Predicting and modelling availability of fluoride in soil from sorption properties     

Johannes Bernhard Wehr  Scott A. Dalzell  Neal W. Menzies 《Soil Use and Management》2023,39(1):521-534

Usage of alkaline and saline groundwater with elevated concentrations of fluoride (F⁻) for irrigation of pastures requires an assessment of the mobility of F⁻ within the plant-water-soil continuum. Factors influencing F⁻ sorption and desorption in 95 Australian soils were examined. Pronounced differences in F⁻ sorption were observed across the soils, but these differences could not be explained by differences in soil pH, electrical conductivity or organic carbon. Rather, sorption was correlated with the content of Fe/Al hydrous oxides and kaolinite in soil. Sorption of F⁻ onto soils increased the solution pH and the ratio of (F⁻ adsorbed) to (OH⁻ desorbed) was consistently below 1, thereby indicating that adsorption of F⁻ results in the release of water and hydroxyl groups from, or co-adsorption of protons to, the sorbent surface. Maximum sorption occurred at pH values of approximately 5–6, whilst sulphate slightly increased (<5%) F⁻ sorption. Desorption was slightly decreased (~3%–7%) in presence of sulphate anions. Hence, it is unlikely that irrigation of soil with alkaline and saline groundwater, in combination with soil applications of gypsum and sulphur to limit pH fluctuations, would increase mobility of F⁻ in soil. Finally, the irrigation of soil columns with 1200–1500 mm of alkaline and saline groundwater containing 0.18 mM F⁻, as would commonly occur in irrigation systems using coal seam gas associated water in Australia, resulted in a F⁻ concentration of 0.05 mM at 10 cm depth and the measured values were in excellent agreement with modelled F⁻ movement based on sorption parameters. Thus, sorption parameters can be used to identify soils which minimize movement of F⁻ because of their strong F⁻ sorption. Based on these results, safe limits for irrigation of soil can be established which avoid F⁻ toxicity risks to plants, animals and contamination of water resources.  相似文献   

A high soil potential net nitrification was observed at 4 m depth: What are the driving factors?     

Kasaina Sitraka Andrianarisoa  Lydie Dufour  Séverine Bienaimé  Bernhard Zeller  Caroline Choma  Christian Dupraz 《European Journal of Soil Science》2023,74(4):e13390

Studies about nitrogen (N) mineralization and nitrification in deep soil layers are rare because N processes are considered to occur mainly in topsoil that hosts active and diverse microbial communities. This study aimed to measure the soil potential net N mineralization (PNM) and nitrification (PNN) down to 4 m depth and to discuss factors controlling their variability. Twenty-one soil cores were collected at the Restinclières agroforestry experimental site, where 14-year-old hybrid walnut trees were intercropped with durum wheat. Soil cores were incubated in the dark in the laboratory at both 6 and 25°C. The soil was a deep calcic fluvisol with a fluctuating water table. It featured a black layer that was very rich in organic matter and permanently water saturated at depths between 3.0 and 4.0 m. The mean soil mineral N content was 3 mg N kg⁻¹ soil in the upper 0.0–0.2 m layer, decreasing until a depth of 2 m and increasing to the maximum value of 25.8 mg N kg⁻¹ soil in the black layer. While nitrate (NO₃⁻) was the dominant form of mineral N (89%) in the upper 0.0–0.2 m layer, its proportion progressively decreased with depth until ammonium (NH₄⁺) became almost the only form of mineral N (97%) in the saturated black layer. Laboratory soil incubation revealed that PNM and PNN occurred at all depths, although the latter remained low at 6°C. The soil nitrate content in the black layer was multiplied by 48 times after 51 days of incubation at 25°C, whereas it was almost inexistent at the sampling date. While the soil total N, the pH and the incubation temperature explained 84% of the variation in PNM, only 29% of the percent nitrification variance was explained by the incubation temperature (T_inc) and the soil C-to-N ratio. These results point out the necessity to consider soil potential net N mineralization and nitrification of deep soil layers to improve model predictions.  相似文献   

Growth performance and body composition of pike perch (Sander lucioperca) fed varying formulated and natural diets     

Carsten Schulz  Steffen Günther  Manfred Wirth  Bernhard Rennert 《Aquaculture International》2006,14(6):577-586

To assess the effect of dietary composition on growth performance and body composition of pike perch (Sander lucioperca), fingerlings with an initial body weight of 1.36 g (just trained to accept formulated feed) were fed three experimental diets in triplicate for 90 days. Two feeding groups were fed with formulated diets (CD, CD+7) containing varying levels of crude lipid (CL) of 14.65% and 21.94% dry matter (d.m.) with crude protein (CP) levels of 59.73% and 56.56%, and one feeding group was fed a natural diet (chironomids, CP = 65.93% d.m.; CL = 7.20% d.m.). Furthermore, pike perch of the same age caught in different natural habitats were analysed to determine their naturally fluctuations in body composition. Specific growth rate (SGR; CD = 3.36, CD+7 = 3.47) and feed conversion ratio (FCR; CD = 1.02, CD+7 = 0.93) of fish fed formulated diets did not differ significantly with rising dietary lipid content, due to high variability within the individuals of each feeding groups. In contrast, pike perch fed with chironomids showed a significantly lower SGR of 2.49 and higher FCR of 2.37 (on a dry matter basis). Body composition of pike perch fed formulated diets was affected by dietary composition and showed increased lipid contents [CD=6.25% original matter (o.m.), CD+7 = 9.00% o.m.] with rising dietary lipid levels. Pike perch of CD and CD+7 feeding groups showed significant increased hepatosomatic indices (HSIs) of 1.99 and 2.05 in contrast to fish fed chironomids with HSI of 1.11. Fish caught in the different natural habitats were characterised by low body lipid and dry matter contents of 0.64–1.88% o.m. and 21.08–23.75% o.m. Higher lipid incorporation of fish fed with formulated diets accompanied with poor benefit on growth performance at higher dietary lipid content indicated that pike perch ability to utilise lipids is low when dietary crude protein content is higher than 56.56%.  相似文献