Biogaserzeugung ohne Flächenkonkurrenz auf Basis von Zwischenfrüchten, Kleegras und Reststoffen

Cover or catch crops have beneficial effects for soil, water, erosion, etc. If harvested, they also provide feedstock for biogas without competition for arable land. The latter also applies to clover grass ley or other residues on organic farms without ruminants and for manure. With an explorative approach, combining field experiments and data collection of practical implementation, we investigated achievable yields and identified recommendations for practical use. Gross energy yields of cover crops varied between 700 and 2000 m³ methane (CH4) ha-1 in Austria. The energy return on energy invested (EROI) ranges from 4 to 7, if biogas is upgraded and com¬pressed for biofuel use. Therefore, about 1000 m³ CH4 ha-1 are remaining as net energy yield from 4.5 t of dry matter (DM). With an adequate harvesting process and a price of 85 € t-1 DM cost-covering can be reached with about 4.5 t DM ha-1. If positive side effects are taken into account, 2.5 t DM ha-1 may be sufficient. Even if harvested and organic matter relevant for humification is returned with digestate, beneficial effects of cover crops on soil, water and climate may be improved. 7 – 16 % of the gross biogas yield of cover crops are sufficient for the entire production of cover and main crop from cultivation to harvest including transport. Therefore biogas enables organic farming without fossil fuels. Tractors fuelled with CH4 to 70 – 80 % are already available

Bioabfallkompost im biologischen Landbau – Auswirkungen auf die Gehalte von bioverfügbaren Schwermetallen im Boden

The accumulation of heavy metals in soils is a potential risk that may keep organic farmers from using biowaste compost. As the ecological effects of metals are related to mobile fractions rather than to total contents in the soil, we measured the total (aqua regia extractable) heavy metal contents, the readily available water soluble and the potentially bioavailable LiCl-extractable fraction of soil heavy metals in a field experiment after ten years with total applications of 95, 175 and 255 t ha-1 biowaste compost (fresh matter). Total soil contents of Cd, Cr, Cu, Ni and Pb in the compost treatments were not significantly higher than in the unfertilized control. Total Zn contents increased in the treatment with the highest application rate. In the mobile fractions Cd and Pb were not detectable. Cr, Ni and Zn contents were in the range published for unpolluted soils in other studies and did not show any differences according to treatment. Easily exchangeable Cu (in LiCl extract) was increased with compost fertilization. In several crops, lower Cd contents were measured with compost fertilization than without fertilization. Potatoes which had received mineral fertilizer had significantly higher Cd contents. Crop Zn contents were increased in the compost treatments. In conclusion, fertilization with high quality biowaste compost at such rates and after ten years of application gives no cause for concern with regard to both total heavy metal contents and available heavy metal fractions

Auswirkungen zweijähriger Düngung mit NAWARO-Biogasgülle auf chemische und physikalische Bodeneigenschaften

Using biomass from intercrops as feedstock for biogas production makes it possible to produce renewable energy without compromising food production. In order that using intercrops for biogas and fertilizing with liquid digestate is sustainable, it must be secured that this practice does not have adverse effects on soil fertility. Two-year randomised field experiments were conducted on two different soil types near Bruck/Leitha (A). On chernozem soil, soil pH and composition of the cation exchange complex were hardly influenced by liquid digestate. Also on a parachernozem with pH 5.9 short-term effects of liquid digestate were small due to the low salt content and high C/N ratio of the digestate. Nevertheless the distinct increase in soil K content shows that if fertilization with liquid digestate is continued at rates clearly above K offtake by crops, K percentage on the exchange complex will exceed the critical value of 5% soon. Aggregate stability of the parachernozem was increased by the organic matter applied via digestate. Aggregate stability and infiltration rate of the chernozem were not affected. For a long-term sustainable use of intercrops for biogas and recycling of liquid digestate as a fertilizer, it is necessary that the rate of digestate fertilization corresponds to the amount of intercrop biomass harvested, and that digestate fertilization is adjusted to the potassium requirements and potassium uptake of the crops

Carbon storage in soil size-density fractions after 20 years of compost fertilization

Fractionation by particle size provides a rough differentiation between young active, and older intermediate and passive soil organic matter. Soil samples from three treatments of a 20 years` fertilization experiment, C2 which had been fertilized with 10 t ha-1 (wet wt.) compost per year on average, N2 with mineral N fertilizer at 32 kg N ha-1 year-1, and the unfertilized control (O) were subjected to particle size fractionation and to density fractionation. After low-energy sonication the samples were separated into the size fractions coarse sand (200-200 µm), fine sand (200-63 µm) silt (63-2 µm) and clay (2-0,1 µm). Density fractionation using Na-polytungstate with 1.8 g cm-3 density was applied to separate particulate organic matter (POM) from the sand-sized fraction. Compost fertilization resulted in an increase in Corg in all size and density fractions. In total, the Corg content was 10 % higher with compost fertilization than in the unfertilized control. Approximately 40 % of the additional soil carbon was located in the POM, 56 % in the silt-sized fraction and 3 % in the clay-sized fraction. With mineral N fertilization the sum of Corg contents of all fractions was about the same as without fertilization, with an increase of POM-Corg and a decrease of Corg in the silt and clay-sized fraction.Keywords: fractionation, particulate organic matter, POM, soil organic matte

Biogas from Cover Crops and Field Residues: Effects on Soil, Water, Climate and Ecological Footprint

Cover or catch crops have beneficial effects for soil, water, erosion, etc. If harvested, they also provide feedstock for biogas without competition for arable land in regions, where only one main crop can be produced per year. On average gross energy yields of approx. 1300 m³ methane (CH4) ha-1 can be expected from 4.5 tonnes (t) of cover crop dry matter (DM) in Austria. Considering the total energy invested from cultivation to compression for biofuel use a net energy yield of about 1000 m³ CH4 ha-1 is remaining. With the straw of grain maize or Corn Cob Mix (CCM) similar energy yields can be achieved. In comparison to catch crops remaining on the field as green manure or to complete fallow between main crops the effects on soil, water and climate can be improved if cover crops are harvested without soil compaction and digestate is returned to the field in an amount equivalent to cover crop removal. In this way, the risk of nitrate leaching can be reduced approx. by 25% in comparison to full fallow. The risk of nitrous oxide emissions may be reduced up to 50% by contrast with cover crops serving as green manure. The effects on humus content and erosion are similar or better than those of cover crops used as green manure when the same amount of biomass was produced. With higher biomass production the positive effects increase even if cover crops are harvested and the only digestate is brought back to the fields. The ecological footprint of arable farming can be reduced by approx. 50% considering the substitution of natural gas with CH4 produced from cover crops

Electric-field-controlled reversible order-disorder switching of a metal tip surface

While it is well established that elevated temperatures can induce surface roughening of metal surfaces, the effect of a high electric field on the atomic structure at ambient temperature has not been investigated in detail. Here we show with atomic resolution using in situ transmission electron microscopy how intense electric fields induce reversible switching between perfect crystalline and disordered phases of gold surfaces at room temperature. Ab initio molecular dynamics simulations reveal that the mechanism behind the structural change can be attributed to a vanishing energy cost in forming surface defects in high electric fields. Our results demonstrate how surface processes can be directly controlled at the atomic scale by an externally applied electric field, which promotes an effective decoupling of the topmost surface layers from the underlying bulk. This opens up opportunities for development of active nanodevices in, e.g., nanophotonics and field-effect transistor technology as well as fundamental research in materials characterization and of yet unexplored dynamically controlled low-dimensional phases of matter.peerReviewe

Reversible metal-insulator transition of Ar-irradiated LaAlO3/SrTiO3 interfaces

The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAlO3 (LAO) and SrTiO3, can be made completely insulating by low-energy, 150-eV, Ar+ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation