Composition and stability of soil aggregates in Fluvisols under forest,meadows, and 100 years of conventional tillage

Conversion of meadow and forest ecosystems to agricultural land generally leads to changes in soil structure. This comparative study presents the composition and stability of structural aggregates in humus horizons (0–30 cm) of noncarbonate silty‐clay Fluvisols in the Kolubara River Valley, W Serbia. Aggregates collected from under a native forest were compared to aggregates from meadows and arable fields which underwent crop rotation for > 100 y. The results show that size distribution and stability of structural aggregates in the humus horizons of arable soil are significantly impaired due to long‐term anthropogenization. In the humus horizons, the content of the agronomically most valuable aggregates (0.25–10 mm) decreased by a factor of ≈ 2, from 68%–74% to 37%–39%, while the percentage of cloddy aggregates (>10 mm) increased by a factor of ≈ 2, from 23%–31% to 48%–62%, compared to forest aggregates. The long‐term‐arable soil had significantly (p < 0.05) lower aggregate stability, determined by wet sieving, than meadow and forest soils. The lowest aggregate stability was found in aggregates > 3 mm. Their content is ≈ 2.5–3 times lower in arable soil (13%–16%) than in forest soil (32%–42%) at a depth of 0–20 cm. The largest mean weight diameters of dry aggregates (dMWD) with a range between 12.6 and 14.7 mm were found in arable soil, vs. 9.5–9.9 mm in meadow and 6.5–8.3 mm in forest. The arable soil had significantly lower mean weight diameters of wet‐stable aggregates (wMWD) and a lower structure coefficient (Ks) than forest and meadow soils. The dispersion ratio (DR) of arable soil was significantly higher than that of forest and meadow soils. Forest and meadow showed a significantly higher soil organic‐matter content (SOM) by 74% and 39%, respectively, compared with arable soil, while meadow uses decreased the SOM content by 57% compared with forest at a depth of 0–10 cm. In conclusion, the results showed that long‐term conventional tillage of soils from natural forest and meadow in the lowland ecosystems of W Serbia degraded soil aggregate–size distribution and stability and reduced SOM content, probably resulting in lower productivity and reduced crop yields.     

Effect of the biota diversity on the composition of low-molecular-weight water-soluble organic compounds in southern tundra soils

Water extracts from the organic horizons of southern-tundra loamy permafrost-affected soils (a surface-gleyed tundra soil, a surface-gleyed soddy tundra soil (Haplic Stagnosols (Gelic)), and a peaty tundra soil (Histic Cryosol (Reductaquic)) and their undecomposed moss layers have been analyzed. The total weight concentration of the cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) determined by the atomic absorption method reaches 20 mg/dm³ in the organic horizons and 40–90 mg/dm³ in the undecomposed moss layers. Potassium and calcium ions dominate in all the organic horizons (80–90% of the total weight); potassium ions prevail in the mosses (about 70%). The weight concentration of carbon in the water-soluble organic compounds is 0.04–0.07 g/dm³ in the organic horizons and 0.20–0.40 g/dm³ in the undecomposed moss layers. The content of low-molecular-weight organic compounds (alcohols, carbohydrates, and acids) identified by gas chromatography and chromatomass spectrometry is 1–30 mg/dm³ in the organic horizons of the soils and 80–180 mg/dm³ in the mosses, which does not exceed 26% of the total organic carbon in the extracts.     

黄土高原淋溶土黏粒、氧化铁与颜色的关系及发生学解释——以山西土系调查的31个黏化层为例

以黄土高原山西省14个淋溶土剖面的31个偏红的黏化层(Bt)为研究对象,分析了其全铁、游离氧化铁、无定形态氧化铁的含量与土壤颜色参数、黏粒含量之间的相关性,并建立了定量关系模型。结果表明:Bt的黏粒含量与氧化铁含量之间呈极显著正相关(P0.01);颜色的红度与全铁、游离氧化铁和无定形氧化铁含量之间均呈极显著正相关(P0.01),其中游离氧化铁是最直接的土壤红色"染色剂";其他色调、明度与彩度等颜色参数与土壤全铁、游离氧化铁含量之间亦呈现出显著的相关性,这也间接说明了黏粒含量与土壤颜色具有一定相关性。野外观测发现,某些黏化层结构体表面颜色较结构体内基质颜色更红,证实了在土壤结构体表面氧化铁随着黏粒在土壤空隙中的迁移淀积。黄土高原淋溶土偏红的黏化层多是来自由于土壤侵蚀而出露地表或接近地表的第三纪保德红土和第四纪红黏土,其黏粒含量、土壤颜色等指标均表明第三纪的古气候条件较第四纪更为湿热。     

Diversity of humus stocks in the arable soils of the Late Pleistocene ground morains in Mecklenburg,West Pomerania,Germany

Abstract

Local humus stocks (= contents of soil organic matter, SOM in kg · m^?2) of arable soils were investigated in several regions of the seemingly uniform ground moraine-landscape. Depending on relief position, quantifiable effects of humus removal or enrichment are evident, caused by denudation or colluviation. The depth (thickness) of the investigated humus-bearing topsoil horizons varies between 15 and 150 cm overall and amounts on average to 67 cm. Extreme values of SOM (resp. C_org) stocks are 2.73 (1.58) and 137.41 (79.70) kg · m^?2. The average values of all found SOM (resp. C_org) stocks in the investigated arable soils amount to 10.78 (6.25) kg · m^?2. Humus stocks are not only of importance for the agricultural yield potential but also because of their function as a sink for, or a source of, atmospheric CO₂, which is of special current interest due to its influence on menacing climate change. The total carbon content of the corresponding column of atmosphere, 1.60 kg · m^?2, amounts to only one quarter of the average in our arable soils.     

Leaching of imidazolinones in soils under a clearfield system

Herbicides with high mobility can leach to deeper layers of the soil and to contaminate underground aquifers. The potential of herbicide leaching in soil can be monitored by chromatography or bioassay methods. This study evaluated the leaching of imazethapyr, imazapic and its commercial mixture (imazethapyr + imazapic) in three tropical soils via a bioassay method. The herbicides were applied in a polyvinyl chloride column and an 80 mm rainfall was simulated. The bioindicator species sorghum (Sorghum vulgare) BRS 655 was sown. Imazethapyr, imazapic and the commercial herbicide mixture showed high leaching in the soils. The presence of imazethapyr and the commercial mixture was detected up to 25 cm deep in Haplic Plinthosol and Oxisol. Imazapic showed less leaching to tree soil, being found at depth 10–15 cm. The pH, texture and iron oxide amount levels affected herbicide leaching. The mobility of the herbicides imazethapyr and imazapic in the Haplic Plinthosol and the Oxisol at depth 25 cm indicates a high risk of groundwater contamination.     

Priming effects in different soil types induced by fructose, alanine, oxalic acid and catechol additions

It is well established that certain substrate additions to soils may accelerate or retard the mineralisation of soil organic matter. But up to now, research on these so called ‘priming effects’ was almost exclusively conducted with arable soils and with plant residues or glucose as additives. In this study, the effects of the uniformly ¹⁴C-labelled substrates fructose, alanine, oxalic acid and catechol on the mineralisation of soil organic carbon (SOC) from different horizons of two forest soils (Haplic Podzol and Dystric Cambisol) and one arable soil (Haplic Phaeozem) under maize and rye cultivation were investigated in incubation experiments for 26 days. Apart from the controls, all samples received substrate additions of 13.3 μg substrate-C mg⁻¹ C_org. During the incubation, CO₂-evolution was measured hourly and the amount of ¹⁴CO₂ was determined at various time intervals. In almost all soils, priming effects were induced by one or several of the added substrates. The strongest positive priming effects were induced by fructose and alanine and occurred in the Bs horizon of the Haplic Podzol, where SOC mineralisation was nearly doubled. In the other soil samples, these substrates enhanced SOC mineralisation by +10 to +63%. Catechol additions generally reduced SOC mineralisation by −12 to −43% except in the EA horizon of the Haplic Podzol where SOC-borne CO₂-evolution increased by +46%. Oxalic acid also induced negative as well as positive priming effects ranging from −24 to +82%. The data indicate that priming effects are ubiquitously occurring in surface and subsoil horizons of forest soils as well as in arable soils. Although a broad variety of soils was used within this study, relationships between soil properties and priming effects could not be ascertained. Therefore, a prediction on occurrence and magnitude of priming effects based on relatively easily measurable chemical and physical soil properties was not possible. Nevertheless, the data suggest that positive priming effects are most pronounced in forest soils that contain SOC of low biodegradability, where the added substrates may act as an important energy source for microbial metabolism.     

不同pH条件下黄壤胶体凝聚的动态光散射研究

土壤胶体的凝聚或分散紧密地联系着许多环境问题,并受胶体表面电荷性质的调控.以黄壤为实验材料,利用动态光散射技术研究pH作用下该可变电荷胶体颗粒的凝聚动力学.结果发现:土壤胶体的凝聚与否强烈依赖于pH.不同浓度HNO3和KOH诱发的土壤胶体凝聚均表现出慢速和快速凝聚特征,在快速凝聚中,HNO3作用较KOH作用的黄壤胶体平均凝聚速率更高、变化更快,表明表面电荷中和诱发的凝聚远大于压缩双电层诱发的凝聚.通过快速平均凝聚速率变化的反转点对应的pH,估计电荷零点(Zero pointof charge,ZPC),提供了一个实验测定ZPC的新方法.     

Simple methods for estimating field capacity using Mamdani inference system and regression tree

Using easily measurable soil properties could save time and cost for field capacity (FC) prediction. The objective of this study was to compare Mamdani fuzzy inference system (MFIS) and regression tree (RT) for FC predicting using such properties. One hundred and sixty-five soil samples from Unsaturated Soil hydraulic database data-set and 45 from Hydraulic Properties of European Soils data-set were used for the development and validation of MFIS and RT, respectively. Fuzzy rules and tree diagram based on the relationships between these predictor variables and the response variable FC were defined and 48 rules were written. Results showed a positive linear relevancy in terms of standardized independent variable weight, W*, between clay content and FC and negative linear relevancy between geometric mean particular size diameter (d_g) and FC. Among predictor variables, d_g (W* = 0.81) and bulk density (BD) (W* = 0.49) had the highest and lowest influence on FC, respectively. A tree diagram is presented for the prediction of FC using clay content, dg, and BD. Overall, based on statistical parameters, RT method (R² = 0.78, geometric mean error (GME) = 1.02, mean error (ME) = 0.01 cm³ cm^?3, and root mean square error (RMSE) = 0.04 cm³ cm^?3) showed a higher performance than MFIS method (R² = 0.72, GME = 1.16, ME = 0.08 cm³ cm^?3, and RMSE = 0.06 cm³ cm^?3) to predict FC.     

Zu Eigenschaften,Horizontaufbau und Gliederung der „Haftnässepseudogleye”︁

Properties, horizons and classification of the “Haftnässepseudogleye” (Stagnosols periodically waterlogged with capillary water) The term “Haftnässe” (soil wetness due to capillary moisture) can be used in describing soils with Sg-horizons in which long-term waterlogging and anaerobic conditions occur in the absence of gravitational water. “Haftnässe” is caused by water held in pores with an equivalent diameter of 0.2–50 μm by soil-water tension (pF) between 1.8 and 4.2, when the air capacity of the horizons is very low. “Haftnässe” moves primarily by capillary forces and is available to plants (available water). In some soils, the horizon below the Sg-horizon contains large pores, is well aerated and tends to impede the movement of capillary water. This type of horizon is often wetter than the overlying and underlying horizons, due to the presence of capillary water in the immediately overlying Sg-horizon. The symbol “So” is proposed for such horizons. In these soils, in the Sg-horizon reduced iron compounds are oxidized and precipitated, forming rusty mottles. The sequence of horizons developed in the “Haft(nässepseudo)-gleye” (Stagnosols periodically waterlogged with capillary water) typically affects the continuity of the pathways along which capillary water normally moves. The “Haft(nässepseudo)gleye” are divided into two subtypes on the basis of the sequence of horizons in the soil profile:

• Typical “Haft(nässepseudo)gley” (Shn) exhibits a sequence Ah/Sg/(II)So and shows transitions to Luvisol and Glossisol,
• Thick “Haft(nässepseudo)gley” (Shm) exhibits a sequence Ah/Sg and shows transitions to “Stau(wasserpseudo)gley” (Gleysol periodically waterlogged due to perched water), Gleysol, Fluvisol and tidal marsh soil.

     

Distribution of iron oxides forms on a transect of calcareous soils,north-west of Iran

The iron oxides fractions of four major physiographic units obtained from a transect of calcareous materials were studied to assess the effects of key pedogenic processes and local hydrology conditions as well as physiographic units in controlling iron oxides forms in the north-west of Iran. Samples from different horizons belonging to six pedons were selected and analyzed for soil physicochemical properties, clay minerals, and Fe oxides forms (Fe_d, Fe_o, Fe_p). In general, the soils indicated some variation in the concentration of iron oxides that could be related to rate of weathering, pedogenic accumulations, geomorphologic conditions (as results of different in physiographic units), wet and dry cycle, and organic matter. A wide relative variation in mean values of Fe_d (6.4–9.9 g kg^?1), Fe_o (2.9–4 g kg^?1), and Fe_p (0.68–1.3 g kg^?1) was observed among physiographic units. On the plateau unit, the presence of the most stable geomorphologic conditions and high rate in situ weathering (reflected in clay content), coupled with minor deposition of sediment suggest that the soils have more dynamic conditions than other units, reflecting in the greatest amount Fe_d and the lowest Fe_o/Fe_d ratio. Fe_d content of the soils containing less clay content (15–25%) was significantly different from those with greater clay content (25–35%).     

Influence of afforestation on soil genesis,morphology and properties in glacial till deposits

A study of soil morphological, physical and chemical properties was performed in woodland of different ages, in which spruce (Picea abies), aspen (Populus tremula) and birch (Betula pendula) growing stocks have colonized former agricultural land. The aim of the study was to clarify changes in soil genesis, morphology and properties due to the afforestation of abandoned agricultural land in glacial till deposits. The research showed that soil in these deposits (loamy sand, loam, clay) retains the morphological properties of agricultural land for up to 100 years. Secondary podzolization features in the soil profiles were observed within 100 years of the start of afforestation, whereas the diagnostic properties of Albic and Spodic horizons had not developed in the soil profile after 200 years. This study demonstrated that the morphological and physico-chemical properties of forest litter horizons, including the accumulation of organic substances, are dependent on forest age; however, changes in the properties of mineral soil horizons are mainly related to woodland age. Following the afforestation of agricultural lands, changes in soil pH_KCl, organic matter content and extractable Al and Fe concentrations occur more rapidly than changes in soil diagnostic properties and profile formation.     

Chemical properties and pedogenesis of yellowish/yellow brown forest soils in the submontane and mountain zones of Kyushu district,southwestern Japan

Abstract

This study aimed to clarify pedogenetic processes and classification of yellowish Brown Forest Soils according to the Classification of Forest Soils in Japan and the Yellow Brown Forest soils according to the Unified Soil Classification System of Japan in the warm and cool temperate forest of Kyushu district, Japan. In addition, the study aimed to clarify a problem with the Unified Soil Classification System of Japan. Thirty-six soil profiles of Brown Forest Soils, including 13 yellowish Brown Forest Soils and 15 Yellow Brown Forest soils, were compared with regard to their chemical properties and the relationship with climatic conditions was assessed. The yellowish Brown Forest Soils had thin A horizons, low pH and low levels of free oxides in the B horizons, and a low amount of silica and a high aluminum and iron to silica ratio. These features were related to the paleo reddish weathering. The immaturely developed A horizon of the yellowish Brown Forest Soils was caused by these weathered, low-activity substances. The Yellow Brown Forest soils had low levels of active iron oxides and a low activity ratio of free iron oxides compared with the Haplic Brown Forest soils in the same thermal climatic conditions. The activity ratio of free iron oxides was correlated to mean annual air temperature with the carbon stocks and with many other chemical properties. Accordingly, classification of Brown Forest Soils was clearer according to thermal climatic conditions. The activity ratio of free iron oxides can become an effective index that distinguishes Yellow Brown Forest soils under warm temperate lucidophyllous forest and Haplic Brown Forest soils under cool temperate broad-leaved deciduous forest with considerable vertical soil zonality.     

Specific Features of Profile Distribution and Crystallochemistry of Phyllosilicates in Soils of the Cisbaikal Forest-Steppe

The mineralogical composition of agrogray, dark gray, and agro-dark gray soils (Luvic Greyzemic Retic Phaeozems); agro-dark gray residual-calcareous soils (Calcaric Cambic Phaeozems); clay-illuvial agrochernozems (Luvic Chernic Phaeozems); and agrochernozems with migrational–mycelial carbonates (Haplic Chernozems) developed in the forest-steppe of Central Siberia within the Irkutsk Depression has been studied. The clay (<1 μm) fraction separated from these soils consists of mixed-layer minerals with alternating layers of hydromica, smectite, vermiculite, and chlorite; the proportions between them change within the soil profiles. The clay fraction also contains hydromicas, kaolinite, chlorite, and some admixture of the fine-dispersed quartz. Each type of the soils is characterized by its own distribution pattern of clay material with specific alternation of layers in the mixed-layer formations. Mixed-layer minerals of the chlorite–vermiculite type predominate in the upper horizons of texture-differentiated soils. Down the soil profile, the content of mixed-layer mica–smectitic minerals increases. In the clay fraction of arable dark gray-humus soils with residual carbonates, the distribution of the clay fraction and major mineral phases in the soil profile is relatively even. An increased content of well-crystallized kaolinite is typical of these soils. The parent material of agrochernozems has a layered character: the upper horizons are generally depleted of clay, and the middle-profile and lower horizons are characterized by the considerable kaolinite content. In general, the clay material of soils of the Tulun–Irkutsk forest-steppe differs considerably from the clay material of foreststeppe soils developed from loesslike and mantle loams in the European part of Russia. In particular, this difference is seen in the proportions between major mineral phases and between biotitic and muscovitic components, as well as in the degree of crystallinity and behavior of kaolinite and chlorite.     

Soil aggregate stability and organic matter as affected by land-use change in central Iran

This study aimed to evaluate the soil aggregate stability and selected soil quality indicators in various land uses in a semiarid region in central Iran. Random soil sampling was used to collect soil samples from surface (0–5 cm) and subsurface (5–25 cm) soil layers in rangelands of different condition classes, dry farmland and abandoned land. The aggregate size distribution indices including mean weight diameter (MWD), geometric mean diameter (GMD) and median diameter (D₅₀) of water-stable aggregates in the collected soil samples were measured. Our findings showed that percent of macroaggregates (>0.25 mm) of the surface and subsurface layers in rangelands of different condition classes were significantly higher than dry farmlands and abandoned lands (P < 0.05). Results showed that the trend of changes in soil organic matter was similar to soil aggregate stability in different land uses in both soil layers as follows: rangeland with good condition > rangeland with poor condition > abandoned land > dry farmlands. The structural stability indices (i.e. MWD, GMD and D₅₀) of rangelands with good condition were significantly greater than other land uses (P < 0.05). This highlights the importance of maintaining native rangeland to prevent organic matter loss, structure deterioration and soil erosion.     

Reduction of Hexavalent Chromium in Soil and Ground Water Using Zero-Valent Iron Under Batch and Semi-Batch Conditions

Chemical remediation of soil and groundwater containing hexavalent chromium (Cr(VI)) was carried out under batch and semi-batch conditions using different iron species: (Fe(II) (sulphate solution); Fe⁰ _G (granulated elemental iron); ZVIne (non-stabilized zerovalent iron) and ZVIcol (colloidal zerovalent iron). ZVIcol was synthesized using different experimental conditions with carboxymethyl cellulose (CMC) and ultra-sound. Chemical analysis revealed that the contaminated soil (frank clay sandy texture) presented an average Cr(VI) concentration of 456?±?35 mg kg^?1. Remediation studies carried out under batch conditions indicated that 1.00 g of ZVIcol leads to a chemical reduction of ～280 mg of Cr(VI). Considering the fractions of Cr(VI) present in soil (labile, exchangeable and insoluble), it was noted that after treatment with ZVIcol (semi-batch conditions and pH 5) only 2.5% of these species were not reduced. A comparative study using iron species was carried out in order to evaluate the reduction potentialities exhibited by ZVIcol. Results obtained under batch and semi-batch conditions indicate that application of ZVIcol for the “in situ” remediation of soil and groundwater containing Cr(VI) constitutes a promising technology.     

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.     

Practices sustaining soil organic matter and rice yield in a tropical monsoon region

ABSTRACT

Sandy soils are usually dominant in tropical monsoon regions, due to the high weathering potential associated with high temperatures and precipitation. The organic matter content of sandy soils is low due to low clay content and high microbial activity. Therefore, soil management practices that alter the soil organic carbon (SOC) content may be important for the sustainable management of crop yields. Thus, the present study investigates the distribution of rice yield and SOC content under different land management practices and analyzes the relationship between rice yield and SOC with pertinent management practices (manure and fertilizer applications). The soil horizons from 0- to 40-cm depths were collected in each layer to measure SOC and soil properties at 64 sites. At each sampling site, farmers were given questionnaires and the record book for the standards for good agricultural practices of farm owners were gathered to assimilate information on rice yield and their practices during 2010–2014. The mean rice yield of the whole crop year and SOC were 2.93 Mg ha^?1 and 47.09 Mg C ha^?1, respectively, in the irrigated areas, and were 2.38 Mg ha^?1 and 32.08 Mg C ha^?1 in the rain-fed areas. Significantly higher values were obtained in the irrigated areas (p < 0.05). There was a significant positive correlation between rice yield and SOC in both the irrigated areas (R² = 0.72, p < 0.01) and the rain-fed areas (R² = 0.85, p < 0.01); however, the slopes of these regression equations were significantly different. In both irrigated and rain-fed areas, manure should be applied every year, with an optimal application rate of N, P, and K fertilizers being selected. The combination of manure, fertilizer, and increasing irrigation facilities the maintenance of SOC levels and substantially increases rice yields.     

Vertical distribution of soil properties under short‐rotation forestry in Northern Germany

Short‐rotation forestry (SRF) on arable soils has high potentials for biomass production and leads to long‐term no‐tillage management. In the present study, the vertical distributions of soil chemical and microbial properties after 15 y of SRF with willows and poplar (Salix and Populus spp.) in 3‐ and 6‐year rotations on an arable soil were measured and compared to a pertinent tilled arable site. Two transects at different positions in the relief (upper and lower slope; transect 1 and 2) were investigated. Short‐rotation forestry caused significant changes in the vertical distribution of all investigated soil properties (organic and microbial C, total and microbial N, soil enzyme activities), however, the dimension and location (horizons) of significant effects varied. The rotation periods affected the vertical distribution of the soil properties within the SRF significantly. In transect 1, SRF had higher organic‐C concentrations in the subsoil (Bv horizon), whereas in transect 2, the organic‐C concentrations were increased predominantly in the topsoil (Ah horizon). Sufficient plant supply of P and K in combination with decreased concentrations of these elements in the subsoil under SRF pointed to an effective nutrient mobilization and transfer from the deeper soil horizons even in the long term. In transect 1, the microbial‐C concentrations were higher in the B and C horizons and in transect 2 in the A horizons under SRF than under arable use. The activities of β‐glucosidases and acid phosphatases in the soil were predominantly lower under SRF than under arable use in the topsoil and subsoil. We conclude, that long‐term SRF on arable sites can contribute to increased C sequestration and changes in the vertical distribution of soil microbial biomass and soil enzyme activities in the topsoil and also in the subsoil.     

Dynamics of Sodium in Saline and Sodic Soils

Abstract

Soil salinization and sodication affect large areas of agricultural land in the world. Amelioration of these soils to make them suitable for agricultural production depends on understanding sodium dynamics and chemical interactions governing nutrient availability. Three locations in eastern Croatia were characterized to the 5‐m depth. The two solonetz‐solonchak soils were alkaline, whereas the solonetz soil had near‐neutral A/E horizon and alkaline deeper horizons. Electrical conductivity of the saturated extract (ECe) was greater than 4 dS m^?1 in the top horizons in the solonetz‐solonchak soils. The solonetz soil had 2.8–4.7 dS m^?1 in shallow A/E, CG, and G horizons and up to 6.3 dS m^?1 below 1.5 m. Highly alkalinized sodic horizons (exchangeable sodium percentage, ESP >20) had 24–47% Ca²⁺ and 27–33% Mg²⁺ on the cation exchange complex. Sodium adsorption ratio (SAR) was high (18–26) in the P horizon and even more so in Bt,na horizon (35–36) of solonetz‐solonchak soils. A strong negative exponential relationship existed between soluble Ca²⁺ and SAR (SAR increased greatly when Ca²⁺ dropped to around 3 mg dm^?3). An increase in pH to greater than 8.4 resulted in an exponential increase in SAR. Leaching of Na⁺ with successive volumes of water was similarly effective for the P and Bt,na horizons in the solonetz‐solonchak soils, but SAR remained greater than 15 even after six successive cycles of leaching. In conclusion, extensive amelioration of tested soils with gypsum and leaching will be required to overcome poor physical and chemical characteristics caused by various degrees of alkalization and sodication to bring these soils into production.     

Effect of particle-size distribution on wind erosion rate and soil erodibility

Wind erosion is a serious problem, especially in arid and semi-arid regions. This study was conducted to assess the effects of wind speed as well as soil particle-size distribution on erosion rate (ER) using a wind tunnel. For this purpose, two clay loam soil samples (C2 and C10) in addition to a sandy clay loam (S2) were exposed to different wind velocities of 2, 9 and 18 m s^?1. The result showed that erosion rate increased significantly with increasing wind speeds. In addition, a critical diameter of 0.84 mm for soil particles was supported; for larger particles the changes in erosion rate were negligible. Furthermore, soil erodibility (K) was determined, which for S2, C2 and C10 was 57.73, 10.27 and 1.43, respectively. To predict soil erodibility, a power relationship as K = 3.382 MWD^?1.732 (R ² = 0.99) was established. The results indicated with increasing wind speed, the sensitivity of S2 remained constant, whereas C2 and C10 resisted wind speed. The finding of this research indicates the importance of particle-size distribution on wind erosion rate as well as soil erodibility.