An appraisal of the problems in classifying saline-sodic soils of the indo-gangetic plain in NW India

Most of the salt-affected soils of the Indo-Gangetic plain in NW India do not find suitable places in the 1970 U.S. system of soil classification. According to the current class definitions, soils with high salts, ESP, pH, chromas and yellower hues key out as Typic or Aquic Calciorthids, Camborthids and Haplustalfs which does not spell out their saline-sodic nature. For land-use recommendations, the authors believe it will be useful to set these soils apart at some high categoric level in the system.It is proposed that the structural requirements for the natric horizon be modified to include horizons with high ESP (? 40) but having simple blocky structure with or without tongues of eluvial material. New subgroups, viz. Natric, within the orders of Inceptisols, Alfisols and Aridisols is suggested for the high sodium-saturated soils lacking natric horizons. For similar practical considerations, the high concentrations of salts in soils when associated with high ESP pose problems in leaching and consequently new subgroups, viz. Salic and Salic Natric, within the orders of Aridisols and Alfisols are suggested.The modifications proposed not only place more emphasis on the saline-sodic nature of these soils but also result in better groupings for practical land use.     

Viscoelastic Behavior of Vertic Solonetz in the Kamennaya Steppe

Eurasian Soil Science - The aim of this work is to determine viscoelastic behavior parameters of soil pastes and micromonoliths of natric and vertic horizons in the profile of Vertic Solonetz from...     

土壤遥感自动分类与制图的初步试验

自从美国通过所发射的第一、二、三颗资源卫星获得了大量的航天遥感资料以来,很多国家都在利用这些资料进行土壤自动分类与制图的试验,企图用以提高土壤调查制图工作的质量与速度。但从所发表的资料看来,均没有说明所得最后结果是否能满足所需精度的要求^[1,2,5]。     

Saline-alkali soils of Russia

Diagnostics, methods of evaluation, and geography of saline-alkali (soda) soils are discussed. The saline-alkali soils include soils of different genetic types with the following chemical properties: the pH of the water suspensions equal to or higher than 8.5; the total alkalinity exceeding 1.4 meq/100 g of soil and the sum of water-soluble calcium and magnesium; and the presence of soluble “alkaline” salts in the soil profiles, the hydrolysis of which results in the alkaline reaction of the soils. The chemical properties of the saline-alkali soils are largely related to the presence of soda (Na₂CO₃, NaHCO₃) in the soils. According to their morphological properties, saline-alkali soils are divided into two groups: alkaline soils with an undiferentiated profile and without a morphologically pronounced solonetzic (natric) horizon, and alkaline soils with a pronounced natric horizon (solonetzes). Solonetzes, in turn, are divided into (a) alkaline solonetzes (with soda or with soda and neutral salts), (b) solonetzes salinized with neutral salts (saline soils) with increased alkalinity in the solonetzic and lower lying horizons, (c) saline solonetzes throughout the profile, and (d) leached solonetzes containing no soluble salts in the profile and almost no exchangeable sodium in the soil exchange complex (SEC) (“dead” solonetzes). The latter two groups of solonetzes cannot be ranked among the alkaline soils. The alkalinity of the saline-alkali soils under study is due to carbonate and bicarbonate ions (carbonate alkalinity), organic acid anions (organic alkalinity), and borate ions (borate alkalinity). The carbonate alkalinity is due to both soda (Na₂CO₃, NaHCO₃) and CaCO₃.     

Influence of cattle trampling on preferential flow paths in alkaline soils

Abstract. Preferential flow paths (PFP) are important in water and solute movement through soils, especially in regions where vertical water movements predominate, such as the flooding Pampa (Argentina). The impact of grazing on PFP and its interactions with other properties were studied in three soils with natric horizons in the flooding Pampa using an iodide colouring technique. In the soil with a mollic horizon (Typic Natraquoll), % PFP was decreased by trampling but was later restored by shrink-swell. In the Typic Natraqualf, the most alkaline of the studied soils, % PFP was very small under both grazed and ungrazed conditions. In a coarser textured soil (Mollic Natraqualf) trampling did not affect % PFP. The % PFP of the Ah horizons increased with increasing organic carbon and sand contents and decreased as clay content, pH and sodium adsorption ratio (SAR) increased. The Bt horizons had small % PFPs and were not affected by cattle trampling.     

Water,salt and sodium dynamics in a Natraquoll in Argentina

The influence of soil and environmental factors on water and salt dynamics in a typic Natraquoll of the center of the Flooding Pampa (Argentina) was studied. In phreatimeters, the water table reached the soil surface during floods, but in the soil profile it was never above the bottom of the B31 horizon (0.65 m). This horizon and the over-laying B22 one showed a permanent unsaturation. The A1, B1 and B21 horizons, however, often became saturated with water.The typical floods in the region are caused by the accumulation of rainwater on the previously saturated upper horizons. Simultaneously, phreatic water undergoes an abrupt increase in electrical conductivity (ECw). These saline peaks (ECw of up to 45.00 dS m⁻¹) caused the immediate salinization of the deep horizons, probably by diffusion. The arrival of salts at the soil surface was episodic and by convection. However, salt leaching prevailed in the course of time in the upper horizons. The soil saturation extracts showed a balanced proportion of anions, but among cations, Na⁺ prevailed over Mg⁺⁺, Ca⁺⁺ and K⁺. Soil alkalinity was low and with some significant variations in the surface horizons, that depended on episodic salt rises or salt leaching processes. In the deep horizons soil remained permanently natric.This dynamic balance of water and salt showed that, in this part of the region, the soil profile exhibits two zones which are relatively independent of each other. Each represents different stages of the evolution as stated by Gedroiz's theory. The deep horizons undergo a continuous salinization and alkalinization process. The upper horizons tend to be similar to zonal soils. The slight halomorphism in this profile zone is due to the episodic salt rises.     

流域减沙效益拓扑分析──以延河流域为例

该以流域治理前径流站实测输沙值为依据，运用拓扑分析法预测流域治理后理输沙值，与治理后实测输沙值对比，求得流域上垫面及坡面减沙效益。并以延河流域为例，与水保，水方法对照，取得令人满意的效果。     

“MIRSED” towards an MIR approach to modelling hillslope soil erosion at the national scale

This paper reports a new methodology for assessing regional and national patterns of hillslope scale soil erosion rates in the UK using a MIR (minimum information requirement) version of WEPP (Water Erosion Prediction Project) known as MIRSED. WEPP is parameterised using a national coverage, environmental database containing topographic, soil, land management and climate variables for all hillslopes within each grid cell to be modelled. The MIRSED matrix summarises the behaviour of WEPP in a multi-dimensional parameter space, allowing results to be queried using a subset of key, spatially variable parameters to produce an averaged hillslope soil erosion response from each 1 km² grid cell. The approach is demonstrated for the Great Ouse catchment, Cambridgeshire, UK and highlights highest hillslope erosion rates of 2.2 t ha⁻¹ year⁻¹ associated with steepest slopes, erodible soils and management practices that leave the soil exposed for critical times of the year. A mean soil erosion rate of 0.4 t ha⁻¹ year⁻¹ is predicted from hillslopes across the catchment which compares well with observed data collated at different scales, using contrasting measurement techniques.     

Defoliation and fertiliser influences on the soil microbial community associated with two contrasting Lolium perenne cultivars

The influence of repeated defoliation on soil microbial community (SMC) structure and root turnover was assessed in two contrasting Lolium perenne cultivars (AberDove and S23) grown in fertilised (+F) and non-fertilised (NF) soil. BiOLOG sole carbon source utilisation profiles (SCSUPs) indicated consistently greater potential carbon utilisation in defoliated (+D) compared to non-defoliated (ND) soils regardless of cultivar and fertiliser, and was accounted for in a variety of substrate groups (sugars, carboxylic, amino and phenolic acids). Potential carbon utilisation was also stimulated in +F compared to NF soils, primarily through increased potential utilisation of carboxylic acids. PLFA indicators for the bacterial biomass did not significantly differ between cultivar, soil fertilisation, or defoliation. Defoliated swards grown in fertilised soil (+F+D) had a higher fungal:bacterial ratio and a greater bacterial stress index (cy19:0/18:1w7c), compared to that of +F ND, NF ND and NF+D, and regardless of cultivar. Overall SMC structure (canonical variate (CV) analysis of PLFAs) discriminated based on cultivar, defoliation and soil fertilisation. Primary discrimination of the SMCs could be related to differences in root density and total plant biomass, and in the case of NF soils, secondary community shifts, evident with defoliation, related to root disappearance over the growing season. Despite the strong common effects of defoliation, and to a lesser extent soil fertilisation, cultivar specific drivers of the soil microbial community were maintained, resulting in consistent, but subtle, discrimination of the SMC associated with the contrasting L. perenne cultivars.     

Kinetics of Soil Urease in Four Agricultural Soils Affected by Urease Inhibitor PPD at Contrasting Moisture Regimes

An incubation test was conducted on four agricultural soils to investigate effects of phenyl phosphorodiamidate (PPD) on soil urease kinetics at contrasting moisture regimes with contrasting fertility levels. The PPD made the Michaelis constant (Km) increase and the maximum enzyme reaction velocity (Vmax) decrease, behaving as a mixed inhibitor. With incubation time, Km first increased and then decreased under saturation condition, whereas it decreased under field-moist condition, the opposite of the changes of Vmax. Compared with black soil and albic soils, brown and cinnamon soils had larger Km and lower Vmax and Vmax/Km ratios, indicating that the effectiveness of PPD was greater in soils with low fertility. Compared with brown soil and cinnamon soil, black soil and albic soil showed more increases in Km and decreases in Vmax. To apply PPD under waterlogged, saturated, and low-fertility conditions could be a reasonable way to increase fertilizer nitrogen (N)–use efficiency.     

Quantifying the impact of microbes on soil structural development and behaviour in wet soils

There is evidence that microbial populations play an important role in altering soil pore geometry, but a full understanding of how this affects subsequent soil behaviour and function is still unclear. In particular the role of microorganisms in soil structural evolution and its consequence for pore morphological development is lacking. Using a combination of bio-chemical measurements and X-ray Computed Tomography (CT) imaging, a temporal comparison of microscale soil structural development in contrasting soil environments was made. The aim was to quantify the effect of microbial activity in the absence of other features likely to cause soil deformation (e.g. earthworms, roots etc.) on soil structural development in wet soils, defined by changes in the soil porous architecture i.e. pore connectivity, pore shape and pore volume during a 24 week period. Three contrasting soil textures were examined and changes compared between field soil, sterilised soil and a glucose enhanced soil treatment. Our results indicate that soil biota can significantly alter their microhabitat by changing soil pore geometry and connectivity, primarily through localised gaseous release. This demonstrates the ability of microorganisms to modify soil structure, and may help reveal the scope by which the microbial-rich rhizosphere can locally influence water and nutrient delivery to plant roots.     

Increased Carbon Stabilization in Australian Ferrosol with High Carbon Saturation Deficit

The concept of carbon (C) saturation implies that soils have a finite capacity to store C in a stable form, depending on their silt + clay content. We hypothesized that the stabilization of added organic C would be low in C saturated soil. We tested experimentally the influence of C saturation deficit on stabilization of added grass residue. We incubated 12 highly weathered, oxic soil samples collected from three contrasting land uses (i.e. cropping, improved pasture, and forest) with grass residue for 8 months. Carbon saturation deficit of the forest soils was lower than pasture and cropping soils. After incubation, we found increases in silt + clay associated C in grass residue treatment positively correlated with C saturation deficit of soils. Our results suggest that stabilization of added C was high in soil with low C saturation level and hence higher C saturation deficit.     

New indices for quantifying the resistance and resilience of soil biota to exogenous disturbances

The stability (resistance and resilience to disturbance) of a soil system is a key factor influencing ecosystem properties and processes. To compare the stability of different systems, it is necessary to have indices that provide a relative quantitative measure of both the resistance and resilience of a response variable in all possible scenarios. However, the indices currently in use are frequently unable to do this, or are difficult to interpret. Here, we present new indices that avoid these problems. We compare our indices with previously published indices of stability, and also test their performance by using a real data set. We show that our indices accurately represent the response of soil properties (e.g. soil microbial biomass) to a disturbance, and that they are capable of determining differences in stability between contrasting soils.     

Trivalent metal (Cr, Y, Rh, La, Pr, Gd) sorption in two acid soils and its consequences for bioremediation

The recent addition of trivalent metals to soil and their subsequent movement within the biosphere are of concern. For this reason, the sorption of chromium (Cr), yttrium (Y). rhodium (Rh), lanthanum (La), praseodymium (Pr) and gadolinium (Gd) in two contrasting acid soils has been determined. Except for Rh, the sorption of the other trivalent metals conformed well to the Langmuir equation with derived sorption parameters similar for all the trivalent species tested. Calculation of the buffer powers indicated that under both small (0·01 mmol kg^?1) and large (1 mmol kg^?1) trivalent metal soil loadings > 99·5% of the metals will be associated with the exchange phase with small quantities present in the bulk soil solution (<0·5%). It seems that the slight availability of metals within the bulk soil solution will slow the rate of trivalent metal bioremediation of contaminated sites.     

Soil Health and Soil Fertility Assessment by the Haney Soil Health Test in an Agricultural Soil in West Tennessee

The Haney Soil Health Test (HSHT) is a recent approach to quantify soil health by focusing mostly on soil biology. It uses a new extractant (H3A) for the extraction of plant available nutrients, a new method of soil respiration measurement (24-hr CO₂ burst) using Solvita® gel system, and a new approach in determining bioavailable carbon (C) and nitrogen (N) namely water extractable organic C (WEOC) and water extractable organic N (WEON). A soil health score is calculated by combining Solvita® respiration, WEOC, and WEON data. The objective of this study was to test the feasibility of HSHT to detect the management-induced changes in soil nutrient levels and soil health in the production systems of west Tennessee. We tested soils collected from a cover crop field trial established in 2013 on a no-till corn (Zea mays L.) – soybean [Glycine max (L.) Merr.] rotation. Compared to Mehlich-1 and Mehlich-3, H3A extracted the lowest amount of soil extractable phosphorus, potassium, calcium and magnesium. Neither the soil health score nor its component parameters showed significant differences between cover crop treatments and the control. In addition, the Solvita® CO₂ data did not provide a reliable estimation of potentially mineralizable N. Overall, the HSHT did not detect differences in soil health due to cover cropping in west Tennessee. We conclude that HSHT, though a promising concept due to its focus on linking soil biology with soil fertility and soil health, may need extensive field evaluation and refinement in contrasting soils and climates across the US.     

The application of the FAO and US soil taxonomy systems to saline soils in relation to halophytic vegetation in SE Spain

Twenty-three pedons from six salt marshes in SE Spain, occurring under a semiarid Mediterranean climate, were classified according to various FAO and USDA Soil Survey Staff (SSS) systems. In each salt marsh, the sampling sites were selected to represent seven different plant communities. For the plant communities studied, less diversity of soil classes was observed at the Unit level using the 1998 version of the FAO soil classification system than the 1994 edition and less at the Great Group level for the 1996, 1998 and 1999 versions of the USDA system than the 1992 version. The FAO 1988 version defines the characteristics of these soils better than the 1994 edition because the former includes the possibilities of classifying at the third level and of using salic and sodic phases. The 1998 version offers greater possibilities for expressing the characteristics of these soils, but two considerations would improve the results: (i) the use of the term Hyposalic instead of Endosalic in the Calcisols group; (ii) the possibility of using the petrocalcic horizon in the Solonchak group. The main shortcomings of the 1996 and 1998 versions of the USDA system for classifying these soils are: (i) the lack of a class to indicate a high concentration of salts in the Mollisol Order independently of the presence of a natric horizon and/or aquic conditions; (ii) failure to indicate the existence of a petrocalcic horizon at the Salids Great Group level. These two problems can be overcome in the 1999 version by the use of the adjectives Halic and Petrocalcic, respectively.     

Effects of long-term grassland management on the chemical nature and bioavailability of soil phosphorus

Relationships between the relative solubility of soil phosphorus (P) and short-term plant P uptake were investigated using soils obtained from a field trial that had been maintained under contrasting mowing regimen (no mowing, mowing with clippings left, mowing with clippings removed) for 15?years. In a glasshouse pot experiment, P uptake by red clover and Italian ryegrass was found to be 40% lower for the clippings removed treatment compared with the no mowing treatment, which was consistent with the fact that concentrations of readily extracted inorganic P were 42% lower in the clippings removed treatment soil. However, P uptake was 51–54% higher for the clippings left treatment soil compared with no mowing, despite the fact that levels of readily extracted soil inorganic P were similar in both treatments. This indicated that biological and biochemical processes associated with enhanced mineralisation of organic P and turnover of P through the microbial biomass made a greater contribution to increased plant P uptake in the clippings left soil compared with the other treatments. These findings highlight the importance of soil biological processes in determining the P nutrition and productivity of managed grasslands.     

Method to quantify root border cells in sandy soil

Root border cells are cells that detach from the growing root cap, and serve both physical and biological roles in the rhizosphere. Most work on border cells has been confined to agar, or hydroponic culture, because of the difficulty in separating them from soil particles. We present a new method to separate the root border cells from soil, and quantify border cell numbers in non-sterile sandy loam soil at contrasting matric potentials (−20 and −300 kPa). Recovery rates of 90±1% were achieved using a combination of surfactants, sonication, and centrifugation. Root border cell numbers in the dry soil (1.4×10³ after 24 h) were significantly decreased as compared with those in the wetter soil (1.7×10³ after 24 h). Possible reasons for the decreased release of border cells are discussed.     

Aggregation and carbon storage in silty soil using physical fractionation techniques

Soil texture and degree of aggregation affect the stabilization of organic matter. We studied their influences in silty soils using samples from two field experiments with contrasting long‐term use (cropped versus bare fallow). The cropped soil had a larger organic C content than the bare fallow, and allowed us to compare a soil with pools of organic C differing in turnover time with a soil dominated by the passive organic C pool. Increasingly dispersive treatments applied to the soils yielded aggregates of various sizes, stabilities, and organic matter contents. We found an intimate interaction between soil structure and organic matter by demonstrating that aggregation is hierarchical and that active pools of organic matter are responsible for this hierarchy. Microaggregates were found to consist of a constant ratio of clay to silt particle‐size fractions. We propose that such a property be used to estimate true microaggregation and aggregate stability by estimating the amount of soil material dispersed by a given treatment. Organic matter associated with clay is confirmed as an important sink of long‐term stabilized C, and it appears to have been increasingly preserved when in increasingly larger aggregates. However, most of the soil mass and associated organic C is in smaller aggregates. We hypothesize that the physical protection within macroaggregates does not directly control long‐term stabilization of organic C in the soil, but rather contributes indirectly through the time and local conditions it offers for organic matter to gain chemical or physico‐chemical protection by interacting with the soil environment.     

Extractability of Cu in Alkaline Biosolids-Amended Soils as Influenced by γ-Irradiation

An incubation experiment was conducted to investigate the microbial biomass associated Cu in four contrasting soils to which an alkaline stabilised sewage sludge cake was applied. The organisms of sludgeamended and control soils were killed using γ-irradiation technique, and the aqueous and acid-extractable Cu concentrations were determined. Addition of the sludge product increased significantly the concentration of both the aqueous and dilute HOAc-extractable Cu in all the irradiated soils compared to the non-sterilised sludge/soil mixtures, but the increase was more pronounced in the dilute acid-extractable Cu, indicating that the Cu rendered extractable in water and dilute acetic acid by γ-irradiation existed in the both soil liquid and solid phases. The additional increase in extractable Cu following the biocidal treatment is likely to be due to release of Cu from the same fraction of soil microbial biomass.