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1.
Field traffic may reduce the amount of air-filled pores and cavities in the soil thus affecting a large range of physical soil properties and processes, such as infiltration, soil water flow and water retention. Furthermore, soil compaction may increase the mechanical strength of the soil and thereby impede root growth.

The objective of this research was to test the hypotheses that: (1) the degree of soil displacement during field traffic depends largely on the soil water content, and (2) the depth to which the soil is displaced during field traffic can be predicted on the basis of the soil precompression stress and calculated soil stresses. In 1999, field measurements were carried out on a Swedish swelling/shrinking clay loam of stresses and vertical soil displacement during traffic with wheel loads of 2, 3, 5 and 7 Mg at soil water contents of between 11 and 35% (w/w). This was combined with determinations of soil precompression stress at the time of the traffic and predictions of the soil compaction with the soil compaction model SOCOMO. Vertical soil displacement increased with increased axle load. In May, the soil precompression stress was approximately 100 kPa at 0.3, 0.5 and 0.7 m depth. In August and September, the soil precompression stress at 0.3, 0.5 and 0.7 m depth was 550–1245 kPa. However, when traffic with a wheel load of 7 Mg was applied, the soil displacements at 0.5 m depth were several times larger in August and September than in May, and even more at 0.7 m depth. An implication of the results is that the precompression stress does not always provide a good indication of the risk for subsoil compaction. A practical consequence is that subsoil compaction in some soils may occur even when the soil is very dry. The SOCOMO model predicted the soil displacement relatively well when the soil precompression stress was low. However, for all other wheeling treatments, the model failed to predict that any soil compaction would occur, even at high axle loads.

The measured soil stresses were generally higher than the stresses calculated with the SOCOMO model. Neither the application of a parabolic surface load distribution nor an increased concentration factor could account for this difference. This was probably because the stress distribution in a very dry and strongly structured soil is different from the stress distribution in more homogeneous soils.  相似文献   


2.
In recent years, agricultural land in Switzerland has been increasingly used as temporary access ways for heavy machinery in road and pipeline construction operations. The Swiss soil protection law requires that measures are taken to prevent soil compaction in such operations, but gives no criteria to determine tolerable loads. We studied the compaction sensitivity of a loess soil (Haplic Luvisol) at different soil moisture conditions in a field traffic experiment and by a numerical model on the computer using finite element analysis. Two plots, one wetted by sprinkling and one left dry (no sprinkling), were traversed by heavy caterpillar vehicles during construction of a large overland gas pipeline. Compaction effects were determined by comparing precompression stresses of samples taken from trafficked and non-trafficked soil. A finite element model with a constitutive relation, based on the concept of critical state soil mechanics, was used to interpret the outcome of the field trials.

We found significantly higher precompression stresses in the trafficked (median 97 kPa) compared with the non-trafficked (median 41 kPa) topsoil of the wet plot. No effect was evident in the topsoil of the dry plot as well as in the subsoils of the wet and the dry plot. The observed compaction effects were in agreement with the model predictions if the soil was assumed to be partially drained, but disagreed for the wet subsoil if fully drained conditions were assumed. Agreement between model and experimental results also required that the moisture dependence of the precompression stress was taken into account.  相似文献   


3.
Laboratory compressibility tests were done on soil samples taken from a field experiment 21 years old, located on a Stagnic Luvisol, with deep ripping performed with various frequencies: no ripping, ripping every 8, 4 and 2 years, and ripping yearly. Precompression stress was found to increase with depth of the soil profile down to some 60 cm, and somewhat decreasing at the depth of 70–75 cm, which corresponds to the Bt horizon. Due to ripping, the values of the precompression stress decreased; for soils from experimental treatments with different periodicity of ripping operations, the differences were small, and not in a very definite direction. The estimation procedures suggested by Lebert to predict precompression stress for “normal” arable soils could not be applied to ameliorated soil samples investigated in this paper because repeated ripping prevents a continuous aggregate formation and results mainly in structural texture dependent relations. The compression index showed an increase down to 60 cm and a decrease in the Bt horizon (70–75 cm). In the different experimental treatments, it showed a less clear variation, although some trend of increasing with increased number of rippings may be considered. As inferred from these parameters, soil strength and compressibility do not affect directly crop yields.  相似文献   

4.
In a field experiment, a sandy loam was subjected to single passes with a sugar beet harvester at two different soil water potentials. Different hopper fillings resulted in ground contact pressures of 130 kPa (partial load) and 160 kPa (full load) underneath the tyre. Bulk density, macroporosity (equivalent pore radius >100 μm), penetrometer resistance, air permeability and pre-consolidation pressure were measured within and next to the wheel tracks at depths of 0.12–0.17, 0.32–0.37 and 0.52–0.57 m. Furthermore, the soil structure at two horizons (Ahp 7–24 cm, B(C) 24–38 cm) was visually assessed and classified.

The moist plot responded to a wheel load of 11.23 mg (160 kPa) with an increase in bulk density and pre-consolidation pressure as well as with a decrease in air permeability and macroporosity at a depth of 0.12–0.17 m. With a wheel load of 7.47 mg (130 kPa) on the moist plot and with both wheel load levels on the dry plot, only slight changes of the soil structure were detected. At a depth of 0.32–0.37 and 0.52–0.57 m, the measurements did not indicate any compaction. An ANOVA indicates that the factor “soil water potential” and the factor “wheel load” significantly influence the bulk density at a depth of 0.12–0.17 m. No interactions occurred between these two factors. The wheel traffic on the test plot had no effect on the yield of winter wheat planted after the experimental treatment.

Bulk density, macroporosity and pre-consolidation pressure proved to be sensitive to detect compaction because they varied only slightly and are easy to measure. In contrast, the standard deviation of air permeability is large. The soil structure determined visually in the field confirms the values measured in the laboratory. The results of the penetrometer resistance measurements were not explainable.  相似文献   


5.
I. Celik   《Soil & Tillage Research》2005,83(2):270-277
Forest and grassland soils in highlands of southern Mediterranean Turkey are being seriously degraded and destructed due to extensive agricultural activities. This study investigated the effects of changes in land-use type on some soil properties in a Mediterranean plateau. Three adjacent land-use types included the cultivated lands, which have been converted from pastures for 12 years, fragmented forests, and unaltered pastures lands. Disturbed and undisturbed soil samples were collected from four sites at each of the three different land-use types from depths of 0–10 cm and 10–20 cm in Typic Haploxeroll soils with an elevation of about 1400 m. When the pasture was converted into cultivation, soil organic matter (SOM) pool of cultivated lands for a depth of 0–20 cm were significantly reduced by, on average 49% relative to SOM content of the pasture lands. There was no significant difference in SOM between the depths in each land-use type, and SOM values of the forest and pasture lands were almost similar. There was also a significant change in soil bulk density (BD) among cultivation (1.33 Mg m−3), pasture (1.19 Mg m−3), and forest (1.25 Mg m−3) soils at depth of 0–20 cm. Only for the pasture, BD of the depth of 0–10 cm was significantly different from that of 10–20 cm. Depending upon the increases in BD and disruption of pores by cultivation, total porosity decreased accordingly. Cultivation of the unaltered pasture obviously increased the soil erodibility measured by USLE-K factor for each soil depth, and USLE-K factor was approximately two times greater in the cultivated land than in the pasture indicating the vulnerability of the cultivated land to water erosion. The mean weight diameter (MWD) and water-stable aggregation (WSA) were greater in the pasture and forest soils compared to the cultivated soils, and didn’t change with the depth for each land-use type. Aggregates of >4.0 mm size were dominant in the pasture and forest soils, whereas the cultivated soils comprised aggregates of the size ≤0.5 mm. I found that samples collected from cultivated land gave the lowest saturated hydraulic conductivity values regardless of soil depths, whereas the highest values were measured on samples from forest soils. In conclusion, the results showed that the cultivation of the pastures degraded the soil physical properties, leaving soils more susceptible to the erosion. This suggests that land disturbances should be strictly avoided in the pastures with the limited soil depth in the southern Mediterranean highlands.  相似文献   

6.
Soil damage, compaction and displacement, during logging or clearing and cultivation affects both soil physical and chemical properties and reduces growth of regenerated or planted tree seedlings. Understanding the factors involved will aid management and set limits for indicators of sustainable management in eucalypt forests. In the first of two glasshouse studies, three Eucalyptus species were grown for 110 days in soils from six forest sites in Tasmania, Australia. Sites sampled ranged from low rainfall dry forest to very high rainfall wet forest. Soil was collected from three soil depths, in 10 cm increments to 30 cm, each packed in pots to four different bulk densities, ranging from that present in undisturbed field sites to that plus 0.17 g cm−3. In the second study Eucalyptus globulus Labill. seedlings were grown in soil collected from disturbed and undisturbed sites, packed to two bulk densities, and fertilized with combinations of N and P. Increasing soil compaction, in Study 1, caused a proportional decrease in final mass of seedlings of up to 25%. Growth on soil from lower horizons (10–30 cm) averaged only 41% of that on topsoil, a significantly greater restriction of growth than that achieved through compaction. It was concluded that topsoil displacement and profile disturbance was a more significant form of soil damage than compaction. Above-ground dry weight of seedlings was most strongly correlated with soil total N but poorly correlated with other macronutrients. Growth of E. globulus seedlings grown on disturbed soils, in Study 2, averaged 30% of that on undisturbed sites. With added P and N on undisturbed sites growth averaged seven times that of the unfertilized seedlings indicating a general deficit of available P and N on the three soils tested. On soils from disturbed areas, there was also a response to fertilizing with N and P together but the response varied on the three soils. The effects of profile disturbance were ameliorated with fertilizer applications on only one of the soils. The results highlighted the importance of retaining topsoil in situ during forest operations.  相似文献   

7.
The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.  相似文献   

8.
Due to its persistence, subsoil compaction should be avoided, which can be done by setting stress limits depending on the strength of the soil. Such limits must take into account soil moisture status at the time of traffic. The objective of the work presented here was to measure soil water changes during the growing period, use the data to calibrate a soil water model and simulate the soil susceptibility to compaction using meteorological data for a 25-year period. Measurements of soil water content were made in sugarbeet (Beta vulgaris L.) from sowing until harvest in 1997 on two sites classified as Eutric Cambisols in southern Sweden. Sampling was carried out at 2-week intervals in 0.1 m layers down to 1 m depth, together with measurements of root growth and crop development. Precompression stress of the soil at 0.3, 0.5 and 0.7 m depth was determined from uniaxial compression tests at water tensions of 6, 30, 60 and 150 kPa and adjusted as a logarithmic function of the soil water tension. Soil water content was simulated by the SOIL model for the years 1963–1988. Risk calculations were made for a wheel load of 8 t and a ground pressure of 220 kPa, corresponding to a fully loaded six-row sugarbeet harvester. Subsoil compaction was expected to occur when the major principal stress was higher than the precompression stress. The subsoil water content was very low in late summer, but increased during the autumn. At the end of August, there was practically no plant available water down to 1 m depth. There was in general good agreement between measured and simulated values of soil water content for the subsoil, but not for the topsoil. In the 25-year simulations, the compaction risk at 50 cm depth was estimated to increase from around 25% to nearly 100% between September and late November, which is the period when the sugarbeet are harvested. The types of simulation presented here may be a very useful tool for practical agriculture as well as for society, in giving recommendations as to how subsoil compaction should be avoided.  相似文献   

9.
Soil compaction affects hydraulic properties, and thus can lead to soil degradation and other adverse effects on environmental quality. This study evaluates the effects of three levels of compaction on the hydraulic properties of two silty loam soils from the Loess Plateau, China. Undisturbed soil cores were collected from the surface (0–5 cm) and subsurface (10–15 cm) layers at sites in Mizhi and Heyang in Shaanxi Province. The three levels of soil compaction were set by increasing soil bulk density by 0% (C0), 10% (C1) and 20% (C2) through compression and hammering in the laboratory. Soil water retention curves were then determined, and both saturated hydraulic conductivity (Ks) and unsaturated hydraulic conductivity were estimated for all of the samples using standard suction apparatus, a constant head method and the hot-air method, respectively. The high level of compaction (C2) significantly changed the water retention curves of both the surface and subsurface layers of the Heyang soil, and both levels of compaction (C1 and C2) changed the curves of the two layers from the Mizhi site. However, the effects of compaction on the two soils were only pronounced below water tensions of 100 kPa. Saturated hydraulic conductivities (Ks) were significantly reduced by the highest compaction level for both sampled layers of the Heyang soil, but no difference was observed in this respect between the C0 and C1 treatments. Ks values decreased with increasing soil compaction for both layers of the Mizhi soil. Unsaturated hydraulic conductivities were not affected by soil compaction levels in the measured water volume ratio range, and the values obtained were two to five orders of magnitude higher for the Mizhi soil than for the Heyang soil. The results indicate that soil compaction could strongly influence, in different ways, the hydraulic properties of the two soils.  相似文献   

10.
Precompression stress has been proposed as a criterion for subsoil compression sensitivity in regulations, limiting mechanical loads by vehicles, trafficking on agricultural and forest soils. In this study we investigated the applicability of this criterion to the field situation in the case of tracked heavy construction machinery. ‘Wet’ and ‘dry’ test plots at three different test sites (soil types: Eutric Cambisol and Haplic Luvisol under crop rotation and Dystric Cambisol under forest) along an overland gas pipeline construction site were experimentally trafficked with heavy tracked machines used for the construction work. The comparison of samples taken from beneath the tracks with samples taken from non-trafficked areas beside the tracks showed that no significant increase in precompression stress occurred in the subsoil. Comparing calculated mean and peak vertical stresses with precompression stress in the subsoil, only little compaction effects could have been expected. Precompression stress was determined by the Casagrande procedure from confined uniaxial compression tests carried out in the laboratory on undisturbed samples at −6 kPa initial soil water potential. Dye tracer experiments showed little differences between flow pattern of trafficked and non-trafficked subsoils, in agreement with the results of the precompression stress, bulk density and macroporosity measurements. The results indicate that Casagrande precompression stress may be a suitable criterion to define the maximum allowable peak stresses in the contact area of a rigid track in order to protect agricultural and forest subsoils against compaction.  相似文献   

11.
Tillage choices affect biochemical properties in the soil profile   总被引：1，自引：0，他引：1  
Intensive conventional farming and continuous use of land resources can lead to agro-ecosystem decline and increased releases of CO2 to the atmosphere as soil organic matter (OM) decays. The aim of this research was to evaluate the influence of varying types and depths of tillage on microbial biomass, C content, and humification in the profile of a loamy-sandy soil in the Mugello valley, close to the Apennine Mountains, in Italy. Soil samples were collected to depths of 0–10, 10–20, 20–30 and 30–40 cm, in the ninth year following introduction of tillage practices. Highest content of all C forms examined (total, extractable and humified) was found at the 0–10 cm depth with minimum tillage (MT) and ripper subsoiling (RS) and at the 30–40 cm depth with conventional tillage (CT). Humified C decreased with depth in soils under MT and RS. None of the tillage systems showed any difference in total N and microbial biomass C in the upper depths, but concentrations were greater below 20 cm in soils subjected to CT, than other tillage systems. Crop production was similar in all tillage systems. Stratification and redistribution of nutrients were consistent with the well known effects of tillage reduction. Total organic C and its distribution in the profile depended on the tillage system employed. MT and RS can be regarded as excellent conservation tillage systems, because they also sequester C.  相似文献   

12.
The relative importance of wheel load and tyre inflation pressure on topsoil and subsoil stresses has long been disputed in soil compaction research. The objectives of the experiment presented here were to (1) measure maximum soil stresses and stress distribution in the topsoil for different wheel loads at the same recommended tyre inflation pressure; (2) measure soil stresses at different inflation pressures for the given wheel loads; and (3) measure subsoil stresses and compare measured and simulated values. Measurements were made with the wheel loads 11, 15 and 33 kN at inflation pressures of 70, 100 and 150 kPa. Topsoil stresses were measured at 10 cm depth with five stress sensors installed in disturbed soil, perpendicular to driving direction. Contact area was measured on a hard surface. Subsoil stresses were measured at 30, 50 and 70 cm depth with sensors installed in undisturbed soil. The mean ground contact pressure could be approximated by the tyre inflation pressure (only) when the recommended inflation pressure was used. The maximum stress at 10 cm depth was considerably higher than the inflation pressure (39% on average) and also increased with increasing wheel load. While tyre inflation pressure had a large influence on soil stresses measured at 10 cm depth, it had very little influence in the subsoil (30 cm and deeper). In contrast, wheel load had a very large influence on subsoil stresses. Measured and simulated values agreed reasonably well in terms of relative differences between treatments, but the effect of inflation pressure on subsoil stresses was overestimated in the simulations. To reduce soil stresses exerted by tyres in agriculture, the results show the need to further study the distribution of stresses under tyres. For calculation of subsoil stresses, further validations of commonly used models for stress propagation are needed.  相似文献   

13.
The fertile, but naturally poorly drained soils of the western Fraser Valley in British Columbia, Canada are located in an area subject to about 1200 mm of rainfall annually. These soils were under intensive conventional tillage practices for years, which contributed to their poor infiltrability, low organic matter, and overall poor structure. Development of tillage practices that incorporate winter cover crops and reduce traffic in spring is required to reduce local soil degradation problems. The objective of this study was to determine short-term responses of soil physical properties to fall and spring tillage (ST) and fall and no spring tillage (NST) systems, both using spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) as winter cover crops. Field experiments were conducted for 3 years following seeding of the winter cover crops in fall 1992 on a silty clay loam Humic Gleysol (Mollic Gleysol in FAO soil classification). Average aeration porosity was 0.15 m3 m−3 on NST and 0.22 m3 m−3 on ST, while bulk density was 1.22 Mg m−3 on NST and 1.07 Mg m−3 on ST at the 0–7.5 cm depth. Neither of these two soil properties should limit seedling and root growth. After ST, mechanical resistance was consistently greater for 500–1000 kPa in NST than in ST, but never reached value of 2500 kPa considered limiting for root growth. The NST system did not increase soil water content relative to ST, with soil water contents being similar at 10 and 40 cm depth in all years. In 2 out of 3 years NST soil was drier at the 20 cm depth than was ST soil. Three years of NST did not result in a significant changes of aggregate stability relative to ST. This experiment showed that limiting tillage operations to the fall did not adversely affect soil physical conditions for plant growth in a humid maritime climate.  相似文献   

14.
The precompression stress value defines the transition from the reloading curve to the virgin compression line in the stress–strain curve, which can be used to quantify the highest load or the most intense predrying previously applied to the soil. Thus, in soils with well-defined structured soil horizons, each layer can be characterized by such mechanical strength. Penetration resistance measurements, on the other hand, can be used to determine total soil strength profiles in the field. The effect of long-term tillage systems on physical and mechanical properties was determined in undisturbed and remolded samples collected at 5 and 15 cm depth, 6 months after applying no-till (NT), chisel plow (CP), and conventional tillage (CT) treatments, along with the application of mineral fertilizer and poultry litter. The compressibility tests were performed under confined conditions, with normal loads varying from 10 to 400 kPa after a defined predrying to −6 or −30 kPa. Penetration resistance was determined in the field, after seeding, in three positions: seeding row (SR), untrafficked interrow (UI), and recently trafficked interrow (TI). No-till system showed greater soil resistance to deformation than tilled treatments, as determined by the higher precompression stress and lower coefficient of compressibility. When original soil structure was destroyed (remolded samples), smaller differences were found. The application of extra organic matter (poultry litter) resulted in a reduction of precompression stress in undisturbed samples. Penetration resistance profiles showed greater differences among tillage treatments in the upper layer of the untrafficked interrow, where NT system showed the higher values. Smaller differences were found in the seeding row (with lower values) and in recently trafficked interrow (with higher values), showing that even traffic with a light tractor after soil tillage reduced drastically the effect of previous tillage by loosening up the soil. On the other hand, the tool used to cut the soil and to open the furrow for seeding, incorporated in the direct seeding machine, was sufficient to realleviate surface soil compaction.  相似文献   

15.
Abstract. Forest soil sustainability and future crop productivity is at risk if mechanised harvesting operations cause soil damage. In UK upland forestry, soil protection is usually provided by placing harvesting residues (brash) over areas where machinery traffic is required. In this study, various thicknesses of brash mat were tested for their ability to reduce compaction of a surface water gley soil at Kielder Forest, Northumberland. Changes in penetration resistance and dry soil bulk density were studied after passes by forest harvesting and timber extraction machinery running on the brash. The study shows that normal harvesting operations caused some soil compaction. However, the brash mat system was shown as important in protecting the soil. Soil under brash mats experienced some compaction to at least 45 cm depth. The thickest brash mat, composed of residues from 10 rows of trees, was unable to prevent compaction completely. Nevertheless, the protective role of the brash mat system was clearly confirmed when compared to timber extraction over bare soil. The point at which compaction has a detrimental effect on the establishment and stability of future tree rotations remains uncertain.  相似文献   

16.
Subsoil compaction is persistent and can affect important soil functions including soil productivity. The aim of this study was to develop recommendations on how to avoid subsoil compaction for soils exposed to traffic by machinery at field capacity. We measured the vertical stress in the tyre–soil contact area for two traction tyres at ca. 30‐ and 60‐kN wheel loads on a loamy sand at field capacity. Data on resulting stress distributions were combined with those from the literature for five implement tyres tested at a range of inflation pressures and wheel loads. The vertical stress in the soil profile was then predicted using the Söhne model for all tests in the combined data set. The predicted stress at 20 cm depth correlated with the maximum stress in the contact area, tyre inflation pressure, tyre–soil contact area and mean ground pressure. At 100 cm depth, the predicted vertical stress was primarily determined by wheel load, but an effect of the other factors was also detected. Based on published recommendations for allowable stresses in the soil profile, we propose the ‘50‐50 rule’: At water contents around field capacity, traffic on agricultural soil should not exert vertical stresses in excess of 50 kPa at depths >50 cm. Our combined data provide the basis for the ‘8‐8 rule’: The depth of the 50‐kPa stress isobar increases by 8 cm for each additional tonne increase in wheel load and by 8 cm for each doubling of the tyre inflation pressure. We suggest that farmers use this simple rule for evaluating the sustainability of any planned traffic over moist soil.  相似文献   

17.
Under conventional farming practices, lime is usually applied on the soil surface and then incorporated into the soil to correct soil acidity. In no-till (NT) systems, where lime is surface applied or only incorporated into the soil to very shallow depth, lime will likely not move to where it is required within reasonable time. Consequently, lime may have to be incorporated into the soil by mechanical means. The objective of this laboratory study was to characterize the effect of lime, incorporated to different depths, on chemical and biological soil properties in a long-term NT soil. Soil samples taken from the 0–5, 0–10, and 0–20 cm depths were analyzed in incubation studies for soil pH, nitrate, CO2 respiration, and microbial biomass-C (MBC). Lime (CaCO3) was applied at rates equivalent to 0, 4.4, 8.8, and 17.6 Mg ha−1. Application of lime to both 0–10 and 0–20 cm depths increased soil pH from about 4.9 by 1, 1.7, and 2.8 units for the low, medium, and high liming rates, respectively. Soil nitrate increased over time and in proportion to liming rate, suggesting that conditions were favorable for N-mineralization and nitrification. Greater respiration rates and greater MBC found in lime-treated than in non-limed soils were attributed to higher soil pH. Faster turnover rates and increased mineralization of organic matter were found in lime-treated than in non-limed soils. These studies show that below-surface lime placement is effective for correcting soil acidity under NT and that microbial activity and nitrification can be enhanced.  相似文献   

18.
Soil compaction is widespread but tends to be most prevalent where heavy machinery is used in landfill sites, agriculture and forestry. Three forest sites strongly disturbed by heavy logging machinery were chosen to test the physical effects of different levels of compaction on soil bacterial community structure and soil functions. Community analysis comprised microbial biomass C and T-RFLP genetic profiling. Machine passes, irrespective of the compaction level, considerably modified soil structural characteristics at two soil depths (5–10 cm; 15–20 cm). Total porosity decreased up to 17% in the severe compaction. Reflected in this overall decline were large decreases in macroporosity (>50 μm). Reduction in macroporosity was associated with higher water retention and restricted gas exchange in compacted soils. The strongest effect was observed in the severely compacted wheel tracks where air and water conductivities were reduced permanently to 10% or even lower of the original conductivities of undisturbed soils. Very slow drainage in combination with a dramatically reduced gas permeability led to unfavorable soil conditions in severely disturbed traffic lanes reflecting the changes in the total bacterial community structures at both soil depths. Additionally, microbial biomass C tended to be lower in compacted soil. Our results indicate that the type of severe treatments imposed at these forest sites may have strong adverse effects on long-term soil sustainability.  相似文献   

19.
The physically defined concept “precompression stress (Pc)” is presented at farm scale, including two operation methods in order to define precaution and critical values for the legislation and executive level according to the German Soil Protection Law. The first step is the prevention of subsoil compaction in general by the definition of the mechanical strength of soils, which is defined by the Pc. This Pc value is used as the precaution value, to ensure site-adjusted land use. The second step is to predict the change of soil functions after exceeding the Pc and furthermore to assess if critical values (test and action values) caused by subsoil compaction are reached or already exceeded. Criteria for the definition of critical values by subsoil compaction concerning crop production are discussed in order to also establish such values in the European Soil Framework Directive. The “Pc” concept, which includes predicted and regionalized “Pc”-maps, was verified on a research farm in the weichselian moraine landscape in Northern Germany for areas resistant or susceptible to soil deformation at the given water content throughout the year. Furthermore, the stress-dependent changes of the air capacity after exceeding the Pc was predicted by pedotransfer functions and linked with the farm soil map. As an additional proof for the validity of the Pc concept, a field experiment on a Stagnic Luvisol was also conducted in order to measure the stress distribution up to 60 cm depth using the Stress State Transducer (SST) system at two different wheel loads (3.3 and 6.5 Mg) using a tractor-pulled mono-wheeler. According to the effective soil strength, the wheel load should not exceed 3.3 Mg at field capacity to avoid subsoil compaction.  相似文献   

20.
The present study described the relationship between growth and soil physico-chemical properties in Eucalyptus camaldulensis (Myrtaceae) and Pinus caribaea (Pinaceae), two important species in Nigerian forest recovery programs. The study sites were located in a 17-year-old plantation in a Northern Nigeria forest reserve. The soils at the study sites were nutrient poor compared with other plantations. Growth of E. camaldulensis was positively correlated with exchangeable K content in soils 0–20 cm deep, and negatively correlated with total N and exchangeable Na in soils 20–150 cm deep. Growth of P. caribaea was positively correlated with available P in soils 0–20 cm deep, and volumetric water content in soils 20–150 cm deep. Soils in the top layers were very hard and plinthite layers were well developed at shallow soil depths at most sites. E. camaldulensis exhibited a comparatively high survival rate, and its growth was comparable to that in other plantations. However, the survival rates of P. caribaea were low and its growth was lower than that in other plantations. The survival rate of E. camaldulensis was lower at sites where plinthite layers were found within 50.8 cm of the surface. These results indicated that E. camaldulensis is suitable for afforestation in Northern Nigeria. However, it is not recommended for sites where the plinthite layer occurs at shallow soil depths.  相似文献   

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