Einfluß der Strohdüngung auf den Verlauf der N-Mineralisation eines Löß-Parabraunerde-Ap-Horizontes im Säulen-Brutversuch

The influence of straw manure on the course of N-mineralization of a luvisol-A_p-horizon in incubation experiments with soil columns In 1983 and 1984, different treated soil columns were incubated at 35°C to investigate N-mineralization and -immobilization of a luvisol-Ap-horizon (length of the column: 30 cm; diameter: 8 cm). Treatments were as follows: ?undisturbed”?, ?disturbed”? and ?disturbed + straw”? (quantity of straw: =8 t/ha/30 cm; particle size: 10 cm). (soil characteristics: 17,5% clay, 76,5% silit, 6% sand). In 1983 up to 65 kg/ha/30 cm of inorganic nitrogen were assimilated microbially as the result of straw (C/N of straw: 132:1) compared to ?undisturbed”? and ?disturbed”?. After 65 days of incubation immobilization was reserved. The soil water content amounted 65% of the water holding capacity. In 1984 incubation under same conditions, but a C/N of straw of about 80:1, yielded an immobilization of about 55 kg/ha/30 cm compared to ?undisturbed”?. Comparing the straw treatment to ?disturbed”? a maximal immobilization of 45 kg/ha/30 cm was registrated. In the treatments with field capacity up to 55 kg/ha/30 cm were determined as difference between ?straw incorporated”? and ?disturbed”?. A reverse of immobilization resulted after ca. 65 days at both water levels. Concerning the untreated monoliths netto-mineralization was highly reduced particularly in the lower part of the Ap-horizon.     

Comparing chloride transport in undisturbed and disturbed soil columns under turfgrass conditions

Abstract

Transport of surface applied chloride (Cl) in undisturbed soil columns with intact macropores was compared to disturbed, repacked columns of the same soil. The total amount of Cl that leached from 20 cm deep soil columns was 2.0 times higher for the undisturbed columns than for the disturbed columns, and the total quantity of leachate was 1.4 times higher for undisturbed columns than for the disturbed columns. Chloride recovered (mass basis) in layer #2 (6.7 to 13.4 cm) was 1.79 times higher and in layer #3 (13.4 to 20.0 cm) was 2.72 times higher for the disturbed soils than for the undisturbed. For the plant and thatch layer (0.0 to 2.0 cm) the opposite was observed, total Cl recovered from the undisturbed columns was 2.4 times higher than in the disturbed columns.     

Temporal variability of soil macroporosity in a fine sandy loam under mouldboard ploughing and direct drilling

The temporal variability of soil porosity, especially macropores (> 50 μm), and associated porosity factors such as pore continuity, percent water-filled pore space (%WFPS), and earthworm numbers and biomass were determined over 3 years under direct-drilling and mouldboard ploughing. The study was conducted on a Charlottetown fine sandy loam, an Orthic Podzol with a humid to perhumid soil-moisture regime.Differences in soil porosity between tillage systems were mainly confined to the surface 0–8-cm soil depth. Fissures (> 300 μm), or large pores, were reduced under direct drilling compared with mouldboard ploughing, but subject to regeneration over the winter period. The absence of soil loosening caused the volume of macropores to fall below 10% during the growing season. Tillage had a residual effect on soil porosity, maintaining the volume of macropores between 11 and 18%. Differences between tillage and ice-induced porosity influenced the degree of macropore regeneration. In general, water-storage pores were similar between tillage systems. A close relationship (r² = 0.832) was observed between dry bulk density and macroporosity under both tillage systems. The relationship between macroporosity and pore continuity (K_sat), which differed between tillage systems, indicated that a macroporosity of between 8 to 10% (v/v) would maintain adequate soil permeability. In contrast, the %WFPS, which was closely related (R² = 0.952) to macroporosity and soil water content, indicated that the volume of macropores should exceed 14% to provide an optimum level of air-filled pore space.Under humid soil-moisture regimes, the use of macroporosity as an index of critical soil structure or limiting density needs to be based both on adequate soil permeability and on water-filled pore space. Although direct drilling maintained adequate functional porosity, the need for an optimum aerobic environment may necessitate loosening of the surface soil on an annual basis.     

Phosphorus adsorption and desorption in undisturbed samples from subtropical soils under conventional tillage or no‐tillage

The dynamics of P in soil is greatly influenced by the adsorption of phosphate onto Fe‐oxides. Access of phosphate to the surface of these minerals depends on the degree of soil aggregation, which in turn is influenced by soil management system. The primary purpose of this work was to investigate P adsorption and desorption in undisturbed and disturbed soil samples from an Ultisol (Rhodic Paleudult) and an Oxisol (Humic Hapludox) under conventional tillage (CT) or no‐tillage (NT). Phosphorus adsorption and desorption in undisturbed soil was studied by using a continuous flux system containing a P solution for adsorption measurements or deionized water and Mehlich‐I solution for desorption measurements. The Oxisol, which had higher clay, hematite, and goethite contents than the Ultisol, exhibited the highest maximum P adsorption capacity (P_max) values in disturbed samples. Also, the disturbed Ultisol samples had lower P_max values under NT than under CT. The undisturbed soil samples exhibited no significant differences in P adsorption between soil management systems, but P desorption was more marked under NT than under CT. The samples of Oxisol under NT exhibited lower P adsorption rates and higher P desorption rates than the CT samples of the same soil. The decreased P adsorption in undisturbed samples relative to disturbed samples suggests that P adsorption is influenced by physical properties of soil.     

Comparison of Disturbed and Undisturbed Soil Core Methods to Estimate Nitrogen-Mineralization Rates in Manured Agricultural Soils

Ion exchange resin?/?soil cores are a common in situ approach to estimating soil nitrogen (N) mineralization rates. However, no studies compare the two common methods of core preparation (disturbed and undisturbed). The objective of our study was to compare N mineralized and soil temperature in disturbed versus undisturbed cores of manured agricultural soils. Undisturbed cores were prepared by driving aluminum tubes (25 cm long with 10 cm inner diameter) into soil, removing the tubes, and then inserting an ion-exchange resin bag beneath the soil at the bottom of the tube. Disturbed cores were prepared with the same materials, but soil was excavated, mixed, and then filled into tubes fitted with ion-exchange resin bags at the bottom. Soil from six agricultural fields (five of which had more than 10 years of regular dairy manure application) was incubated over four time periods during summer and winter. A total of 13 soil?/?incubation-period combinations were tested. Disturbed cores tended to have more N mineralized than undisturbed cores (P < 0.10), especially in cores prepared with the lowest clay content soil. However, variability of N mineralized was lower in disturbed cores than undisturbed cores for 11 of the 13 soil?/?incubation periods. This lower variability was significant in two of the four incubation periods (P < 0.10). There was little difference in mean soil temperatures in disturbed versus undisturbed cores or within cores versus outside but adjacent to cores. However, in summer, the daily temperature range inside cores was significantly greater than the temperature range in soil outside cores (P < 0.01).     

Abundance, body size and movement patterns of a tropical treefrog in continuous and fragmented forests in the Brazilian Amazon

Phyllomedusa tarsius is a hylid frog that breeds in ponds located in a range of habitats from continuous forests to severely disturbed matrix habitats in Central Amazon. During three reproductive seasons, we followed the movement patterns, measured body size and registered abundance and residency time of this species in five habitats: pasture, Vismia regrowth, Cecropia regrowth, 1 and 10 ha forest fragments, and continuous forest. The frog captures were strongly correlated with rainfall in all disturbed habitats, but not in continuous forest, probably because individuals respond more directly to rainfall patterns in more open habitats. Males in disturbed habitats were smaller than those found in continuous forest, perhaps as a result of differences in habitat quality. Males remained at sites for longer periods in fragments and continuous forest compared to matrix habitats. Here again, the quality and suitability of breeding sites in matrix habitats may be lower than in continuous forest resulting in the need for more movement. We found bigger subpopulations in matrix habitat ponds and a higher percentage of individuals moving among them when compared to continuous forest ponds. Constant movement of individuals among disturbed subpopulations decreases population isolation and increases interbreeding among different subpopulations. No movement between individuals from continuous forest ponds and disturbed habitats was observed. This suggests that the disturbed habitat subpopulations are not acting as sink subpopulations for continuous forest populations. The maintenance of individuals in fragments is more dependent on local conditions for reproduction and on subpopulations in the matrix habitat than on recruitment of individuals from populations in continuous forest.     

PORE CHARACTERISTICS OF SOILS FROM TWO CULTIVATION EXPERIMENTS AS SHOWN BY GAS DIFFUSIVITIES AND PERMEABILITIES AND AIR-FILLED POROSITIES

Gas diffusivity and permeability, and air-filled porosity, were measured in undisturbed soil cores at six water potentials between -2 kPa and oven dryness. All increased as water potential fell. In silt loam at 30 to 80 mm depth, relative diffusivity and air permeability at -2 kPa were 0.0013 and 5 × 10^?8cm² after direct drilling, and were 6 and 15 times greater respectively after ploughing, presumably because of the larger volume of air-filled large pores in the ploughed soil. These pores may also have been more continuous or less tortuous than in the direct drilled soil. However, at equal air-filled porosities up to 0.18 v/v, the pores were apparently more continuous and less tortuous in the direct drilled than in the ploughed soil. In the direct drilled silt loam at any given matric potential, air-filled porosity, gas diffusivity and permeability within and below the previously ploughed layer were isotropic. In clay loam at 30 to 80 mm depth gas diffusivity and permeability at -2 kPa were greater than in the silt loam irrespective of tillage but increased less on oven drying.     

Microtomographic analysis of pore space in a virgin soddy-podzolic soil

The method of X-ray microtomography was applied to study pore space of a virgin soddy-podzolic soil at the natural soil water content. The morphometric parameters of the pores of more than 100 μm in diameter were determined in the vertically oriented undisturbed soil monoliths (d = 3 cm, h = 3–4 cm) from the genetic horizons of the most differentiated part of the soil profile (the AY, AEL, EL, BEL, BT1, and BТ2 horizons). A tendency for the horizontal orientation of these pores was found in all the horizons, except for the humus (AY) horizon. Isolated vesicular pores of different sizes were abundant in the eluvial part of the profile. Numerous recent and relict phytogenic channels were found in the intraped mass of the BT2 horizon. Differently directed interfaces of structural units in the soil horizons were visualized. Cluster analysis was applied to estimate differences between the genetic horizons with respect to their textures, aggregate sizes, and shapes of pores as seen in vertical two-dimensional X-ray images.     

Microbial community composition on native and drastically disturbed serpentine soils

During construction of roads, entire hillsides can be cut away, dramatically disturbing the ecosystem. Microbial communities play important, but poorly understood roles in revegetating roadcuts because of the many functions they perform in nutrient cycling, plant symbioses, decomposition, and other ecosystem processes. Our objective was to determine relationships among microbial community composition, soil chemistry, and disturbance on a serpentine soil disturbed by a roadcut and then partially revegetated. We hypothesized that the adjacent undisturbed serpentine soil would have a different microbial community composition from barren and revegetated sections of the roadcut and that undisturbed soils would have the greatest microbial biomass and diversity. We measured phospholipid fatty acids (PLFA) and soil nutrient concentrations on barren and revegetated sections of the roadcut and on adjacent undisturbed serpentine and nonserpentine soils. Most roadcut samples had soil chemistry similar to the serpentine reference soil. The microbial biomass and diversity of barren sites was lower than that of revegetated or the serpentine reference site. The nonserpentine reference site had significantly (P≤0.05) greater microbial biomass than serpentine or disturbed sites but significantly lower relative proportions of actinomycetes, and slow growth biomarkers. The Barren site had the lowest microbial biomass and a significantly (P≤0.05) greater proportion of that biomass was fungi. Barren, revegetated, and serpentine sites all had dissimilar microbial community composition. The composition of the revegetated communities, however, was intermediate between the serpentine reference and barren soils, suggesting that community composition of revegetated soils is approaching that of an undisturbed site with similar soil chemistry.     

Characterizing the soil moisture regime of a Typic Haplohumod

The saturated hydraulic conductivities (K_sat) of 22 spodic horizons with and without a thin iron pan, were measured in situ with a new technique, using large, carved-out columns, encased in gypsum. Measured infiltration rates and pressure heads above and below the spodic horizons allowed calculation of K_sat, which averaged 8 cm d^?1. Flow rates averaged 32 cm d^?1, however, due to a hydraulic head gradient across the spodic horizon of 4 cm cm^?1. Occurrence of a thin iron pan in the spodic horizon did not affect its K_sat-value. The measured high flow rates exclude the occurrence of perched watertables. Lateral flow of water, forming surface ponds in local depressions, was due to surface runoff, rather than to lateral movement of perched water: surface ponding of water occurred also in soils in which the spodic horizon had been mixed by tillage.     

Spatial demographic and genetic consequences of harvesting within populations of the terrestrial orchid Cymbidium goeringii

Populations of many orchids, especially terrestrial species, have been rapidly decreasing due to mass collection by plant sellers and enthusiasts. Given the presumably negative demographic and genetic consequences, such anthropogenic activity should be taken into consideration for predicting ecological and evolutionary dynamics and for planning conservation strategies. To determine how recent human disturbance alters spatial demographic and population genetic processes, populations of the terrestrial orchid Cymbidium goeringii located in South Korea were examined to quantify the spatial distributions of individuals and genotypes with respect to three levels of disturbance: “disturbed” (four populations), “putatively disturbed” (two), and “undisturbed” (two). Undisturbed and putatively disturbed populations were found to possess significantly positive spatial clustering of individuals over a range of spatial scales. In contrast, disturbed populations exhibited little or no spatial aggregation, consistent with the selective removal of plants by collectors from higher density areas within these populations. Although overall genetic differentiation among populations was moderate and significant (F_ST = 0.082), levels of genetic diversity within populations were similar despite the different disturbance histories (mean H_e = 0.257-0.324). Spatial genetic autocorrelation analyses revealed that the undisturbed populations exhibited significant declines in kinship (F_ij) with distance, that mean kinship at interplant distances of ?4-6 m was significantly greater than zero and between plants ?0.5 m apart was in the range expected for first cousins to half-sibs. In contrast, only one putatively disturbed and one disturbed population exhibited significant declines in kinship with distance. These differences between disturbed versus putatively disturbed and undisturbed populations in the spatial distribution of individuals and genetic variation likely reflect the consequences of mass collections. Since these differences (and reduced population density) have important implications for future ecological and evolutionary trajectories, conservation managers of endangered terrestrial orchids may want to analyze the spatial distribution of individuals and their genotypes to infer whether a population with few individuals represents a natural state or the likely outcome of mass collection.     

Disturbance of biological soil crusts: impacts on potential wind erodibility of sandy desert soils in southeastern Utah

Friction threshold velocities (FTVs) were determined for biological soil crusts in different stages of recovery. Particles on the surface of crusts that had been relatively undisturbed for at least 20 years were found to have significantly higher FTVs than those that had been disturbed 5, 10 or 1 years previously (376, 87, and 46 cm sec⁻¹, respectively). FTV's for crust breakage was also much higher for undisturbed crusts when compared to the previously disturbed crusts (573, 148, and 88 cm sec⁻¹, respectively). All crusted surfaces were more stable than bare sand, which had an FTV of 16 cm sec⁻¹. Disturbance treatments were then applied to the three crustal classes. Disturbance significantly reduced the FTVs of all classes by 73–92 per cent. Comparing crustal FTVs with mean and high monthly wind speeds found in this region, it was observed that only crusts that had been undisturbed for approximately 20 years or more were able to protect soil surfaces from wind gusts expected on the average of once a month. Other crustal classes, as well as all disturbance treatments, had FTVs lower or equal to that of commonly occurring winds in this region. Because most of the crustal biomass occurs in the top 0·3 mm of soils, even slight soil loss can negatively influence stability and nutrient inputs to this ecosystem. © 1997 John Wiley & Sons, Ltd.     

Phosphorus Entrainment Due to Resuspension in a Lowland River, Spree, NE Germany – A Laboratory Microcosm Study

Resuspension of benthic phosphorus (P) often constitutes a high percentage of the annual P flux in lowland rivers. To study P entrainment at controlled shear velocity (u*) sediment from lowland River Spree of slower flowing (0.1–0.3 m s^?1) stretch Kossenblatt (KOB) and of faster flowing (0.5–0.7 m s^?1) stretch Freienbrink (FRB) was incubated in a microcosm at incrementally enhanced u* (0.34–1.9 cm s^?1). Particle and P entrainment rates as well as the number of particle-associated bacteria of fine-grained mud-like KOB sediment were much higher (16.7 g m^?2 h^?1, 104.9 mg P m^?2 h^?1, 15.47 10⁶ cells ml^?1) than those (4.3 g m^?2 h^?1, 2.1 mg P m^?2 h^?1, 3.06 10⁶ cells ml^?1) of coarser sandy FRB sediment. The microcosm used so far in marine research is suited to compare riverine resuspension suggesting the lower u* the more particles are deposited and the more P can be retained (KOB ? FRB). Conversely, correspondingly more and easier particulate P and bacteria can again be remobilised (KOB ? FRB) if u* increases. The general relationship found for u* and the entrainment of particulate P and bacteria as well as their decelerated and selective deposition where bacteria may stay longer in the water implies a temporarily enhanced P bioavailability, turnover and subsequent P transformations.     

Charcoal production at kiln sites affects C and N dynamics and associated soil microorganisms in Quercus spp. temperate forests of central Mexico

Temperate forests dominated by Quercus spp. cover large parts of Central Mexico and rural communities depend on these forests for wood and charcoal. The impacts of charcoal production on selected chemical properties including C and N dynamics, and populations of ammonifiers, nitrifiers and denitrifiers were investigated on surface soils (0–15 cm) collected during the dry and rainy season of these forests. Organic C was halved in soil at the kiln sites compared to undisturbed forest soil. Concentrations of exchangeable Ca²⁺, K⁺ and Mg²⁺ increased >1.6 times at kiln sites and pH increased from 4.5 in undisturbed soil to 7.0 at kiln sites. The kiln sites had 1.3 times and 2.4 times lower microbial biomass C and N, respectively, than undisturbed forest sites during the rainy season. Although the effect of charcoal production on NH₄⁺, NO₂^? and NO₃^? concentrations was small, the ammonifying, nitrifying and denitrifiers were 16 times lower at the kiln sites than in the undisturbed forest soil. This research found that the charcoal production had a negative effect on the cultivable microorganisms involved in N cycling and the soil microbial biomass C and N compared to undisturbed forest soil. Differences in inorganic N dynamics were more affected by seasonality, i.e. precipitation, than by charcoal production.     

A seasonal behavior of surface soil moisture condition in a reclaimed tropical peatland

Soil moisture condition is essential to regulate the release of soil carbon from a drained peatland since aerobic microbial activities can be encouraged through oxygen supply associated with dewatering the soil layer while they may be discouraged under too dry conditions. Aiming to characterize the soil moisture condition in a reclaimed tropical peatland, we monitored the volumetric water content at 5?cm depth (θ _5?cm), groundwater level (GWL) and rainfall for 20 months from March 2010 to November 2011 in an oil palm field in Nakhon-Si-Thammarat, Thailand. We also measured the soil water retention curve and the unsaturated hydraulic conductivity (k) for a series of matric potential (h) to simulate the moisture condition monitored in the field by using the Buckingham-Darcy's flux law. During the dry season in 2010, the θ _5?cm consistently stayed lower than 0.35?m³?m^–3 with the GWL lower than a depth of 30?cm. In the transition from the dry season to the rainy season in 2010, the GWL rose to the land surface with peaks and dips across the time for about one month with the θ _5?cm increasing toward saturation. During the rainy season where the GWL stayed near or above the land surface, the θ _5?cm remained the field-saturated value of 0.58?m³?m^–3 on average, less than the laboratory-saturated value of 0.63?m³?m^–3, suggesting the development of a significant amount of entrapped air-phase. Hysteretic behavior in the measured θ _5?cm–GWL relation also supported that the top soil layer refuses to absorb water in wetting processes. The simulated θ _5?cm based on the measured k(h) and soil water retention curves demonstrated that the ease with which the top soil dries during a dry season was due mainly to the low k(h) value in the dried condition, while the slope of the θ(h) curve was so moderate that the soil layer could retain moisture for maintaining liquid water supply to the surface from the dropped GWL. Sensitivity analyses while varying the magnitude of both k(h) and evaporation rate (E) suggested that the k(h) function was more deterministic than the value of E in making the land surface easily dried. As the GWL stayed lower than 30?cm in depth for a total of 187 days out of the year monitored, while surface-ponding conditions took place for 120 days of the year, it was concluded that either the extremely dried condition or the saturated-moisture condition had dominantly occurred in the study site through a year and, thus, there may only be a limited time when soil organic matter near the land surface is in favorable moisture conditions for aerobic decomposition.     

Hydraulic conductivity and porosity under conventional and no-tillage and the effect of three species of cover crop in northern France

We studied soil hydraulic conductivity (K) and porosity in five combinations of soil tillage and cover crop management systems. Treatments were winter wheat (Triticum aestivum L.) grown on a conventionally tilled soil (CT), on a no‐till soil (NT), and on an NT with three different cover crops: red fescue (Festuca rubra L.; Fr), bird's‐foot‐trefoil (Lotus corniculatus L.; Lc) and alfalfa (Medicago sativa L.; Ms). Measurements were made on a loamy soil in Grignon, France, in November 2004, May 2005 and October 2005. K and mean size of hydraulically active pores were measured in situ at three water potentials (?0.6, ?0.2 and ?0.05 kPa) at the soil surface and at 10 cm depth. In November 2004 and May 2005, pore space was described using 2D image analysis of pores on undisturbed soil samples in the 0–10 cm layer and in the 10–20 cm layer. The major differences were caused by soil tillage that created two heterogeneous soil layers and increased K in the 0–10 cm layer relative to NT. The effects of cover crop on K and porosity were not affected by the root type: there were no major differences between the grass cover crop (fibrous‐root type) and the leguminous ones (tap‐root type). However, we recorded larger functional pores and more tubules in the no‐till treatments with a cover crop, compared with the no‐till treatment without cover crop; this was probably the result of root activity. Although these changes generally did not result in larger values of K, they participated in the maintenance of soil structure and K over time.     

Effects of tracked vehicles on the morphological and physical properties of tundra soils

The agricultural lands of typic tundra of the Yamal Peninsula in Russia are pastures for reindeer (Rangifer tarandus sibiricus Murr.) herds. Currently, degradation of tundra soil cover is mainly caused by mechanical impacts of tracked vehicles used in construction operations. The objective of this study was to evaluate changes in morphological, micro-structural, and physical properties of Cryozems and Cryogenic peaty soils affected by these tracked vehicles. Soil samples were taken from the surface and underlying horizons before and 5 years after four and 100 passes of tracked vehicles. Surface horizons (0–10 cm) of the undisturbed Cryozems and Cryogenic peaty soils were organogenic. Passage of tracked vehicles caused mixing of these horizons with lower sandy loam and loam mineral horizons. Properties of the organomineral horizons formed in this way differed essentially from those of the surface horizons of the undisturbed soils. Microaggregates were completely disturbed, even after only four passes of tracked vehicles. Large inter-aggregate pores disappeared and thin pores or cracks formed as a result of vehicle-induced mechanical impacts. Humification of plant residues was observed to be faster in the compacted organomineral horizons of disturbed soils compared with undisturbed ones. The organic substances formed in the compacted organomineral horizons readily moved downward within the soil profile or were lost during runoff events. High correlation coefficients of organic carbon content with both specific surface area and water retention showed that the above-mentioned organic substances were hydrophilic. Specific surface area and water retention of the disturbed soils rose with increasing organic carbon content. The results obtained in this study demonstrated a high susceptibility of Cryozems and Cryogenic peaty soils to mechanical impacts.     

The tripartite symbiosis between legumes, rhizobia and indigenous mycorrhizal fungi is more efficient in undisturbed soil

We investigated how the rate of colonization by indigenous arbuscular mycorrhizal fungi (AMF) affects the interaction between AMF, Sinorrhizobium meliloti and Medicago truncatula Gaertn. To generate a differential inoculum potential of indigenous AMF, five cycles of wheat, each of 1 month, were grown in sieved or undisturbed soil before M. truncatula was sown. The early colonization of M. truncatula roots by indigenous AMF was faster in undisturbed soil compared with sieved soil, but by pod-fill the frequency of hyphae, arbuscules and vesicles was similar in both treatments. At this latter stage, M. truncatula grown in undisturbed soil had accumulated a greater biomass in aboveground tissues, had a greater P concentration and derived more N from the atmosphere than plants grown in disturbed soil, although soil compaction resulted in plants having a smaller root system than those from disturbed soil. The difference in plant P content could not be explained by modifications in hydrolytic soil enzymes related to the P cycle as the activity of acid phosphatase was greater in sieved than in undisturbed soil, and the activity of alkaline phosphatase was unaffected by the treatment. Thus, the results observed were a consequence of the different rates of AMF colonization caused by soil disturbance. Together with earlier results for soybean, this study confirms that soil disturbance modifies the interaction between indigenous AMF, rhizobia and legumes leading to a reduced efficacy of the bacterial symbiont.     

Profile carbon and nutrient levels and management effect on soil quality indicators in the Mardi watershed of Nepal

Abstract

Soil organic carbon (SOC) and nutrient stocks in the soil profile (0–80 cm) in four dominant land uses [forest, upland maize and millet (Bari), irrigated rice (Khet), and grazed systems)] and 0–15 cm depth along elevation gradient 1000 to 3000 m, and aspects in the Mardi watershed were measured. Soil properties at 0–15 cm depth were also measured in undisturbed forest, forest with free grazed system, managed forest, and grassland to compare the soil quality index (SQI) of topsoils. The SOC and nutrient concentration decreased with increasing profile depth. The SOC and N contents in the 0–15 cm depth of forest soils were significantly greater than the corresponding depth in upland maize and millet, irrigated rice, and grazed systems. On the other hand, available P and K concentrations at the same depth were significantly greater in upland maize and millet compared to irrigated rice, grazed system, and forest land uses. The SOC and N stocks (0–15 cm) increased from agricultural land at the valley bottom at about 1000 m above mean sea level (a.s.l.) (24 and 3 Mg ha^?1) compared to undisturbed forest (74 and 5.9 Mg ha^?1) at 2600 m a.s.l, demonstrating the effects of cover and elevation. Both SOC and N stocks decreased sharply in grassland (54 and 4.5 Mg ha^?1) at elevations of 2600 to 2800 m a.s.l. compared with undisturbed forest. Above 2800 m a.s.l. the cover type changed from grass to coniferous forest, and the SOC and N stocks steadily increased at the summit level (3200 m a.s.l.) to 65 and 6.9 Mg ha^?1, respectively. Slope and aspect significantly affected SOC with the northwest aspect having significantly higher concentrations (46 g kg^?1) than other aspects. Similarly, SOC concentration at the lowest slope position (39 g kg^?1) was significantly higher than the middle or upper positions (25 and 13 g kg^?1). Integrated soil quality index (SQI) values varied from 0.17 to 0.69 for different land uses, being highest for undisturbed forest and lowest for irrigated rice. The SQI demonstrated the degradation status of land uses in the following ascending order: irrigated rice?>?grazed system?>?forest with free grazing?>?upland maize and millet?>?managed forest?>?grass land?>?undisturbed forest. The irrigated rice, grazed system, upland maize and millet, and freely grazed forestlands need immediate attention to minimize further deterioration of soil quality in these land uses.     

A comparative analysis of microbiomes in natural and anthropogenically disturbed soils of northwestern Kazakhstan

The goal of this study was to determine the relationships between the structure of the soil microbiome and the agroecological state of soils by the example of natural undisturbed (steppe areas) and anthropogenically disturbed (pastures, croplands, fallows) areas in the territory of northwestern Kazakhstan. The highest abundance of proteobacteria was found in the anthropogenically disturbed of fallows and in undisturbed soils; in other cases, actinobacteria and representatives of the Firmicutes phylum predominated. Different kinds of anthropogenic impacts resulted in the decrease in the portions of bacteria from the Acidobacteria, Gemmatimonadetes, and Firmicutes phyla. In the disturbed soils, the portions of bacteria from the Erysipelothrix, Mycobacterium, Methylibium, Skermanella, Ralstonia, Lactococcus, Bdellovibrio, Candidatus nitrososphaera, Catellatospora, Cellulomonas, Stenotrophomonas, and Steroidobacter genera increased. Bacteria of the Erysipelothrix and Methylibium genera occurred only in the undisturbed soils. The anthropogenically disturbed and undisturbed soils differed significantly in the taxonomic structure of their microbiomes forming two separate clusters, which confirms the efficiency of using the data on the structure of soil microbiomes when assessing the agroecological status of soils.