Gero Benckiser

Influence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in comparison to dicyandiamide (DCD) on nitrous oxide emissions, carbon dioxide fluxes and methane oxidation during 3 years of repeated application in field experiments

Abstract. In a 3-year field experiment, the effect of the nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the release of N2O, CO2, and on CH4 oxidation, was examined in comparison to that of dicyandiamide (DCD) on N-fertilized and unfertilized experimental sites. Soil samples were analysed simultaneously for the concentrations of N2O retained in the soil body, NH4+, NO2–, NO3–, and for the degradation kinetics of DMPP as well as DCD. DMPP decreased the release of N2O on fertilized plots by 41% (1997), 47% (1998) and 53% (1999) (on average by 49%) while DCD reduced N2O emissions by 30% (1997), 22% (1998) and 29% (1999) (on average by 26%). In addition, the NIs seemed to decrease the CO2 emissions of each fertilized treatment. DCD reduced the release of CO2 by an average of 7% for the 3 years (non-fertilized 10%), and DMPP reduced it by an average of up to 28% (non-fertilized 29%). Furthermore, both NIs failed to affect CH4 oxidation negatively. The plots that received either DCD or DMPP even seemed to function as enhanced sinks for atmospheric CH4. DMPP apparently stimulated CH4 oxidation of N-fertilized plots by ca 28% in comparison to the control. In total, DCD and DMPP reduced the global warming potential of N-fertilized plots by 7% and 30%, respectively. Further, DCD and DMPP diminished the amount of N2O retained in the soil by 52% and 61%, respectively. The concentrations of NH4+ remained unaffected by both NIs, whereas the amounts of NO2– diminished in the plots treated with DCD by 25% and with DMPP by 20%. In both NI treatments NO3– concentrations in the soil were 23% lower than in the control. DMPP and DCD did not affect the yields of summer barley, maize and winter wheat significantly. DCD was mineralized more rapidly than DMPP.

Nitrification and denitrification as sources of atmospheric nitrous oxide – role of oxidizable carbon and applied nitrogen

Abstract. Laboratory incubation experiments were conducted to study the influence of easily oxidizable C (glucose) and mineral N (NH4+ and NO3–) on N2O emission, evolution of CO2 and consumption of O2. A flush of N2O was always observed during the first few hours after the start of soil incubation, which was significantly higher with NH4+ compared to NO3– applications. The increase in N2O emission was attributed mainly to enhanced soil respiration and subsequent O2 limitation at the microsite level. Application of NH4+ helped to develop denitrifying populations since subsequent additions of NO3– and a C source significantly enhanced N2O emissions. In soils treated with NH4+, N2O emissions declined rapidly, which was related to decreasing concentrations of easily oxidizable C. Addition of glucose in different amounts and pre-incubation of soil for different lengths of time (to create variation in the amount of easily oxidizable C) changed the pattern of N2O emissions, which was ascribed to changes in soil respiration.

Influence of environmental conditions on the amount of N2O released from activated sludge in a domestic waste water treatment plant

Waste water purification is characterized by intensive mineralization and nitrification processes. Because of the high O2 demand, temporarily anaerobic conditions may be produced, and denitrification by nitrifying organisms as well as heterotropic denitrification may contribute to N2O release. In situ measurements (1993–1994) suggest that N2O is released from activated sludge in a domestic waste water treatment plant at an average rate of 1040 μg m−2h−1 with a range between zero and 6198 μg m−2h−1. The production of N2O seems to be related to the concentration of NO 2 − and NO 3 − as well as to the pH. In the waste water about 75–200 μg N2O l−1 is dissolved. This N2O is released after discharge into the receiving waters. The N2O is produced essentially by nitrification rather than by heterotropic denitrification. On a long-term scale the increasing use of mechanical-biological waste water purification plants world-wide may add increasingly to the anthropogenic production of N2O, although the present amount of N2O produced is negligible compared to its global terrestrial production.

Emissions of nitrous oxide from a constructed wetland using a groundfilter and macrophytes in waste-water purification of a dairy farm

Abstract In less populated rural areas constructed wetlands with a groundfilter made out of the local soil mixed with peat and planted with common reed (Phragmites australis) are increasingly used to purify waste water. Particularly in the rhizosphere of the reed, nitrification and denitrification processes take place varying locally and temporally, and the question arises to what extent this type of waste-water treatment plant may contribute to the release of N2O. In situ N2O measurements were carried out in the two reed beds of the Friedelhausen dairy farm, Hesse, Germany, irrigated with the waste water from a cheese dairy and 70 local inhabitants (12 m3 waste water or 6 kg BOD5 or 11 kg chemical O2 demand (CODMn) day–1). During November 1995 to March 1996, the release of N2O was measured weekly at 1 m distances using eight open chambers and molecular-sieve traps to collect and absorb the emitted N2O. Simultanously, the N2O trapped in the soil, the soil temperature, as well as the concentrations of NH4+-N, NO3–-N, NO2–-N, water-soluble C and the pH were determined at depths of 0–20, 20–40 and 40–60 cm. In the waste water from the in- and outflow the concentrations of CODMn, BOD5, NH4+-N, NO3–-N, NO2–-N, as well as the pH, were determined weekly. Highly varying amounts of N2O were emitted at all measuring dates during the winter. Even at soil temperatures of –1.5  °C in 10 cm depth of soil or 2  °C at a depth of 50 cm, N2O was released. The highest organic matter and N transformation rates were recorded in the upper 20 cm of soil and in the region closest to the outflow of the constructed wetland. Not until a freezing period of several weeks did the N2O emissions drop drastically. During the period of decreasing temperatures less NO3–-N was formed in the soil, but the NH4+-N concentrations increased. On average the constructed wetlands of Friedelhausen emitted about 15 mg N2O-N inhabitant equivalent–1 day–1 during the winter period. Nitrification-denitrification processes rather than heterotrophic denitrification are assumed to be responsible for the N2O production.

Effects of concentration, incubation temperature, and repeated applications on degradation kinetics of dicyandiamide (DCD) in model experiments with a silt loam soil

SummaryThe kinetics of dicyandiamide (DCD) decomposition were studied (at 80% water-holding capacity) in pretreated and non-pretreated soils, using model experiments. DCD was added in different concentrations (6.7, 16.7, and 33.3 μg DCD-N g−1 dry soil) and incubated at various temperatures (10°, 20°, and 30°C). Additionally, DCD decomposition was examined in sterile soil (with or without Fe2O3) after inoculation with a DCD-enrichment culture. In the sterile variant, (30°C)the applied dicyandiamide concentration remained constant, even after 36 days. In the sterilized and reinoculated variant, DCD disappeared within 7 days. Addition of Fe2O3 powder to the sterilized soil had no effect on DCD degradation. In the pretreated soils, DCD mineralization started immediately at all temperatures and concentrations without a lag phase. A temperature increase of 10°C doubled the mineralization rate. The mineralization rates were independent of the initial concentrations. In the non-pretreated soils (except at 30°C with 16.7 and 33.3 μg DCD-N g−1 dry soil) DCD decreased only after a short (30°C) or a long (10°C) lag phase. These results suggest that an inducible metabolic degradation occurred, following zeroorder kinetics.

Effect of an increasing carbon: nitrate-N ratio on the reliability of acetylene in blocking the N2O-reductase activity of denitrifying bacteria in soil

SummaryIn model experiments with a silty loam soil the effect of different C : NOinf3sup--N ratios on the reliability of C2H2 (1% v/v) in blocking N2O-reductase activity was examined. The soil was carefully mixed with different amounts of powdered lime leaves (Tilia vulgaris) to obtain organic C contents of about 1.8, 2.3, and 2.8%, and of NOinf3sup-solution to give C : NOinf3sup--N ratios of 84, 107, 130, 156, 200, and 243. The soil samples were incubated in specially modified anaerobic jars (22 days, 25°C, 80% water-holding capacity, He atmosphere) and the atmosphere was analysed for N2, N2O, CO2, and C2H2 by gas chromatography at regular intervals. Destruction jars were used to analyse soil NOinf3sup-, NH4+and C. The results clearly showed that N2O-reductase activity was completely blocked by 1% (v/v) C2H2 only as long as NOinf3sup-was present. In the presence of C2H2, NOinf3sup-was apparently entirely converted into N2O. The C2H2 blockage of N2O-reductase activity ceased earlier in soils with a wide C : NOinf3sup--N ratio (156, 200, and 243) than in those with closer C : NOinf3sup--N ratios (84, 107, and 130). As soon as NOinf3sup-was exhausted, N2O was reduced to N2 in spite of C2H2. The wider the C : NOinf3sup--N ratio, the earlier the production of N2 and the less the reliability of the C2H2 blockage. In the untreated control complete inhibition of N2O-reductase activity by C2H2 lasted for 7–12 days. In the field, estimates of total denitrification losses by the C2H2 inhibition technique should be considered reliable only as long as NOinf3sup-is present. Consequently, NOinf3sup-monitoring in the field is essential, particularly in soils supplied with easily decomposable organic matter.

Degradation of the fungicide difenoconazole in a silt loam soil as affected by pretreatment and organic amendment

Degradation of the fungicide difenoconazole was examined in a silt loam soil under controlled conditions (60% WHC, 30 degrees C) in the laboratory. Difenoconazole was applied at 0.1 and 1.0 mg kg(-1) dry soil, respectively. The experiments were run with non-pretreated and pretreated field soil, respectively, partly mixed with easily decomposable organic matter (leaf powder). In all experiments, degradation curves showed a sigmoidal shape with clear acclimation phases. Pretreatment with difenoconazole in the field decreased the acclimation phases, DT(50)- and, in some cases, DT(90)-values. The incorporation of easily decomposable organic matter decreased both DT(50)- and DT(90)-values and increased the general microbial activity significantly. We conclude that difenoconazole is metabolized by an acclimated part of the soil microflora. However, the degradation seems to be stimulated in the presence of suitable co-substrates.

N2O emissions from different cropping systems and from aerated, nitrifying and denitrifying tanks of a municipal waste water treatment plant

Nitrous oxide emissions, nitrate, water-soluble carbon and biological O2 demand (BOD5) were quantified in different cropping systems fertilized with varying amounts of nitrogen (clayey loam, October 1991 to May 1992), in an aerated tank (March 1993 to March 1994), and in the nitrification-denitrification unit (March to July 1994) of a municipal waste water treatment plant. In addition, the N2O present in the soil body at different depths was determined (February to July 1994). N2O was emitted by all cropping systems (mean releases 0.13–0.35 mg N2O m-2 h-1), and all the units of the domestic waste water treatment plant (aerated tank 0–6.2 mg N2O m-2 h-1, nitrification tank 0–204,3 mg N2O m-2, h-1, denitrifying unit 0–2.2 mg N2O m-2 h-1). During the N2O-sampling periods estimated amounts of 0.9, 1.5, 2.4 and 1.4 kg N2O−N ha-1, respectively, were released by the cropping systems. The aerated, nitrifying and denitrifying tanks of the municipal waste water treatment plant released mean amounts of 9.1, 71.6 and 1.8 g N2O−N m-2, respectively, during the sampling periods.The N2O emission were significantly positively correlated with nitrate concentrations in the field plots which received no N fertilizer and with the nitrogen content of the aerated sludge tank that received almost exclusively N in the form of NH4+. Available carbon, in contrast, was significantly negatively correlated with the N2O emitted in the soil fertilized with 80 kg N ha-1 year. The significant negative correlation between the emitted N2O and the carbon to nitrate ratio indicates that the lower the carbon to nitrate ratio the higher the amount of N2O released. Increasing N2O emissions seem to occur at electron donorto-acceptor ratios (CH2O or BOD5-to-nitrate ratios) below 50 in the cropping systems and below 1200–1400 in the waste water treatment plant. The trapped N2O in the soil body down to a depth of 90 cm demonstrates that agricultural production systems seem to contain a considerable pool of N2O which may be reduced to N2 on its way to the atmosphere, which may be transported to other environments or which may be released at sometime in the future.

Relationships between field-measured denitrification losses, CO2 formation and diffusional constraints

Abstract Approaches to quantify denitrification losses from arable land and other ecosystems are frequently hampered by the methods available. Extensive measurements of denitrification losses with the acetylene inhibition technique (AIT) over 3 years in various soils and crops (N 2 O surface fluxes and soil air concentrations), when compared with simultaneously CO 2 -production determinations, revealed that NO 3 -respiration in well-aerated soils depends primarily on carbon and nitrate availability. N 2 O concentrations in soil air exhibited significant correlations with soil depth, whereas the correlations between the N 2 O soil air concentrations at 10cm depth and the N 2 O soil surface fluxes were not significant. Increasing soil water contents reduced N 2 O diffusion through the silty sand soil columns considerably, especially in the carbon-enriched upper 10cm. Denitrification losses ha −1 , calculated from the N 2 O concentrations in soil air and an assumed mean annual air-filled pore volume of about 20%, were higher than losses at the soil surface, suggesting that other soil variables besides carbon, nitrate and water availability are influencing N 2 O + N 2 surface fluxes measured by the AIT. Soil processes controlling N 2 O formation in the presence of C 2 H 2 as well as the N 2 O fluxes from the place of production to the soil surface are ranked and discussed.

Ants and sustainable agriculture. A review

Abstract60% of the world’s ecosystems are not used in a sustainable way. Modern agriculture is blamed for declining soil carbon and biodiversity. Climate change, habitat fragmentation and other obstacles impede the movement of many animal species, and distribution changes are projected to continue. Therefore, we need alternative management strategies. The colony organisation of social insects, especially of ants, is seen as a model to design an improved agricultural management, because ants are very experienced agriculturists. Ants represent half of the global insect biomass. Their individuals work like a super organism. This article focuses on harvester and leaf cutter ants by considering Lasius species. It reviews the organisation structure of social ant communities. Harvester and leaf cutter ants represent a high percentage of the worldwide ant societies. They collect plant saps with carbon nitrogen (C/N) ratios of about 40 for their own nourishment and leaf fragments with C/N ratios of about 100 for fungi gardens and brood nourishment. They sustain huge numbers of individuals with their low N-based organic imports and their colony commensalisms enable them to convert these polymers into lower molecular, partly volatile compounds, adenosinetriphosphate (ATP), and heat. Digging improves water infiltration, drainage and soil aeration. Ants maintain fungi as a food source for the scleroproteinous brood, carry out food preservation, infection control and waste management, and construct with endurance new nests and rebuild them after damage. All these activities move the nest sites far away from the thermodynamic equilibrium. Physical, chemical and biological gradients emerge and the growing populations, together with nest-penetrating mycorrhized plant roots, absorb the released nutrients and form biomass by lowering energy flows into potentially strong consumer-resource interactions or runaway consumptions. The plant material import of leaf cutter ants, rich in carbon but low in proteins, amounts to 85–470 kg dry weight per year. It keeps the electron donor/acceptor ratio in favour of the electron donor so that denitrifiers can reduce nitrate predominantly to N2. Ants living in highly N-polluted areas bind the pollutant in the cuticle. In their low N-input environments harvester, leaf cutter and honeydew-sucking ants furnish the N demand of adult ants with the help of N2-fixing bacteria. The low N-input management of harvester, leaf cutter and honeydew-sucking ants is therefore a resourceful concept for approaching a highly productive agriculture by avoiding soil carbon decline and N2O emissions increase.