Loamy Luvisol Research Articles

Mineralization and temperature sensitivity of soil organic matter pools of contrasting lability

AbstractUnderstanding the temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is crucial to predict CO2 emissions and carbon (C) stocks under global warming. This study describes the decomposition and Q10 of four soil C pools: (1) very labile (glucose addition (GLU), representing root exudates), (2) labile (microbial turnover, MT), (3) potentially labile (primed C pool, PE), and (4) resistant (inherent soil C, RES). The soil (loamy Luvisol) was incubated for 4 and 144 days at five temperatures (0, 10, 20, 30, and 40°C) with or without 14C‐labeled glucose. The dynamics of CO2 fluxes were measured during short (0–4 days) and long (5–144 days) term incubations. Glucose was mineralized following a two‐pool exponential function. The half‐life of the decomposition of the GLU pool decreased by 3 times as temperature increased from 10 to 40 °C. The flux of unlabeled CO2 over 4 days reflects a strong contribution to the apparent priming especially at high temperature, which was due to the accelerated microbial biomass turnover. Accordingly, the CO2 flux increased during short‐term incubation and was dominated by the decomposition of labile SOM and microbial biomass turnover, whereas during the long‐term incubation, the CO2 was mainly released from the temperature‐stimulated decomposition of RES pool. The short‐term Q10 of the soil C pools decreased in the order: GLU (2.1) > MT (1.8) > PE (1.3) ≈ RES (1.6) over a few days (0–4 days), but the Q10 measured over the long‐term period (144 days) was in the range of 1.2 (PE) to 1.8 (RES) and decreased in the order RES > MT > PE > GLU. In conclusion, CO2 emissions linearly increased with temperature in all pools over short‐ and long‐term incubation, except for the GLU pool during long‐term incubation. The Q10 strongly depends on the availability of C pools for microorganisms and decreases over time with the exhaustion of available substances in soil. This needs to be considered when estimating temperature effects on CO2 emissions and C turnover in soil.

Food for microorganisms: Position-specific 13C labeling and 13C-PLFA analysis reveals preferences for sorbed or necromass C

Sorption to mineral surfaces is one of the most important processes contributing to soil organic matter (SOM) stabilization. While this stabilization is commonly attributed to inaccessibility of the sorbed SOM to microorganisms, recent findings have revealed increased metabolic efficiency from sorbed substrates. The application of position-specifically 13C labeled sorbed tracer, combined with compound-specific 13C analysis of phospholipid fatty acids (PLFA), enables determination of whether this higher efficiency is due to a metabolic shift in a) the whole microbial community or b) microbial specialists adapted to sorbed C sources.To assess metabolic changes induced by sorption in individual microbial groups, we added uniformly and position-specifically 13C labeled alanine to a loamy Luvisol and incubated the soil samples for 10 days. Two different amendments were compared: i) alanine sorbed to sterilized soil, and ii) free alanine in solution. Incorporation of C from individual alanine positions was evaluated in distinct microbial groups classified by 13C-PLFA analysis.Most of the microbial groups took up sorbed and free alanine equally. The metabolic pattern was also similar in most microbial groups: incorporation of C from carboxylic C-1 into PLFA was negligible, whereas C from the amino-bound C-2 and the methyl C-3 were preferentially incorporated into PLFA. This pattern reflects the basic microbial metabolism of C3 molecules - fast mineralization of C-1 via pyruvate decarboxylation. Only fungi incorporated more C from sorbed than free alanine into their PLFA. Their metabolic pattern also revealed a more complex metabolization via gluconeogenesis, followed by pentose-phosphate pathway.While the incorporation into most microbial groups’ PLFA remained stable or decreased over 10 days, the 13C in Actinobacteria PLFA increased up to 7 times from day 1 to day 10. This strong 13C increase in Actinobacteria was explained by their uptake of secondary substrates derived from microbial necromass or secretion products.This experiment showed that the more efficient metabolization of sorbed substrates is the work of microbial specialists: While uniform labeling revealed the higher incorporation of sorbed than free substrate into fungus PLFAs, position-specific labeling allowed the reconstruction of metabolic changes triggered by sorption of the substrate.To assess changes in the transformation pathways of individual microbial groups caused by sorption, we added uniformly and position-specifically 13C and 14C labeled alanine—a common amino acid in soil—in two ways: i) sorbed to sterilized soil (loamy Luvisol) or ii) free in solution, and incubated for 10 days. Microbial incorporation of alanine’s individual C positions was evaluated in distinct microbial groups classified by 13C-PLFA analysis.Most of the microbial groups were able to take up sorbed and free alanine equally. The metabolic pattern also remained similar in most microbial groups: the C from carboxylic C-1 was nearly not incorporated into PLFA, whereas the C from the amino-bound (C-2) and the methylic C-3 were preferentially incorporated into PLFA of microorganisms. This reflects the basic microbial metabolism of C3 molecules via glycolysis. Only fungi incorporated more C from sorbed than free alanine into their PLFA. Their metabolic pattern also revealed a much more complex metabolization via gluconeogenesis, followed by pentose-phosphate pathway.While the incorporation into all microbial groups’ PLFA remained stable or decreased over 10 days, the 13C in Actinomycetes PLFA increased up to 7 times from day 1 to day 10. This strong 13C increase in Actinomycetes was explained by their uptake of secondary substrates derived from microbial necromass or secretion products.While uniform labeling was able to reveal the preference of fungi for sorbed versus free substrates, position-specific labeling allowed the reconstruction of metabolic changes triggered by sorption of the substrate and reflected a metabolic preference in fungi for sorbed, charged monomers.

N use efficiencies and N2O emissions in two contrasting, biochar amended soils under winter wheat—cover crop—sorghum rotation

Biochar, a carbon-rich, porous pyrolysis product of organic residues, is evaluated as an option to tackle major problems of the global food system. Applied to soil, biochar can sequester carbon and have beneficial effects on nitrogen (N) cycling, thereby enhancing crop yields and reducing nitrous oxide (N2O) emissions. There is little understanding of the underlying mechanisms, but many experiments indicated increased yields and manifold changes in N transformation, suggesting an increase in N use efficiency. Biochar’s effects can be positive in extensively managed tropical agriculture, however less is known about its use in temperate soils with intensive fertilisation. We tested the effect of slow pyrolysis wood chip biochar on N use efficiency, crop yields and N2O emissions in a lysimeter system with two soil types (sandy loamy Cambisol and silty loamy Luvisol) in a winter wheat—cover crop—sorghum rotation. 15N-labelled ammonium nitrate fertiliser (170 kg N ha−1 in 3 doses, 10% 15N) was applied to the first crop to monitor its fate in three ecosystem components (plants, soil, leachate). Green rye was sown as cover crop to keep the first year’s fertiliser N for the second year’s sorghum crop (fertilised with 110 kg N ha−1 in two doses and natural abundance 15N). We observed no effects of biochar on N fertiliser use efficiency, yield or N uptake for any crop. Biochar reduced leaching by 43 ± 19% but only towards the end of the experiment with leaching losses being generally low. For both soils N2O emissions were reduced by 15 ± 4% with biochar compared to the control treatments. Our results indicate that application of the chosen biochar induces environmental benefits in terms of N2O emission and N leaching but does not substantially affect the overall N cycle and hence crop performance in the analyzed temperate crop rotation.

Early detection of the effects of compaction in forested soils: evidence from selective extraction techniques

Soil compaction resulting from mechanisation of forest operations reduces air permeability and hydraulic conductivity of soil and can result in the development of hydromorphic and/or anoxic conditions. These hydromorphic conditions can affect physico-chemical properties of the soils. However, early detection of these effects on mineralogical portion of soils is methodologically difficult. To analyse the effects of soil compaction on iron minerals in loamy Luvisol, three compacted and three non-compacted soil profiles up to the depth of 50 cm were collected from an artificially deforested and compacted soils after 2 years of treatment. Soil was compacted with the help of 25 Mg wheeler’s load to increase the dry bulk density of soil from 1.21 ± 0.05 to 1.45 ± 0.1 g cm−3. Soil samples were analysed by X-ray diffraction (XRD) and were treated by citrate bicarbonate (CB) and dithionite citrate bicarbonate (DCB) under controlled conditions. Major and minor elements (Fe, Al, Mg, Si and Mn) were analysed by ICP-AES in the CB and DCB extracts. It was found that X-ray diffraction is not an enough sensitive method to detect the quick mineralogical changes due to soil compaction. Results obtained from CB-DCB extractions showed that soil compaction resulted in larger CB and smaller DCB extractable elements as compared to non-compacted soil. Labile Fe was found 30 % of total Fe oxides in compacted soil against 10–14 % in non-compacted soils. Compaction thus resulted in Fe transfer from non-labile to labile oxides (s.l.). Results showed that soil compaction leads to the reduction of Fe3+ to Fe2+. The effects of hydromorphic conditions due to soil compaction were observed up to the depth of 35 cm in forest soil profile. Furthermore, a close association of Al with Fe oxides was observed in the soil samples, while Mn and Si were mainly released from other sources, Mg showing an intermediate behaviour. Hydromorphic conditions owing to soil compaction affect the mobility and crystallisation process of iron mineral. CB-DCB selective extraction technique, in contrast to XRD technique, can be effectively used to examine the possible effects of soil compaction on iron minerals.

Impact of two root systems, earthworms and mycorrhizae on the physical properties of an unstable silt loam Luvisol and plant production

Soil organisms are known to engineer the soil physical properties, but their impact is difficult to assess and poorly documented. Shrinkage analysis has a good potential for such assessment. This study analyses the effects of mycorrhizae (Glomus intraradices), earthworms (Allolobophora chlorotica) and two plants, Allium porrum (leek) and Petunia hybrida (petunia), on the physical properties of an unstable loamy Luvisol, as well as the biological interactions between the soil organisms. In addition to soil organism biomass, shrinkage analysis and soil aggregate stability analysis were used to characterize the soil physical properties. The soil aggregate stability, specific volume and structural pores volumes were increased with plant roots compared to control. The drilling effect of roots could not explain the pore volume increase, which was several orders of magnitude larger than the volume of the roots. Leek had larger impact on volumes while petunia mostly increased soil aggregate stability. Mycorrhizae increased the soil stability and the soil volume. Earthworms alone decreased the pore volumes at any pore size, and plant roots mitigated this. Our results highlight (1) the large impact of soil biota on soil physical properties, (2) that their separated effects can either combine or mitigate each other and (3) that the observed changes are varying in intensity according to soil type and plant type.

Impact of the antibiotic sulfadiazine and pig manure on the microbial community structure in agricultural soils

Large amounts of veterinary antibiotics enter soil via manure of treated animals. The effects on soil microbial community structure are not well investigated. In particular, the impact of antibiotics in the presence of manure is poorly understood. In this study, two agricultural soils, a sandy Cambisol (KS) and a loamy Luvisol (ML), were spiked with manure and sulfadiazine (SDZ; 0, 10 and 100 μg g −1) and incubated for 1, 4, 32 and 61 days. Untreated controls received only water. The microbial community structure was characterised by investigating phospholipid fatty acids (PLFA) and using PCR–denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. The total concentration of PLFA increased with addition of manure and was reduced by both SDZ concentrations at incubation times >4 days. The SDZ addition decreased the bacteria:fungi ratio. The largest stress level, measured as ratio of PLFA (cyc17:0 + cyc19:0)/(16:1ω7c + 18:1ω7c), was found for the controls, followed by the manure treatments and the SDZ treatments. A discriminant analysis of the PLFA clearly separated treatments and incubation times. Both soils differed in total PLFA concentrations and Gram −:Gram + ratios, but showed similar changes in PLFA pattern upon soil treatment. Effects of manure and SDZ on the bacterial community structure were also revealed by DGGE analysis. Effects on pseudomonads and β-proteobacteria were less pronounced. While community structure remained altered even after two months, the extractable concentrations of SDZ decreased exponentially and the remaining solution concentrations after 32 days were ≤27% of the spiking concentration. Our results demonstrate that a single addition of SDZ has prolonged effects on the microbial community structure in soils.

Load effect upon soil stress and deformation state in structured and disturbed sandy loam for two tillage treatments

Soil stress and deformation state under loads inform us about mechanical properties of soil. There are numerous factors influencing stresses and deformations generating in soil, where load and tillage treatments are two of them. Monolith samples (600×400×300 mm 3 , L×W×H ) of sandy loamy Luvisol derived from glacial till (Ap horizon) were investigated using stress state transducer (SST) with a displacement measuring system. The SST used in the experiment was a spherical body, 60×50×50 mm 3 (L×W×H ) with six pressure sensors. Pore water pressure in soil samples was set up to −60 hPa prior to the measurements. The soil used in the experiment was taken from two tillage treatments: conventional, with the loosening depth of 350 mm, and conservation, with the loosening depth of 80–100 mm. The same procedure was repeated in disturbed soil samples compacted to bulk density of monoliths. The experiment was conducted in respect to free gravity loading of soil surface by a circular plate. The complete stress state in soil, i.e. the three major stresses, mean normal stress and shearing stress were calculated from measured pressures. Vertical displacement of the SST and bulk density changes were also quantified. The effects of external load as well as tillage variants and soil state on stress and deformation state were discussed. The effect of load was significant for all the soil variants. The measured stress values increase for the greater load, although the intensity of stress increase was different for the soil variants. A superiority of the shearing over the compression in the soil failure process was observed based upon the analysis of shear to normal stresses ratio. Tillage variants influence soil stress and deformation significantly, but stress and strain determination as a function of the load applied does not show the same tendency for the ploughed and rototilled soil.

Immobilization of Zinc and Cadmium in Polluted Soils by Polynuclear Al13 and Al-Montmorillonite

We investigated the suitability of two aluminum-based binding agents, polynuclear Al13 and Al-coated montmorillonite (Al-mont-morillonite), for the immobilization of heavy metals in two contaminated agricultural soils: a loamy luvisol from an arable site in Rafz, Canton Zürich, Switzerland, and a sandy podsol from Szopienice, Upper Silesia, Poland. Both soils were polluted by lead, zinc, and cadmium: the soil from Szopienice by the emissions of a nearby zinc-lead smelter, and the soil from Rafz by sewage sludge applications. While the samples from Szopienice exhibited extremely high loads of these metals, the samples from Rafz were only moderately contaminated. The samples from both soils were slightly acidic. The Rafz soil contained 2.5% organic matter, that from Szopienice only 1.5%. Destruction of the organic matter in the Szopienice samples by H2O2 led to a significant release of Zn and Cd into solution. This indicated that organic matter is an important factor for the immobilization of heavy metals in this soil. The treatment of the Szopienice samples with 8 mmol Al13 per kg dry soil resulted in a considerable mobilization of the two metals. As the pH of the samples did not decrease, this effect was presumably due to direct interactions between the applied aluminium and organic matter. After destruction of soil organic matter, the two binding agents exhibited an immobilizing effect on Zn, which, however, was weak compared with the binding of the metal by the organic matter prior to its destruction. In the case of the Rafz samples, metal mobilization was observed only for Al13 if applied in high doses (4 and 8 mmol per kg soil), but not for Al-montmorillonite. In this soil, Al-montmorillonite as well as Al13 at low doses (1.2 mmol per kg soil and less) decreased soluble zinc concentrations significantly. The mobilization of metals at high doses of the applied binding agents and the dependence of this effect on the type of soil show that care has to be taken with this remediation method and that the proper doses of applied binding agents can be crucial for the success of metal immobilization in polluted soils.

Flux between soil and atmosphere, vertical concentration profiles in soil, and turnover of nitric oxide: 2. Experiments with naturally layered soil cores

Intact soils cores were taken with a stainless steel corer from a sandy podzol and a loamy luvisol, and used to measure the flux (J) of NO between soil and atmosphere and the vertical profile of the NO mixing ratios (m) in the soil atmosphere, both as function of the NO mixing ratio (ma) in the atmosphere of the headspace. These measurements were repeated after stepwise excavation of the soil column from the top, e.g. by removing the upper 2 cm soil layer. The gaseous diffusion coefficients of NO in the soil cores were either computed from soil porosity or were determined from experiments using SF6. The NO fluxes (J) that were actually measured at the soil surface were compared to the fluxes which were calculated either from the vertical NO profiles (J c ) or from the NO production and uptake rates (J m ) determined in the excavated soil samples. In the podzol, the actually measured (J) and the calculated (J m , Jm) NO fluxes agreed within a factor of 2. In the luvisol, the measured NO fluxes (J) and those calculated from the vertical NO profiles (J c ) also agreed well, but in the upper 6 cm soil layer the NO fluxes (J m ) calculated from NO production and uptake rates were up to 7 times higher than the measured NO fluxes. This poor agreement was probably due to the inhomogeneous distribution of NO production and consumption processes and the change of diffusivities within the top layers of the luvisol. Indeed, the luvisol showed a pronounced maximum of the NO mixing ratios at about 6 cm depth, whereas the podzol column exhibited a steady and exponential decrease of the NO mixing ratios with depth. The inhomogeneities in the luvisol were confirmed by incubation of the soil cores under anoxic conditions. This treatment resulted in production of NO at several depths indicating a zonation of increased potential activities within the luvisol profile which may have biased the modelling of the NO surface flux from turnover measurements in soil samples. Inhomogeneities could be achieved even in homogenized soil by fertilization with nitrate solution.

Biological activity and organic matter transformations in typical soils of Schleswig-Holstein

The biological activity in a loamy Luvisol and a sandy Podzol was characterized in the field in Schleswig Holstein under forest as well as under conventional and ecological farming by measuring soil respiration and cellulose decomposition. These activities were influenced considerably by the thermal, water, air and nitrogen supply. The decomposition of litter in the Podzol under spruce, which is dependent on nutrients, is low. In the Luvisol under beech, however, it is moderate and counter-measures against soil degradation are necessary. Organic fertilizing increases biological activity in agricultural soils, independent of the farming method. A good nutrient supply (N, Ca) in the soil solution of the agricultural soils due to fertilizing caused an increase in the biological activity relative to forest soils.