ABSTRACT1. In rearing experiments performed between 1997 and 2007, captive-bred juvenile mussels were harvested shortly after they had dropped off their host fish, and exposed to different types of cages and holding systems.2. Survival of juveniles ranged from 0 to 92% in the first 4 months, but the mean annual mortality was high in all trials and with all systems. In three trials with sheet cages and sediment boxes exposed to mussel rivers from an initial number of 1440 to 1660 only one to eight mussels reached 4 years of age.3. With the exception of mussels kept in spring water no relationship between growth and survival was observed.4. Low survival rates were obtained in sheet cages exposed to very oligotrophic and highly eutrophic brook stretches. Several natural sites that were lacking recruitment in the wild nevertheless showed good results in the cages.5. All holding systems showed irregular variations in survival rates. Pairs of sheet cages showed no correlation between the survival of mussels in the adjacent cages. In contrast, growth rates were correlated. 6. No relationship could be found between the growth or survival in sheet cages at different sites and brooks and the corresponding data on water chemistry.7. The systems tested for rearing young mussels involving a minimal time and effort in the natural habitat were not successful due to the elevated mortality rates of juveniles.8. The rearing success of young pearl mussels in cages in the water flow of mussel rivers gives no information about the suitability of these sites for natural reproduction. Thus, to find potential natural habitats for Margaritifera, it is imperative to survey water quality, sediments and habitat structure.

Ammonia volatilization from slurry in the field is either measured under open atmosphere from large field plots (integrated horizontal flux [IHF], mass balance) or in closed, ventilated chambers (e.g., wind tunnels), which allow the measuring of small plots but influence the climatic conditions. We conducted this study to evaluate a new method for measuring NH3 volatilization on small experimental plots under ambient climatic conditions (including rain and wind). Various pretreated cattle slurries were applied to small plots (2 by 2 m) in tillering winter wheat (Triticum aestivum L.). Ammonia collected by passive samplers on manured plots was compared with NH3 collected on standard plots, where known rates of NH3 were being released via a tubing system (standard comparison [SC] method). Forty‐five manured plots were measured simultaneously by comparison with two standard plots. The specific detection limit of this experiment was 2.5 µg NH3‐N m−2 s−1 (90 g NH3‐N ha−1 h−1). Below this value, the coefficient of variation of measured NH3 release exceeded 30%. Slurry was applied to plastic gutters on two control plots. Measured NH3 losses from these plots accounted for 78% of the absolute NH4‐N losses determined by sampling and analyzing slurry from the gutters. Measurement of the control plots was repeated during the ripening of the wheat. A strong deviation between the measurements of the two plots suggested that the accuracy of the new method is limited in dense vegetation. The results are discussed with respect to measurement accuracy and possible sources of error. A comparison with literature reports indicated that the accuracy of the SC method compared favorably to micrometeorological methods and wind‐tunnel systems.

Summary -ZusammenfassungStrategies reducing NH, volatilisation from slurry include separation of slurry, special application techniques and additives. We studied the impact of manure separation and application technique on N20 release after manure application. Untreated and separated cattle slurry (dry matter content of 7.1% and 4.4%. respectively) was applied to winter wheat using broadcast and banded application and injection.The N20 emissions were measured at high frequency for 14 to 20 days after slurry treatment by the closed chamber method. Manured plots showed significantly higher N20 emissions than the control plots but neither dry matter reduction of slurry nor application technique significantly influenced the N20 emissions. The variability of N2O emission was influenced by the application technique and increased in the order: banded application -injection -broadcast application. There was no correlation between NH3 losses from applied slurry and N20 emissions. Thus reducing ammonia volatilisation will not necessarily increase N20 emissions.

Summary -ZusammenfassungAmmonia volatilization from slurry is undesirable because of environmental N eutrophication and loss of fertilizer value. The dry matter content of slurry, the application technique and the weather conditions are the main factors influencing NH, losses from landspread slurry. In a field of winter wheat a two factor plot experiment was conducted to study single and combined effects of slurry separation and application techniques, including broadcast and banded application, as well as incorporation by injection and the flexible harrow. Ammonia volatilization from all treatments could be measured simultaneously, and at ambient climatic conditions by an indirect, open measurement technique. The experiment was repeated four times. Due to varying weather conditions and treatment effects, cumulative NH, volatilization from the slurry during the first 48 hours ranged from 4 to 90% of total ammoniacal nitrogen (TAN). Both separation and incorporation significantly decreased NHJ losses, but only the combination of dry matter reduction and injection or harrowing reduced NH, volatilization to about 30% ofTAN in all weather conditions. Banding alone did not efficiently conserve slurry N, but even enhanced NH, volatilization in wet conditions.

Ammonia volatilisation from field applied slurries causes environmental hazards and loss of fertilizer value. Acidification of slurry, usually with inorganic or organic acids has previously been used to reduce NH3 emissions. In this study, we present an alternative technique for the acidification of slurry, namely the use of fermentation by endogenous microbes to form organic acids from readily degradable organic compounds. In laboratory experiments, the addition of different sugars (sucrose in dosages of 0.003, 0.01, 0.03, 0.1 and 0.3 mol l(-1), glucose in dosages of 0.05 and 0.1 mol l(-1)) and organic residues (sugar beet residues in dosages of 33 and 330 g fresh weight l(-1), biowaste at 50 g fresh weight l(-1)) to cattle slurry resulted in a considerable decrease in pH, with a minimum pH of 4.7. A subsequent pH increase indicated that the organic acids were probably further degraded with a resultant loss of acidity in the slurry. In a field study, the NH3 emissions from untreated and acidified (pH = 6) slurries were compared after field application (20 m3 ha(-1)). During the first 20 hours, the acidified slurry showed NH3 emissions of less than 5% of the applied ammonia compared to a 26% loss from the untreated slurry. The total emissions of NH4+-N were 32% for acidified and 54% for untreated slurry. Easily degradable organic amendments therefore have the potential to effectively reduce NH3 emissions from slurries and may be an alternative for the use of acids.

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