41. Trends in organic carbon and nitrogen contents in agricultural soils in Bavaria (south Germany) between 1986 and 2007

• Authors:
  • Capriel, P.
• Source: European Journal of Soil Science
• Volume: 64
• Issue: 4
• Year: 2013
• Summary: In the last 60 years traditional agriculture in industrialized European countries, which had initially been dependent on available natural resources, has shifted towards a massive intensification of nutrient turnover because of cheap energy and low-cost synthetic fertilizers. At the same time farm structure has undergone profound changes, resulting in an increase in the number of specialized farms to the detriment of traditional non-specialized ones. All these trends have had a significant impact on agricultural management. The intensification of agricultural management together with climate change could affect the quantity and quality of soil organic matter (SOM). That could imply decreasing soil fertility, reduced harvest yields, increasing nutrient losses and additional greenhouse gas emission. In order to measure the long-term development of SOM in agricultural soils a monitoring programme was initiated in Bavaria in 1986. The measurements are based on 92 representative plots located on cropland and 21 plots located on managed permanent grassland. Between 1986 and 2007 the monitoring plots have been sampled four times. The monitoring results suggest a decrease of soil organic carbon content, total nitrogen content and C:N ratio in cropland as well as in grassland in Bavaria between 1986 and 2007. Crops and organic fertilizers are together with the initial SOM content the main causes of the observed changes in SOM quantity and quality. A climatic effect could be neither proved nor excluded. The results in Bavaria are consistent with the reported changes in organic carbon of agricultural soils in Austria, Belgium, France, the Netherlands and England. In Bavaria we should expect declining SOM stocks, particularly soil organic carbon, in agricultural soils if the supply of organic matter remains constant or even decreases.

42. Energy balances and greenhouse gas-mitigation potentials of bioenergy cropping systems (Miscanthus, rapeseed, and maize) based on farming conditions in Western Germany

• Authors:
  • Emmerling, C.
  • Fries, J.
  • Froeba, N.
  • Felten, D.
• Source: Renewable Energy
• Volume: 55
• Year: 2013
• Summary: Biomass for bioenergy is an important option within global change mitigation policies. The present research focused on energy net production, net reduction of greenhouse gases (GHG) (considered as CO2-equivalents), and energy output:input ratio of the energy cropping systems 'rapeseed', 'maize', and 'Miscanthus'. The system-specific main products were biodiesel (rapeseed), electricity from biogas (maize), and Miscanthus chips (loose, chopped material); the related substituted fossil resources were diesel fuel (rapeseed), electricity from the German energy mix (maize), and heating oil (Miscanthus). However, research did not aim for a direct quantitative comparison of the crops. The study followed a case study approach with averaged data from commercial farms within an enclosed agricultural area (<5 km(2)) in Western Germany. Cultivation techniques were considered as communicated by farmers and operation managers; the diesel fuel consumption of agricultural machinery was modeled using an online-based calculator of the German Association for Technology and Structures in Agriculture (KTBL). Overall, rounded net energy production amounted to 66 GJ ha(-1) (rapeseed), 91 GJ ha(-1) (maize), and 254 GJ ha(-1) yr(-1) (Miscanthus); the related energy output:input ratios were 4.7 (rapeseed), 5.5 (maize), and 47.3 (Miscanthus), respectively. Compared to the respective fossil fuel-related energy supply, CO2-equivalent reduction potential ranged between 30 and 76% for electrical energy from maize biomass, 29 -82% for biodiesel from rapeseed, and 96-117% for Miscanthus chips, depending on whether or not the accruing by-products rapeseed cake, glycerin (rapeseed cropping system), and waste heat (maize) were considered. True 'CO2-neutrality' was only reached by the Miscanthus cropping system and was related to an additional credit from carbon sequestration in soil during the cultivation period; thus, this cropping system could be attributed to be a CO2-sink. The study indicated that bioenergy can be produced sustainably under commercial farming conditions in terms of a significantly reduced consumption of natural resources.

43. Greenhouse gas mitigation potential of a second generation energy production system from short rotation poplar in Eastern Germany and its accompanied uncertainties

• Authors:
  • Prochnow, A.
  • Meyer-Aurich, A.
  • Hansen, A.
• Source: Biomass and Bioenergy
• Volume: 56
• Year: 2013
• Summary: This study investigates the variance of the overall greenhouse gas mitigation potential of a complete second generation stationary bio-electricity production system, generated by poplar wood chips (Populus spec.) in Germany, using Monte Carlo simulations. We computed the GHG emissions as E-B = (-0.034 +/- 0.021) kg CO2e MJ(-1) (mean +/- SD) and the mitigation factor as MFB = (0.274 +/- 0.021) kg CO2e MJ(-1) following a life cycle assessment-based approach. Additionally, avoided nitrous oxide (N2O) emissions due to land use change were considered in the assessment. The most important factor for the overall mitigation variability was the uncertainty of the organic carbon changes in the soil, followed by the variability of yields. The uncertainty of (i) direct N2O emissions from the poplar site or (ii) the reference rye site as well as (iii) the uncertainty of heat recovery percentage was of minor importance. Uncertainties in the global warming potentials of nitrous oxide and methane and in the transport distance were found to be irrelevant. The uncertainty of the GHG mitigation which was associated with this specific electricity generation by poplar wood chips gasification was significantly lower compared to the variability of another common bio-electricity system (biogas). Uncertainty implications seem to be system-specific and therefore should be analysed separately for each bioenergy pathway under consideration. (C) 2013 Elsevier Ltd. All rights reserved.

44. Biogas Production from Maize: Current State, Challenges and Prospects. 2. Agronomic and Environmental Aspects

• Authors:
  • Herrmann, A.
• Source: BioEnergy Research
• Volume: 6
• Issue: 1
• Year: 2013
• Summary: Several European countries have expanded the traditional use of anaerobic digestion, i.e. waste treatment, to energy generation through attractive incentives. In some countries, it is further promoted by additional payments to generate biogas from biomass. This review aims to summarise agronomic aspects of methane production from maize, to address resulting abiotic environmental effects and to highlight challenges and prospects. The opportunities of biogas production are manifold, including the mitigation of climate change, decreasing reliance on fossil fuels and diversification of farm income. Although the anaerobic digestion of animal manure is regarded as the most beneficial for reducing greenhouse gas (GHG) emission from manure storage, the energy output can be substantially enhanced by co-digesting manure and maize, which is the most efficient crop for substrate provision in many regions. Although first regarded as beneficial, the rush into biogas production strongly based on maize (Zea mays ssp. mays) is being questioned in view of its environmental soundness. Main areas of concern comprise the spatial concentration of biogas plant together with the high amount of digestate and resulting pollution of surface and ground water, emission of climate-relevant gases and detrimental effects of maize cultivation on soil organic matter degradation. Key challenges that have been identified to enhance the sustainability of maize-based biogas production include (1) the design of regionally adapted maize rotations, (2) an improved management of biogas residues (BR), (3) the establishment of a more comprehensive data base for evaluating soil C fluxes in maize production as well as GHG emissions at the biogas plant and during BR storage and (4) the consideration of direct and indirect land use change impact of maize-based biogas production.

45. Field-scale manipulation of soil temperature and precipitation change soil CO 2 flux in a temperate agricultural ecosystem.

• Authors:
  • Niklaus, P. A.
  • Back, F.
  • Marhan, S.
  • Poll, C.
  • Kandeler, E.
• Source: Agriculture Ecosystems and Environment
• Volume: 165
• Year: 2013
• Summary: Modifications in temperature and precipitation due to climate change will likely affect carbon cycling and soil respiration in terrestrial ecosystems. Despite the important feedback mechanism of ecosystems to climate change, there is still a lack of experimental observation in agricultural ecosystems. In July 2008, we established the Hohenheim Climate Change (HoCC) experiment to investigate effects of elevated temperature and altered precipitation on soil respiration in an arable soil (mean annual temperature and precipitation 8.7°C and 679 mm, respectively). We elevated soil temperature to 4 cm depth by 2.5°C, reduced the amount of summer precipitation by 25%, and extended dry intervals between precipitation events. For two years, CO 2 fluxes were measured weekly and aboveground plant biomass and soil microbial biomass was determined. The results of the two-year study underline the importance of soil moisture as a driving factor in ecosystem response to climate change. Soil warming did not increase soil respiration in the first year; in the second year, a 27% increase was measured. The differential response of soil respiration to warming was most likely driven by soil moisture. In summer 2009, water limitation reduced microbial biomass in the heated plots thereby suppressing the stimulatory effect of elevated temperature on soil microorganisms. In summer 2010, the reduction in soil moisture was less pronounced and microbial biomass and respiration were not affected by water limitation. Temperature elevation significantly reduced Q10 values of soil respiration by 0.7-0.8. Altered precipitation showed only minor effects during the first two years of the experiment. We conclude from our study that the moisture regime of soils under elevation of temperature will largely determine whether different soils will serve either as carbon sources or as carbon sinks.

46. Amount, distribution and driving factors of soil organic carbon and nitrogen in cropland and grassland soils of southeast Germany (Bavaria).

• Authors:
  • Schilling, B.
  • Reischl, A.
  • Hangen, E.
  • Geuss, U.
  • Sporlein, P.
  • Barthold, F.
  • Hubner, R.
  • Wiesmeier, M.
  • Lutzow, M. von
  • Kogel-Knabner, I.
• Source: Agriculture Ecosystems and Environment
• Volume: 176
• Year: 2013
• Summary: Agricultural soils have a high potential for sequestration of atmospheric carbon due to their volume and several promising management options. However, there is a remarkable lack of information about the status quo of organic carbon in agricultural soils. In this study a comprehensive data set of 384 cropland soils and 333 grassland soils within the state of Bavaria in southeast Germany was analyzed in order to provide representative information on total amount, regional distribution and driving parameters of soil organic carbon (SOC) and nitrogen (N) in agricultural soils of central Europe. The results showed that grassland soils stored higher amounts of SOC (11.8 kg m -2) and N (0.92 kg m -2) than cropland soils (9.0 and 0.66 kg m -2, respectively) due to moisture-induced accumulation of soil organic matter (SOM) in B horizons. Surprisingly, no distinct differences were found for the A horizons since tillage led to a relocation of SOM with depth in cropland soils. Statistical analyses of driving factors for SOM storage revealed soil moisture, represented by the topographic wetness index (TWI), as the most important parameter for both cropland and grassland soils. Climate effects (mean annual temperature and precipitation) were of minor importance in agricultural soils because management options counteracted them to a certain extent, particularly in cropland soils. The distribution of SOC and N stocks within Bavaria based on agricultural regions confirmed the importance of soil moisture since the highest cropland SOC and N stocks were found for tertiary hills and loess regions, which exhibited large areas with potentially high soil moisture content in extant floodplains. Grassland soils showed the highest accumulation of SOC and N in the Alps and Pre-Alps as a result of low temperatures, high amounts of precipitation and high soil moisture content in areas of glacial denudation. Soil class was identified as a further driving parameter for SOC and N storage in cropland soils. In total, cropland and grassland soils in Bavaria store 242 and 134 Mt SOC as well as 19 and 12 Mt N down to a soil depth of 1 m or the parent material, respectively.

47. Linear and nonlinear dependency of direct nitrous oxide emissions on fertilizer nitrogen input: A meta-analysis

• Authors:
  • Giltrap, D.
  • Hernandez-Ramirez, G.
  • Kim, D.-G.
• Source: Agriculture, Ecosystems & Environment
• Volume: 168
• Issue: March
• Year: 2013
• Summary: Rising atmospheric concentrations of nitrous oxide (N2O) contribute to global warming and associated climate change. It is often assumed that there is a linear relationship between nitrogen (N) input and direct N2O emission in managed ecosystems and, therefore, direct N2O emission for national greenhouse gas inventories use constant emission factors (EF). However, a growing body of studies shows that increases in direct N2O emission are related by a nonlinear relationship to increasing N input. We examined the dependency of direct N2O emission on N input using 26 published datasets where at least four different levels of N input had been applied. In 18 of these datasets the relationship of direct N2O emission to N input was nonlinear (exponential or hyperbolic) while the relationship was linear in four datasets. We also found that direct N2O EF remains constant or increases or decreases nonlinearly with changing N input. Studies show that direct N2O emissions increase abruptly at N input rates above plant uptake capacity. The remaining surplus N could serve as source of additional N2O production, and also indirectly promote N2O production by inhibiting biochemical N2O reduction. Accordingly, we propose a hypothetical relationship to conceptually describe in three steps the response of direct N2O emissions to increasing N input rates: (1) linear (N limited soil condition), (2) exponential, and (3) steady-state (carbon (C) limited soil condition). In this study, due to the limited availability of data, it was not possible to assess these hypothetical explanations fully. We recommend further comprehensive experimental examination and simulation using process-based models be conducted to address the issues reported in this review. (C) 2012 Elsevier B.V. All rights reserved.

48. Effects of soil tillage and fertilization on resource efficiency and greenhouse gas emissions in a long-term field experiment in Southern Germany

• Authors:
  • Huelsbergen, K.-J.
  • Munch, J. C.
  • Kuestermann, B.
• Source: European Journal of Agronomy
• Volume: 49
• Issue: August
• Year: 2013
• Summary: Two factorial long-term field experiments were carried out at the experimental site of Scheyern, located in southern Germany, 40 km north of Munich (48 degrees 30'0' N, 11 degrees 26'60' E). Here three soil tillage systems were investigated: CT (conventional tillage with moldboard plough, 25 cm plowing depth), RT1 (reduced tillage with chisel plow, 18 cm working depth), and RT2 (reduced tillage with chisel plow, 8 cm working depth). At the same time, three fertilization systems were analyzed (high (N3), medium (N2) and low (N1) mineral N input) with a crop rotation of winter wheat (Triticum aestivum L) - potatoes (Solanum tuberosum L.) - winter wheat-corn (Zea mays L). The long-term effects of tillage and fertilization on yields, soil properties, nitrogen and energy efficiency, as well as greenhouse gas emissions (GGE) were investigated for the period of 1994-2005. On average conventional tillage (CT) produced yields of 8.03 (N1), 8.82 (N2) and 8.88 (N3) GE (grain equivalents) ha(-1) yr(-1); reduced tillage (RT1) yields of 7.82 (N1), 8.54 (N2) and 9.10 (N3) GE ha(-1) yr(-1) and RT2 yields of 6.9 (Ni), 7.82 (N2) and 8.6 (N3) GE ha(-1) yr(-1). The benefit of reduced soil tillage over CT. is a lower consumption of diesel fuel (reduced by 35%) and fossil energy (by 10%), C sequestration and N accumulation in soil. We recorded the highest soil organic carbon (SOC) in the RT2 treatments with the lowest tillage intensity (52.5 Mg ha(-1)) and the lowest SOC reserves in the CT plowed treatments (41.1 Mg ha(-1)). During the reported period, SOC reserves in the plowed treatments decreased by about 300 kg C ha-1 yr-1, whereas they increased by 150-500 kg C ha(-1) yr(-1) in the chiseled treatments. Similar results were achieved with the soil organic nitrogen (SON) reserves based on the type of tillage. This amounted to around 4000 kg ha-1 (CT), 4500 kg ha (RT1) and more than 5000 kg N ha-1 (RT2). The RT1 treatments were marked by high nutrient and energy efficiency. The disadvantage of reduced tillage lies in higher pesticide consumption and stronger soil compaction. The influence of reduced tillage was more pronounced in RT2 than in RT1 (higher SOC and SON content, higher soil dry bulk density, lower consumption of diesel fuel, higher pesticide input). The significant decreases in yield in the RT2 treatments reduced the nitrogen and energy efficiency and raised yield-related greenhouse gas emissions (GGE) in comparison to the RT1 treatments. In the case of reduced tillage combined with high N doses (RT1/N3, RT2/N2, RT2/N3), high N2O emissions of 10 to 12 kg ha(-1) yr(-1) were measured using closed chambers. It was found that as input of mineral N increased, GGE for tillage treatments, both area and yield related also increased. In RT1/N1, negative net GGE were recorded due to high C sequestration combined with moderate N2O and CO2 emissions (-220 kg CO2 (eq) ha(-1) yr(-1), -28 kg CO2 eq GE-(1)), whereas CT/N3 produced the highest net GGE (3587 kg CO2 (eq) ha(-1) yr(-1), 404 kg CO2 eq GE(-1)). (C) 2013 Elsevier B.V. All rights reserved.

49. Greenhouse gas mitigation with scarce land: The potential contribution of increased nitrogen input

• Authors:
  • Prochnow, A.
  • Olesen, J. E.
  • Meyer-Aurich, A.
  • Brunsch, Reiner
• Source: Mitigation and Adaptation Strategies for Global Change
• Volume: 18
• Issue: 7
• Year: 2013
• Summary: Agricultural lands have been identified to mitigate greenhouse gas (GHG) emissions primarily by production of energy crops and substituting fossil energy resources and through carbon sequestration in soils. Increased fertilizer input resulting in increased yields may reduce the area needed for crop production. The surplus area could be used for energy production without affecting the land use necessary for food and feed production. We built a model to investigate the effect of changing nitrogen (N) fertilizer rates on cropping area required for a given amount of crops. We found that an increase in nitrogen fertilizer supply is only justified if GHG mitigation with additional land is higher than 9-15 t carbon dioxide equivalents per hectare (CO2-eq.(.)/ha). The mitigation potential of bioenergy production from energy crops is most often not in this range. Hence, from a GHG abatement point of view land should rather be used to produce crops at moderate fertilizer rate than to produce energy crops. This may change if farmers are forced to reduce their N input due to taxes or governmental regulations as it is the case in Denmark. However, with a fertilizer rate 10 % below the economical optimum a reduction of N input is still more effective than the production of bioenergy unless mitigation effect of the bioenergy production exceeds 7 t carbon dioxide (CO2)-eq.(.)/ha. An intensification of land use in terms of N supply to provide more land for bioenergy production can only in exceptional cases be justified to mitigate GHG emissions with bioenergy under current frame conditions in Germany and Denmark.

50. Possible impact of the Renewable Energy Directive on N fertilization intensity and yield of winter oilseed rape in different cropping systems

• Authors:
  • Boettcher, U.
  • Pahlmann, I.
  • Kage, H.
  • Sieling, K.
• Source: Biomass & Bioenergy
• Volume: 57
• Year: 2013
• Summary: In 2009, the Renewable Energy Directive (RED), established sustainability criteria for biofuels including legal thresholds for specific greenhouse gas (GHG) emissions, expressed as g CO(2)eq per MJ of biofuel. Because biofuels are a major market for winter oilseed rape (WOSR), investigating the possible impact of the RED on WOSR cropping practices is prudent. This study analyses GHG emissions for WOSR cropping practices (namely N fertilization intensity, tillage method and crop rotation) basing on a 6-year field trial in a high yielding area of northern Germany. Using the International Panel on Climate Change (IPCC) methodology the field emissions of nitrous oxide (N2O) are calculated from the nitrogen (N) inputs to the cropping system. Results showed that the predominant source of GHG emissions is the N related emissions from production of fertilizer and N2O field emissions. Specific GHG emissions are lowest without N fertilizer but rise continuously with increasing N rates. Yield per ha also responded to N fertilization resulting in lowered acreage productivity when reducing GHG emissions by reducing N fertilization level. Most calculated scenarios and cropping systems result in a drastic decrease of N fertilization to achieve thresholds, causing substantial yield losses. To a certain extent, the required drastic reduction of N fertilization in some scenarios is driven by using the IPCC methodology for calculating N2O emissions. Therefore characteristics of this methodology are also discussed within this study. To mitigate the impact of the RED on WOSR, peas (legumes) may be a possible preceding crop to WOSR. (C) 2013 Elsevier Ltd. All rights reserved.