Johannes C. G. Ottow

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.

Crop rotation and residue management effects on carbon sequestration, nitrogen cycling and productivity of irrigated rice systems

The effects of soil aeration, N fertilizer, and crop residue management on crop performance, soil N supply, organic carbon (C) and nitrogen (N) content were evaluated in two annual double-crop systems for a 2-year period (1994–1995). In the maize-rice (M-R) rotation, maize (Zea mays, L.) was grown in aerated soil in the dry season (DS) followed by rice (Oriza sativa, L.) grown in flooded soil in the wet season (WS). In the continuous rice system (R-R), rice was grown in flooded soil in both the DS and WS. Subplot treatments within cropping-system main plots were N fertilizer rates, including a control without applied N. In the second year, sub-subplot treatments with early or late crop residue incorporation were initiated after the 1995 DS maize or rice crop. Soil N supply and plant N uptake of 1995 WS rice were sensitive to the timing of residue incorporation. Early residue corporation improved the congruence between soil N supply and crop demand although the size of this effect was influenced by the amount and quality of incorporated residue. Grain yields were 13-20% greater with early compared to late residue incorporation in R-R treatments without applied N or with moderate rates of applied N. Although substitution of maize for rice in the DS greatly reduced the amount of time soils remained submerged, the direct effects of crop rotation on plant growth and N uptake in the WS rice crops were small. However, replacement of DS rice by maize caused a reduction in soil C and N sequestration due to a 33–41% increase in the estimated amount of mineralized C and less N input from biological N fixation during the DS maize crop. As a result, there was 11–12% more C sequestration and 5–12% more N accumulation in soils continuously cropped with rice than in the M-R rotation with the greater amounts sequestered in N-fertilized treatments. These results document the capacity of continuous, irrigated rice systems to sequester C and N during relatively short time periods.

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.

A rapid chloroform-fumigation extraction method for measuring soil microbial biomass carbon and nitrogen in flooded rice soils

Abstract A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for measuring microbial biomass C (CBIO) and N (NBIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots or changing soil water content (0.44–0.55 kg kg–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both CBIO and NBIO (P<0.001) suggesting that the simple and rapid CFAP is a reliable alternative to the CFE. It appeared, however, that a small and relatively constant fraction of well-protected microbial biomass may only be lysed during fumigation under vacuum. Determinations of microbial C and N were highly reproducible for both methods, but neither fumigation technique generated NBIO values which were positively correlated with CBIO. The range of observed microbial C:N ratios of 4–15 was unexpectedly wide for anaerobic soil conditions. Evidence that this was related to inconsistencies in the release, degradation, and extractability of NBIO rather than CBIO came from the observation that increasing the fumigation time from 4 h to 48 h significantly increased NBIO but not CBIO. The release pattern of CBIO indicated that the standard fumigation time of 24 h is applicable to water-saturated rice soils. To correct for the incomplete recovery of CBIO, we suggest applying the kC factor of 2.64, commonly used for aerobic soils (Vance et al. 1987), but caution is required when correcting NBIO data. Until differences in fumigation efficiencies among CFE and CFAP are confirmed for a wider range of rice soils, we suggest applying the same correction factor for both methods.

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.

GROWTH AND N2-FIXATION OF TWO STEM-NODULATING LEGUMES AND THEIR EFFECT AS GREEN MANURE ON LOWLAND RICE

Abstract Two stem-nodulating tropical legumes (Sesbania rostrata and Aeschymmene afraspera) show promise as green manure in lowland rice farming systems. Their performance as biofertilizers for lowland rice was studied at different growth stages, seasons and sites. Both species exhibited fast growth and high N2 fixation and produced high biomass in a short growth period. Due to photoperiod sensitivity, the use of S. rostrata was limited during the short-day period. A. afraspera was found to be less sensitive to photoperiodism. Both species increased significantly the grain yield of rice. In the short-day period A. afraspera seemed superior-its productivity is higher than that of S. rostrata. In the long-day period, the same increase in yield was reached with both species but A. afraspera had lower biomass and was less labor-intensive to incorporate into soil.

Isolation and identification of iron-reducing bacteria from gley soils

Abstract Seventy-one facultative anaerobic bacteria, capable of reducing iron oxide in pure culture, were isolated from three differently gleyed subsoils. The bacteria were picked at random from poured plates (10−5 and 10−6) inoculated with serially diluted soil samples. An attempt was made to identify these strains by morphological and biochemical tests. Among these 71 iron-reducing bacteria, all except three were capable of reducing nitrate to nitrite and 35 reduced nitrite further into gaseous compounds (denitrification), but only one strain (Bacillus subtilis) produced H2S. Based upon their physiological and morphological properties, 38 strains were allotted to the genus Pseudomonas, 31 sporeformers to the genus Bacillus and two were regarded to be coryneform (Arthrobacter?) bacteria. Species identified were Ps. denitrificans (23), ps. stutzeri (8) ps. fluorescens-putida (5), Bacillus cereus (6), B. cereus var. mycoides (14) and Bacillus subtilis (9). Two spore-forming bacilli, two non-pigmented pseudomonads and two coryneform type of bacteria could not be identified. The significance of the enzyme nitrate reductase (nitratase) of these bacteria for anaerobic respiration and as a mechanism of iron reduction is discussed.

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.