Kaj Henriksen

Effects of application technique and anaerobic digestion on gaseous nitrogen loss from animal slurry applied to ryegrass ( Lolium perenne )

Ammonia volatilization and denitrification were measured in a ryegrass field in Denmark after direct injection and application with trail hoses of an untreated cattle slurry and an anaerobically digested slurry in late May-early June 1993 and 1994. Ammonia volatilization was measured using a wind-tunnel system for a period of 8 days after slurry application. Denitrification was measured for a period of 21 days after slurry application. In an adjacent field experiment, nitrogen-uptake (N-uptake) was determined in the first two cuts of the ryegrass harvested after slurry application. N losses through ammonia volatilization were larger in 1993 than in 1994 due to differences in climatic conditions. Ammonia volatilization was lowered substantially (47-72 %), when slurry was injected compared with surface application. In 1993 the loss from surface-applied digested slurry was only 35 % of total ammoniacal nitrogen (TAN), while the loss from the raw slurry was 47 %. There were no significant differences in ammonia volatilization from the two slurry types in the other experiments. N losses through denitrification were low (< 2% of TAN), but there were clear differences in the losses, depending on slurry type, application method and experimental year. Injection of the slurry gave a larger N-uptake in the first cut of grass compared to the trail-hose application. In 1993 N-uptake from the digested slurry treatment gave significantly larger N-uptake compared to the raw slurry in the first cut.

Toxic Effects of Linear Alkylbenzene Sulfonate on Metabolic Activity, Growth Rate, and Microcolony Formation of Nitrosomonas and Nitrosospira Strains

ABSTRACT Strong inhibitory effects of the anionic surfactant linear alkylbenzene sulfonate (LAS) on four strains of autotrophic ammonia-oxidizing bacteria (AOB) are reported. TwoNitrosospira strains were considerably more sensitive to LAS than two Nitrosomonas strains were. Interestingly, the two Nitrosospira strains showed a weak capacity to remove LAS from the medium. This could not be attributed to adsorption or any other known physical or chemical process, suggesting that biodegradation of LAS took place. In each strain, the metabolic activity (50% effective concentration [EC50], 6 to 38 mg liter−1) was affected much less by LAS than the growth rate and viability (EC50, 3 to 14 mg liter−1) were. However, at LAS levels that inhibited growth, metabolic activity took place only for 1 to 5 days, after which metabolic activity also ceased. The potential for adaptation to LAS exposure was investigated with Nitrosomonas europaea grown at a sublethal LAS level (10 mg liter−1); compared to control cells, preexposed cells showed severely affected cell functions (cessation of growth, loss of viability, and reduced NH4+ oxidation activity), demonstrating that long-term incubation at sublethal LAS levels was also detrimental. Our data strongly suggest that AOB are more sensitive to LAS than most heterotrophic bacteria are, and we hypothesize that thermodynamic constraints make AOB more susceptible to surfactant-induced stress than heterotrophic bacteria are. We further suggest that AOB may comprise a sensitive indicator group which can be used to determine the impact of LAS on microbial communities.

Modeling diffusion and reaction in soils : IV. New models for predicting ion diffusivity

Salt diffusivity as a function of soil-water content and soil-water characteristic curves was measured on three sieved soils of different texture. The data were used together with ion diffusivity data for sieved soils from literature to test different diffusivity models. No significant differences between salt-, counter-, and self-diffusion data were observed, suggesting an insignificant effect of diffusion type in most cases, two new models for predicting ion diffusivity, based on the Campbell soil-water retention model parameter b, were proposed : (i) a model with a b-dependent threshold water content θ th (soil-water content where the ion diffusivity approaches zero) and (ii) a power function model where the power term η, representing the liquid phase tortuosity, is a linear function of b. In both models, the diffusivity at the soil-water content equal to the total porosity was estimated from a simple impedance factor model. Both b-dependent models gave improved predictions of ion diffusivity compared with existing models. The b-dependent power function model with η = 0.3b gave better predictions than both the θ th -dependent model and a recent model for gas diffusivity in undisturbed soil (Part III of this series, Soil Sci. 161 :366-375) where the tortuosity term η was best described as a function of b -1 . For use of the new b-dependent ion diffusivity models in the absence of soil-water characteristic data, it is shown that b can be fairly accurately estimated from soil texture.

Direct fingerprinting of metabolically active bacteria in environmental samples by substrate specific radiolabelling and lipid analysis

Substrate specific radio assays were used for enumeration and fingerprinting of microorganisms in environmental samples. Direct fingerprinting was based on incorporation of 14C-labelled substrates into microbial lipids. A radioactive fingerprint was obtained by subsequent radio analysis of whole sample phospholipid ester-linked fatty acids (14C-PLFA fingerprint). This approach provided a 14C-PLFA fingerprint of the organism actively metabolizing the added 14C-labelled substrate. Labelled and unlabelled PLFAs were analysed as methyl ester derivatives by gas–liquid chromatography with flame ionization detection. The presence of 14C-PLFAs were determined by collection of 14CO2 produced after combustion of the fatty acids. Additional analysis of the microbial community was carried out by analysis of the radioactivity assimilated into poly-β-hydroxyalkanoates relative to that assimilated into total phospholipids (14C-PHA/14C-PL ratio). The number of organisms involved in the degradation of a 14C-labelled substrate was estimated using a 14C-most-probable-number technique. These different 14C-based methods were evaluated by studying [14C]methane oxidation in agricultural soil, and [14C]phenanthrene degradation in activated sludge and marine sediment. The radio assays resulted in distinct fingerprints of the bacterial populations capable of degrading the different radiolabelled substrates. Manipulation of the incubation conditions (e.g., oxygen status) resulted in significant changes in population specific metabolic activity and labelling pattern. Phenotypically related microorganisms appeared to dominate [14C]phenanthrene degradation in activated sludge and marine sediment under oxic conditions. Anaerobic [14C]phenanthrene degraders in activated sludge produced a very different 14C-PLFA fingerprint. In methane enriched agricultural soil, aerobic methane oxidation was dominated by organisms most similar to the Type I methanotrophic bacteria. Several of the findings obtained by the 14C-PLFA analysis could not have been established on the basis of conventional PLFAs analysis alone. The results suggest that variations of this simple 14C-fingerprinting method may be applicable to studies of substrate metabolism in mixed microbial communities. Direct fingerprinting based on substrate specific radiolabelling may also aid in phenotypic characterization of heterotrophic microorganisms without the need for enrichment or cultivation.

Soil nitrogen transformations along a successional gradient from Calluna heathland to Quercus forest at intermediate atmospheric nitrogen deposition

Abstract Soil nitrogen transformations were studied in a Danish Calluna heathland, a 70-year-old Quercus scrub, and a 200-year-old Quercus forest. These three ecosystems were chosen to represent a secondary successional gradient from Calluna heathland to Quercus forest in an area with intermediate atmospheric N deposition. An NPK-fertilized heathland plot with Deschampsia vegetation was studied as well. In situ net mineralization and net nitrification rates were estimated during the growth season, using intact soil cores. Two additional experiments were conducted in the laboratory to show mineralization/immobilization dynamics and potential nitrification: intact soil cores were subjected to artificial rain in a percolation system; and sieved soil was incubated with combinations of mineral N, urea and CaCO 3 . The morlayer (L,F,H horizon) of the Calluna heathland had a very small mineral N pool and an in situ net mineralization rate of less than 3 mg NH 4 + –N kg −1 month −1 . Both the mineral N pool and the net mineralization rate was higher in the Quercus soils with highest rates (27 mg NH 4 + –N kg −1 month −1 ) in the old Quercus forest. Net nitrification rates were low or zero, and soil N pools were low during the growth season, which indicated a tight recycling of N. The increase in net mineralization rates along the successional gradient was confirmed by the laboratory incubations, and a low nitrification activity was seen only in the Quercus soils in the percolation system. No potential nitrification activity was observed in any of the incubations. The Calluna morlayer revealed a remarkable ability for short term immobilization of NH 4 + and NO 3 − . A mass balance of plant N uptake vs. N deposition and net mineralization in situ indicated that the heather vegetation has access to soil N pools other than the inorganic N originating from net mineralization. The NPK fertilized heath plot with Deschampsia vegetation showed an increase in mineral N pool, net mineralization and nitrification rates as compared to the Calluna soil during laboratory incubations. The results presented here are in accordance with the traditional descriptions of Calluna heath soils, but they are in contrast to recent studies, which have shown high net mineralization rates and occurrence of net nitrification in Dutch Calluna soils. These differences may relate to high atmospheric N deposition in Dutch heathlands as compared to the intermediate N deposition in the area studied here.

Factors controlling nitrification and denitrification: A laboratory study with gel-stabilized liquid cattle manure.

Nitrification and denitrification were studied in a millimeterscale microenvironment using a two-phase system with a liquid manure-saturated layer. Samples consisted of liquid cattle manure and air-dried soil stabilized with silica gel, placed between two aerobic soil phases with a water content near field capacity. A high potential for NH4+ oxidation developed within 0–2 mm distance from the interface, and NH4+ diffused only 10–20 mm into the soil. Some NH4+ was probably immobilized by microorganisms in the soil between 0 and 4 days, after which nitrification was the only sink for NH4+. A potential for denitrification developed within the manure-saturated zone. Maximum rates of both potential and actual denitrification were recorded by Day 4, but denitrification continued for at least 2–3 weeks. The potential for nitrification peaked after 14 days. When the pH of the manure was adjusted to 5.5, nitrification was reduced close to the interface, and NH4+ penetrated further into the soil before it was oxidized. The pH adjustment had an inhibitory effect on denitrification: Both potential and actual rates of denitrification were almost eliminated for several days. The size of the manure-saturated layer strongly affected denitrification losses. With layers of 8 and 16 mm thickness, losses equivalent to 33 and 40% of the original NH4+ pool, respectively, were estimated. When manure corresponding to a 12 mm layer was homogeneously mixed with the soil, only 0.3% was lost.

Modeling Diffusion and Reaction in Soils: VI. Ion Diffusion and Water Characteristics in Organic Manure-Amended Soil

Knowledge of short-term changes in soil physical properties attributable to manure application is a prerequisite for estimating water and solute movement in manure-amended soils. Ion diffusivity and water transport characteristics were measured after the application ofliquid cattle manure in two soils of different texture. Chloride diffusivity apparently decreased in a mixture of a coarse sand and 17% cattle manure compared with diffusivity in the sand without manure application. No difference was seen for a similar mixture using a sandy loam. A large dry matter content in the extracted pore liquid suggested that the coarse sand with low specific surface area only adsorbed small amounts of the added manure dry matter, explaining the increased tortuosity for ion diffusion. Addition of 15-20% manure gave a large increase in water holding capacity (0.10 cm 3 cm -3 at a soil-water potential of -1500 cm H 2 O) and an increase of the Campbell soil-water retention parameter, b, by a factor of3 to 4 for both soils. When manure was applied by direct injection into slits in the soil, the dry matter content of the manure controlled the rapid initial redistribution of water. A model for the relative soil-liquid sorptivity (ratio of sorptivity when applying manure, S, to sorptivity when infiltrating water, S 0 ) as a function of manure dry matter content is proposed.

Modeling Diffusion and Reaction in Soils: V. Nitrogen Transformations in Organic Manure-amended Soil

Measurements of nitrogen transformation with high temporal and spatial resolution are needed to better understand and predict nitrogen losses from manure-amended soil. Centimeter-scale measurements of nitrogen transport and transformations were carried out in a soil-manure model system corresponding to direct injection of liquid manure into soil. Influence of manure type (cattle or pig manure), initial soil-water, and soil-nitrate content were investigated. The manure type was the dominating factor with respect to both the initial redistribution of water and solutes and the subsequent nitrogen transformation processes. The liquid transport from the pig manure into the soil was rapid and extensive compared with the cattle manure. In both systems, the initial water transport created a low-nitrate zone at the manure-soil interface, possibly limiting denitrification that was found to be insignificant. Nitrification was inhibited initially in the cattle manure systems with high NH4+ and DOC concentrations. A small N immobilization during the first 2 days of incubation, followed by a net mineralization, was seen in all experiments. An Inverse Diffusion-Reaction Model (IDRM) was used to calculate spatial and temporal variations in net nitrate production rates after the initial water transport had ceased. Good agreement was found between IDRM-calculated net nitrate production rates and measured nitrification rates. The net nitrate production rates were higher in the pig manure than in the cattle manure systems in the first 8 to 10 days, but they then decreased rapidly as a result of NH4+ limitation in the pig manure system. Unlike the frequently used mass balance considerations, the IDRM includes the effects of diffusion and, therefore, seems promising for high resolution analyses of solute transformation processes.

Direct measurements of oxygen microprofiles and distribution of phospholipid-P in a two-phase soil—manure system

Abstract Concentrations of phospholipid-P (Plip-P) were used as an estimate of biomass in soil. Plip-P was correlated with biomass-C, as determined by chloroform fumigation-direct extraction, in soil from a fertilizer experiment, although a background of non-biomass Plip-P was suggested. The distribution of Plip-P was followed during three weeks in a two-phase model system designed to study microbial processes in and around a manure-saturated zone. Concentrations of Plip-P in the soil were unaffected by the presence of manure at ⩾ 4 mm distance from the soil-manure interface. A sharp gradient between manure and soil phases was maintained throughout the three weeks. Oxygen microelectrodes (i.d. ca. 5 μm, o.d. 150–200 μm) were used for direct measurements of oxygen penetration into the manure-saturated zone. No decrease in oxygen concentration was recorded in the soil phase. By Day 1 oxygen penetrated only 0.15 mm into the manure, increasing to 2-2.5 mm after 21 days. During this period the diffusive flux of oxygen decreased five-fold. Aerobic decomposition of dissolved C in the manure was apparently restricted to a thin layer of 0–2 mm thickness below the soil-manure interface.

Photodegradation of the synthetic fragrance OTNE and the bactericide triclosan adsorbed on dried loamy sand--results from models and experiments.

Fragrances such as OTNE (marketed as Iso-E-Super®) and bactericides such as triclosan (marketed as Igrasan) are present in waste water and thus finally sorbed to sewage sludge. With that sludge they can reach agricultural fields where they potentially can undergo photodegradation processes. In this study the photodegradation of OTNE and triclosan on dried loamy sand was measured under artificial sunlight conditions in laboratory experiments. These compounds were artificially added with concentrations of 1 μg g(-1) on pre-rinsed dried loamy sand. The decrease in concentration with light irradiation was measured for 32d in comparison to soil samples without light irradiation. The estimated light source intensity was 27 W m(-2). Within the experiment, the apparent half-life was 7 and 17d for OTNE and triclosan respectively. The decrease did not simply follow first-order kinetics. The apparent rate constant decreased in the latter stage of reaction, suggesting that part of the chemicals were inaccessible for degradation. Two models, i.e., a diffusion-limited model, and a light penetration-limited model, were used in comparison to the measured data to explain the observed degradation limitations in the latter stages of the experiments. Comparing the hereby obtained model parameters with estimated physico-chemical parameters for the soil and the two chemical compounds, the light penetration-limited model, in which the degradation in the soil surface layer is assumed to be limited due to the shading effect of light in the upper thin soil layer, showed to be the most realistic in describing the photodegradation.