Rhizosphere soil microbial index of tree species in a coal mining ecosystem

Microbial characterization of the tree rhizosphere provides important information relating to the screening of tree species for re-vegetation of degraded land. Rhizosphere soil samples collected from a few predominant tree species growing in the coal mining ecosystem of Dhanbad, India, were analyzed for soil organic carbon (SOC), mineralizable N, microbial biomass carbon (MBC), active microbial biomass carbon (AMBC), basal soil respiration (BSR), and soil enzyme activities (dehydrogenase, urease, catalase, phenol oxidase, and peroxidase). Among the tree species studied, Aegle marmelos recorded the highest value for MBC (590 mg kg⁻¹), urease (190.5 μg NH₄⁺-N g⁻¹ h⁻¹), catalase (513 μg H₂O₂ g⁻¹ h⁻¹), dehydrogenase (92.3 μg TPF g⁻¹ h⁻¹), phenol oxidase (0.057 μM g⁻¹ h⁻¹) and BSR/AMBC (0.498 mg CO₂-C mg biomass⁻¹ day⁻¹); Tamarindus indica for mineralizable N (69.5 mg kg⁻¹); Morus alba for catalase (513 μg H₂O₂ g⁻¹ h⁻¹) and phenol oxidase (0.058 μM g⁻¹ h⁻¹); Tectona grandis for peroxidase (0.276 μM g⁻¹ h⁻¹), AMBC/MBC (99.4%), and BSR/MBC (0.108 mg CO₂-C mg biomass⁻¹ day⁻¹); Ficus religiosa for AMBC (128.4 mg kg⁻¹) and BSR (12.85 mg CO₂-C kg⁻¹ day⁻¹); Eugenia jambolana for MBC/SOC (8.03%); Butea monosoperma for AMBC/SOC (1.32%) and Azadirachta indica for BSR/AMBC (0.1134 mg CO₂-C mg biomass⁻¹ day⁻¹). Principal component analysis was employed to derive a rhizosphere soil microbial index (RSMI) and accordingly, dehydrogenase, BSR/MBC, MBC/SOC, EC, phenol oxidase and AMBC were found to be the most critical properties. The observed values for the above properties were converted into a unitless score (0–1.00) and the scores were integrated into RSMI. The tree species could be arranged in decreasing order of the RSMI as: A. marmelos (0.718), A. indica (0.715), Bauhinia bauhinia (0.693), B. monosperma (0.611), E. jambolana (0.601), Moringa oleifera (0.565), Dalbergia sissoo (0.498), T. indica (0.488), Morus alba (0.415), F. religiosa (0.291), Eucalyptus sp. (0.232) and T. grandis (0.181). It was concluded that tree species in coal mining areas had diverse effects on their respective rhizosphere microbial processes, which could directly or indirectly determine the survival and performance of the planted tree species in degraded coal mining areas. Tree species with higher RSMI values could be recommended for re-vegetation of degraded coal mining area.     

The role of hydropedologic vegetation zones in greenhouse gas emissions for agricultural wetland landscapes

Net greenhouse gas (GHG) source strength for agricultural wetland ecosystems in the Prairie Pothole Region (PPR) is currently unknown. In particular, information is lacking to constrain spatial variability associated with GHG emissions (CH₄, CO₂, and N₂O). GHG fluxes typically vary with edaphic, hydrologic, biologic, and climatic factors. In the PPR, characteristic wetland plant communities integrate hydropedologic factors and may explain some variability associated with trace gas fluxes at ecosystem and landscape scales. We addressed this question for replicate wetland basins located in central North Dakota stratified by hydropedologic vegetation zone on Jul 12 and Aug 3, 2003. Data were collected at the soil-atmosphere interface for six plant zones: deep marsh, shallow marsh, wet meadow, low prairie, pasture, and cropland. Controlling for soil moisture and temperature, CH₄ fluxes varied significantly with zone (p < 0.05). Highest CH₄ emissions were found near the water in the deep marsh (277,800 μg m^− 2 d^− 1 CH₄), which declined with distance from water to − 730 μg m^− 2 d^− 1 CH₄ in the pasture. Carbon dioxide fluxes also varied significantly with zone. Nitrous oxide variability was greater within zones than between zones, with no significant effects of zone, moisture, or temperature. Data were extrapolated for a 205.6 km² landscape using a previously developed synoptic classification for PPR plant communities. For this landscape, we found croplands contributed the greatest proportion to the net GHG source strength on Jul 12 (45,700 kg d^− 1 GHG-C equivalents) while deep marsh zones contributed the greatest proportion on Aug 3 (26,145 kg d^− 1 GHG-C equivalents). This was driven by a 30-fold reduction in cropland N₂O–N emissions between dates. The overall landscape average for each date, weighted by zone, was 462.4 kg km^− 2 d^− 1 GHG-C equivalents on Jul 12 and 314.3 kg km^− 2 d^− 1 GHG-C equivalents on Aug 3. Results suggest GHG fluxes vary with hydropedologic soil zone, particularly for CH₄, and provide initial estimates of net GHG emissions for heterogeneous agricultural wetland landscapes.     

N2O and NO fluxes between a Norway spruce forest soil and atmosphere as affected by prolonged summer drought

Global change scenarios predict an increasing frequency and duration of summer drought periods in Central Europe especially for higher elevation areas. Our current knowledge about the effects of soil drought on nitrogen trace gas fluxes from temperate forest soils is scarce. In this study, the effects of experimentally induced drought on soil N₂O and NO emissions were investigated in a mature Norway spruce forest in the Fichtelgebirge (northeastern Bavaria, Germany) in two consecutive years. Drought was induced by roof constructions over a period of 46 days. The experiment was run in three replicates and three non-manipulated plots served as controls. Additionally to the N₂O and NO flux measurements in weekly to monthly intervals, soil gas samples from six different soil depths were analysed in time series for N₂O concentration as well as isotope abundances to investigate N₂O dynamics within the soil. N₂O fluxes from soil to the atmosphere at the experimental plots decreased gradually during the drought period from 0.2 to −0.0 μmol m⁻² h⁻¹, respectively, and mean cumulative N₂O emissions from the manipulated plots were reduced by 43% during experimental drought compared to the controls in 2007. N₂O concentration as well as isotope abundance analysis along the soil profiles revealed that a major part of the soil acted as a net sink for N₂O, even during drought. This N₂O sink, together with diminished N₂O production in the organic layers, resulted in successively decreased N₂O fluxes during drought, and may even turn this forest soil into a net sink of atmospheric N₂O as observed in the first year of the experiment. Enhanced N₂O fluxes observed after rewetting up to 0.1 μmol m⁻² h⁻¹ were not able to compensate for the preceding drought effect. During the experiment in 2006, with soil matric potentials in 20 cm depth down to −630 hPa, cumulative NO emissions from the throughfall exclusion plots were reduced by 69% compared to the controls, whereas cumulative NO emissions from the experimental plots in 2007, with minimum soil matric potentials of −210 hPa, were 180% of those of the controls. Following wetting, the soil of the throughfall exclusion plots showed significantly larger NO fluxes compared to the controls (up to 9 μmol m⁻² h⁻¹ versus 2 μmol m⁻² h⁻¹). These fluxes were responsible for 44% of the total emission of NO throughout the whole course of the experiment. NO emissions from this forest soil usually exceeded N₂O emissions by one order of magnitude or more except during wintertime.     

A simultaneous model for ultrasonic aggregate stability assessment

Aggregate stability is a difficult to quantify, complex soil property. Ultrasonic processing of soil–water suspensions enables quantifiable and readily reproducible assessment of the level of mechanical energy applied to soil aggregates. Here, we present a method of investigating the stability and comminution of soil aggregates by simultaneously modeling the redistribution of particles throughout any arbitrarily-selected set of soil particle-size intervals as ultrasonic energy is applied to a soil–water suspension. Following model development, we demonstrate its application to 5 particle-size subgroups (0.04–2000 μm) of a Dystroxerept subject to 12 levels of ultrasonic energy between 0 and 5800 J g^− 1 (750 mL^− 1). Laser granulometry was used for particle-size distribution (PSD) analysis, providing precise, non-disruptive measurements of changes in the volume of PSD subgroups in both the microaggregate (< 250 μm; 3 subgroups) and macroaggregate (> 250 μm; 2 subgroups) fractions throughout ultrasonic treatment. Two groups of aggregates were detected exhibiting significantly (p < 0.05) different ultrasonic stability: a group composed exclusively of macroaggregates ranging 250–2000 μm in size, and a finer, relatively stable group ranging 20–1000 μm. The PSD of particles liberated from two aggregate groups significantly (p < 0.05) differed: the coarser, less-stable group liberated 13% clay (0.04–2 μm), 53% fine silt (2–20 μm), and 34% coarse silt and sand (20–250 μm); while the finer, more-stable group liberated 26% clay and 74% fine silt. The ultrasonic energy required to disrupt 25%, 50%, and 75% of all aggregates within a given PSD interval significantly (p < 0.05) differed between all selected intervals, showing a trend of declining stability with increasing particle-size. Both the flexibility of the proposed model and the extension of ultrasonic stability assessment to simultaneous analysis of both microaggregate and macroaggregate subgroups can facilitate broader application of ultrasonic methods to soil processes related research.     

Spatial distribution of isopods in an oak–beech forest

Soil macroinvertebrates were studied in a Mediterranean-type forest on brown-pebble forest soils in southern Russia. At the site, 144 intact soil cores (76 cm² each) forming a grid of 24 × 6 units were taken in order to determine animal spatial distribution. Abundance of isopods was 166.3 ± 16.0 indiv. m^–2 and they constituted about 12% of the total macrofaunal abundance. Biomass of isopods was 3.5 g m^–2, or about 21% of the total biomass of macrofauna. Three woodlice genera (Armadillidium, Cylisticus, and Trachelipus) were found at the site. The two latter genera formed almost all (93%) of the isopod population. We found that spatial distribution of woodlice was heterogeneous: areas with 4–5 individuals per sample were neighboring those without animals. In order to study soil factors influencing isopod distribution in the brown-pebble forest soil, the size of a sample was artificially increased by combining adjacent sample units. Litter mass (r = 0.41) and loss on ignition (LOI) (r = –0.55) significantly influenced isopod distribution. Soil pH was near neutral (6.79), LOI was 8.39, and the water holding capacity was 70.9%. Pebbles comprised up to 84% of the sample's mass. Ca. 40 samples are recommended for estimation of isopod abundance in brown forest soil.     

Influence of different land uses on soil nitrogen transformations after conversion from an Indian dry tropical forest

The effects of alternate land uses, such as grassland, cropland and mine spoil on mineral nitrogen (N), N-transformation rate and microbial biomass N (MBN) in dry tropical forest soils of India were studied. The mean annual mineral N in the forest, grassland, cropland and mine spoil ecosystems, respectively ranged from 15.24 to 19.58, 17.8 to 18.56, 16.49 to 19.85 and 10.52 to 13.44 µg g^− 1, net nitrification rate from 14.15 to 23.4, 10.11 to 11.38, 8.07 to 9.16, 10.52 to 13.44 µg g^− 1mo^− 1; net N-mineralization rate from 17.38 to 26.36, 13.99 to 15.41, 10.99 to 12.5, 5.43 to 7.68 µg g^− 1mo^− 1and and microbial biomass N from 41.25 to 58.87, 34.47 to 47.95, 27.88 to 30.43 and 22.95 to 25.26 µg g^− 1, respectively. The values were within the range reported by previous studies in different tropical environments. The mean annual net nitrification rates declined after conversion into grassland, cropland and mine spoil by 43, 54 and 78%, respectively, net N mineralization by 33, 46 and 70%, and microbial biomass N by 29%, 42% and 52%, respectively.The MBN was positively related to root biomass and total plant biomass, while microbial-N and inorganic N are reciprocally, while nitrification and N-mineralization are directly related to seasonal soil moisture and temperature. The microbial biomass N, nitrification and N-mineralization are negatively related to smaller fraction (< 0.1 mm) of the soil. Above- and below-ground biomass also have had their impact on microbial biomass N, and thereby N-mineralization. Thus, in dry tropical forests, land-use change affects remarkably the nitrogen transformation process in soil.     

Changes of pore morphology, infiltration and earthworm community in a loamy soil under different agricultural managements

Earthworm activity produces changes at different scales of soil porosity, including the mesoporosity (between 1.000 and 30 μm eq. dia.) where both water retention and near-saturated infiltration take place. At this scale, the structural changes are poorly described in temperate agricultural systems, so we do not yet fully understand how these changes occur. The present study was conducted to determine the relationships between the morphology of the mesopores, which is mainly affected by earthworm activity, and the hydrodynamic behaviour (near-saturated infiltration) of topsoil under different agricultural managements inducing a large range of earthworm populations.Investigations were carried out at the soil surface in three fields under different management practices giving rise to three different earthworm populations: a continuous maize field where pig slurry was applied, a rye-grass/maize rotation (3/1 year, respectively) also with pig slurry, and an old pasture sown with white clover and rye-grass.Pore space was quantified using a morphological approach and 2D image analysis. Undisturbed soil samples were impregnated with polyester resin containing fluorescent pigment. The images were taken under UV light, yielding a spatial resolution of 42 μm pixel⁻¹. Pores were classified according to their size (which is a function of their area) and their shape. Hydraulic conductivity K(h) was measured using a disc infiltrometer at four water potentials: −0.05, −0.2, −0.6, and −1.5 kPa. The abundance and ecological categories groups of earthworms were also investigated.Continuous soil tillage causes a decrease in both abundance and functional diversity (cf. maize compared with old pasture) when soil tillage every 4 years causes only a decrease in abundance (cf. rotation compared with old pasture). There were no relationships between total porosity and effective porosity at h=−0.05 kPa. Image analysis was useful in distinguishing the functional difference between the three managements. Fewer roots and anecic earthworms resulted in fewer effective tubular voids under maize. There were fewer packing voids in the old pasture due to cattle trampling. Greater hydraulic conductivity in the pasture phase of rotation may arise from a greater functional diversity than in the maize and absence of cattle trampling compared with the pasture. We point to some significant differences between the three types of agricultural management.A better understanding is required of the influence of agricultural management systems on pore morphology. This study provides a new methodology in which we consider the earthworm activity as well as community in order to assess the effects of agricultural management on soil structure and water movement.     

Land-use impacts on surface runoff and soil detachment within agricultural sloping lands in Northern Vietnam

Two consecutive years of investigation on soil surface features, surface runoff and soil detachment within 1-m² microplots on 40% slope highlighted the effects of land-use change, vegetation cover and biological activity on the water pathways in Northern Vietnam. Three replicate plots were set up on each of five land-uses: cassava (CAS), grass fodder of Bracharia ruziziensis (BRA), a 3-year old fallow (FAL), tree stands of Acacia mangium and Venicia montana (FOR), and a fallow with regrowth of Eucalyptus regularly cut (EUC). The second year, two of the microplots under FAL and EUC were treated with herbicide (FALh, EUCh), one of them was burnt (FALh+b, EUCh+b). The highest yearly surface runoff coefficient of 16%, and soil detachment rate of 700 g m^− 2 yr^− 1 in average with a maximum of 1305 g m^− 2 yr^− 1 have been recorded under CAS. On FALh and FALh+b, runoff ratios were 8.7 and 13.5%, respectively and detachment rates were 86 and 389 g m^− 2. On FAL and BRA the yearly runoff ratio varied from 5.9 to 9.8% but the detachment rate was limited at 24 to 35 g m^− 2. FOR and EUC annual runoff was ≤ 3.1% and annual soil detachment ≤ 71 g m^− 2. These values were very low compared to the values reported on steep slopes in Laos within similar climate and vegetation cover.The runoff and detachment rates underlined the importance of rainfall intensities, soil physical properties, soil surface features, soil vegetation cover and biological activity. The annual surface runoff was highly correlated to the soil surface crusting. CAS and BRA plots were prone to crusting especially after weeding at the onset of the rainy season, when the soil surface was still uncovered. Soil bioturbation (earthworm casting activity) was the second factor that explains local variation of surface runoff and soil detachment. The continuous production of earthworms casts on soil surface, especially on FOR and EUC microplots, induced a marked surface roughness and reduced the surface runoff. The production of casts was very limited in FAL and completely absent in CAS microplots. So it is evident that our results confirm the deleterious effects of cassava on soil and water conservation.     

Increased microbial catabolic activity in diesel contaminated soil following addition of earthworms (Dendrobaena veneta) and compost

This study sought to assess the influence of compost and earthworms (Dendrobaena veneta) upon the level of hydrocarbon catabolism in petroleum contaminated forecourt soil (extractable petroleum hydrocarbons (EPH) 10 + 1.8 g kg⁻¹ and total 16 United States Environment Protection Agency (USEPA) polycyclic aromatic hydrocarbons (PAH) 1.62 ± 0.5 g kg⁻¹). The catabolic activity of the indigenous microorganisms within uncombined materials (soil and compost) and within the combined treatments (soil plus compost; either with or without earthworms) was assessed by ¹⁴C-radiorespirometry (¹⁴C-hexadecane, ¹⁴C-toluene and ¹⁴C-phenanthrene). Maximum levels of catabolic activity were observed (at the end of the incubation period; 84 d) for all three compounds in the combined contaminated soil, compost and earthworm mixtures. Significant (p < 0.05) enhancement factors (relative to the soil only control) in catabolic activity in the combined treatments (soil:compost (1:0.5)) of 3.6 times, 1.5 times and 3.5 times were observed for ¹⁴C-hexadecane, ¹⁴C-phenanthrene and ¹⁴C-toluene, respectively; with maximum levels of catabolic activity for these substrates being 68.6 ± 1.7%, 37.9 ± 5.3% and 85.9 ± 1.3%.     

Effect of di-(2-ethylhexyl) phthalate (DEHP) on microbial biomass C and enzymatic activities in soil

The effects of di-(2-ethylhexyl) phthalate (DEHP) at five different doses from 10 to 1000 mg kg⁻¹ soil on biological properties were investigated over a period of 56 days. Meanwhile, the dissipation of DEHP was also monitored. The results indicated that the microbial biomass C (C_mic) fluctuated at around 70 mg kg⁻¹ soil for the control, whereas the C_mic varied significantly for the soil samples contaminated by DEHP. The catalase activities in all five treatments were stimulated at most time, and the activities of phosphatase in the soils treated by DEHP with 500 mg kg⁻¹ or 1000 mg kg⁻¹ were significantly higher than the other treatments from the 20th day. Urease was more sensitive and inhibited significantly during the initial period of incubation. Additionally, the dose–response relationship of invertase was presented in the later phase of incubation. The activities of urease and invertase might indicate soil perturbations caused by the introduction of DEHP. The dissipation of DEHP was found to follow the pseudo first-order kinetics behavior.     

Spatial patterns of soil biological and physical properties in a ridge tilled and a ploughed Luvisol

The present study was conducted to determine the spatial heterogeneity of bulk density, soil moisture, inorganic N, microbial biomass C, and microbial biomass N in the ridge tillage system of Turiel compared to conventional mouldboard ploughing on three sampling dates in May, July, and August. The soil sampling was carried out under vegetation representing the ridge in a high spatial resolution down the soil profile. Bulk density increased with depth and ranged from 1.3 g cm⁻³ at 10 cm depth to 1.6 g cm⁻³ at 35 cm in ploughed plots and from 1.0 g m⁻³ at 5 cm to 1.4 g m⁻³ at 35 cm in the ridges. In the ploughed plots, the contents of microbial biomass C and microbial biomass N remained roughly constant at 215 and 33 μg g⁻¹ soil, respectively, throughout the experimental period. The microbial biomass C/N ratio varied in a small range around 6.4. In the ridged plots, the contents of microbial biomass C and microbial biomass N were 5% and 6% higher compared to the ploughed plots. Highest microbial biomass C contents of roughly 300 μg g⁻¹ soil were always measured in the crowns in July. The lowest contents of microbial biomass C of 85–137 μg g⁻¹ soil were measured in the furrows. The ridges showed strong spatial heterogeneity in bulk density, soil water content, inorganic nitrogen and microbial biomass.     

Physical properties of tsunami-affected soils in Aceh, Indonesia: 2½ years after the tsunami

On 26 December 2004, a tsunami caused extensive loss of life, damaged property and degraded agricultural land in the province of Aceh, Indonesia. While some of the associated soil chemical changes have been documented, information on soil physical properties is sparse. The objective of this study was to quantify physical properties of some tsunami-affected upland agricultural soils in Aceh, Indonesia. Soil was sampled approximately 21/2 years after the tsunami, from the 0–0.1 m, 0.1–0.3 m and 0.3–0.5 m depths in four sites in the villages of Kling Cot Aroun in Aceh Besar sub-district, Kuta Kruen in Aceh Utara sub-district, Udjong Blang Mesjid in Bireuen sub-district and Meue in Pidie Jaya sub-district on the east coast of Aceh. These sites were located within 1 km from the sea at elevations ranging from 0 to 5 m ASL. The soils were Ultisols except for Meue, which was an Entisol. Soil properties measured were bulk density, structural stability and particle size distribution. Soil water retention, pore-size distribution and saturated hydraulic conductivity were estimated by inserting the values of bulk density, clay, sand and silt contents into pedotransfer functions from the literature. The analyses conducted during this study did not permit us to ascertain what proportion of the soil particles were of tsunami-origin. Nonetheless, deposition of finer-textured material may have occurred in two of the sites. In comparison with the greyish-white, coarse textured soil in the rest of the profile, a finer-textured yellow horizon was present in the lower slopes of the Udjong Blang Mesjid site. At Meue, clay and silt contents were higher in the surface 0.3 m than in the 0.3–0.5 m depth, although a distinct horizon was absent. Particle size distribution in all sites was dominated by the sand fraction, although clay and silt contents were relatively high (20–30 g 100 g^− 1) at Kuta Kruen. Among the sand fractions, fine sand (0.02–0.25 mm) was highest at Kling Cot Aroun, Kuta Kruen and in the “yellow horizon” at Udjong Blang Mesjid, making them more prone to hardsetting and compaction after intensive tillage. Soil compaction was present in all sites with that in the “yellow horizon” at Udjong Blang Mesjid being highest. The relatively low porosity in this layer may be beneficial, as it is likely to reduce the high rates of water drainage and nutrient leaching in this sandy soil. The more compacted soils were characterised by higher numbers of micropores (r, pore radius < 4.3 μm), lower water retention at saturation, smaller numbers of macropores (r > 14.3 μm), lower hydraulic conductivity and intensive gleying, indicating frequent waterlogging. The soils in all depths from Kling Cot Aroun and the “yellow horizon” at Udjong Blang Mesjid were very dispersive, that at Meue moderately dispersive in the 0.3–0.5 m depth but stable in the 0–0.1 m depth, and at Kuta Kruen very stable in all depths. Soil physical degradation was a feature of the soils examined, and its amelioration will be the key to improving and sustaining crop yields in these soils. Possible management interventions include organic amendments such as compost or manure, and minimum tillage options such permanent beds or zero tillage with retention of crop residues as in situ mulch together with suitable cover crops.     

土法炼锌区大气沉降Pb、Zn、Cd及其对土壤质量的影响

Dust emissions from smelters, as a major contributor to heavy metal contamination in soils, could severely influence soil quality. Downwind surface soils within 1.5 km of a zinc smelter, which was active for 10 years but ceased in 2000, in Magu Town, Guizhou Province, China were selected to examine Pb, Zn, and Cd concentrations and their fractionation along a distance gradient from a zinc smelter, and to study the possible effects of Pb, Zn, and Cd accumulation on soil microorganisms by comparing with a reference soil located at a downwind distance of 10 km from the zinc smelter. Soils within 1.5 km of the zinc smelter accumulated high levels of heavy metals Zn (508 mg kg-1), Pb (95.6 mg kg-1), and Cd (5.98 mg kg-1) with low ratios of Zn/Cd (59.1--115) and Pb/Cd (12.4--23.4). Composite pollution indices (CPIs) of surface soils (2.52--15.2) were 3 to 13 times higher than the reference soils. In metal accumulated soils, exchangeable plus carbonate-bound fractions accounted for more than 10% of the total Zn, Pb, and Cd. The saturation degree of metals (SDM) in soils within 1.5 km of the smelter (averaging 1.25) was six times higher than that of the reference soils (0.209). A smaller soil microbial biomass was found more frequently in metal accumulated soils (85.1--438 μg C g-1) than in reference soils (497 μg C g-1), and a negative correlation (P < 0.01) of soil microbial biomass carbon to organic carbon ratio (Cmic/Corg) with SDM was observed. Microbial consumption of carbon sources was more rapid in contaminated soils than in reference soils, and a shift in the substrate utilization pattern was apparent and was negatively correlated with SDM (R = -0.773, P < 0.01). Consequently, dust deposited Pb, Zn, and Cd in soils from zinc smelting were readily mobilized, and weredetrimental to soil quality mainly in respect of microbial biomass.     

Phenylpyrazoles impact on Folsomia candida (Collembola)

Effects of the broad-spectrum insecticide fipronil were investigated on a non-target insect living in the soil, the springtail Folsomia candida Willem. Fipronil induced a significant reduction in juvenile production (PNEC = 250 μg kg⁻¹ dry soil), which seemed to be linked with an impact on the first stages of springtail development: juveniles and 7-day-old adults. These young organisms have a thinner integument, a smaller mass body and a weaker detoxification efficiency and were more sensitive than adults (14 days old) to fipronil and phenylpyrazole derivatives. Contact toxicity for juveniles was measured (LC₅₀(96 h)) giving the following values: fipronil, 450 μg l⁻¹; sulfone-fipronil, 430 μg l⁻¹; sulfide-fipronil, 160 μg l⁻¹. F. candida organisms were able to avoid contaminated food because phenylpyrazoles decreased food appetency. However, F. candida could bioaccumulate fipronil through trans-tegumental penetration (BAF_96 h = 160) and its high biotransformation rate inside springtail bodies (1 ng fipronil metabolized day⁻¹ individual⁻¹) was suspected to increase this process. Under natural conditions, phenylpyrazoles risk assessment on springtails seems to be weak due to their capacity of avoiding high contaminated zones and their biochemical tolerance to this class of insecticides.     

Short-term effects of an exceptionally hot and dry summer on decomposition of surface peat in a restored temperate bog

The restoration of drained peat bogs in Northwest (NW) Europe is an important task of soil protection, but needs to cope with warmer and drier summers. Our examination took place in the Pietzmoor bog (Schneverdingen, NW Germany) that had been drained for fuel peat extraction until the 1970s and rewetted since then. We determined carbon dioxide (CO₂) efflux in situ and in laboratory incubations. Also, we analyzed pore water for dissolved organic carbon (DOC), total and dissolved organic N (DON), nitrate (NO₃^–) and ammonium (NH₄⁺) concentration. In Schneverdingen, the summer 2003 was record-breaking hot (mean temperature June to August elevated > 3 K compared to long-term average) and dry (precipitation during the same period < 59% of long-term average). In July 2003, the water table in the Pietzmoor subsided to > 42 cm below the surface in July 2003, when in situ soil CO₂ efflux was up to 23.4 g m^–2 d^–1 compared to 15.7 g m^–2 d^–1 in September. Prior to March 2003, DOC concentrations in pore water were < 180 mg l^–1 and NH₄⁺ was the dominant fraction of mineral N. In July 2003, DOC concentration rose to 249 g l^–1, DON concentrations more than doubled, and NO₃^– became the dominant fraction of mineral N. Due to the increased future likelihood of hot and dry summers in NW Germany, peat bog restoration efforts need take care that a water table close to the surface is maintained.     

Factors affecting runoff and erosion under simulated rainfall in Mediterranean vineyards

Data on surface runoff and soil loss on gentle slopes with vineyards are analysed. Using a rainfall simulator, 22 rainstorms with varied intensities from 30 to 117.5 mm h⁻¹ and return periods from 2 to 127 years were reproduced. The experimental plots were installed on vineyards planted in straight rows and oriented with the slope direction having a mean gradient of 3.8°. The texture of soils was loamy, with a very heterogeneous surface gravel cover. Values of measured surface runoff varied from 7.2 mm h⁻¹ for low rainfall intensities (30 mm h⁻¹) and short return periods (2 years) to 41.9 mm h⁻¹ with simulation experiments of higher rainfall intensity (104 mm h⁻¹) and long return periods (68 years). Runoff increased linearly with rainfall intensity resulting in soil losses that also increased with rainfall intensity (18.2 g m⁻² h⁻¹ with storms of 30 mm h⁻¹, and 93.2 g m⁻² h⁻¹ with storms of 104 mm h⁻¹); however, r² explains only 36% of the variance. It was necessary to add other factors to improve the coefficient of determination (0.74; p = 0.001) and the predictive function of the equation. These variables were rainfall intensity, kinetic energy of the storm, runoff, soil resistance to drop detachment, surface gravel cover, and gradient. The equation obtained was validated with the USLE-M. In comparison with similar experiments in other regions, the results obtained for soil loss were very moderate, especially those caused by rainstorms of intermediate and low intensity.     

Evaluation of ultrasonic aggregate stability and rainfall erosion resistance of disturbed and amended soils in the Lake Tahoe Basin, USA

Application of organic soil amendments to disturbed soil has been shown to improve aggregate stability and reduce soil susceptibility to erosion. Employing ultrasonic aggregate stability assessment techniques described earlier [Fristensky, A. and Grismer, M.E., 2008. A simultaneous model for ultrasonic aggregate stability assessment. Catena, 74: 153–164.], we assess the effect of two experimental organic soil amendments – a compost and a woodchip mulch incorporated at a rate of 2000–6000 kg ha^− 1 N-equivalence – on soil aggregation and aggregate stability at four drastically disturbed sites within the Lake Tahoe Basin, USA. Experimental plots were established 1–3 years prior to testing. The soils were of granitic or volcanic origin, and disturbed by either ski run or road development. Soil treatments were observed to significantly (p < 0.05) increase both aggregation (300% average increase) and ultrasonic aggregate stability (600% average increase) relative to the untreated soil. However, at the two sites disturbed by ski run development, the control treatment (tilling and surface application of pine–needle mulch) performed comparably to the two incorporated compost treatments, suggesting that the effects of the experimental amendments on aggregation were negligible at these sites, or their effective duration was shorter than the evaluation period.Rainfall simulations (72–120 mm h^− 1) were performed on the treatment plots, and results were compared with the ultrasonic aggregate stability indices. Significant (p < 0.05) positive correlations were obtained between the measurements of aggregate instability and indices of soil susceptibility to runoff, including steady-state infiltration rate (measured values between 1 and 120 mm h^− 1), and the level of kinetic energy of applied rainfall at which runoff commences (EBR, measured values between 12 and 224 J m^− 2). However, no correlation was found between the ultrasonic aggregate stability indices and observed soil erosion variables. Interestingly, positive relationships (p < 0.05) were observed between both infiltration rate and EBR and the proportion of 2–20 μm and < 2 μm particles liberated from the largest aggregates detected in each soil. Our results suggest that ultrasonic aggregate stability indices may be useful indicators of soil susceptibility to runoff and erosion under rainfall.     

Ploughing frequency and compost application effects on soil infiltrability in a cotton–maize (Gossypium hirsutum–Zea mays L.) rotation system on a Ferric Luvisol and a Ferric Lixisol in Burkina Faso

One of the key issues to increase soil productivity in the Sahel is to ensure water infiltration and storage in the soil. We hypothesised that reducing tillage from annual to biennial ploughing and the use of organic matter, like compost, would better sustain soil hydraulic properties. The study had the objective to propose sustainable soil fertility management techniques in the cotton–maize cropping systems. The effects of reduced tillage (RT) and annual ploughing (AP) combined with compost application (Co) on soil infiltration parameters were assessed on two soil types. Topsoil mean saturated hydraulic conductivities (K_s) were between 9 and 48 mm h⁻¹ in the Luvisol, while in the Lixisol they were between 18 and 275 mm h⁻¹. In the two soil types compost additions with reduced tillage or with annual ploughing had the largest effect on K_s. Soil hydraulic behaviour was in reasonable agreement with soil pore size distribution (mean values varied from 19.5 to 237 μm) modified by tillage frequency and organo-mineral fertilization. Already the first 3 years of this study showed that use of organic matter, improved soil infiltration characteristics when annual ploughing was used. Also biennial ploughing showed promising results and may be a useful strategy for smallholders to manage these soils.     

The cost of soil erosion in vineyard fields in the Penedès–Anoia Region (NE Spain)

On-site and off-site environmental impacts of runoff and erosion are usually stressed in order to bring to the public's attention the importance and implications of soil erosion. However, few studies are aimed at calculating the economic implications of erosion, this being the message that farmers and/or policy makers understand best. In this current work we estimated the cost of erosion in vineyards in the Penedès–Anoia region (NE Spain), in which high intensity rain storms (> 80–100 mm h^− 1) are frequent. Modern plantations in the region consist of trained vines, usually planted perpendicular to the maximum slope direction. Broadbase terraces are interspersed between vine rows to intercept surface runoff and convey it out of the field. Part of the sediment generated above these terraces is deposited in them and other parts are either deposited beyond the boundaries of the fields or are exported to the main drainage network. High intensity rainfall produces heavy soil losses (up to 207 Mg ha^− 1 computed in an extreme event in June 2000, which had a maximum intensity in 30-min periods of up to 170 mm h^− 1). To estimate the cost of erosion in vineyard fields of this region, two important aspects were considered. These were a) the cost incurred by the maintenance of the broadbase terraces, drainage channels and filling of ephemeral gullies and b) the cost incurred by the loss of fertilisers (mainly N and P) caused by erosion. According to farmers' records, the former was estimated at 7.5 tractor-hour ha^− 1 year^− 1 (as average), which comprises 5.4% of the income from grape sales. Regarding N and P losses, nutrients exported by runoff were 14.9 kg ha^− 1 N and 11.5 kg ha^− 1 of P, which, if compared to the annual intakes, represent 6% and 26.1% of the N and P respectively. In economic terms, the replacement value of the N and P lost represents 2.4% for N or 1.2% for P of the annual income from the sale of the grapes.     

A protocol for the assay of arylesterase activity in soil

We set up a protocol for the assay of the arylesterase activity, using p-nitrophenyl acetate (p-NPA) as substrate, dimethylsulfoxide as solvent, modified universal buffer at pH 7.5, and determination of the reaction product (p-nitrophenol) after separation of non-hydrolysed p-NPA after reaction, and tested it using eight soils with a wide range of characteristics. Various incubation temperatures and times, pH values and substrate concentrations were also used to find the optimal conditions for the enzyme activity and to determine characteristics and kinetic parameters of soil arylesterase. Arylesterase activity was significantly correlated with total organic C, total N, and soil ATP content. Soil arylesterase activity showed a pH optimum at 7.5, optimal temperature between 55 and 65 °C and linear increase with incubation time. The K_m values ranged from 4.3 to 8.5 mM, the V_max values from 326 to 803 μmol p-NP g⁻¹ h⁻¹, with higher K_m values observed in soils with higher organic matter content. We conclude that the proposed assay protocol is suitable to determine the arylesterase activity in a wide range of soils.