CO2 emission and source partitioning from carbonate and non-carbonate soils during incubation

The accurate quantification and source partitioning of CO₂ emitted from carbonate (i.e., Haplustalf) and non-carbonate (i.e., Hapludult) soils are critically important for understanding terrestrial carbon (C) cycling. The two main methods to capture CO₂ released from soils are the alkali trap method and the direct gas sampling method. A 25-d laboratory incubation experiment was conducted to compare the efficacies of these two methods to analyze CO₂ emissions from the non-carbonate and carbonate-rich soils. An isotopic fraction was introduced into the calculations to determine the impacts on partitioning of the sources of CO₂ into soil organic carbon (SOC) and soil inorganic carbon (SIC) and into C₃ and/or C4 plant-derived SOC. The results indicated that CO₂ emissions from the non-carbonate soil measured using the alkali trap and gas sampling methods were not significantly different. For the carbonate-rich soil, the CO₂ emission measured using the alkali trap method was significantly higher than that measured using the gas sampling method from the 14th day of incubation onwards. Although SOC and SIC each accounted for about 50% of total soil C in the carbonate-rich soil, SOC decomposition contributed 57%–72% of the total CO₂ emitted. For both non-carbonate and carbonate-rich soils, the SOC derived from C4 plants decomposed faster than that originated from C₃ plants. We propose that for carbonate soil, CO₂ emission may be overestimated using the alkali trap method because of decreasing CO₂ pressure within the incubation jar, but underestimated using the direct gas sampling method. The gas sampling interval and ambient air may be important sources of error, and steps should be taken to mitigate errors related to these factors in soil incubation and CO₂ quantification studies.     

Selection criteria for potato tubers to minimize acrylamide formation during frying

A number of parameters linked to the selection of potato tubers were evaluated with regard to their potential to influence acrylamide formation in French fries. The formation of acrylamide, which is a potential human carcinogen, can be minimized for a big extent by the selection of an appropriate tuber. This study focused on the following selection criteria: variety as influenced by storage time and soil type, underwater weight, and tuber size. A total of 16 varieties were compared, concerning their potential for acrylamide formation. From that survey, certain varieties, such as Tebina and Quincy, could be appointed as unsuitable for frying. The differences in the potential of acrylamide formation between the varieties could mainly be explained by the reducing sugar content of the potato (R2 = 0.82, n = 96). The investigated type of soil and storage time at 8 degrees C appeared to have a minor influence on the acrylamide formation during frying. On the other hand, the tuber size of the potato did contribute in a significant manner to the acrylamide formation. Smaller tubers were more susceptible to acrylamide formation and should be avoided in the frying process. The last selection parameter, the underwater weight, appeared to be of minor importance in the acrylamide formation. On the basis of these simple selection criteria, it is possible to make a first screening of potatoes to reduce the acrylamide formation during frying.     

Venturia inaequalis-inhibiting Diels-Alder adducts from Morus root bark

In organic apple orcharding there is a continuous need for natural fungicides effective against Venturia inaequalis (Cooke) Winter, the causal agent of apple scab. In this study an in vitro assay is presented for determining the germination inhibitory potential of extracts and pure compounds. From a screening of plant extracts, the methanol extract of Morus root bark revealed distinct V. inaequalis inhibiting qualities, which were subjected to a bioguided fractionation. Among the isolated metabolites [moracins M (1), O/P (2), kuwanon L (3), and sanggenons D (4), B (5), G (6), O (7), E (8), and C (9)] all the Diels-Alder adducts (3-9) showed an antifungal activity with IC50 values between 10 and 123 microM. The in vitro activity of the most active fraction (A5, IC50 39.0 +/- 4.2 microg/mL) was evaluated in vivo, confirming a distinct antifungal activity against V. inaequalis for the tested natural material.     

Nitrogen fertilization and liming increased CO2 and N2O emissions from tropical ferralsols,but not from a vertisol

The application of nitrogen (N) fertilizers and liming (CaCO₃) to improve soil quality and crop productivity are regarded as effective and important agricultural practices. However, they may increase greenhouse gas (GHG) emissions. There is limited information on the GHG emissions of tropical soils, specifically when liming is combined with N fertilization. We therefore conducted a full factorial laboratory incubation experiment to investigate how N fertilizer (0 kg N ha⁻¹, 12.5 kg N ha⁻¹ and 50 kg N ha⁻¹) and liming (target pH = 6.5) affect GHG emissions and soil N availability. We focussed on three common acidic soils (two ferralsols and one vertisol) from Lake Victoria (Kenya). After 8 weeks, the most significant increase in cumulative carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes compared with the unfertilized control was found for the two ferralsols in the N + lime treatment, with five to six times higher CO₂ fluxes than the control. The δ¹³C signature of soil-emitted CO₂ revealed that for the ferralsols, liming (i.e. the addition of CaCO₃) was the dominant source of CO₂, followed by urea (N fertilization), whereas no significant effect of liming or of N fertilization on CO₂ flux was found for the vertisol. In addition, the N₂O fluxes were most significantly increased by the high N + lime treatment in the two ferralsols, with four times and 13 times greater N₂O flux than that of the control. No treatment effects on N₂O fluxes were observed for the vertisol. Liming in combination with N fertilization significantly increased the final nitrate content by 14.5%–39% compared with N fertilization alone in all treatment combinations and soils. We conclude that consideration should be given to the GHG budgets of agricultural ferralsols since liming is associated with high liming-induced CO₂ and N₂O emissions. Therefore, nature-based and sustainable sources should be explored as an alternative to liming in order to manage the pH and the associated fertility of acidic tropical soils.     

Seasonal,annual and long-term variability in the water chemistry of a remote high mountain lake: Acid rain versus natural changes

Seasonal fluctuations as well as long-term trends in water chemistry were studied in Schwarzsee ob Sölden (Tyrol, Austria), an oligotrophic softwater lake situated at 2796 m a.s.l. The catchement is composed of granite, plagioclase and micaschists containing considerable amounts of sulphur, with little soil cover. The lake is ice covered for about nine months, during this time the deepest layers (>16m) become anoxic. During summer overturn, alkalinity (ALK) is lowest (?8 μeq l^?1) in the whole water column, whereas pH reaches its minimum (4.88) at the surface during snowmelt. A decrease of pH from 5.8 to 5.4 during winter is caused by CO₂ oversaturation, but deep water ALK increases to up to 130 μeq l^?1 due to in-lake ALK generation by reductive processes and base cation (BC) release. The seasonal pattern of ALK in SOS is driven by in-lake processes in winter, the snowmelting in spring and watershed processes and precipitation during summer. Since 1989 summer sulfate concentrations in SOS, originating mainly from the catchment, show a tendency to increase presumably caused by enhanced weathering. In contrast, SO₄ ^2? concentrations in other high mountain lakes which are dominated by atmospheric depositions show a decreasing trend. SOS is a good example for the complexity of interactions between catchment and in-lake processes which act at different time scales and depend on climate changes and atmospheric inputs.     

Phosphorus‐31–nuclear magnetic–resonance spectroscopy to trace organic dung phosphorus in a temperate grassland soil

Cattle dung contributes to hot‐spot inputs of nutrients to grassland systems, but not much is known about its organic P (P_o) composition and fate in the grassland soils. We used ³¹Phosphorus (P)–Nuclear Magnetic–Resonance (NMR) spectroscopy of alkaline soil extracts to examine potentials for tracing of different functional P_o forms into a temperate grassland soil amended with dung. The proportion of monoester, DNA‐diester, and phospholipid+teichoic acid P were comparable in dung extracts, but the soil was dominated by monoester P. The temporal trends in the DNA‐diester P–to–monoester P (D_DNAM) and diester P–to–monoester P (DM) ratio of dung, native soil, and soil amended with dung were monitored in the 70 d field experiment. The D_DNAM and DM ratio in the dung‐amended soil (0–1 and 1–5 cm depth) were always intermediate between the dung and (unamended) control soil. Clearly, extracted soil P was a mixture of incorporated dung‐derived P and native soil P. The dung‐P contribution in the 0–1 cm samples peaked at 47% of the total extracted P at day 70 and at 15% after 42 d in the 1–5 cm soil depth (based on the DM ratio). The proportions of dung‐derived P and C in the soil were positively correlated with: 1) topsoil, using the D_DNAM ratio (r² = 0.975), and 2) top‐ and subsoil, using the DM ratio (r² = 0.656). We concluded that our D_DNAM and DM‐P ratios approach (obtained from solution‐³¹P NMR) did trace successfully the short‐term dynamics and fate of dung P_o in soil. It indicated that dung‐derived P_o varied as rapidly in soil as the dung‐derived C.     

Innovative methods in soil phosphorus research: A review

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state‐of‐the‐art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q‐TOF MS/MS, high resolution‐MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum‐chemical modeling, microbial biomass P, enzymes activity, DGT, ³³P isotopic exchange, ¹⁸O isotope ratios). Required experimental set‐ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.     

Labile water soluble components govern the short-term microbial decay of hydrochar from sewage sludge

Due to higher proportions of labile carbon (C) compounds the suitability of biochar produced by hydrothermal carbonization (HTC) for C sequestration is questionable. We hypothesized that pre-treatment with water would reduce the biological decay of hydrochar from sewage sludge. Unwashed and washed feedstock and hydrochar were incubated in a short-term experiment. The kinetics of the biological decomposition of the materials was calculated on the basis of a double exponential model and the C sequestration potential using the CANDY Carbon Balance (CCB) model. Biological decomposition of the carbonized materials was governed by the percentage of labile C compounds. Mean residence time of a fast (MRT_fast) and slow decay pool (MRT_slow) of unwashed hydrochars varied clearly (MRT_fast: 0.8 – 5.0 months and the MRT_slow: 5.0–18.6 months). The pre-treatment with water removed labile hydrochar C and reduced the biological accessibility. MRT_fast and MRT_slow was increased by intensive washings (MRT_fast: 5.0–7.4 months and the MRT_slow: 14.9 months). High synthesis coefficients suggest that hydrochar C was humified and transferred into stabilized SOC. The results clearly show that once adsorbed components were eliminated, and as compared to pyrolysed biochar hydrochar from sewage sludge may also be useful for soil C sequestration.