SummaryHere we provide the first demonstration of the potential for N 2O --sufficient (22 mM) conditions. C-to-NO 3 -ratio had a major influence on the products of nitrate ammonification, with NO 2 -, rather than NH4 + , being the major product at low C-to-NO 3 -ratios in batch cultures. N2O production was maximum and accompanied by high NO 2 -production under C-limitation/NO3-sufficiency conditions in chemostat cultures. In media with lower C-to-NO 3-N ratios (5-and 10-to-1) up to 2.7% or 5.0% of NO 3 -was reduced to N2O by Bacillus sp. and Citrobacter sp., respectively, but these reduction efficiencies were only 0.1% or 0.7% at higher C-to-NO 3 -ratios (25-and 50-to-1). As the highest N2O production did not occur under the same C-to-NO 3 -conditions as highest NH 4 + production we suggest that a re-evaluation may be necessary of the environmental conditions under which nitrate ammonification contributes to N 2O emission from soil.

Abstract:Peat is used as rooting medium in greenhouse horticulture. Biochar is a sustainable alternative for the use of peat, which will reduce peat derived carbon dioxide emissions. Biochar in potting soil mixtures allegedly increases water storage, nutrient supply, microbial life and disease suppression but this depends on feedstock and the production process. The aim of this paper is to find combinations of feedstock and production circumstances which will deliver biochars with value for the horticultural end user. Low-temperature (600 • C-750 • C) gasification was used for combined energy and biochar generation. Biochars produced were screened in laboratory tests and selected biochars were used in plant experiments. Tests included dry bulk density, total pore space, specific surface area, phytotoxicity, pH, EC, moisture characteristics and microbial stability. We conclude that biochars from nutrient-rich feedstocks are too saline and too alkaline to be applied in horticultural rooting media. Biochars from less nutrient-rich feedstocks can be conveniently neutralized by mixing with acid peat. The influence of production parameters on specific surface area, pH, total pore space and toxicity is discussed. Biochar mildly improved the survival of beneficial micro-organisms in a mix with peat. Overall, wood biochar can replace at least 20% v/v of peat in potting soils without affecting plant growth.

Purpose Sediments can function as secondary source for water pollution of aerobically biodegradable nonhalogenated organic compounds, which are persistent in anaerobic sediments. The mass transfer of compounds from sediment to bulk water depends on hydraulic conditions. In this study, desorption, mass transfer and biodegradation are investigated under settled and resuspended sediment conditions for branched nonylphenol (NP), which was used as model compound for aerobically biodegradable and anaerobic persistent compounds. Materials and methods Continuous flow through reactor experiments were performed in duplicate with aged NP polluted sediment under sterile and non-sterile conditions to investigate the mass transfer and combined mass transfer and biodegradation. Results and discussion The mass transfer of NP from the sediment bed to the bulk water decreased from 5.1± 0.6 μg d -1 to a stable value of 0.3±0.02 μg d -1 . The desorbed NP in the non-sterile reactors was biodegraded in the first 20 days of the experiment. At the end of the settled sediment conditions, the biodegradation became very limited, and the mass transfer was comparable to the mass transfer under sterile conditions. Upon resuspension, the NP concentration in the bulk water increased instantaneously in all reactors with a factor of 100. This immediate, increased mass transfer of NP from the sediment was larger than the amount that can be biodegraded under optimal conditions. Under non-sterile conditions, a second increase in the mass transfer was observed. However, the amount of desorbing NP during this second increase in mass transfer can be biodegraded under optimal environmental conditions. Conclusions NP desorbs continuously at low concentrations from the sediment bed into the bulk water, which can almost be completely biodegraded. Resuspension of NP-polluted sediment initially led to an increase in the desorbing NP concentrations and can be followed by a subsequent reduction of the concentrations due to biodegradation under environmental conditions where biodegradation of NP can occur.

Anaerobic soil disinfestation (ASD) for the control of multiple soilborne pathogens is a viable alternative to the application of biocides and soil steaming. ASD implies soil wetting, incorporation of fresh organic matter, and covering with airtight plastic foil for several weeks. To speed up the whole process, Thatchtec has developed a procedure based on defined agricultural products (referred to as Herbie). To further optimize ASD, the mechanism of pathogen inactivation should be unraveled. Therefore, we performed an incubation experiment in 11-L polypropene containers with 6 soil types (glacial sand, dune sand, river clay, marine loam, peat soil, and an artificially composed soil lacking any organic matter) in triplicate. After wetting the soil to field capacity, Herbie was added to it (equivalent to 4 g crude protein L-1 soil) and containers were filled with soil (8 L, head space 3 L). A similar treatment without Herbie served as control. Nylon mesh bags containing cysts of potato cyst nematode (PCN; Globodera pallida) were added and the containers were sealed off. Destructive sampling was performed 3, 7, 14, and 28 d after start of the experiment and biotic (cyst content survival, free-living nonplant parasitic nematode community, total and functional groups of bacteria, fungi and protozoa) and abiotic (organic matter, pH, nutrients, EC, fatty acids) parameters measured. Additionally, concentrations of several gases (O 2 , H 2 S, CH 4 , CO 2 , NH 3 , N 2 O) were measured in the head space before each destructive sampling. Survival of eggs within the cysts declined in all treatments to levels <0.5% at the end of the experiment. The rate of egg inactivation depended significantly on soil type, although texture (sand vs. clay) appeared unimportant. Egg survival in the treatments correlated negatively with concentrations of acetic, propionic and butyric acid. As a potential quick-to-measure proxy for incubation time and efficacy, level of O 2 combined with the density of free-living non-plant parasitic nematodes might be interesting.

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