Soil Specific Surface Area Research Articles

Specific surface area of soils with different clay mineralogy can be estimated from a single hygroscopic water content

The soil specific surface area (SSA) is an important variable for soil science and geoenvironmental engineering applications, but traditional measurement methods are difficult and time-consuming. Regression models or pedotransfer functions are often used to estimate SSA from other soil properties (e.g., clay content and cation exchange capacity), but these models do not consider the impact of clay mineralogy. Hygroscopic water content (wh) is intimately linked to these soil properties, which suggests that wh may be a better parameter for SSA estimation. This study (i) proposes regression models that estimate SSA from wh at different relative humidity values (5 to 90%) for kaolinite-rich samples (KA), illite-rich or mixed clay samples (IL/MC), montmorillonite-rich samples (ML), and a combination of all samples (ALL) and (ii) compares the performance of the wh models to other published models that comprise clay, silt and soil organic carbon contents and cation exchange capacity. We found that the sample-specific wh regression models accurately estimated SSA for KA, IL/MC and ML samples. For KA and IL/MC samples, the performance of the KA model (e.g., for adsorption, average RMSE = 10.5 m2/g) and IL/MC model (average RMSE = 21.3 m2/g) were better than the ALL-calibration model (KA: average RMSE = 18.7 m2/g; ML: average RMSE = 22.4 m2/g). For ML samples, similar model performance between the ML-calibration model (average RMSE = 41.4 m2/g) and the ALL-calibration model (average RMSE = 41.1 m2/g) was observed. In addition, the model performance of regression models based on wh was superior to models published in the literature that are based on clay, silt and soil organic carbon contents and cation exchange capacity. Overall, this study confirms that a single measure of wh can provide reliable estimates of the SSA while revealing a significant impact of clay mineralogy on model performance.

Unit Weight of Water in Clayey Soil

A soil water unit weight of 9.8 kN/m3 has been universally considered to quantify soil volumetric phase properties such as void ratio and degree of saturation, but has been found to greatly vary depending on soil type and the volume scale with which it is defined. Recent experimental and theoretical evidence has indicated that the unit weight of soil water can be significantly greater than 9.8 kN/m3 for clayey soils when gravimetric water content is less than 30%. A soil water unit weight as high as 18.8 kN/m3 is evident for some expansive soils at low water content. The significance of abnormally high water unit weight in quantifying soil phase volumes, saturation, and void ratio was experimentally assessed for various clayey soils and theoretically interpreted as a function of water content and soil type. For clayey soils with low liquid limit, average soil water unit weight can be as high as 12.5 kN/m3 for gravimetric water content less than 10%. This leads to an overestimation of liquid-phase saturation and void ratio by as much as 8% if a soil water unit weight of 9.8 kN/m3 is used. For clayey soil with a high liquid limit, the average soil water unit weight can be as high as 18.8 kN/m3 for water content less than 18%, leading to overestimation of liquid-phase saturation by as much as 36% and void ratio by as much as 20% if 9.8 kN/m3 is used. Charts were developed to estimate average soil water unit weight as a function of soil specific surface area and water content, and as a function of liquid limit and water content. The commonly used value of 9.8 kN/m3 for water unit weight can lead to significant errors in estimating phase volumes, void ratio, and saturation for clayey soils.

Contribution of organic carbon to the total specific surface area of soils with varying clay mineralogy

Soil specific surface area (SA) reflects the quantity and quality of the soil mineral and organic fractions. For soil samples that have similar clay mineral types, clay content and or organic carbon (OC) contents are good predictors of SA. However, the magnitude of the OC contribution to SA for different soil types is unclear, particularly since SA varies depending on which method or probe molecule is used to measure it. Consequently, we set out to (i) quantify the contribution of soil OC to total SA for soils with varying clay mineralogy, and (ii) assess the effect of probe molecule (EGME or H2O) and water sorption direction on the contribution of OC to the total SA. We utilized 330 soil samples (clay = 1 to 89 %; silt = 2 to 78 %; OC = 0.03 to 34.9 %) that were grouped according to clay mineralogy and OC content. The total SA was measured using EGME adsorption (SAE) and water adsorption and desorption (SAH2O). The contribution of OC to SA was examined using regression and partial correlation analyses that combined clay, silt, and OC as explanatory variables. Results showed that SAE values were strongly correlated to SAH2O, except for OC-rich soils where SAE was significantly lower than SAH2O. Apart from montmorillonite-rich samples, OC contribution to SAE was smaller than for SAH2O. Organic carbon had a positive contribution to desorption SAH2O for all sample groups, except for montmorillonite-rich samples; OC contribution was 7.5, 10.7, and 13.9 m2/g per %C for illite-rich, kaolinite-rich and OC-rich samples, respectively. There was no significant effect of water sorption direction on the OC contribution to SAH2O. Partial correlation analyses that accounted for clay and silt contents confirmed a negative contribution of OC to SAE or SAH2O for soil samples dominated by montmorillonite clay minerals. We can conclude that for the soil types investigated here (except montmorillonitic soils), OC has a positive contribution to total SA, and the magnitude of the contribution depends on the clay type.

Mechanism of Different Passivating Agents on the Solidification of Heavy Metals in Soil

Through the mechanism study, it can be seen that the three kinds of passivating agents can increase the soil pH value and cation exchange capacity, which is beneficial to the transformation of heavy metals from ion exchange state to residue state. The addition of organic fertilizer can increase the activities of urease and acid phosphatase, and montmorillonite is beneficial to activate the activity of catalase in the soil. MO treatment can simultaneously increase the activities of the three enzymes and increase the absorption of soil carbon, nitrogen and organic phosphorus. Electron microscope scanning results showed that MO effectively increased the connectivity between soil particles and increased the specific surface area of soil. Therefore, the synergistic effect of MO treatment on the passivation of heavy metals is obvious, and the passivation effect is the best.

Specific Surface Area of Plastic Clays from Equilibrium Sediment Volume under Salt Environment

Abstract Specific surface area is one of the crucial surface properties of clay soils. The surface area is used as the surrogate compatibility index and is related to many engineering properties of clays. Accurate estimation of the surface area, Sa, is essential for predicting the saturated and unsaturated characteristics of clays in engineering applications. A simple technique for a routine estimation of the surface area of plastic clays was developed based on the sediment volume in the salt environment. The method utilized equilibrium sediment volume measurement of clay soil in 0.1 N sodium chloride solution and used the theoretical equation for the surface area estimation, which accounts for both the surface and body forces. A comparative assessment of the proposed method with commonly used techniques on 12 clay soils is presented. The proposed method showed a good agreement, qualitatively, with the ethylene glycol monoethyl ether (EGME) and methylene blue methods for the studied soils. The estimated surface area by the proposed method was, however, higher than the existing two methods for the highly plastic clays, such as the bentonites. The relative merits of different methods are discussed in detail. The utilization of water as the probe molecule in the proposed method in a dispersed state of the swollen clay structure ensured greater accessibility to the internal surface. The proposed method was a quick and simple way to estimate the specific surface area of soil with great repeatability. The method is beneficial for routine practice to estimate the surface area of soils and should be readily adopted in the standard practice as an additional method.

The role of biochar particle size and application rate in promoting the hydraulic and physical properties of sandy desert soil

Enhancing the resistance of sandy desert soil to drought and wind erosion is key to controlling aeolian desertification. Using biochar as an amendment can improve soil quality. This study aimed to determine the impacts of biochar particle size and application rate on the hydraulic and physical properties of sandy desert soil. Biochars were produced by pyrolyzing corn straw at 500 °C with limited oxygen. Samples of sandy desert soil were collected from the Tengger Desert in Northwestern China. Tests were designed with three biochar particle sizes (0–0.25, 0.25–1, and 1–2 mm) and five biochar application rates (wt%: 0, 0.5%, 1%, 2%, and 4%). Soil hydraulic and physical properties were characterized by the soil–water characteristic curve, soil porosity, soil specific surface area (SSA), and soil structural index (SI). The results showed that biochar significantly increased the soil porosity and the number of extreme micropores, micropores, and small pores. As a consequence, the saturated soil water content (θs), permanent wilting point (PWP), field capacity (FC), and available water content (AWC) were significantly enhanced. The significant improvement in SI demonstrated that biochar enhanced the soil aggregate stability, therefore, the resistance of sandy desert soil to wind erosion is enhanced. Biochar dosage was a more important factor that influenced the FC, AWC, PWP, SI, and SSA of the soil more than biochar particle size. The properties of θs, PWP, FC, AWC, and SI were all closely related to SSA, indicating that SSA played a key role in the mechanism affecting the response of the soil to biochar application. The significant increase in water retention and aggregate stability of sandy desert soil with added biochar suggests a novel strategy to control aeolian desertification by amending the soil.

Soil available nitrogen and phosphorus contents and the environmental impact factors across different land use types in typical karst rocky desertification area, Southwest China.

In this study, we collected soil samples from four different land use types (forest land, shrub land, grassland and abandoned land) in Huajiang valley of Guizhou Province, a typical karst rocky desertification area in Southwest China. Correlation analysis and redundancy analysis were used to examine the distribution of available nitrogen (N) and available phosphorus (P) in diffe-rent soil layers from 0 to 30 cm and the relationships between soil environmental factors (soil physical indexes, organic carbon components, electrochemical properties, metal oxides and enzyme activities) and the contents of available N and available P. The results showed that the concentrations of soil total N, total P, available N, available P decreased significantly with the increases of soil depth. The concentrations of soil available N and available P in forest land and shrub land were significantly higher than those in grassland and abandoned land, which were significantly positively correlated with soil organic carbon composition, enzyme activity, surface electrochemical properties and amorphous mental oxide while significantly negatively correlated with soil silt and free metal oxides. Results of the redundancy analysis showed that the environmental factors affecting soil availa-ble N and available P of the four land use types were basically the same, with soil particulate organic carbon, total organic carbon and soil specific surface area playing a key role in driving the variations of soil available N and available P. The efficient explanation of variation to soil available N and P contents by soil particulate organic carbon might be due to the reduction of soil nutrient loss by the storage of N and P in organic matter. Except for high enzyme activity and electrochemical properties of forest land and shrub land, the higher soil available N and available P concentrations compared with grassland and abandoned land might be resulted from the inhibition of free iron and aluminum oxides information by higher soil organic carbon content and the reduced adsorption and fixation of N and P by iron and aluminum oxides.

Estimation of soil specific surface area from adsorbed soil water content

AbstractThe adsorbed water content is an attractive predictor for estimation of soil specific surface area (SSA) as its measurement is less laborious and more cost effective than standard laboratory techniques. We analysed the effects of total specific surface area (SSAtot), external specific surface area (SSAex) and internal specific surface area (SSAin) on water vapour sorption on 21 soil samples, and proposed models for estimating SSAex, SSAtot and SSAin from organic carbon content and the slope of soil water vapour sorption isotherm (SL0.5) and water content (WC0.5) at a water activity of 0.5. The results indicated that the variation of correlation coefficients between water content change at 0.05 water activity interval (WCC0.05) and SSAtot with water activity was mainly due to the differences in water vapour adsorption in interlayer spaces at different water activity levels. Furthermore, in the soil water content range from ~0.001 to ~0.03 g g−1 (within the water activity range from ~0.45 to ~0.75), water vapour adsorption was related closely to SSAex. Cross‐validation results on estimated SSAex, SSAtot and SSAin of the 21 samples produced root mean square error (RMSE) values less than 9.39 m2 g−1 and Nash‐Sutcliffe model efficiency coefficients (E) greater than 0.93, suggesting that the proposed models provided reasonable estimates of SSA components. Thus, soil water vapour adsorption data can be applied to simultaneously estimate SSAex, SSAtot and SSAin. Variation of correlation between WCC0.05 and SSAtot with water activity depended on SSAin. Soil water vapour sorption is related closely to SSAex at water activities from ~0.45 to ~0.75. The proposed models yield reasonable estimates of SSAtot, SSAex and SSAin. Adsorbed water content can be used as a predictor for SSA estimation.Highlights Variation of correlation between WCC0.05 and SSAtot with water activity depended on SSAin. Soil water vapor sorption relates closely to SSAex at water activities from ~0.45 to ~0.75. The proposed models yield reasonable estimates of SSAtot, SSAex, and SSAin. Adsorbed water content can be used as a predictor for SSA estimation.

The influence of soil particle size distribution and clay minerals on ammonium nitrogen in weathered crust elution-deposited rare earth tailing

Even after being abandoned for many years, a large number of weathered crust elution-deposited rare earth (WCED-RE) tailings continue to release ammonia nitrogen (AN) pollution into their surrounding environments. However, the influences of particle size distribution and clay minerals on AN pollution caused by these tailings have been insufficiently studied, and its causes are poorly understood. In this study, soil samples at different depths (5, 7, 9, 11 and 14 m) were collected from a rare earth tailing in Ganzhou City, Jiangxi Province, China. Particles were screened by size into six groups (2–1, 1–0.5, 0.5–0.25, 0.25–0.1, 0.1–0.075 and < 0.075 mm), and AN forms were extracted. The results showed that as soil particle size decreases, both soil specific surface area and clay content increase, leading to stronger AN enrichment ability. With increased sampling depth, the distribution of clay across the six particle fractions became more uniform, such that the accumulation of AN in soil with fine particle size was less obvious. Clay minerals with different capacities for AN enrichment vary with sampling depth. This variation is responsible for the profile of AN distribution in the mine, where AN first increases and then decreases as vertical depth is increased. Although AN content was highest at 11 m, water soluble AN content was higher in the upper part of the completely weathered layer (5 and 7 m), which poses a higher environmental risk. This study provides significant information to deepen our understanding of the distribution characteristics of AN and its main influencing factors, as well as a foundation for the prevention and remediation of nitrogen pollution from WCED-RE tailings.

Влияние агромелиоративных мероприятий на удельную поверхность почвы

The article is devoted to the study of the regularity of changes in the specific surface of soil under the influence of agromeliorative measures, mainly irrigation and agrotechnical works carried out in the gray-brown soils of the Absheron Peninsula of Azerbaijan. Based on four years of experiments, it was determined that changes occur in the specific surface of the soil in the plowed layer as a result of the agromeliorative measures taken. Thus, a decrease in the specific surface area was observed in the 0–20 cm soil layer, and an increase in the specific surface area was observed in the 20–40 cm soil layer. In the first year of the experiments, the value of the average specific surface in the 0–20 cm soil layer was 3,098–3,988 cm2/g, and in the 20–40 cm soil layer it was 1,056–3,567 cm2 /g. However, after four years, the value of the special surface was 1,949–3,340 cm2/g in the 0–20 cm soil layer and 3,290–5,023 cm2/g in the 20–40 cm layer. The increase in the specific surface area in the lower layers of the soil is due to the gradual washing of dust, silt and colloidal particles from the plow layer to the lower layers. The reduction of the specific surface in the topsoil leads to the degradation of the topsoil, the deterioration of the water-physical properties, the formation of compaction below the topsoil, and ultimately the reduction of soil fertility. The article makes specific suggestions to prevent this process. It was also identified based on the calculations that the specific surface area of the soil, rich in silt, dust and colloidal particles, is many times larger than the specific surface area of sandy soil. The specific surface area of colloidal silt is 43,000 times larger than the specific surface area of dust and 130,000 times larger than the specific surface area of sand.

Dissolved organic carbon sorption dynamics in tidal marsh soils

AbstractCoastal wetlands are significant sources of dissolved organic carbon (DOC) to adjacent waters and, consequently, exert a strong influence on the quantity and quality of DOC exported to the coastal oceans. Our understanding of the factors that control the exchange of DOC at the tidal marsh‐estuarine interface, however, remains limited. We hypothesize that tidal marsh soils act as a regulator and that their physical characteristics, such as organic carbon content and mineral phase composition, are key controls on DOC exchange between soil surfaces and both surface and interstitial waters. To test this hypothesis, we generated traditional Langmuir sorption isotherms using anaerobic batch incubations of four tidal wetland soils, representing a range of soil organic carbon content (1.77% ± 0.12% to 36.2% ± 2.2%) and salinity regimes (freshwater to mixoeuhaline), across four salinity treatments. Results suggest that the maximum soil sorption capacity and DOC binding affinity increase and decrease with greater salinity, respectively, though the enhancement of maximum soil sorption capacity is somewhat mitigated in soils richer in poorly crystalline iron minerals. Initial natively sorbed organic carbon showed a significant positive correlation with soil specific surface area and K showed a moderate yet significant positive correlation with poorly crystalline iron mineral content. Taken together, these results point to a strong mineralogical control on tidal marsh sorption dynamics and a complex physicochemical response of those dynamics to salinity in tidal marsh soils.

Estimating Atterberg limits of soils from hygroscopic water content

A number of environmental, agronomic and engineering applications require knowledge of the Atterberg limits (liquid limit, LL; plastic limit, PL) and the plasticity index, PI of soils. The tedious and costly nature of standard experimental methods, as well as challenges with measurement repeatability motivated the development of regressions as well as more sophisticated techniques to estimate the Atterberg limits from other properties such as clay content, cation exchange capacity (CEC), and soil specific surface area. The amount of water adsorbed to particle surfaces at relative humidity (RH) < 95% is intimately linked to these soil properties, which suggests that hygroscopic water content (wh) may be a better predictor of the Atterberg limits. The present study (i) proposes regression models that estimate the LL, PL, and PI from wh at different relative humidity values ranging from 10 to 90% and considering water sorption hysteresis, and (ii) compares the performance of the models to other models that comprise clay, silt and organic carbon contents and CEC. For model development, wh was measured by water adsorption and desorption for 168 soil samples that varied widely in terms of geographic origin, clay mineralogy, and soil organic carbon content. The LL and PL were determined with the drop cone penetrometer and rolling device, respectively. Regression models were developed for both sorption directions for nine RH values between 10 and 90%. For 44 independent soil samples, the models estimated LL, PL and PI accurately (e.g., for desorption wh measured at 90% RH, RMSE and r2 values were 6.43% & 0.89; 3.95% & 0.83 and 6.69% & 0.79, respectively). There was no clear effect of sorption direction on the estimation accuracy. The wh determined at higher RH tended to better estimate the Atterberg limits compared to that measured at lower RH. The wh models were superior in estimating LL and PL compared to models that were based on clay content and organic carbon or CEC. For the PI, the models based on CEC performed slightly better than the wh models. Thus, a single measure of wh can provide reliable estimates of the Atterberg limits and PI.

Soil properties governing phosphorus adsorption in soils of Southern Brazil

Southern Brazil is carachterized by soil classes with contrasting mineralogical composition and chemical behavior that directly affect the P adsortion capacity. This study is a first detailed regional assessment of the main factors (including mineralogical composition, total organic C, and specific surface area) that determine P adsorption in 60 representative soils of southern Brazil under natural vegetation. Most soils showed medium to clay texture. Organic C increased with increasing altitude and rainfall but decreasing temperature. Kaolinite, goethite and hematite were the dominant minerals in the highly weathered soils (Ferralsols and Nitisols), associated with smaller amounts of 2:1 clay minerals, quartz and gibbsite. In soils with a textural gradient (Acrisols, Alisols and one Plinthosol), minerals in the clay fraction consisted of kaolinite and quartz together with lower proportions of Fe oxides, 2:1 clay minerals and mica. The less weathered soils (Cambisols, Chernozems, Vertisols and Luvisols) abounded with kaolinite and 2:1 clay minerals in addition to goethite, ferrihydrite and quartz. P adsorption was positively correlated with clay and organic C content and specific soil surface area. The mineral most strongly influencing P adsorption was gothite, and hematite and gibbsite to a lesser extent.

Characteristics of phosphorus adsorption and desorption in erosive weathered granite area and effects of soil properties.

Highly weathered acidic soils tend to have high phosphorus adsorption rates. Studying the differential phosphorus adsorption and desorption characteristics of these soils is of great significance to improve phosphorus utilization efficiency and reduce soil phosphorus loss in agricultural management. Erosive weathered granite soil (TL-Tillage layer, LL-Laterite layer, and SL-Sand layer) in Anji County, Zhejiang Province were selected for batch experiments and phosphorus fractionation test. The soil properties that are generally considered to have a greater impact on phosphorus adsorption and desorption are also studied. Derived from the Langmuir adsorption isotherm, the maximum absorption capacity (Qmax) of phosphorus in TL soil was greater than that in LL and SL soil. With a pH of 4.3-5.0, the three soils have the most phosphorus adsorption. The desorption ratio (Dr) in the SL soil is larger than the LL and TL soil. Six key soil property indicators can fit Qmax and Dr values well. Al-P is the main fraction in the phosphorus adsorption-desorption process. The particle size classification (PSC) method can be used to accurately calculate soil-specific surface area. The results of the soil phosphorus adsorption-desorption test can be used as an explanation of the results of artificial rainfall tests. Our results reveal the differential adsorption-desorption mechanism of eroded weathered granite soil, and provide a reference for selecting soil indicators for soil adsorption-desorption studies in different regions.

Spectroscopy and Water Sorption Can Estimate Soil Specific Surface Area

Spectroscopy and Water Sorption Can Estimate Soil Specific Surface Area

Estimating low eroded sediment concentrations by turbidity and spectral characteristics based on a laboratory experiment.

Automatic and real-time monitoring of sediment concentrations in eroded runoff is an effective way to accurately assess soil erosion process on slopes. It is assumed that low sediment concentrations could be inferred from turbidity and spectral characteristics, which are two simple and economical observation methods, and the soil properties would affect this kind of measurements. Four kinds of soil are used to obtain water samples with low sediment concentrations (0.1-10mg/L), namely, black soil (BS), albic soil (AS), cinnamon soil (CS), and brown soil (BRS). The turbidity and spectral characteristics of the samples are measured to evaluate the relationships by calibration and validation between sediment concentrations and turbidity (method 1), sediment concentrations and reflectance with several transformations (method 2), and sediment concentrations and both indicators (method 3). The influences of soil properties on these relationships are also discussed. The linear relationship between sediment concentrations and turbidity is significant in each sample (method 1). Method 2 has a lower accuracy than method 1, in which the obtained characteristic bands and fitting models are different among samples, with a poor result for BS samples and acceptable results for the other samples. Overall, method 3 has the highest accuracy. The order of simulation accuracy from high to low is generally BS > AS > BRS > CS. The influences of soil properties are obvious and various. The effects of soil median diameter (d50) and specific surface area (SSA) on turbidity coefficients and characteristic spectral bands are not significant, but the soil organic matter (SOC) contents are. The results indicate that measurement of sediment concentration within low ranges by both turbidity and spectroscopic techniques has good accuracy in method 3, and different samples should be calibrated in application due to the effects of various soil properties.

Combining visible near‐infrared spectroscopy and water vapor sorption for soil specific surface area estimation

AbstractThe soil specific surface area (SSA) is a fundamental property governing a range of soil processes relevant to engineering, environmental, and agricultural applications. A method for SSA determination based on a combination of visible near‐infrared spectroscopy (vis‐NIRS) and vapor sorption isotherm measurements was proposed. Two models for water vapor sorption isotherms (WSIs) were used: the Tuller–Or (TO) and the Guggenheim–Anderson–de Boer (GAB) model. They were parameterized with sorption isotherm measurements and applied for SSA estimation for a wide range of soils (N = 270) from 27 countries. The generated vis‐NIRS models were compared with models where the SSA was determined with the ethylene glycol monoethyl ether (EGME) method. Different regression techniques were tested and included partial least squares (PLS), support vector machines (SVM), and artificial neural networks (ANN). The effect of dataset subdivision based on EGME values on model performance was also tested. Successful calibration models for SSATO and SSAGAB were generated and were nearly identical to that of SSAEGME. The performance of models was dependent on the range and variation in SSA values. However, the comparison using selected validation samples indicated no significant differences in the estimated SSATO, SSAGAB, and SSAEGME, with an average standardized RMSE (SRMSE = RMSE/range) of 0.07, 0.06 and 0.07, respectively. Small differences among the regression techniques were found, yet SVM performed best. The results of this study indicate that the combination of vis‐NIRS with the WSI as a reference technique for vis‐NIRS models provides SSA estimations akin to the EGME method.

A statistical model for estimating microwave thermal sampling depth of bare soil

One of the greatest advantages of microwave remote sensing over other remote sensing techniques is penetrability.Quantitatively estimating the sensing depth of passive microwave remote sensing is meaningful for simulation of satellite signals and validation of land surface parameters to estimate the sensing depth of passive microwave remote sensing. In this paper, a simple statistical model for estimating the thermal sampling depth in microwave frequencies of soil was developed and validated.Thermal Sampling Depth(TSD) was introduced to describe the source of the main signals of passive microwave remote sensing. To develop a simple statistical model for estimating the TSD of soil, a theoretical model was introduced to describe the emission characteristics of a three-layer case, which incorporates all multiple reflections at the two boundaries. Based on radiative transfer theory, the total emission of the three layers was calculated. Sensitivity analysis was then performed to demonstrate the effects of the soil properties and frequency on the TSD based on a simulation database covering a wide range of soil characteristics and frequencies. Based on the sensitivity analysis results, a statistical model for estimating TSD was developed. This model can estimate the TSD using four common and easily acquired parameters: soil moisture, temperature, frequency, and soil specific surface area. For validation, a controlled field experiment using a Truckmounted Multi-frequency Microwave Radiometer(TMMR) was designed and performed.The total Root Mean Square Error(RMSE) between the TSD measured in field experiment and estimated using the statistical model was approximately 0.5 cm for the TRMM’s four frequencies.The results indicated that the developed statistical model offers a relatively accurate and simple way to estimate the TSD.

A conceptual model of carbon stabilisation based on patterns observed in different soils

In principle, greenhouse gas emissions can be offset by increasing soil carbon stocks. Full utilisation of that potential, however, requires a good understanding of the controls on carbon stocks to identify factors that can be modified through management changes and distinguish those from factors that are inherent soil properties that cannot be modified. Here, we present a conceptual model of protected (or stabilised) carbon stocks in soils based on observations from two farms in New Zealand, and from a combined soils data set from observations from throughout New Zealand. These data showed that1)When other factors, such as climate, plant cover and pasture management, were identical, soil carbon stocks were highly, and linearly correlated with the soil's specific surface area estimated from soil water adsorption.2)The slopes of these relationships decreased with soil depth.3)Extrapolation of the relationships to zero specific surface area resulted in relatively small intercepts on the soil carbon axis. These intercepts decreased with soil depth.4)The intercepts were considered to correspond to unprotected labile carbon, with highest contents near the soils surface where most carbon inputs are received by soils.5)Together, these observations implied that virtually all protected carbon in the analysed soils was protected by the soil matrix rather than biochemically, and that mineral surface area was the functionally relevant key attribute that defined the soils' protective capacity.6)It implied that protected organic carbon, Cp, in a soil can be described as: Cp=kCinAm/f(T,W,pH,Al,…), where k is a simple constant, Cin is the total carbon inflow rate into the soil, Am is specific surface area, and f(T, W, pH, Al, …) is a specific turn-over rate of protected carbon as a function of temperature, soil water, pH, aluminium concentration, or any other factors apart from soil texture that may affect soil-carbon turn-over rates.These observations improve our understanding of the important carbon-protection mechanisms in the soil, with significant implications for the optimal manipulation of carbon input rates into different soils to maximise overall soil carbon storage. They imply that overall carbon storage of soils could be enhanced by physically transferring any available carbon from soils with low to soils with high specific surface areas.

Evaluation of the effect of modern drainage technologies on the physical properties and productivity of mineral hydromorphic soils

Main features of water regime of Umbric Albeluvisols Abruptic and Gleyic Albeluvisols Abruptic were studied. Two layers of surface water appear in soils in spring and fall, hence, the yields are decreased or crops die. Drainage is shown to eliminate surface water. Plastic drainage causes more intensive drainage effect than ceramic trench drainage in wet years. Regardless of the type of drainage, it is always an additional reason for the deep desiccation of surface soil horizons during the summer drought. Drainage leads to an increase in specific surface area of soils, total soil porosity, number of water stable aggregates, including those in the lower horizons. Favorable conditions for the cultivation of crops, especially for grain crops, are formed on drained soils of the Nonchernozem region.