Andreas Gattinger

Enhanced top soil carbon stocks under organic farming

It has been suggested that conversion to organic farming contributes to soil carbon sequestration, but until now a comprehensive quantitative assessment has been lacking. Therefore, datasets from 74 studies from pairwise comparisons of organic vs. nonorganic farming systems were subjected to metaanalysis to identify differences in soil organic carbon (SOC). We found significant differences and higher values for organically farmed soils of 0.18 ± 0.06% points (mean ± 95% confidence interval) for SOC concentrations, 3.50 ± 1.08 Mg C ha−1 for stocks, and 0.45 ± 0.21 Mg C ha−1 y−1 for sequestration rates compared with nonorganic management. Metaregression did not deliver clear results on drivers, but differences in external C inputs and crop rotations seemed important. Restricting the analysis to zero net input organic systems and retaining only the datasets with highest data quality (measured soil bulk densities and external C and N inputs), the mean difference in SOC stocks between the farming systems was still significant (1.98 ± 1.50 Mg C ha−1), whereas the difference in sequestration rates became insignificant (0.07 ± 0.08 Mg C ha−1 y−1). Analyzing zero net input systems for all data without this quality requirement revealed significant, positive differences in SOC concentrations and stocks (0.13 ± 0.09% points and 2.16 ± 1.65 Mg C ha−1, respectively) and insignificant differences for sequestration rates (0.27 ± 0.37 Mg C ha−1 y−1). The data mainly cover top soil and temperate zones, whereas only few data from tropical regions and subsoil horizons exist. Summarizing, this study shows that organic farming has the potential to accumulate soil carbon.

Variability of soil methane production on the micro-scale: spatial association with hot spots of organic material and Archaeal populations

Abstract High temporal and spatial variability is a key problem when quantifying methane emissions from soils. Whereas the spatial variability on the landscape scale has been investigated in different studies, we investigated the spatial heterogeneity of CH4 production on 1 cm scale, as well as the role of organic material as a relevant factor. Undisturbed soil cores (dia. 6 cm) of two mineral and one peaty wetland soils (Typic Humaquept, Aeric Endoaquept and Limnic Haplohemist) from the cool-humid region in southwest Germany were anaerobically incubated for 3 months. The time course of the CH4 production rates was dependent on the water-table-level history of the incubated horizon and on the soil type. However, the absolute amounts of CH4 production differed largely between parallel cores from each soil type, although they were obtained within 1 m2. The native structures of the soil cores were determined by computed tomography. Fresh organic material was observed in all highly productive soil cores, whereas soil cores with low methanogenic activity included far less fresh organic material. The observed hot spots of fresh organic material were correlated to high amounts of Archaea, as analyzed by etherlipid analysis as well as by in situ hybridization using an Archaea-specific probe. The most dominant factor for the spatial variation in CH4 production on the micro-scale is the distribution of fresh organic material, which activates and possibly attracts methanogenic Archaea (methanogens).

Greenhouse gas fluxes from agricultural soils under organic and non-organic management — A global meta-analysis

It is anticipated that organic farming systems provide benefits concerning soil conservation and climate protection. A literature search on measured soil-derived greenhouse gas (GHG) (nitrous oxide and methane) fluxes under organic and non-organic management from farming system comparisons was conducted and followed by a meta-analysis. Up to date only 19 studies based on field measurements could be retrieved. Based on 12 studies that cover annual measurements, it appeared with a high significance that area-scaled nitrous oxide emissions from organically managed soils are 492 ± 160 kg CO2 eq. ha(-1) a(-1) lower than from non-organically managed soils. For arable soils the difference amounts to 497 ± 162 kg CO2 eq. ha(-1) a(-1). However, yield-scaled nitrous oxide emissions are higher by 41 ± 34 kg CO2 eq. t(-1) DM under organic management (arable and use). To equalize this mean difference in yield-scaled nitrous oxide emissions between both farming systems, the yield gap has to be less than 17%. Emissions from conventionally managed soils seemed to be influenced mainly by total N inputs, whereas for organically managed soils other variables such as soil characteristics seemed to be more important. This can be explained by the higher bioavailability of the synthetic N fertilisers in non-organic farming systems while the necessary mineralisation of the N sources under organic management leads to lower and retarded availability. Furthermore, a higher methane uptake of 3.2 ± 2.5 kg CO2 eq. ha(-1) a(-1) for arable soils under organic management can be observed. Only one comparative study on rice paddies has been published up to date. All 19 retrieved studies were conducted in the Northern hemisphere under temperate climate. Further GHG flux measurements in farming system comparisons are required to confirm the results and close the existing knowledge gaps.

Effects of cattle husbandry on abundance and activity of methanogenic archaea in upland soils

In the present study, we tested the hypothesis that animal treading associated with a high input of organic matter would favour methanogenesis in soils used as overwintering pasture. Hence, methane emissions and methanogen populations were examined at sections with different degree of cattle impact in a Farm in South Bohemia, Czech Republic. In spring, methane emission positively corresponded to the gradient of animal impact. Applying phospholipid etherlipid analysis, the highest archaeal biomass was found in section severe impact (SI), followed by moderate impact (MI) and no impact. The same trend was observed for the methanogens as showed by real-time quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes. The detection of monounsaturated isoprenoid side chain hydrocarbons (i20:1) indicated the presence of acetoclastic methanogens in the cattle-impacted sites. This result was corroborated by the phylogenetic analysis of mcrA gene sequences obtained from section SI, which showed that 33% of the analysed clones belonged to the genus Methanosarcina. The majority of the sequenced clones (41%) showed close affiliations with uncultured rumen archaeons. This leads to the assumption that a substantial part of the methanogenic community in plot SI derived from the grazing cattle itself. Compared to the spring sampling, in autumn, a significant reduction in archaeal biomass and number of copies of mcrA genes was observed mainly for section MI. It can be concluded that after 5 months without cattle impact, the severely impact section maintained its methane production potential, whereas the methane production potential under moderate impact returned to background values.

MICROBIAL COMMUNITY STRUCTURE VARIES IN DIFFERENT SOIL ZONES OF A POTATO FIELD

Analyses of phosholipid fatty acids (PLFA) and phospholipid etherlipids (PLEL) revealed differences in size and structure of microbial communities in the three soil zones of a potato field: ridge (RS), uncompacted interrow (IS), and tractor-compacted interrow soil (CS). The quantity of phosholipid biomarker concentrations (= microbial biomass) showed large differences among different zones, when lipid contents were related to fresh soil volume instead of soil dry matter. Compaction of interrow soil caused an increase in bacterial and eukaryotic biomass, expressed as total PLFA concentration, as well as an increase in total archaeal biomass, expressed as total PLEL concentration and caused a decrease in the fungi-to-bacteria ratio. Due to the higher waterfilled pore space (an indirect measure for reduced O2 availability) in CS, a more pronounced anaerobic microbial community was estimated than in IS, which serves as an explanation for the elevated N2O fluxes in this soil zone. Apart from the effect of O2 availability, microbial communities, especially populations of aerobic bacteria, ascinomycetes, fungi, algae, protozoa, and aerobic archaea responded to organic matter composition in the individual zones. Only in RS PLEL derived cyclic isoprenoids were found, which presumably indicate root-colonizing archaea. Following principal component analyses of specific biomarker profiles, the assumed substrate effect had the strongest influence on the differences in microbial community structure between the three soil zones. Struktur von mikrobiellen Gemeinschaften in den verschiedenen Bodenkompartimenten eines Kartoffelackers Untersuchungen von Phospholipid-Fettsauren (PLFA) und Phospholipid-Etherlipiden (PLEL) zeigten Unterschiede in Grose und Zusammensetzung von mikrobiellen Gemeinschaften in den unterschiedlichen Bodenkompartimenten eines Kartoffelackers: Damm (RS), nicht verdichteter Zwischendamm (IS) und Traktor-verdichteter Zwischendamm (CS). Aufgrund unterschiedlicher Bodendichten traten z. T. grose Unterschiede in der Quantitat der Phospholipid-Biomarker-Konzentrationen (= mikrobielle Biomasse) auf, wenn die Lipid-Gehalte auf Bodenfrischvolumen, anstatt auf Bodentrockensubstanz bezogen wurden. Bodenverdichtung fuhrte zu einer Erhohung der Biomassen von Bakterien, Eukaryonten und Archaeen und bewirkte zudem eine Verringerung des Pilz-Bakterien-Verhaltnisses. Aufgrund des groseren wassergefullten Porenvolumens (ein Mas fur reduzierte O2-Verfugbarkeit), wurde CS von einer ausgepragteren Anaerobengemeinschaft besiedelt, was sich im Einklang mit den erhohten N2O-Flussraten befindet. Neben der O2-Verfugbarkeit zeigte es sich, dass Mikroorganismengemeinschaften, vor allem Populationen von aeroben Bakterien, Pilzen, Algen, Protozoen und aeroben Archaeen, in den jeweiligen Kompartimenten von der Qualtitat der organischen Substanz beeinflusst wurden. PLEL-gebundene zyklische Isoprenoide wurden nur in RS nachgewiesen, die vermutlich auf wurzelbesiedelnde Archaeen hinweisen. Ferner zeigte die Hauptkomponentenanalyse, dass der vermutete Substrateffekt einen groseren Einfluss auf die strukturellen Unterschiede von mikrobiellen Gemeinschaften in den drei Bodenkompartimenten hatte als die O2-Verfugbarkeit.

Estimation by PLFA of Microbial Community Structure Associated with the Rhizosphere of Lygeum spartum and Piptatherum miliaceum Growing in Semiarid Mine Tailings

The objective of this study was to compare the microbial community composition and biomass associated with the rhizosphere of a perennial gramineous species (Lygeum spartum L.) with that of an annual (Piptatherum miliaceum L.), both growing in semiarid mine tailings. We also established their relationship with the contents of potentially toxic metals as well as with indicators of soil quality. The total phospholipid fatty acid (PLFA) amount was significantly higher in the rhizosphere soil of the annual species than in the rhizosphere soil of the perennial species. The fungal/bacterial PLFA ratio was significantly greater in the perennial species compared to the annual species. The fatty acid 16:1ω5c, the fungal/bacterial PLFA ratio and monounsaturated/saturated PLFA ratio were correlated negatively with the soluble contents of toxic metals. The cyc/prec (cy17:0 + cy19:0/16:1ω7 + 18:1ω7) ratio was correlated positively with the soluble contents of Pb, Zn, Al, Ni, Cd, and Cu. The results of the PLFA analysis for profiling microbial communities and their stress status of both the plant species indicate that perennial and annual gramineous species appear equally suitable for use in programmes of revegetation of semiarid mine tailings.

Influence of chronic ozone stress on carbon translocation pattern into rhizosphere microbial communities of beech trees (Fagus sylvatica L.) during a growing season

The influence of long-term chronic ozone exposure on carbon fluxes from young beech trees (Fagus sylvatica L.) into the phospholipid fraction of microbial communities (PLFA) in the rhizosphere and into the dissolved organic carbon (DOC) fraction was studied in a lysimeter experiment using 13C depleted CO2 over one vegetation period to identify possible changes in below ground carbon translocation processes due to the plant stress. It could be shown that microbial biomass as well as individual microbial communities and their activity pattern in the rhizosphere of young beech trees are mainly driven by the vegetation period. An increase in total microbial biomass as well as individual microbial communities was detected during the vegetation period from June to September. However, also a clear ozone effect was visible mainly at the end of the vegetation period. Enzyme activities and PLFA data indicated earlier induced plant senescence as a response to the elevated ozone treatment. Furthermore higher microbial biomass and abundance of plant C utilizing microbes was observed in elevated ozone treatments over the whole vegetation period.

A continuous labelling approach to recover photosynthetically fixed carbon in plant tissue and rhizosphere organisms of young beech trees (Fagus sylvatica L.) using 13C depleted CO2.

A continuous labelling experiment using 13C-CO2 was set up in open-top chambers in order to follow fluxes of assimilates from the plant into the rhizosphere. Labelling was performed for one growing season by adding low amounts of CO2 depleted in 13C to the atmosphere of the open-top chambers, resulting in a difference of ∆ 13C 5‰ V-PDB compared to ambient conditions. The label was recovered in both plant parts and soil microbial communities, analysed via phospholipid fatty acid (PLFA) side chains. PLFA 18:2ω6,9 showed a significant incorporation of the 13C label in October, indicating that fungi utilized plant derived carbon. In bacterial PLFA no label incorporation was detected, probably due to a lower use of rhizodeposits or a preference to older carbon compounds as energy sources. This experimental setup represents a low-cost continuous labelling method for field experiments with only minor increase of CO2 concentrations.

Organic farming enhances soil microbial abundance and activity - A meta-analysis and meta-regression

Population growth and climate change challenge our food and farming systems and provide arguments for an increased intensification of agriculture. A promising option is eco-functional intensification through organic farming, an approach based on using and enhancing internal natural resources and processes to secure and improve agricultural productivity, while minimizing negative environmental impacts. In this concept an active soil microbiota plays an important role for various soil based ecosystem services such as nutrient cycling, erosion control and pest and disease regulation. Several studies have reported a positive effect of organic farming on soil health and quality including microbial community traits. However, so far no systematic quantification of whether organic farming systems comprise larger and more active soil microbial communities compared to conventional farming systems was performed on a global scale. Therefore, we conducted a meta-analysis on current literature to quantify possible differences in key indicators for soil microbial abundance and activity in organic and conventional cropping systems. All together we integrated data from 56 mainly peer-reviewed papers into our analysis, including 149 pairwise comparisons originating from different climatic zones and experimental duration ranging from 3 to more than 100 years. Overall, we found that organic systems had 32% to 84% greater microbial biomass carbon, microbial biomass nitrogen, total phospholipid fatty-acids, and dehydrogenase, urease and protease activities than conventional systems. Exclusively the metabolic quotient as an indicator for stresses on microbial communities remained unaffected by the farming systems. Categorical subgroup analysis revealed that crop rotation, the inclusion of legumes in the crop rotation and organic inputs are important farming practices affecting soil microbial community size and activity. Furthermore, we show that differences in microbial size and activity between organic and conventional farming systems vary as a function of land use (arable, orchards, and grassland), plant life cycle (annual and perennial) and climatic zone. In summary, this study shows that overall organic farming enhances total microbial abundance and activity in agricultural soils on a global scale.

Environmental performance of organic farming

As a typical cradle-to-cradle approach, organic farming suits the notion of a green technology. However, a generally valid quantification of the environmental performance of organic agriculture is difficult because there is a high variability between countries, regions, farm types, and products. Furthermore, different assessment methods lead to partly contradicting conclusions on the environmental impacts of organic farming. This chapter gives an overview on the environmental impacts of organic agriculture compared with those of conventional agriculture based on state-of-the-art literature and discusses methodological implications for the comparison of environmental impacts of farming systems. According to most of the reviewed literature organic farming performs better in terms of biodiversity, soil fertility and air quality, mitigating resource depletion, climate change mitigation, and groundwater pollution as compared with conventional agriculture. However, there are single environmental indicators in some of the above-mentioned fields, against which organic agriculture performs equally or even worse (N2O emissions and CH4 emissions per unit of product produced), depending on the assumptions and methodology of the study. Finally, this paper highlights nine common methodological problems of quantifying environmental impacts of farming systems that have been identified in the reviewed literature and suggests solutions for improvement.