Changes in the physical properties of typical chernozems of Kursk oblast under the conditions of a long-term stationary experiment

The light clayey typical chernozems were studied on the fields of a long-term experiment on continuous fallowing performed by the Kursk Research Institute of Agroindustrial Production. The experiment was initiated in 1964. It includes the following variants: bare fallow, fallow with NPK application, fallow with manure application, idle land, and cropland under traditional cereal rotation. The fundamental physical properties of the chernozems, such as the particle-size distribution, the aggregate-size distribution, the water stability of the aggregates, the specific surface (as determined by the methods of the equilibrium desorption of water vapor and nitrogen), the mechanical stability of the air-dried aggregates, and the penetration resistance have not changed significantly under the impact of fertilizers and manure application. At the same time, reliable changes have taken place in the physicomechanical properties of the chernozem, including, in particular, the strength of the aggregates and the dependence of the penetration resistance on the water content. This attests to changes in the structural bonds between the soil particles under the impact of the fertilizers. An exponential equation describing the dependence of the penetration resistance on the soil’s water content in the range from the liquid limit to the plastic limit has been suggested. The analysis of the approximation parameters of this equation shows that the application of manure increases the dilatant characteristics of the chernozem and lowers its penetration resistance at the given water content. Reliably higher values of the penetration resistance have been found in the soil of the cropland, which may be related to the somewhat coarser soil texture in this experimental variant.     

青海省东部山区旱作农田土壤团聚体特征研究

比较了青海省东部山区垂直梯度分布的三种旱作农田土壤(黑钙土、栗钙土、灰钙土),在0~60 cm土层的不同粒级土壤风干团聚体和水稳性团聚体含量间的差异,并结合其它土壤质量指标(有机质、粘粒)对不同土壤结构和抗侵蚀能力进行了综合评价。结果表明,>0.25mm风干团聚体、>0.25mm水稳性团聚体含量和土壤有机质含量与土壤类型间有密切关系。均表现为黑钙土>栗钙土>灰钙土。黑钙土和栗钙土的土壤有机质含量与>0.25mm水稳性团聚体间存在显著正相关关系(P<0.05),灰钙土则无明显相关性;三种土壤粘粒含量与>0.25mm风干团聚体和0.25mm水稳性团聚体含量间无明显相关性。各项指标综合比较,三种土壤抗侵蚀能力大小为:黑钙土>栗钙土>灰钙土。     

Stability behavior of soil colloidal suspensions in relation to sequential reduction of soils

Flocculation and dispersion of colloidal particles of nine inorganic paddy soils were studied mainly based on turbidity measurements of the suspensions of soils which were previously incubated at 28°C under in vitro waterlogged conditions. After 1-week of incubation, the turbidity of the soils except for 1) two soils containing larger amounts of sodium salts and 2) one soil containing larger amounts of Fe and Al oxides, significantly decreased, and colloidal particles flocculated with 1) a decrease in soil Eh and 2) an increase in electric conductivity (EC). During the 3- to 4-week period of waterlogging, the turbidity of the three soils significantly increased with the 1) decrease in EC and 2) increase in pH of the soils although the Eh remained low. Infrared (IR) absorption analysis showed that the suspended colloidal particles consisted of layer silicates from respective soil clays. Oxidation of suspensions of waterlogged soils by air-bubbling led to an increase in turbidity with the 1) increase in Eh, and 2) decrease in pH, EC, and water-soluble Fe₂₊ concentration. It was suggested that the stability of the soil colloidal suspensions was affected by soil reduction with alterations in ionic species and their concentrations at clay surfaces and in soil solutions.     

Nutritional status of ‘Hass’ and ‘Fuerte’ avocado (Persea americana Mill.) plants subjected to high soil moisture

Abstract

In this study, the effect of increased soil moisture on the nutritional status of two key commercial avocado (Persea americana Μill.) cultivars, ‘Fuerte’ and ‘Hass’, was examined. The results revealed that prolonged exposure of plants to high soil water content conditions (waterlogging) reduced the total nutrient content (absolute quantity) of almost all of the nutrients in scion’s tissues (leaves and stems) of both cultivars. The decrease of nutrient content in the ‘Fuerte’ leaves was more prominent/severe compared to the ‘Hass’ leaves, which could be the outcome of the reported higher sensitivity of the cultivar to soil waterlogged conditions in previous studies. Interestingly, the inability of ‘Fuerte’ avocado plants to withstand high soil moisture conditions was not reflected in the relative concentrations of most nutrients, both in leaves and stems. Indeed, significantly higher concentrations of P, K, B, Fe, and Zn were found in the leaves of ‘Fuerte’ waterlogged plants than in well-watered ones. This fact reveals that under marginal/stressful conditions, like waterlogging, nutrient concentration in tissues does not reflect potential negative effects on total nutrient uptake of avocado plants, obviously due to concentrated nutrient phenomena primarily created by the stress-dependent growth inhibition. Therefore, total nutrient content is proposed as a more representative indicator for assessing plant response to waterlogged conditions.     

耕作模式对冷浸田水稻产量和土壤特性的影响

为探明不同耕作模式对冷浸田的影响机制,挖掘冷浸田的生产潜力,以冷浸田为研究对象,通过田间试验,以常规平作模式为对照,研究了垄作和稻鱼共作模式对冷浸田水稻产量以及土壤团聚体、温度、pH及有机质和还原性物质含量以及酶活性的影响。结果表明:相比对照(CK),垄作模式(T1)能显著降低土壤微团聚体(0.25 mm)含量,促进大团聚体的形成,提高土壤温度,增加土壤有机质含量,提高土壤pH,抑制水稻分蘖期后土壤亚铁含量的上升,降低土壤亚锰含量,减轻其对水稻根系的毒害作用,提高土壤酶活性,增加土壤速效养分含量。稻鱼共作模式(T2)对冷浸田土壤理化性状影响不显著,但能显著增加土壤速效养分含量,土壤速效钾含量在水稻孕穗期和成熟期分别较对照(CK)增加18.2%和69.2%,从而为水稻生长提供良好的土壤环境和营养,促进水稻生长发育,提高水稻产量。研究表明T1和T2模式能显著提高冷浸田水稻产量,增产范围为8.8%~25.8%,T1模式增产效果最显著,实际产量达到7 623 kg·hm-2。综上所述,垄作模式可以有效地改善冷浸田土壤特性,提高水稻产量,而稻鱼共作模式增产效果主要体现在增加冷浸田水体和土壤的速效养分。     

Abstracts of Nippon Dojo-Hiryogaku Zasshi (Japanese Journal of Soil Science and Plant Nutrition)

The electrokinetic behavior of colloidal particles in three waterlogged soils at 38°C was investigated with reference to the stability changes of soil colloidal suspensions under reductive conditions. The dispersed clay particles of the three soils exhibited a negative zeta (ζ) potential. The absolute value of the ζ-potential, |-ζ|, of these soils in the earlier period of waterlogging decreased, which caused the flocculation of clay particles. The concentrations of divalent cations, i.e., Fe²⁺ and Ca²⁺ in the soil solutions were estimated to be higher than their critical flocculation concentrations (CFCs) on the basis of the observed CFCs of Fe²⁺ and Ca²⁺ for the clay suspension of halloysite as a reference. With the progression of the reduction process, clay particles of one soil still exhibited a low |- ζ| and flocculated. The concentrations of Fe²⁺ and Ca²⁺ in the soil solutions were estimated to be higher than their CFCs, respectively. The clay particles of two sandy soils, however, showed an increase in |- ζ| due to the increase in pH and dispersed. The concentrations of Fe²⁺ and Ca²⁺ in the soil solutions were estimated to be lower than their CFCs, respectively. The stability changes of the soil colloidal suspensions by these divalent cations under sequential soil-reduction can be explained by the alteration of the Stern potential (- ψ _s ), which determines the repulsion energy related to the potential energy of interaction between two particles. The apparent decrease in the Ca²⁺ concentration of the soil solutions in the later period of waterlogging was explained largely by the re-adsorption of water-soluble Ca²⁺ on the exchange sites of soil clays with the decrease in the Fe²⁺ concentration in the soil solution.     

Changes in clay minerals of vertic chernozems under the impact of different ameliorants in a model experiment

The interaction of different ameliorants and fertilizers with the solid phase of clayey vertic chernozems was studied in a model experiment. Changes in the organization and properties of the mineral mass from the plow horizon under the impact of ameliorants took place at several hierarchical levels. At the level of soil aggregates, both the disaggregation of the soil mass and the formation of agronomically valuable soil aggregates under the impact of different ameliorants were observed. The method of fractional peptization of the soil mass was applied to study the behavior of clay minerals. The specificity of the crystallochemistry of smectitic minerals and their changes under the impact of introduced substances were studied in different fractions of clay.     

The humus state of the soils of locally hydromorphic landscapes in the lower reaches of the don river

The humus state of rainfed chernozems affected by local waterlogging was studied. The total humus content in the hydromorphic chernozems increases, as well as the content of fulvic acids, whereas the content of nonhydrolyzable residue (humin) decreases. A significant increase in the portions of the third fractions of humic and fulvic acids is observed. The role of the fine silt and clay fractions in the binding of humic substances increases in the lower horizons of locally hydromorphic soils. The increase in the content of fulvic acids (fulvatization) is mainly due to their predominance in the clay fraction. The latter is specified by the significant narrowing of the C_ha-to-C_fa ratio, the lower content of the nonhydrolyzable residue, and the increased content of the clay-bound (3rd fraction) fulvic and humic acids. The composition of the humus in the fine silt fraction of the studied soils is characterized by an increased amount of humic acids of the second fraction with a decrease in the relative content of fulvic acids.     

石灰岩区土壤分形特征及其与土壤性质的关系

研究了岩溶坡地不同生态系统土壤颗粒组成和团粒结构的分形特征.结果表明,土壤颗粒组成分形维数与黏粒及物理性黏粒含量显著正相关,与砂砾含量显著负相关.团粒结构分形维数与水稳性团聚体含量显著负相关,与团聚体湿筛后的破坏率显著正相关,即分形维数愈高,>0.25 mm水稳性团聚体和水稳性大团聚体含量愈低;团粒结构的分形维数与土壤有机质有负相关趋势,与土壤阳离子交换量显著负相关,与土壤体积质量(容重)呈正相关趋势.次生灌丛岩溶生态系统退化后,土壤黏粒减少,体积质量上升,土壤水稳性团聚体含量及其稳定性下降,土壤颗粒组成分形维数降低,土壤团粒结构分形维数则呈上升趋势.颗粒组成分形维数与团粒结构分形维数对土壤质量和岩溶生态环境状况的反映是一致的.     

Changes in the physical properties of soils in the Kamennaya Steppe under the impact of shelterbelts

The physical properties of ordinary chernozems and meadow-chernozemic soils under different land management practices (maple, larch, birch, and pine sections of the shelterbelts; continuous (since 1959) fallow; and arable field (since 1952)) were studied in the Kamennaya Steppe. The soils had favorable physicochemical properties, light clayey texture, and high microaggregation independently from the type of land management. The long-term impact of the shelterbelts improved the soil structure in the upper part of the humus horizon: the content of agronomically valuable aggregates increased, the content of coarse aggregates (>10 mm) decreased, the aggregation coefficient increased by 3.7–4.3 times, and the water stability of the aggregates became by 8–12% higher. The soils under the shelterbelts were characterized by minimum values of the bulk density and solid phase density and by maximum values of the total, active, and air porosities. At the same time, no considerable differences between water reserves in the studied range of soils were detected. The ratio of the optimum productive water range to the active (productive) water range (OPWR/AWR) within the upper soil meter varied from 0.42–0.44 to 0.45–0.54. This points to changes in the character of perched water: the content of intra-aggregate capillary-perched water decreases, and content of film perched water increases down the soil profile.     

Microbiological parameters of aggregates in typical chernozems of long-term field experiments

The changes in microbiological parameters of aggregates (1–2 mm) in typical chernozems under different land uses as dependent on the intensity and character of anthropogenic loads were studied with the help of the real-time polymerase chain reaction (PCR). The samples from the following long-term field experiments were examined: permanent black fallow, continuous cultivation of potato, 17-year-old unmanaged fallow after permanent black fallow, and annually mown reserved steppe. The soil samples were treated in two ways. In the first case, the samples were air-dried, sieved through the screens to separate aggregate fraction of 1–2 mm, and microbiological parameters were determined in this fraction. In the second case, the samples were frozen immediately after the sampling, and the aggregates of 1–2 mm were manually separated from the samples before the PCR analysis. It was shown that air-dry aggregates of chernozems could be used for the quantitative analysis of DNA of microbial community in comparative studies. According to the quantitative estimate of the content of DNA fragments from different phylogenetic groups, the bacterial community was most sensitive to the type of the soil use, and its restoration after the removal of extreme anthropogenic loads proceeded faster than that of other microorganisms. The content of archaeal DNA in the chernozem under the 17-year-old unmanaged fallow did not differ significantly from its content in the annually plowed chernozems. The changes in the content of micromycetal DNA related to anthropogenic load decrease were intermediate between changes in the contents of archaeal and bacterial DNA.     

Solods of the Baraba Lowland and the Priobskoe Plateau: Their properties and genesis and the methods of their diagnostics

The properties, hydrological features, and genesis of the solods occurring in the Baraba Lowland and Priobskoe Plateau were studied. Methods for determining the hydromorphism degree are considered; the features of the similarity and differences between the solods and other soils with textural profile differentiation are shown. Depending on the reasons for the waterlogging, the solods should be divided into two groups: the solods of groundwater waterlogging and the solods of surface waterlogging. Criteria for their discrimination are suggested: the ratio between the contents of the clay fraction in the parent rock (or in the B2 horizon) and that in the A2 horizon, the changes in the pH values along the soil profiles, and the content of nonsilicate iron compounds. The solods studied are shown to be formed under the conditions of a stagnant-percolative regime and gleying. This circumstance is an obligatory and sufficient reason for the formation of the light-colored acid eluvial (A2) horizons. According to some basic properties of the soil solid phase (the acidity, the total chemical composition, and the clay pattern in the eluvial part), the gleyed solods are close or identical to the gleyed soddy-podzolic and gleyed chernozem-like podzolic soils. At the same time, the solods differ from the gleyed chernozem-like podzolic soils by their thicker A1 (or Ap) horizon and their higher humus content (5–7%).     

Long-term dynamics of the properties of leached chernozems under different forest plantations

The long-term dynamics of the main morphological, physical, chemical, and physicochemical properties of leached chernozems under introduced (Weymouth pine and Siberian larch) and aboriginal (English oak, Scotch pine, and whitewood) trees are discussed. The trees were sown in 1928–1930 in the Mokhovoe Forestry of Orel oblast (the Shatilovo Forest). A comparative analysis of published data and the results obtained in our study has shown some positive changes in the humus horizons under the impact of forest vegetation. The thickness of the humus layer (A + AB) has increased. It has become less compact. The soil structure and the water stability of the soil aggregates in the upper 30-cm-deep layer have improved. The total humus content in the A horizon and its reserves in the layers of 0–20, 0–50, and 0–100 cm have increased. In general, the properties of the leached chernozems have improved under the impact of the artificially planted trees.     

Effect of bentonite on the fertility of an ordinary chernozem

The effect of bentonite clay on the main fertility parameters of an ordinary chernozem has been revealed. The maximum contents of nutrients in the soil have been obtained after the application of bentonite at rates of 7.5 t/ha for nitrate nitrogen and mobile potassium and 10.0 t/ha for available phosphorus. At the application of bentonite at rates of 10.0–15.0 t/ha, the content of agronomically valuable soil aggregates resistant to mechanical impact has increased by 2.7%, while that of water-stable aggregates has increased by 6.8%. The portion of water-stable microaggregates has increased, which has decreased the degree of dispersion. Because of the increased content of fine-silt and clay particles, the portion of physical clay in the soil has increased by 3.13%, and the portion of physical sand has decreased. The optimum application rate of bentonite (7.5 t/ha) has been found, which ensures an increase in the yield of sorghum by 16.3%. Its effect was insignificantly lower than that of mineral fertilizers.     

Parametric estimation of soil physical functions

Relationships between the penetration resistance, water content, and aggregate water stability were experimentally determined for aggregates of ordinary chernozems from the Orenburg region and approximated by nonlinear functions. The approximation parameters had a physical significance; in most cases, they were statistically significant and could be used to estimate the differences between the aggregates of different sizes from the chernozems taken under forest, meadow, and agricultural land. The parametric estimation of soil physical functions depends on the type of mathematical function, whose parameters have physical significance; the statistical significance of the approximation parameters; and (in comparing different objects) the significance of the difference between the approximation parameters of the experimental relationships according to the function selected.     

Light Gray Surface-Gleyed Loamy Sandy Soils of the Northern Part of Tambov Plain: Agroecology,Properties, and Diagnostics

Light gray soils of Tambov oblast mainly develop from sandy and loamy sandy parent materials; these are the least studied soils in this region. Despite their coarse texture, these soils are subjected to surface waterlogging. They are stronger affected by the agrogenic degradation in comparison with chernozems and dark gray soils. Morphology, major elements of water regime, physical properties, and productivity of loamy sandy light gray soils with different degrees of gleyzation have been studied in the northern part of Tambov Plain in order to substantiate the appropriate methods of their management. The texture of these soils changes at the depth of 70–100 cm. The upper part is enriched in silt particles (16–30%); in the lower part, the sand content reaches 80–85%. In the nongleyed variants, middle-profile horizons contain thin iron-cemented lamellae (pseudofibers); in surface-gleyed variants, iron nodules are present in the humus horizon. The removal of clay from the humus horizon and its accumulation at the lithological contact and in pseudofibers promote surface subsidence and formation of microlows in the years with moderate and intense winter precipitation. The low range of active moisture favors desiccation of the upper horizons to the wilting point in dry years. The yield of cereal crops reaches 3.5–4.5 t/ha in the years with high and moderate summer precipitation on nongleyed and slightly gleyed light gray soils and decreases by 20–50% on strongly gleyed light gray soils. On light gray soils without irrigation, crop yields are unstable, and productivity of pastures is low. High yields of cereals and vegetables can be obtained on irrigated soils. In this case, local drainage measures should be applied to microlows; liming can be recommended to improve soil productivity.     

Changes in the content and quality of humus in leached chernozems of the Trans-Ural forest-steppe zone under the impact of their agricultural use

The results of long-term studies of changes in the content and fractional-group composition of humus in leached chernozems (Luvic Voronic Chernozems, WRB 2006) of the Trans-Ural forest-steppe since the beginning of their plowing are considered. These soils are characterized by the high humus pool (up to 500 t/ha in the virgin state and up to 430 t/ha in the plowed state) and the high degree of the organic matter humification. Humus is of the fulvate–humate type in the upper 30 cm and of the humate–fulvate type in the deeper layers. From 1968 to 2006, the total pool of humus in the 1-m-deep soil layer of the plowed chernozems decreased by 8.5% in comparison with the initial virgin soils. The rate of dehumification reached 1.0–1.4 t/ha per year. The long-term plowing of leached chernozems also led to a smaller content of nitrogen in the organic matter (the C/N ratio increased from 11.5 to 13.6). The relative content of free humic acids (HA-1) and humic acids bound to clay minerals (HA-3) increased, whereas the content of calcium humates (HA-2) decreased. The composition of fulvic acids in the plow horizon was characterized by the rise in the content of aggressive (FA-1a) and mobile (FA-1) fractions, while the amount of fulvates bound to calcium (FA-2) decreased.     

The development of chernozems on the Dniester-Prut interfluve in the Holocene

The development of forest-steppe and steppe chernozems on the Dniester-Prut interfluve in the Holocene was studied on the basis of data on the paleosols buried under archaeological monuments of different ages. The parameters of the mathematic models of the development of the soil humus horizons in different subtypes of chernozems were calculated. They were used to determine the rate of this process and the age of the soils formed on the surface of Trajan’s lower rampart. The climate-controlled changes in the character of the soil’s development in the Late Holocene were differently pronounced in the different subtypes of chernozems. The suggested differentiation of the trends in the development of the humus horizon in the studied chernozems corresponds to the differences in the soil-forming potential of particular areas (as judged from the energy consumption for pedogenesis).     

THE MOISTURE RÉGIMES OF SOILS DEVELOPED ON KEUPER MARL

The moisture régimes of several representative profiles of the Worcester series developed on Keuper Marl are described and interpreted using a simple field technique supplemented by determinations of pore space, moisture content, and moisture release characteristics. It is suggested that the textural B horizon of coarse blocky structure is the cause of waterlogging which occurs seasonally in the upper 61 cm of these soils. The C horizon, which has a fine blocky structure and a lower clay content, is more permeable, and determinations of pore space and moisture content showed an appreciable volume of air voids in it when the overlying horizons were fully saturated with water. After subsoiling to a depth of 76 cm at one site, the soil was waterlogged less often and then only for shorter periods than formerly.     

The influence of climate cycles on the water regime and carbonate profile in chernozems of Central European Russia and adjacent territories

The influence of long-term “dry” and “wet” climatic cycles on the water regime, hydrological parameters, and carbonate profiles of chernozems in Central European Russia and adjacent territories was studied. The hydrological and carbonate profiles were found to change during the wet cycle. However, the upper part of the hydrological profile is basically unchanging, whereas in its lower part, the number of hydrological horizons and contrast in their moistening decrease in the forest-steppe chernozems and increase in the steppe chernozems. The frequency of through wetting of chernozems increases during the wet cycles. The vertical lithological heterogeneity of the parent material affects the soil moisture status. In the wet climatic cycle, the moisture content above the lithological contact increases resulting in the development of the features of soil hydromorphism. In the carbonate profile, the character of pedofeatures is changing: some carbonate neoformations disappear, while the other ones develop. Possible variations of the periodically percolative water regime were revealed in chernozems. The classification of water regime proposed by A.A. Rode may be updated based on the data obtained during the dry climatic cycle. Rode’s hypothesis about cyclic variations in the soil water regime is confirmed.