Reiner Ruser

Linking N2O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community

Nitrous oxide (N2O) contributes 8% to global greenhouse gas emissions. Agricultural sources represent about 60% of anthropogenic N2O emissions. Most agricultural N2O emissions are due to increased fertilizer application. A considerable fraction of nitrogen fertilizers are converted to N2O by microbiological processes (that is, nitrification and denitrification). Soil amended with biochar (charcoal created by pyrolysis of biomass) has been demonstrated to increase crop yield, improve soil quality and affect greenhouse gas emissions, for example, reduce N2O emissions. Despite several studies on variations in the general microbial community structure due to soil biochar amendment, hitherto the specific role of the nitrogen cycling microbial community in mitigating soil N2O emissions has not been subject of systematic investigation. We performed a microcosm study with a water-saturated soil amended with different amounts (0%, 2% and 10% (w/w)) of high-temperature biochar. By quantifying the abundance and activity of functional marker genes of microbial nitrogen fixation (nifH), nitrification (amoA) and denitrification (nirK, nirS and nosZ) using quantitative PCR we found that biochar addition enhanced microbial nitrous oxide reduction and increased the abundance of microorganisms capable of N2-fixation. Soil biochar amendment increased the relative gene and transcript copy numbers of the nosZ-encoded bacterial N2O reductase, suggesting a mechanistic link to the observed reduction in N2O emissions. Our findings contribute to a better understanding of the impact of biochar on the nitrogen cycling microbial community and the consequences of soil biochar amendment for microbial nitrogen transformation processes and N2O emissions from soil.

Effect of crop-specific field management and N fertilization on N2O emissions from a fine-loamy soil

Agricultural soils are a major source of atmospheric N2O. This study was conducted to determine the effect of different crop-specific field management and N fertilization rates on N2O emissions from a fine-loamy Dystric Eutrochrept. Fluxes of N2O were measured for two years at least once a week on plots cropped with potatoes (Solanum tuberosum) fertilized with 50 or 150 kg N ha−1 a−1, winterwheat (Triticum aestivum) fertilized with 90 or 180 kg N ha−1 a−1, corn (Zea mays) fertilized with 65 or 130 kg N ha−1 a−1, and on an unfertilized, set-aside soil planted with grass (mainly Lolium perenne and Festuca rubra). The mean N2O emission rate from the differently managed plots was closely correlated to the mean soil nitrate content in the Ap horizon for the cropping period (April to October, r2 = 0.74), the winter period (November to March, r2 = 0.93, one outlier excluded), and the whole year (r2 = 0.81). N2O emissions outside the cropping period accounted for up to 58% of the annual emissions and were strongly affected by frost-thaw cycles. There was only a slight relationship between the amount of fertilizer N applied and the annual N2O emission (r2 = 0.20). The mean annual N2O-N emission from the unfertilized set-aside soil was 0.29 kg ha−1. The annual N2O-N emission from the fertilized crops for the low and the recommended rates of N fertilization were 1.34 and 2.41 kg ha−1 for corn, 2.70 and 3.64 kg ha−1 for wheat, and 5.74 and 6.93 kg ha−1 for potatoes. The high N2O emissions from potato plots were due to (i) high N2O losses from the interrow area during the cropping season and (ii) high soil nitrate contents after the potato harvest. The reduction of N fertilization (fertilizer was applied in spring and early summer) resulted in decreased N2O emissions during the cropping period. However, the emissions during the winter were not affected by the rate of N fertilization. The results show that the crop-specific field management had a great influence on the annual N2O emissions. It also affected the emissions per unit N fertilizer applied. The main reasons for this crop effect were crop-specific differences in soil nitrate and soil moisture content.

N2O and CH4 fluxes in potato fields: automated measurement, management effects and temporal variation

Abstract The large temporal variation in nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) flux rates is a major source of error when estimating cumulative fluxes of these radiative active trace gases. We developed an automated system for near-continuous, long-term measurements of N2O, CH4 and CO2 fluxes from cropland soils and used it to study the temporal variation of N2O and CH4 fluxes from potato (Solanum tuberosum L.) fields during the crop periods of 1997 and 1998, and also to determine the effects of management practices and weather. Additionally, we evaluated the error of other common methods, namely, weekly or monthly measurements, used for estimating cumulative fluxes. The fluxes were quantified separately for the ridges, uncompacted interrows and tractor-compacted interrows. Total N2O–N emission from the potato field during the growing period (end of May to September) was 1.6 kg ha−1 in 1997 and 2.0 kg ha−1 in 1998; emissions were highest for the tractor-compacted soil. Periods of increased N2O losses were induced by heavy precipitation (in particular in compacted soil) and by the killing of potato tops (on the ridges) by herbicide application. The total CH4–C uptake in the potato field during the growing period was 295 g ha−1 in 1997 and 317 g ha−1 in 1998. The major fraction of the total CH4 uptake (≈86%) occurred on the ridges. Weekly measurements of N2O fluxes complemented by additional event-related flux determinations provided accurate estimates of total emissions. The monthly flux determination was not adequate for determining the temporal variation of the N2O emission rates. Weekly measurements were sufficient to provide reliable estimates of the cumulative CH4 uptake.

Nitrous oxide emissions from arable soils in Germany — An evaluation of six long-term field experiments

In this study emissions of N2O from arable soils are summarized using data from long-term N2O monitoring experiments. The field experiments were conducted at six sites in Germany between 1992 and 1997. The annual N-application rate ranged from 0 to 350 kg N ha—1. Mineral and organic N-fertilizer applications were temporarily split adapted to the growth stage of each crop. N-fertilizer input and N-yield by the crops were used to calculate the In/Out-balance. The closed chamber technique was applied to monitor the N2O fluxes from soil into the atmosphere. If possible, plants were included in the covers. Annual N2O emission values were based on flux rate measurements of an entire year. The annual N2O losses ranged from 0.53 to 16.78 kg N2O-N ha—1 with higher N2O emissions from organically fertilized plots as compared to minerally fertilized plots. Approximately 50% of the total annual emissions occurred during winter. No significant relationship between annual N2O emissions and the respective N-fertilization rate was found. This was attributed to site- and crop-specific effects on N2O emission. The calculation of the N2O emission per unit N-yield from winter cereal plots indicates that the site effect on N2O emission is more important than the effect of N-fertilization. From unfertilized soils at the sites Braunschweig and Timmerlah a N-yield of 60.0 kg N ha—1 a—1 and N2O emissions of 2 kg N ha—1 a—1 were measured. This high background emission was assigned to the amount and turnover of soil organic matter. For a crop rotation at the sites Braunschweig and Timmerlah the N In/Out-balance over a period of four years was identified as a suitable predictor of N2O emissions. This parameter characterizes the efficiency of N-fertilization for crop production and allows for N-mineralization from the soil. N2O-Emissionen aus Ackerboden in Deutschland In dieser Arbeit werden die N2O-Emissionen aus Ackerboden zusammengefasst, auf denen Langzeituntersuchungen zur Freisetzung von N2O durchgefuhrt wurden. Die Felduntersuchungen auf sechs Standorten Deutschlands wurden zwischen 1992 und 1997 durchgefuhrt. Die jahrliche Stickstoffdungung variierte zwischen 0 und 350 kg N ha—1. Angepasst an das Pflanzenwachstum erfolgte die mineralische und organische N-Dungung in geteilten Gaben. Aus den N-Entzugen (N-Ertrag) und der N-Dungung wurden Salden errechnet. Das „closed chamber“-Verfahren wurde zur Bestimmung der N2O-Flusse an der Grenzschicht Boden/Atmosphare verwendet, Pflanzen wurden soweit als moglich mit eingeschlossen. Die jahrlichen N2O-Emissionen wurden auf der Basis ganzjahrig gemessener Flussraten bestimmt. Die jahrlichen N2O-Verluste lagen zwischen 0,53 und 16,78 kg N2O-N ha—1, wobei organisch gedungte Flachen hohere Emissionen aufwiesen als mineralisch gedungte. Etwa 50% der anuellen N2O-Emissionen wurden im Winter gemessen. Zwischen den N2O-Emissionen und der N-Dungermenge konnte kein signifikanter Zusammenhang errechnet werden. Dies wurde auf standort- und kulturartspezifische Unterschiede der N2O-Freisetzung zuruckgefuhrt. Die Berechnung der N2O-Emissionen je Ertragseinheit auf Wintergetreideflachen verdeutlichte, dass der Standort einen groseren Einfluss auf die N2O-Emissionen hat als die N-Dungung. Auf ungedungten Flachen der Standorte Braunschweig und Timmerlah wurden durchschnittliche N-Ertrage von 60,0 kg N ha—1 a—1 und N2O-Emissionen von 2 kg N ha—1 a—1 gemessen. Die hohen Hintergrundemissionen resultierten aus der Menge und dem Umsatz der organischen Substanz. Eine Abschatzung der N2O-Emissionen war auf der Basis vierjahriger N-Salden einer Fruchtfolge fur die Standorte Braunschweig und Timmerlah moglich. Mehrjahrige N-Salden berucksichtigen sowohl die Effektivitat der N-Dungung bei der Pflanzenproduktion als auch die N-Nachlieferung aus dem Boden.

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.

Influence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on ammonia-oxidizing bacteria and archaea in rhizosphere and bulk soil

In agricultural plant production nitrification inhibitors like 3,4-dimethylpyrazole phosphate (DMPP) are used to retard the microbial nitrification process of fertilized ammonium to enhance the nitrogen supply for cultivated crops and to reduce nitrogen losses from the production system. Besides the well-known ammonia-oxidizing bacteria (AOB) it is known for a few years that also ammonia-oxidizing archaea (AOA) are able to perform the first step in nitrification, hence being also a target for a nitrification inhibitor. However, so far no information are available concerning the effectiveness of DMPP and its extent towards AOB and AOA, neither in bulk soil nor in the root-rhizosphere complex. We investigated in a field experiment performed according to agricultural practice the effect of DMPP on the abundance of AOB and AOA two, four and eight weeks after fertilization. We observed impaired abundances of AOB but not of AOA in both soil compartments that were still visible eight weeks after application, possibly indicating a reduced effectiveness of the nitrification inhibitor in our study.

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.

Does soil aging affect the N2O mitigation potential of biochar? A combined microcosm and field study

The application of biochar as a soil amendment to improve soil fertility has been suggested as a tool to reduce soil‐borne CO2 and non‐CO2 greenhouse gas emissions, especially nitrous oxide (N2O). Both laboratory and field trials have demonstrated N2O emission reduction by biochar amendment, but the long‐term effect (>1 year) has been questioned. Here, we present results of a combined microcosm and field study using a powdered beech wood biochar from slow pyrolysis. The field experiment showed that both CO2 and N2O emissions were still effectively reduced by biochar in the third year after application. However, biochar did not influence the biomass yield of sunflower for biogas production (Helianthus annuus L.). Biochar reduced bulk density and increased soil aeration and thus reduced the water‐filled pore space (WFPS) in the field, but was also able to suppress N2O emission in the microcosms experiment conducted at constant WFPS. For both experiments, biochar had limited impact on soil mineral nitrogen speciation, but it reduced the accumulation of nitrite in the microcosms. Extraction of soil DNA and quantification of functional marker genes by quantitative polymerase chain reaction showed that biochar did not alter the abundance of nitrogen‐transforming bacteria and archaea in both field and microcosm experiments. In contradiction to previous experiments, this study demonstrates the long‐term N2O emission suppression potential of a wood biochar and thus highlights its overall climate change mitigation potential. While a detailed understanding of the underlying mechanisms requires further research, we provide evidence for a range of biochar‐induced changes to the soil environment and their change with time that might explain the often observed N2O emission suppression.

Gas entrapment and microbial N2O reduction reduce N2O emissions from a biochar-amended sandy clay loam soil

Nitrous oxide (N2O) is a potent greenhouse gas that is produced during microbial nitrogen transformation processes such as nitrification and denitrification. Soils represent the largest sources of N2O emissions with nitrogen fertilizer application being the main driver of rising atmospheric N2O concentrations. Soil biochar amendment has been proposed as a promising tool to mitigate N2O emissions from soils. However, the underlying processes that cause N2O emission suppression in biochar-amended soils are still poorly understood. We set up microcosm experiments with fertilized, wet soil in which we used 15N tracing techniques and quantitative polymerase chain reaction (qPCR) to investigate the impact of biochar on mineral and gaseous nitrogen dynamics and denitrification-specific functional marker gene abundance and expression. In accordance with previous studies our results showed that biochar addition can lead to a significant decrease in N2O emissions. Furthermore, we determined significantly higher quantities of soil-entrapped N2O and N2 in biochar microcosms and a biochar-induced increase in typical and atypical nosZ transcript copy numbers. Our findings suggest that biochar-induced N2O emission mitigation is based on the entrapment of N2O in water-saturated pores of the soil matrix and concurrent stimulation of microbial N2O reduction resulting in an overall decrease of the N2O/(N2O + N2) ratio.

Impact of reduced tillage on greenhouse gas emissions and soil carbon stocks in an organic grass-clover ley - winter wheat cropping sequence

Highlights • First study comparing climate impacts of tillage systems in organic arable farming.• No tillage system impact on N2O and CH4 emissions in grass-clover and wheat.• Higher N2O pulses after tillage operations with increasing soil organic carbon.• Higher soil organic carbon stocks with reduced tillage in slurry fertilised fields.