Ermittlung des Spannungszustandes von Böden aus Werten des Eindringwiderstandes von Sonden

Evaluation of the soil consolidation state by using data from penetration resistance probes Penetration resistance data (EW) from handdriven equipment are easily obtainable because the equipment is simple, cheap, and easily carriable. Measurements are performed quickly without extensive destruction of the site. It is the only method to measure soil strength directly and in situ. Therefore, it is worthwhile to propose an interpretation of the results in order to obtain more conclusive statements on the structural soil state. The procedure applied in our study consists in assigning EW values to the principal stress σ_x and in using an auxiliary construction for the vertical component (σ_z ) as a function of penetration depth. The EW value obtained at the final soil depth is assumed to represent stresses at rest, i.e., K₀ = σ_x/σ_z = 1. Drawing a straight line from this point towards the origin of the coordinates EW and soil depth supplies values of the hydrostatic condition for each depth; e.g., values for σ_z are available for each depth. The coefficient for the equivalent stress at rest (K_0E) per depth can now be calculated simply by comparing the measured EW values with the assumed (hydrostatic) vertical depth function of EW. From a total volume of 29 sets of EW versus depth relations, means and standard deviation of K_0E are presented for arable and forest soils from central Europe. K_0E of forest soils tends to be close to 1 showing approximately normal compaction. In arable sites, K_0E > 2 prevail, indicating precompation. These results confirm the general feasibility of the approach to evaluate the compaction state of soil from EW data. Examples are given to show the K_0E characteristics for special cases of mechanical stress situations.     

Compressive properties of some Swedish and Danish structured agricultural soils measured in uniaxial compression tests

Soil compaction is recognized as a threat to long‐term productivity of agricultural soils and as a cause of environmental problems such as flooding. The use of models to establish strategies for prevention of soil compaction is hampered by lack of model input parameters describing soil mechanical properties. This paper presents the compressive properties N (specific volume at σ = 1 kPa on the virgin compression line), C_c (compression index) and C_r (recompression index) obtained from uniaxial compression testing of 69 individual soil layers and investigates the relationships between these properties and readily quantifiable soil parameters. No correlation was found between compressive properties and soil texture. Instead, N, C_c and C_r were positively correlated to the initial specific volume (v₀). This suggests that compressive properties are more strongly affected by soil structure than by soil texture. Dependency of compressive properties on v₀ could not be expected from classical soil compressive behaviour theory but suggests modifications to the theory of soil unloading‐reloading behaviour. We suggest that the latter is dependent on time between unloading and reloading.     

Roughness of soil fracture surfaces as a measure of soil microstructure

The examination of soil fracture surfaces that are created under tensile stress may reveal a great deal about the internal structural condition of the soil. A simple technique for quantifying the roughness of soil fracture surfaces from a measurement of their topography in cross-section is described. The technique involves calculating the standard deviation of the differences between the measured elevations of soil fracture surfaces and their corresponding running-mean values. The standard deviation, σ_R, is used as a measure of the fracture surface roughness. Advantages of this technique over others are discussed. Two methods for measuring the topography of soil fracture surfaces are presented: a bisection (single transect) method, and a laser scanning (multiple transects) method. The laser scanning method is to be preferred because it requires no sample preparation and enables greater and more rapid replication. Also, fracture surfaces created by applying direct tension in the hands produced values of σ_R that were statistically indistinguishable from those created using indirect tension in a loading frame. This result makes the technique of fracture surface analysis usable for both laboratory as well as field investigations of soil structure. An example of the technique is presented to illustrate the role that air-filled pores play in the brittle fracture of unsaturated soil (air-filled pores are closer together in drier soils and further apart in wetter soils.) A strong positive linear correlation was found between the gravimetric water content, w and σ_R of natural soil clods, which supports the contention that brittle fracture of unsaturated soils under tensile stress occurs at least partly because of the propagation of air-filled pores.     

Long-term cultivation effects on the quantity and quality of organic matter in selected Canadian prairie soils

Sixteen Orthic Chernozemic surface soil samples, one half from virgin prairie and one half from adjacent cultivated prairie (cultivated for 31 to 94 years), were collected from eight sites throughout Southern Saskatchewan, Canada. Samples were analyzed for total organic C and a number of other chemical and physical properties. The virgin and cultivated soils at site No. 4 were selected for more detailed analysis by CP-MAS ¹³C NMR, Curie-point-pyrolysis-gas chromatography/mass spectrometry (Cp-Py-GC/MS), and by pyrolysis-field ionization mass spectrometry (Py-FIMS). Long-term cultivation resulted in large significant decreases in total SOM (soil organic matter), as represented by total soil organic C. There were significant increases in aromaticity of the SOM as a result of long-term cultivation as indicated by CP-MAS ¹³C NMR spectroscopy. This was mainly attributable to the result of cultivation-enhanced degradation of aliphatic C relative to aromatic C. Organic compounds identified in the Cp-Py-GC/MS spectra of the virgin and cultivated soils at site No. 4 consisted of n-alkanes (ranging from C₁₁ to C₂₂) and alkenes (ranging from C_7:1 to C_21:1), with the virgin soil being richer in alkenes than the cultivated soil. Other components identified were cyclic aromatics, carbocyclics, N-containing aromatics, N-heterocyclics, benzene and substituted benzenes, phenols and substituted phenols and substituted furans. The compounds identified appeared to originate from long-chain aliphatics, lignins, polyphenols, aromatics, polysaccharides, and N-containing compounds in the two soils. While qualitatively similar compounds were identified by Py-FIMS in the two soils, the total ion intensity (TII) of the virgin soil was almost 2.5 times as high as that of the cultivated soil. This suggests that cultivation made the organic matter less volatile, either by favouring the formation of higher molecular weight organic matter or by promoting the formation of non-volatile metal-organic matter complexes. The Py-FIMS spectra showed that the virgin soil contained relatively more lignin dimers, lipids, sterols, and n-C₁₆ to n-C₃₄ fatty acids than the cultivated soil. Thus, conversely, the cultivated soil was richer in carbohydrates, phenols and lignin monomers, alkyl aromatics and N-containing compounds, including peptides, than the virgin soil.     

A METHOD OF PREDICTING BULK DENSITY CHANGES IN FIELD SOILS RESULTING FROM COMPACTION BY AGRICULTURAL TRAFFIC

A simplified soil mechanical model was constructed to predict compaction beneath agricultural wheels when running on soils of certain characteristics. Soil strength functions were developed from in situ measurements of field soils and some laboratory measurements. Soil strain was measured by surface sinkage and changes of dry bulk density by gamma-ray transmission methods. Soil stresses were measured by deformable spherical transducers and compared to predicted stresses using equations developed by Söhne. A method of analysis was devised to identify a form of the virgin compression line from field data. Changes of the slope and intercept of this line were monitored over a range of moisture contents for two soils and used in the prediction model. The prediction model was tested against compaction measured during independent experiments at different sites. Good prediction was found for soils of initial dry bulk density greater than 1.1 g cm^?3 and cone resistance greater than 500 kPa, using a 30°, 12.9mm diameter cone. On looser and weaker soils the predicted compaction was often less than measured values. Using the model for simulation of compaction beneath a range of wheels revealed that contact pressure alone can be a misleading guide to compaction. Increases of bulk density below 10cm are considerably influenced by wheel load. The most effective way of reducing compaction requires the use of both a minimum load and a maximum contact area.     

The variation of soil critical state parameters with water content and its relevance to the compaction of two agricultural soils

Examination of the previously published results of laboratory compression tests on a loam and a sandy loam has shown that as the water content and degree of saturation of a soil increase, the gradient of the virgin compression line, expressed in terms of specific volume and log of spherical pressure, increases and its intercept decreases. The water contents of the soils ranged from 5% to 30% and the degrees of saturation ranged from 10% to 40%. For both soils the gradient of the recompression line for previously compressed soils was shown to decrease with decreasing initial specific volume (increasing density) and to approach zero at a specific volume of 1.5 (dry bulk density of 1750 kg/m₃). It was deduced that the position of the critical state line also varies with soil water content and that the critical state theory can be extended to unsaturated soils and therefore be of use in predicting the mechanical behaviour of agricultural soil during cultivation and compaction.     

Structural damage and recovery determined by the colloidal constituents in two forest soils compacted by heavy traffic

The role of colloidal constituents in soil structure and its resistance to compaction was studied in two acid forest soils of contrasting pH, clay type and texture. The soils were trafficked with an eight‐wheel‐drive forwarder, and undisturbed topsoil samples were taken on trafficked and control plots. Shrinkage analysis was used to assess the soil's physical behaviour, and in addition texture, organic carbon content and exchangeable Al³⁺ (Al_ex) and amorphous Al oxide (Al_oxa) contents were determined. The effect of each constituent on the soil's physical properties was assessed with covariance analysis. The hydro‐structural stability and coarse pore (> 150 µm radius) and structural pore volumes of control samples were strongly determined by organic carbon and the forms of Al, whereas the plasma porosity was determined by clay content only. Organic carbon and Al_oxa increased the structural pore and coarse pore volumes and modified their susceptibility to compaction; organic carbon provided a protecting effect, whereas it was the opposite with Al_oxa. We observed contrasting effects of the colloidal constituents and of the behaviour of the pore systems on compaction. The situation is complex and we need to take into account the effects of the colloidal constituents to determine the effects of compaction on the soil's porosity. A simplified approach in which we used the water content at ?10 hPa as a covariate predicted soil bulk density as accurately as with all the analytical covariates, and it seems to be an inexpensive way to assess compaction.     

Aerodynamic roughness of cultivated soil and its influences on soil erosion by wind in a wind tunnel

Serious soil erosion on cultivated soil by wind occurs extensively in semiarid regions. Surface roughness of cultivated soil that can be characterized by aerodynamic roughness length (z₀) has important implications to wind erosion. Here we report the wind tunnel results of aerodynamic roughness lengths of five treated soils and soil wind erosion rates at different z₀ and wind velocities. The results suggest that the diameter of the largest soil clods exposed and uniformly distributed on the soil surface is an important factor that controls aerodynamic roughness length. Negatively related to aerodynamic roughness length under provided wind velocity, wind erosion rate is a function of z₀ and wind velocity for cultivated soil. Erosion rates decreased with aerodynamic roughness length especially when z₀ is smaller than 0.1 cm and increase non-linearly with wind velocity, and that the smaller the aerodynamic roughness is, the more rapid that increase will be. Regression model comprising z₀ and wind velocity is developed for predicting wind erosion rates for cultivated soil, which quantitatively reflects the influences of aerodynamic roughness length on soil erosion at various wind velocities.     

Determination of soil salinity based on WET measurements using the concept of salinity index

We evaluated the Malicki and Walczak model (MW) and its appropriately modification (MMW) in the prediction of the electrical conductivity of the soil solution (σ_p), utilizing the WET dielectric sensor. In the MMW approach, the prediction of σ_p requires determination of the WET‐based salinity index (X_s) and clay and sand contents of the soil. MMW appears to be more effective than MW in all cases except for the cases of finer soils when σ_p > 3 dS m^?1.     

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

Purpose

Soil compaction resulting from mechanisation of forest operations reduces air permeability and hydraulic conductivity of soil and can result in the development of hydromorphic and/or anoxic conditions. These hydromorphic conditions can affect physico-chemical properties of the soils. However, early detection of these effects on mineralogical portion of soils is methodologically difficult.

Materials and methods

To analyse the effects of soil compaction on iron minerals in loamy Luvisol, three compacted and three non-compacted soil profiles up to the depth of 50 cm were collected from an artificially deforested and compacted soils after 2 years of treatment. Soil was compacted with the help of 25 Mg wheeler’s load to increase the dry bulk density of soil from 1.21?±?0.05 to 1.45?±?0.1 g cm^?3. Soil samples were analysed by X-ray diffraction (XRD) and were treated by citrate bicarbonate (CB) and dithionite citrate bicarbonate (DCB) under controlled conditions. Major and minor elements (Fe, Al, Mg, Si and Mn) were analysed by ICP-AES in the CB and DCB extracts.

Results and discussion

It was found that X-ray diffraction is not an enough sensitive method to detect the quick mineralogical changes due to soil compaction. Results obtained from CB-DCB extractions showed that soil compaction resulted in larger CB and smaller DCB extractable elements as compared to non-compacted soil. Labile Fe was found 30 % of total Fe oxides in compacted soil against 10–14 % in non-compacted soils. Compaction thus resulted in Fe transfer from non-labile to labile oxides (s.l.). Results showed that soil compaction leads to the reduction of Fe³⁺ to Fe²⁺. The effects of hydromorphic conditions due to soil compaction were observed up to the depth of 35 cm in forest soil profile. Furthermore, a close association of Al with Fe oxides was observed in the soil samples, while Mn and Si were mainly released from other sources, Mg showing an intermediate behaviour.

Conclusions

Hydromorphic conditions owing to soil compaction affect the mobility and crystallisation process of iron mineral. CB-DCB selective extraction technique, in contrast to XRD technique, can be effectively used to examine the possible effects of soil compaction on iron minerals.

     

Anisotropy of pore functions in structured Stagnic Luvisols in the Weichselian moraine region in N Germany

In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (k_f), and the air permeability (k_a) were measured. The air‐filled porosity (?_a) was determined, and pore‐continuity indices (k_a/?_a, k_a/?_a², N) and blocked porosities (?_b) were derived from the relationship between k_a and ?_a. The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.     

Patterns of Organic Matter Accumulation in Soils of the Semiarid Argentinian Pampas

A-horizons of 48 Haplic Phaeozems and Kastanozems in plain sites of the Semiarid Argentinian Pampas under three contrasting management systems (virgin bushland, permanent pasture and continuous agriculture) were studied. Morphological characteristics, organic carbon and total nitrogen levels and E4:E6 ratios were determined on the assumption that both quantity and quality of organic matter should be related to soil texture of parent materials in this region since other soil forming factors are uniform. The more intensive land use produced an averaged decrease of 7 cm in A-horizon thickness and degradation of soil structure, but little changes in color and properties of boundaries to AC horizons. In virgin soils organic carbon and nitrogen contents correlate with silt + clay fractions (r = 0,92 and 0,99, respectively), while E4:E6-ratios are related to clay contents (r = ?0.69*) confirming the strong influence of soil texture. Agricultural-management and pasture use of soils lead to dispersion of these correlations probably because of differential influence of varying intensities of land use within each management system. Soils under continuous agriculture show lower organic carbon contents than virgin soils only at clay + silt > 40%. Eragrostis curvula-pastures seems to be more effective in restoring organic matter and nitrogen levels in sandy but not in loamy soils with respect to virgin soils. This may be due to a better efficiency of E. curvula-roots in coarse than in fine textured soils to produce humificable residues than the autochthonous grass species.     

IMPACT OF CONTINUOUS SUGAR BEET CROPPING ON POTASSIUM QUANTITY-INTENSITY PARAMETERS IN CALCAREOUS SOILS

One hundred-eighteen surface soil samples (59 samples from cultivated areas and 59 samples from virgin soils) were studied to ascertain if potassium (K) quantity-intensity (Q/I) parameters of the soils are being changed by long-term sugar beet cropping. Long-term cultivation resulted in a significant decline in the equilibrium activity ratio (AR_e ^K) values from 0.012 to 0.0047 (moles/L)^1/2 (a drop of 61%) and from 0.013 to 0.008 (a drop of 38%) in Typic calcixerpts and Typic endoaquepts, respectively. Paired t-test revealed that continuous sugar beet cultivation led to significant changes in the easily exchangeable K (ΔK₀) values from ?0.69 to ?0.28 cmol_c/kg (a rise of 59%) the Typic calcixerepts soils. The highest values for PBC^K were associated with the soil types which had the greatest clay contents and smectite clay minerals. Results suggest that continuous sugar beet cropping caused a great decline in K supplying power of the soils.     

Effects of inorganic speciation on the interpretation of copper adsorption by soils

A previous study with a range of soils indicated that adsorption of copper could not be adequately described by the Freundlich equation. Adsorption curves for all but a highly calcareous soil could be divided into two straight lines with a marked increase in slope at low solution concentrations. A computer program (QELIOS) has now been used to calculate the effects of pH, CO, partial pressure and different inorganic anions on the chemical equilibria of the systems used in the adsorption experiments. At pH 6–8.5, hydrolysed species play a major role in Cu speciation whereas CO^2?₃ species become important only at pH > 8.0. The sensitivity of Cu hydrolysis to pH changes and to total Cu concentration in solution provides a possible explanation for the two surface Freundlich curves for soils of pH 6–7, and for the lack of such double surfaces for soils of pH > 7.     

Characteristics of phosphorus fractions in the soils derived from sedimentary and serpentinite rocks in lowland tropical rain forests,Borneo

ABSTRACT

Soil organic phosphorus (P) is an important P source for biota especially in P-limited forests. Organic P has various chemical formations which differ in bioavailability and these organic P can be degraded by phosphatase enzymes. Here, we report soil P fractions inferred from solution ³¹P-NMR spectroscopy and soil phosphatase activities of two tropical rain forests on contrasting parent materials; sedimentary and ultramafic igneous (serpentinite) rocks. Compared to the sedimentary soils　and previous studies, P fractions of the serpentinite soils have distinctly high proportions of pyrophosphate and scyllo-inositol hexakisphosphate (scyllo-IP₆). The accumulation of pyrophosphate and scyllo-IP₆ may be related to strong sorptive capacity of iron oxides present in the serpentinite soils, which implies a consequent low P availability in the serpentinite soils. Mean value of soil phosphatase activities was higher in the serpentinite soils than in the sedimentary soils, suggesting that biota in these serpentinite forests depend more on soil organic P as a P source.     

Reference bulk density and critical degree-of-compactness for no-till crop production in subtropical highly weathered soils

The concept of degree of compactness (DC), referred to as field bulk density (BD) as a percentage of a reference bulk density (BD_ref), was developed to characterize compactness of soil frequently disturbed, but for undisturbed soil such as under no-tillage critical degree of compactness values have not been tested. The objective of this study was to compare methods to determine BD_ref and limits of DC and BD for plant growth under no-tillage in subtropical soils. Data from the literature and other databases were used to establish relationships between BD and clay or clay plus silt content, and between DC and macroporosity and yield of crops under no-tillage in subtropical Brazil. Data of BD_ref reached by the soil Proctor test on disturbed soil samples, by uniaxial compression with loads of 200 kPa on disturbed and undisturbed soil samples, and 400, 800 and 1600 kPa on undisturbed soil samples, were used. Also, comparisons were made with critical bulk density based on the least limiting water range (BDc LLWR) and on observed root and/or yield restriction in the field (BDc Rest). Using vertical uniaxial compression with a load of 200 kPa on disturbed or undisturbed samples generates low BD_ref and high DC-values. The standard Proctor test generates higher BD_ref-values, which are similar to those in a uniaxial test with a load of 1600 kPa for soils with low clay content but lower for soils with high clay content. The BDc LLWR does not necessarily restrict root growth or crop yield under no-tillage, since field investigations led to higher BDc Rest-values. A uniaxial load greater than 800 kPa is promising to determine BD_ref for no-tillage soils. The BD_ref is highly correlated to the clay content and thus pedotransfer functions may be established to estimate the former based on the latter. Soil ecological properties are affected before compaction restricts plant growth and yield. The DC is an efficient parameter to identify soil compaction affecting crops. The effect of compaction on ecological properties must also be further considered.     

土壤紧实度与土块分配对水稻生长的影响及耕作方法的调节

本文就苏南地区二种粘质水稻土的土壤紧实度和土块组成对水稻生长的影响进行了研究,并对不同方法耕作后耕层土块的组成状况进行了观测,结果指出:土壤紧实度和土块/细土比例的不同对水稻生长有明显的影响,土壤紧实度对水稻生长的影响是通过土壤对根的机械阻力,抑制土壤养分的转化及水分物理特性的改变所致;而土块组成的影响可能主要是影响土壤养分的转化。研磨细了的土壤转化成NH₄-N的量最高,土块大于1厘米者对NH₄-N的产生受到严重抑制,因此认为,春耕后耕层中小于1厘米的土块是评定春耕质量的一个重要指标,耕层土块大于8厘米时妨碍栽秧操作,8-4厘米者影响次之,1-4厘米者对栽秧无影响。对于要获得较小土块组成的耕作质量,旋转耕作效果最好,机耙最差,但土壤经过充分晒垡后,各种耕作方法均可获得较好的相同效果,这时,对合适机具的选择主要可从经济效益考虑。渍水条件下土垡经过挤压受损后,可使土块膨软,这或对土壤养分的释放有利,故一般用于春耕机具,只考虑其切割效果而不同时考虑挤压作用是不足的。     

Effect of Induced Soil Compaction on Changes in Soil Properties and Wheat Productivity under Sandy Loam and Sandy Clay Loam Soils: A Greenhouse Experiment

The continuous use of heavy machinery and vehicular traffic on agricultural land led to an increase in soil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. A pot experiment was conducted under greenhouse conditions to study the effects of induced soil compaction on growth and yield of two wheat (Triticum aestivum) varieties grown under two different soil textures, sandy loam and sandy clay loam. Three compaction levels [C₀, C₁, and C₂ (0, 10 and 20 beatings)], two textural classes (sandy loam and sandy clay loam), and two genotypes of wheat were selected for the experiment. Results indicated that induced soil compaction adversely affected the bulk density (BD) and total porosity of soil in both sandy loam and sandy clay loam soils. Compaction progressively increased soil BD from 1.19 Mg m^?3 in the control to 1.27 Mg m^?3 in C₁ and 1.40 Mg m^?3 in C₂ in sandy loam soil while the corresponding increase in BD in sandy clay loam was 1.56 Mg m^?3 in C₁ and 1.73 Mg m^?3 in C₂ compared to 1.24 Mg m^?3 in the control. On the other hand, compaction tended to decrease total porosity of soil. In case of sandy loam, porosity declined by 5% and 17% in C₁ and C₂, respectively, and declined in sandy clay loam by 29% and 54%, respectively. Averaged over genotypes and textures, shoot length decreased by 15% and 26% at C₁ and C₂, respectively, and straw yield decreased by 21% and 61%, respectively. The compaction levels C₁ and C₂ significantly decreased grain yield by 12% and 41%, respectively, over the control. The deleterious effect of compaction was more pronounced on root elongation and root mass, and compaction levels C₁ and C₂ decreased root length by 47% and 95% and root mass by 41% and 114%, respectively, over the control. Response of soil texture to compaction was significant for almost all the parameters, and the detrimental effects of soil compaction were greater in sandy clay loam compared to sandy loam soil. The results from the experiment revealed that soil compaction adversely affected soil physical conditions, thereby restricting the root growth, which in turn may affect the whole plant growth and grain yield. Therefore, appropriate measures to avoid damaging effects of compaction on soil physical conditions should be practiced. These measures may include soil management by periodic chiseling, controlled traffic, conservation tillage, addition of organic manures, and incorporating crops with deep tap root systems in a rotation cycle.     

Biodegradation kinetics of monosaccharides and their contribution to basal respiration in tropical forest soils

Low molecular weight (LMW) organic compounds in soil solution are easily biodegradable and could fuel respiration by soil microorganisms. Our main aim was to study the mineralization kinetics of monosaccharides using ¹⁴C-radiolabelled glucose. Based on these data and the soil solution concentrations of monosaccharides, we evaluated the contribution of monosaccharides to basal respiration for a variety of tropical forest soils. Further, the factors controlling the mineralization kinetics of monosaccharides were examined by comparing tropical and temperate forest soils. Monosaccharides comprised on average 5.2 to 47.7% of dissolved organic carbon in soil solution. Their kinetic parameters (V _max and K_M ), which were described by a single Michaelis-Menten equation, varied widely from 11 to 152?nmol?g^?1?h^?1 and 198 to 1294?µmol?L^?1 for tropical soils, and from 182 to 400?nmol?g^?1?h^?1 and 1277 to 3150?µmol?L^?1 for temperate soils, respectively. The values of V _max increased with increasing microbial biomass-C in tropical and temperate soils, while the K_M values had no correlations with soil biological or physicochemical properties. The positive correlation between V _max values and microbial biomass-C indicates that microbial biomass-C is an essential factor to regulate the V _max values in tropical and temperate forest soils. The biodegradation kinetics of monosaccharides indicate that the microbial capacity of monosaccharide mineralization far exceeds its rate at soil solution concentration. Monosaccharides in soil solution are rapidly mineralized, and their mean residence times in this study were very short (0.4–1.9?h) in tropical forests. The rates of monosaccharide mineralization at actual soil solution concentrations made up 22–118% of basal respiration. Probably because of the rapid and continuous production and consumption of monosaccharides, monosaccharide mineralization is shown to be a dominant fraction of basal respiration in tropical forest soils, as well as in temperate and boreal forest soils.