset inhibition of soil respiration suggest a re-enhancement of microbial activity. At this state, physical influences were apparently overlapped by biological effects due to higher energy supply to microbes, which could be offered by spatial distribution changes of microorganisms and organic substrates within a given soil structure. This implies the susceptibility of physical protection mechanism for carbon by disruption of soil structure. In future, special focus should be given on a clear distinction between physical and microbiological effects controlling CO2 fluxes in structured soils. (C) 2014 Elsevier B.V. All rights reserved.

83. Energy inputs and GHG emissions of tillage systems

• Authors:
  • Dalgaard, R.
  • Petersen, B. M.
  • Oudshoorn, F. W.
  • Halberg, N.
  • Sorensen, C. G.
• Source: Biosystems Engineering
• Volume: 120
• Issue: April
• Year: 2014
• Summary: Different tillage systems result in different resource uses and environmental impacts. Reduced tillage generates savings in direct energy input and the amount of machinery items needed. As the basics for holistic Life Cycle Assessments, both the influencing direct and indirect energy as sources of greenhouse gas emissions are required. Life Cycle inventories (LCI) were aggregated for a number of optimised machinery systems and tillage scenarios integrating a four crop rotation consisting of spring barley, winter barley, winter wheat and winter rape seed. By applying Life Cycle Assessments to a number of tillage scenarios and whole field operations sequences, the energy efficiency and environmental impact in terms of greenhouse gas emissions (GHG) were evaluated. Results showed that the total energy input was reduced by 26% for the reduced tillage system and by 41% for the no-tillage system. Energy used for traction and machine construction contributed between 6 and 8% of the total GHG emission per kg product. The total emission of GHG was 915 g CO2 equivalents per kg product by using the conventional tillage system, 817 g CO2 equivalents for the reduced tillage system and 855 g CO2 equivalents for the no tillage system. The no tillage system was expected to yield 10% less. The mineralisation in the soil contributed the most (50-60%) to this emission, while the fertiliser production contributed with 28-33%. The results stress the importance of applying a systems approach to capture the implications of, for example, sustained yields as otherwise the environmental benefits can be compromised. (C) 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.

84. Efficiencies of nitrogen fertilizers for winter cereal production, with implications for greenhouse gas intensities of grain

• Authors:
  • Wynn, S. C.
  • Kindred, D. R.
  • Sylvester-Bradley, R.
  • Thorman, R. E.
  • Smith, K. E.
• Source: The Journal of Agricultural Science
• Volume: 152
• Issue: 1
• Year: 2014
• Summary: Fertilizer nitrogen (N) accounts for the majority of the greenhouse gas (GHG) emissions associated with intensive wheat production, and the form of fertilizer N affects these emissions. Differences in manufacturing emissions (as represented in the current carbon accounting methodologies) tend to favour urea, even when using the best available manufacturing technologies (BAT), whereas differences in fertilizer N efficiency and emissions of ammonia tend to favour ammonium nitrate (AN). To resolve these differences, data from 47 experiments in two large UK studies conducted from 1982 to 1987 and from 2003 to 2005 were reanalysed, showing that on average urea efficiency was 0 center dot 9 of AN (although mean ammonia emissions in 10 subsidiary experiments indicated an efficiency difference of 0 center dot 2); treating urea with a urease inhibitor (TU; AGROTAIN((R)), active ingredient N-(n-butyl) thiophosphoric triamide (n-BTPT)) brought its efficiency almost in line with AN; however, a significantly greater mean optimum N amount for TU (+0 center dot 1 of AN) was not fully explained. A standard response function relating wheat yield to applied AN was modified for degrees of relative inefficiency, thus enabling yields and GHG intensities (kg CO(2)e/tonne (t) grain) to be calculated using a PAS2050 compatible model for GHG emissions for any N amount of any N form. With AN manufactured by average European technology (AET), the estimated GHG intensity of wheat producing 8 t/ha was 451 kg/t; whereas with urea or TU made by AET it was 0.87-0.99 or 0.84-0.86 of this respectively. Using BAT for fertilizer manufacture, the grain's GHG intensity with AN and TU was 368kg/t, but was 1 center dot 03-1 center dot 17 of this with untreated urea. The range of effects on GHG intensities arose mainly from remaining uncertainties in the inefficiencies of the N forms. Generally, economic margins and GHG intensities were not much affected by adjustments in N use for relative inefficiencies or different prices of urea-based fertilizers compared with AN. Overall, TU appeared to provide the best combination of economic performance and GHG intensity, unless the price for N as TU exceeded that for N as AN.

85. Sugarcane Crop Residue Increases N2O and CO2 Emissions Under High Soil Moisture Conditions

• Authors:
  • de Andrade, C. A.
  • do Carmo, J. B.
  • Soares, J. R.
  • Martins, A. A.
  • Cantarella, H.
  • Vargas, V. P.
• Source: Sugar Tech
• Volume: 16
• Issue: 2
• Year: 2014
• Summary: Sugarcane crop residues from green cane harvests may affect the greenhouse gas fluxes from the soils. Therefore, it is important to understand how changes in soil moisture covered with cane trash alter the N2O and CO2 emission. The aim of this study was to evaluate N2O and CO2 emission from repacked soil columns incubated with (16 Mg ha(-1)) or without crop residues and N fertilizer (0 or 2.1 g N m(-2)), and as a function of four soil moisture levels (25, 50, 75 and 100 % of water holding capacity). For gas samplings, the columns were closed with a lid and four gas samples were taken in 20 min. The N2O fluxes increased linearly (p < 0.01) with increasing soil moisture regardless of the residue application on soil. However in the columns with trash the moisture effect, on N2O emission rates, was two-fold greater. Every 10 % increase in moisture in relation to the holding capacity resulted in losses equivalent to 790 and 1,640 mu g N m(-2) for the 0 and 16 Mg ha(-1) crop residue rates, respectively. In conditions of low moisture (25 and 50 %), the crop residue did not increase emissions compared to the bare soil. The CO2 emission also was linearly stimulated with increasing soil moisture, regardless of crop residue application. However, the CO2 emission rate was higher with the residue. Our study indicates that the effects of crop residue on greenhouse gas emissions are exacerbated in periods with high soil moisture.

86. Seasonal nitrous oxide emissions from field soils under reduced tillage, compost application or organic farming

• Authors:
  • Nevison, I. M.
  • McKenzie, B. M.
  • Hallett, P. D.
  • Gordon, H.
  • Watson, C. A.
  • Rees, R. M.
  • Walker, R. L.
  • Wheatley, R.
  • Topp, C. F. E.
  • Griffiths, B. S.
  • Ball, B. C.
• Source: Agriculture, Ecosystems & Environment
• Volume: 189
• Issue: May
• Year: 2014
• Summary: Soil management practices shown to increase carbon sequestration include reduced tillage, amendments of carbon and mixed rotations. As a means to mitigate greenhouse gases, however, the success of these practices will be strongly influenced by nitrous oxide (N2O) emissions that vary with soil wetness. Few seasonal data are available on N2O under different soil managements so we measured seasonal N2O emission in three field experiments between 2006 and 2009 in eastern Scotland. The experimental treatments at the three sites were (1) tillage: no-tillage, minimum tillage, ploughing to 20 cm with or without compaction and deep ploughing to 40 cm, (2) organic residue amendment: application of municipal green-waste compost or cattle slurry and (3) rotations: stocked and stockless (without manure) organic arable farming rotations. Most seasons were wetter than average with 2009 the wettest, receiving 20-40% more rainfall than average. Nitrous oxide emissions were measured using static closed chambers. There was no statistical evidence, albeit with low statistical power, that reduced tillage affected N2O emissions compared to normal depth ploughing. With organic residue amendments, only in the wet season in 2008 were emissions significantly increased by high rates of green-waste compost (4.5 kg N2O-N ha(-1)) and cattle slurry (5.2 kg N2O-N ha(-1)) compared to the control (1.9 kg N2O-N ha(-1)). In the organic rotations, N2O emissions were greatest after incorporation of the grass/clover treatments, especially during conversion of a stocked rotation to stockless. Emissions from the organic arable crops (1.9 kg N2O-N ha(-1) in 2006, 3.0 kg N2O-N ha(-1) in 2007) generally exceeded those from the organic grass/clover (0.8 kg N2O-N ha(-1) in 2006, 1.1 kg N2O-N ha(-1) in 2007) except in 2008 when the Wet weather delayed manure applications and increased emissions from the grass/clover (2.8 kg N2O-N ha(-1)). Nevertheless, organic grassland was the land use providing the most effective overall mitigation. Although the magnitude of fluxes did not relate particularly well to rainfall differences between seasons, greater rainfall received during some growing seasons increased the differences between tillage, organic residue and crop rotation phase treatments, negating any possible mitigation by timing management operations in dry periods. This was partly attributed to applying tillage and manures late and/or in wet conditions. Of benefit would be different sampling strategies including closed chambers or eddy covariance with standardised methodology. Controlled soil management experiments with a wide geographic spread to specify land management for mitigation also important. (C) 2014 Elsevier B.V. All rights reserved.

87. The true extent of agriculture's contribution to national greenhouse gas emissions.

• Authors:
  • Rees, R.
  • Cloy, J.
  • Bell, M.
• Source: Environmental Science & Policy
• Volume: 39
• Year: 2014
• Summary: The agricultural sector is a significant contributor to greenhouse gas (GHG) emissions, and a growing global population means that agricultural production will remain high if food demands are to be met. Mitigation methods to reduce emissions from this sector are thus required, along with identification and quantification of emission sources, so that the agricultural community can act and measure its progress. International legislation requires the submission of annual reports quantifying GHG emissions from agriculture. The importance of attributing the correct sources of emissions to the agricultural sector is clear; however the current approach taken by the IPCC, and reported to the UNFCCC, omits emissions from soils during agricultural land-use change from its agricultural inventory. This paper questions the IPCC approach, and the attribution of agricultural land-use change emissions to a separate category: 'Land-use, Land-use change and Forestry'. Here a new approach adopted by the Scottish Government is examined, and compared to IPCC guidelines and national communications submitted to the Department of Energy and Climate Change (DECC) and the UNFCCC. The new Scottish Government approach attributes emissions from both land-use conversion and agricultural land under continuous use to the agricultural sector, in addition to those emissions from livestock and energy use on farms. The extent of emissions attributed to the agricultural sector using the Scottish Government approach is much greater than that using the other approaches-largely resulting from the inclusion of cropland conversion in the Scottish Government calculations. Attribution of these emissions to the agricultural sector gives calculated emissions of 10.63 Mt CO 2eq in 2009, compared to 7.06 Mt CO 2eq using the IPCC guidelines. This has implications for the agricultural community and may influence how and if they choose to act to reduce emissions. A large reduction in emissions from cropland conversion since 1990 means that total agricultural emissions in Scotland have fallen 26.64% when calculated by the Scottish Government, compared to a drop of only 19.13% reported to the UNFCCC.

88. Implications of productivity and nutrient requirements on greenhouse gas balance of annual and perennial bioenergy crops.

• Authors:
  • Preudhomme, M.
  • Fourdinier, E.
  • Machet, J.
  • Boizard, H.
  • Demay, C.
  • Ferchaud, F.
  • Cadoux, S.
  • Chabbert, B.
  • Gosse, G.
  • Mary, B.
• Source: Bioenergy
• Volume: 6
• Issue: 4
• Year: 2014
• Summary: Biomass from dedicated crops is expected to contribute significantly to the replacement of fossil resources. However, sustainable bioenergy cropping systems must provide high biomass production and low environmental impacts. This study aimed at quantifying biomass production, nutrient removal, expected ethanol production, and greenhouse gas (GHG) balance of six bioenergy crops: Miscanthus * giganteus, switchgrass, fescue, alfalfa, triticale, and fiber sorghum. Biomass production and N, P, K balances (input-output) were measured during 4 years in a long-term experiment, which included two nitrogen fertilization treatments. These results were used to calculate a posteriori 'optimized' fertilization practices, which would ensure a sustainable production with a nil balance of nutrients. A modified version of the cost/benefit approach proposed by Crutzen et al. (2008), comparing the GHG emissions resulting from N-P-K fertilization of bioenergy crops and the GHG emissions saved by replacing fossil fuel, was applied to these 'optimized' situations. Biomass production varied among crops between 10.0 (fescue) and 26.9 t DM ha -1 yr -1 (miscanthus harvested early) and the expected ethanol production between 1.3 (alfalfa) and 6.1 t ha -1 yr -1 (miscanthus harvested early). The cost/benefit ratio ranged from 0.10 (miscanthus harvested late) to 0.71 (fescue); it was closely correlated with the N/C ratio of the harvested biomass, except for alfalfa. The amount of saved CO 2 emissions varied from 1.0 (fescue) to 8.6 t CO 2eq ha -1 yr -1 (miscanthus harvested early or late). Due to its high biomass production, miscanthus was able to combine a high production of ethanol and a large saving of CO 2 emissions. Miscanthus and switchgrass harvested late gave the best compromise between low N-P-K requirements, high GHG saving per unit of biomass, and high productivity per hectare.

89. Soil carbon changes under Miscanthus driven by C₄ accumulation and C₃ decompostion - toward a default sequestration function

• Authors:
  • Don, A.
  • Poeplau, C.
• Source: GCB Bioenergy
• Volume: 6
• Issue: 4
• Year: 2014
• Summary: Bioenergy has to meet increasing sustainability criteria in the EU putting conventional bioenergy crops under pressure. Alternatively, perennial bioenergy crops, such as Miscanthus, show higher greenhouse gas savings with similarly high energy yields. In addition, Miscanthus plantations may sequester additional soil organic carbon (SOC) to mitigate climate change. As the land-use change in cropland to Miscanthus involves a C-3-C-4 vegetation change (VC), it is possible to determine the dynamic of Miscanthus-derived SOC (C-4 carbon) and of the old SOC (C-3 carbon) by the isotopic ratio of C-13 to C-12. We sampled six croplands and adjacent Miscanthus plantations exceeding the age of 10 years across Europe. We found a mean C-4 carbon sequestration rate of 0.78 +/- 0.19 Mg ha(-1) yr(-1), which increased with mean annual temperature. At three of six sites, we found a significant increase in C-3 carbon due to the application of organic fertilizers or difference in baseline SOC, which we define as non-VC-induced SOC changes. The Rothamsted Carbon Model was used to disentangle the decomposition of old C-3 carbon and the non-VC-induced C3 carbon changes. Subsequently, this method was applied to eight more sites from the literature, resulting in a climate-dependent VC-induced SOC sequestration rate (0.40 +/- 0.20 Mg ha(-1) yr(-1)), as a step toward a default SOC change function for Miscanthus plantations on former croplands in Europe. Furthermore, we conducted a SOC fractionation to assess qualitative SOC changes and the incorporation of C-4 carbon into the soil. Sixteen years after Miscanthus establishment, 68% of the particulate organic matter (POM) was Miscanthus-derived in 0-10 cm depth. POM was thus the fastest cycling SOC fraction with a C-4 carbon accumulation rate of 0.33 +/- 0.05 Mg ha(-1) yr(-1). Miscanthus-derived SOC also entered the NaOCl-resistant fraction, comprising 12% in 0-10 cm, which indicates that this fraction was not an inert SOC pool.

90. Multicriteria analysis of the effects of field burning crop residues.

• Authors:
  • Mihalache, M.
  • Fintineru, G.
  • Stan, V.
• Source: Notulae Botanicae Horti Agrobotanici Cluj-Napoca
• Volume: 42
• Issue: 1
• Year: 2014
• Summary: Burning crop residues is frequently used by Romanian land users to clean agricultural fields after crop harvest for ease in postharvest soil tillage. Huge amounts of crop residues biomass, on very large areas, were burned in Romania in the last twenty years, as compared to other countries. There are several reasons (e.g. the lack of equipment to gather the crop residues and to transport and store them, the diminishing of the livestock after 1990, the absence of other alternatives, especially in the 1990s, but also the lack of information regarding the good practices) that are evocated to support the use of this method. However, this method is not a sustainable one since it can cause many environmental damages, especially related to soil properties (physical, chemical and biological), greenhouse gas emission and crop yields. Contrary to the above stated, crop residues' addition to the soil may restore damaged soil structure, improve aggregate stability, soil water retention, soil fertility, increase total organic carbon (TOC) and total nitrogen (TN) etc. The purpose of this paper is to make a multicriteria analyze of the effects of crop residue management on the soil, agricultural productivity and environment. At the same time, the use of crop residues biomass as a source of energy is presented as an alternative, given its potential ability to offset fossil fuels and reduce CO 2 emissions.