Stable and labile components of humus in soddy-podzolic soils

A mathematical model was proposed to characterize the seasonal dynamics of the humus composition in loamy soddy-podzolic soils. The results of determining the composition of the organic matter during two successive seasons revealed the presence of labile and stable components in almost all the groups and fractions of the humic substances. The seasonal changes in the content of the humic substances, the exchangeable Ca, and the pH value at the equilibrium state of the soil were found to be identical during the successive years.     

Microtomographic analysis of pore space in a virgin soddy-podzolic soil

The method of X-ray microtomography was applied to study pore space of a virgin soddy-podzolic soil at the natural soil water content. The morphometric parameters of the pores of more than 100 μm in diameter were determined in the vertically oriented undisturbed soil monoliths (d = 3 cm, h = 3–4 cm) from the genetic horizons of the most differentiated part of the soil profile (the AY, AEL, EL, BEL, BT1, and BТ2 horizons). A tendency for the horizontal orientation of these pores was found in all the horizons, except for the humus (AY) horizon. Isolated vesicular pores of different sizes were abundant in the eluvial part of the profile. Numerous recent and relict phytogenic channels were found in the intraped mass of the BT2 horizon. Differently directed interfaces of structural units in the soil horizons were visualized. Cluster analysis was applied to estimate differences between the genetic horizons with respect to their textures, aggregate sizes, and shapes of pores as seen in vertical two-dimensional X-ray images.     

Changes in the humus status of a layland sandy gleyic soddy-podzolic soil

Changes in the content, reserves, and composition of humus in a sandy gleyic iron-humus-illuvial soddy-podzolic soil under intensive, decreasing, and ceased agrotechnical impacts were studied. It was shown that when a well-cultivated soil is removed from economic use, the conditions of humus formation in the former homogeneous plow layer develop differently. A deterioration of the humus status parameters of the layland soil was found as compared to the cultivated soil. It was concluded that, when a soil is removed from economic use, its profile, which was disturbed by the anthropogenic impact, tends to return to the original genetic state. The change in the level of the agricultural practices affected the optical density of the humic acids only slightly, which is indicative of their relative stability under specific soil-forming conditions.     

Actinomycetes in the prokaryotic complex of the rhizosphere of oats in a soddy-podzolic soil

The bacterial population, the length of the actinomycetal mycelium, the total biomass of prokaryotes, and the taxonomic composition of mycelial prokaryotes have been determined in the rhizosphere of hullless and chaffy subspecies of oats (Avena sativa L.) grown in a field experiment on a soddy-podzolic soil. The antifungal potential of actinomycetes associated with the roots of chaffy and naked (hull-less) oats have been compared.     

The effect of oil contamination on bacteria in a soddy-podzolic soil

The effect of oil contamination on bacteria in a soddy-podzolic soil was studied. Oil was introduced into the soil 8, 11, and 17 years ago. It was found that oil contamination has exerted long-term negative effects on the number and biomass of the soil bacteria. The deficiency of available phosphorus was one of the major negative factors affecting these parameters in the old-contaminated soils. The application of Na₂HPO₄ to the contaminated soils eliminated this negative effect. The effect of oil contamination on the taxonomic diversity and structure of the bacterial community in the studied soil was determined with the help of denaturating gradient gel electrophoresis.     

Influence of xenobiotics on the microbiological and agrochemical parameters of soddy-podzolic soil

We studied the influence of various chemical compounds, i.e., azobenzene (an insecticide and acaricide), nitrification inhibitors (DCD, dicyandiamide and DMPP, and 3,4-dimetylpyrazolphosphate), and inhibitors of urease activity (HQ-hydroquinone), on the agrochemical and microbiological parameters of a soddy-podzolic soil. It is proved that these xenobiotics are able to influence the agrochemical parameters (the pH and the content of NO₃⁻ and NH₄⁺, the microbial activity (the basal respiration, the microbial mass carbon, and the microbial quotient), and the number of bacteria of different physiological groups in soddypodzolic soil. The influence of the xenobiotics was preserved for some time, which testified to their persistence in the soil. Upon cultivating the soil microorganisms in different media, the growth of the heterotrophic bacteria was inhibited, the radial growth velocity was slowed down, and the sporogenesis of the micromycetes was retarded. The toxic effect of the xenobiotics was higher with their increasing concentrations.     

Humus status of soddy-podzolic soil upon application of different green manures

Results of studying the effect of different plant species on the humus status of loamy sandy soddy-podzolic soil were generalized. It was found that the application of different green manure species (Lupinus luteus L., Trifolium pratense L., and Raphanus sativus L.) and straw from cereal crops (Secale cereale, Hordeum L.) under percolative conditions helped to sustain a stable humus budget in grain agrophytocenoses. A significant change in the fractional composition of HAs and FAs occurred under the effect of green manure. The fractions of free HAs and those bound to clay minerals accumulated with the application of Trifolium pratense and Raphanus sativus biomass and cereal straw. Lower amounts of aggressive and free FAs were formed in the soil with the application of straw and fallow plants. The decomposition of green manure and the formation of humic substances also depended on the hydrothermal conditions during application of manure.     

Distribution of transformed organic matter in structural units of loamy sandy soddy-podzolic soil

The effect of land use types and fertilizing systems on the structural and aggregate composition of loamy sandy soddy-podzolic soil and the quantitative parameters of soil organic matter has been studied. The contribution of soil aggregates 2–1 mm in size to the total C_org reserve in the humus horizon is higher than the contributions of other aggregates by 1.3–4.2 times. Reliable correlations have been revealed between the contents of total (C_org), labile (C_lab), and active (C₀) organic matter in the soil. The proportion of C₀ is 44–70% of C_lab extractable by neutral sodium pyrophosphate solution. The contributions of each of the 2–1, 0.5–0.25, and <0.25 mm fractions to the total C₀ reserve are 14–21%; the contributions of each of the other fractions are 4–12%. The chemically labile and biologically active components of humic substances reflect the quality changes of soil organic matter under agrogenic impacts. A conceptual scheme has been proposed for the subdivision of soil organic matter into the active, slow (intermediate), and passive pools. In the humus horizon of loamy sandy soddy-podzolic soil, the active, slow, and passive pools contain 6–11, 34–65, and 26–94% of the total C_org, respectively.     

Influence of plants and the microbial activity on the metal content in soil solutions of a soddy-podzolic soil in a model experiment

The influence of plants and microorganisms on the migration of metals in a soddy-podzolic loamy sandy soil was studied in a simulation experiment. It was shown that the biota has a great influence on the release of metal compounds into the soil and lysimetric solutions. In most cases, the metal content was reliably higher in the variants of the experiment with the presence of biota than in the control. The microorganisms maintained a high concentration of metals in the soil solution in the course of the experiment. The influence of the plants on the metal migration begins from the third week of the experiment as the biomass grows. The dose of the introduced metals also influences the concentration of the elements in the solutions and the ratios of the Me in the soil solutions: Me in the lysimetric solutions. In all the variants of the experiment, the ratios become narrower with the increase in the dose; i.e., the migration of the metals becomes more active. The dose of 7 APC (the approximate permissible concentration) has an inhibiting influence on the activity of the microorganisms and mustard plants.     

黄土高原塿土覆盖层与黏化层的土壤水文效应

黄土高原(土娄)土在《中国土壤系统分类(修订方案)》中属土垫旱耕人为土类的相应亚类,其土壤水分状况是诊断表层所属人为表层类堆垫表层(覆盖层)和诊断表下层(黏化层)的重要诊断特征。以土壤持水性能、蒸发性能和水分移动性能为切入点,对(土娄)土覆盖层和黏化层的土壤水文效应进行研究论证,以期对土垫旱耕人为土类及其亚类的诊断层与诊断特征获取更深层的认识。     

Structural and functional features of microbial communities in a soddy-podzolic soil under self-remediation conditions

The microbial component is one of the key factors responsible for soil fertility and soil quality. The sensitivities of some structural and functional parameters of soil microbial communities in soddy-podzolic soils under long-term self-remediation conditions were compared. The suitability of the parameters studied for quantifying the resilience of soil biota to agricultural intervention was studied.     

The effect of liming on the complex of soil microorganisms and the humus status of a soddy-podzolic soil in a long-term experiment

The influence of the prolonged application of different lime doses (including elevated ones) on the complex of soil microorganisms and the humus status of a sandy loamy soddy-podzolic soil was studied in a long-term field experiment. The content of labile humus substances extracted with 0.1 M KCl (pH 4.3–4.4) and that of organic matter extracted with hot water became reduced. When liming, the number of all the bacterial groups significantly increased. On the contrary, the number of micromycetes decreased by 3.5–4.2 times. However, the liming did not cause any changes in the complex of soil microorganisms and the content of organic matter, thus indicating the normal functioning of the whole soil ecosystem.     

Dynamics of the soil solution cationic composition in a limed soddy-podzolic soil contaminated with Co and Cd at variable pH

The dynamics of the cationic composition in the liquid phase of a soddy-podzolic soil contaminated with Co and Cd under different pH (changed by addition of H⁺ ions) was studied in a long-term experiment (for 470 days). Soil solutions were extracted with vacuum samplers installed in the soil for the time of the experiment. It was shown that the concentrations of Co and Cd, as well as those of K, Na, Ca, and Mg, in the solution changed during 3–4 weeks after moistening the air-dry soil to 70% of the maximum water capacity and increased during 5–6 months after addition of H⁺. This indicated the low rate of the processes and reactions occurring in the soil. The addition of Co and Cd to the soil affected the interphase distributions of K, Ca, and Mg; the effect of Co was higher than that of Cd by 3–4 times. When added together, the Co increased the concentration of Cd in the soil solution by 4–6 times, and the effect of Cd on the content of Co was no higher than 1.5 times.     

Resin extraction of labile, soil organic phosphorus

In order to develop a method for estimating labile, soil organic phosphorus (P_o), macroporous anion-exchange and adsorbent (XAD) resins were tested for their ability to extract P_o from a permanent pasture soil. Experimental variables included: ionic form, soil-water resin ratio, addition of cation-exchange resin, extraction time, extraction temperature, continuous and stepwise extraction and soil pretreatment (chloroform and microwaves). The amounts of extracted P_o and P_i (inorganic phosphorus) showed little variation between the anion-exchange resins, when used in the bicarbonate form. In the chloride form, the amounts extracted were less and more variable. XAD resins extracted much less P_o and very little P_i. The macroporous anion-exchange resin, Lewatit MP500A in the bicarbonate form, was chosen for further studies. It extracted 21 mg P_o kg^?1 from air-dried soil and 8 mg P_o kg^?1 from moist, incubated soil. The specific amounts of P_o and P_i extracted were little affected by variations in the ratio between soil, water and resin, but increased with extraction time and temperature. Chloroform pretreatment of the soil mainly increased extracted P_i, whereas microwave pretreatment only increased extracted P_o. The magnitude of these increases was approximately constant irrespective of extraction temperature, indicating that the increases came from killed micro organisms.     

Changes in the content and composition of humus in the sandy loamy soddy-podzolic soil in a long-term liming experiment

The effect of liming on organic matter in sandy loamy soddy-podzolic soil was studied. The study was performed on samples taken from the 50-year-long experiment established by Prof. Kornilov in 1957. It was shown that liming had almost no effect on the total humus content in the soil. The humus composition was studied using two fractionation methods of the humus substances by the Ponomareva-Plotnikova procedure. The regrouping of the humus fractions occurred due to the changes in the mobility of soil mineral components, which involved a regular increase in the content of the Ca-bound fraction of humic acids (HA-2) at the expense of the HA-1 fraction bound to the mobile forms of R₂O₃ reliable at the lime rates equivalent to the total acidity and higher. The levels of the stabilization of the different HA fractions were considered, as well as the stability of the changes in the humus composition during 50 years.     

Changes in the chemical properties and characteristics of humus in soddy-podzolic soil due to main pipeline construction

The multiyear dynamics of the acid–base parameters and humus characteristics of soddy-podzolic soil affected by main pipeline (MP) construction was studied. Distinctions between the properties of technogenically disturbed soil and soil unaffected by MP construction observed 1, 10, 15, and 30 years after construction have been characterized. The deterioration of physical and chemical properties and clearly displayed features of technogenic degradation of humus have been identified throughout the entire observation period.     

Methods for determining labile cadmium and zinc in soil

Isotopically exchangeable cadmium and zinc (‘E values’) were measured on soils historically contaminated by sewage sludge and ones on zinc‐rich mine spoil. The E‐value assay involves determining the distribution of an added metal isotope, e.g. ¹⁰⁹Cd, between the solid and solution phases of a soil suspension. The E values for both metals were found to be robust to changes in the position of the metal solid?solution equilibrium, even though the concentration of dissolved metal varied substantially with electrolyte composition and soil:solution ratio. Concentration of labile metal was also invariant over isotope equilibration times of 2–6 days. The use of a submicron filtration procedure, in addition to centrifuging at 2200 g , proved unnecessary if 0.1 m Ca electrolyte was used to suspend the soils. The proportion of ‘fixed’ metal, in non‐labile forms, apparently increased with increasing pH, although there was considerable variation in both sets of contaminated soil. Zinc and cadmium in the sludged soils were similarly labile. Several possible methods for the measurement of chemically reactive metal were explored for comparison with E values, including single extraction with 1 m CaCl₂ and a ‘pool depletion’ (PD) method. The latter involves comparing solid?solution metal equilibria in two electrolytes with differing degrees of (solution) complex formation, 0.1 m Ca(NO₃)₂ and CaCl₂. Both the single extraction and the PD method gave good estimates of E value for Cd, although the single extraction was more consistent. Neither technique was a useful substitute for determining labile Zn, because of weak chloro‐complexation of Zn^2+. We therefore suggest that 1 m CaCl₂ extraction of Cd alone be used as an alternative to E values to avoid the inconvenience of isotopic dilution procedures.     

Specificity of some soil characteristics in the rhizosphere of fir trees in the AEL horizon of podzolic soil

The total number of bacteria, the length of the fungal mycelium, and some chemical properties are evaluated in the rhizosphere of fir (Picea abies) trees and out of the rhizosphere zone in the AEL horizon of podzolic soil in the Central Forest State Nature Biosphere Reserve (CFSNBR). In the rhizosphere soil, the total number of bacteria is found to be 1.5 times greater and the fungal mycelium length two times greater than in the soil outside of the rhizosphere. The rhizosphere soil is characterized by consistently higher content of C _org in the whole soil and in the clay and fine silt fractions due to the increase in microbial biomass and the continuous supply of organic substances from dead cells and root exudates. The rhizosphere soil has consistently lower values of pH in water and salt extracts and higher values of exchangeable acidity because of the more active functioning of soil biota and the input of protons with root exudates. The content of exchangeable potassium in the rhizosphere is higher than in the nonrhizosphere soil. This difference can be explained by the increase in potassium mobility in the illite–expandable minerals buffer system under more acid conditions and more active functioning of biota.     

农田土壤颗粒组成及其剖面分层的空间变异分析

对60m55m的农田尺度上100个取样点土壤颗粒组成及剖面层次的空间变异性的传统统计分析表明,各属性的变异系数属中等强度。半方差函数模型均为球状模型,各属性具有一定的空间相关性,并表现有一定的各向异性。在对土壤颗粒组成及剖面层次空间分布趋势分析的基础上,根据半方差函数模型,对各属性选择不同趋势和异向性的普通Kriging内插值比较的结果表明,考虑变量在空间分布趋势和异向性的插值结果比不考虑要好。在以上分析基础上,利用Kriging内插值绘制各层深度和颗粒组成的等值线图,并分析了其空间分布规律。     

Strontium in an agrocenosis on a soddy-podzolic soil under conditions of the long-term effect and aftereffect of fertilizers

In a long-term field experiment on a medium loamy soddy-podzolic soil at the Chashnikovo Training and Experimental Soil-Ecological Center of Moscow State University, 16.6 kg/ha of strontium were added to the soil with double superphosphate (P_ds) over 41 years of its regular application (overall, 3320 kg P_ds/ha were applied). As a result, the total strontium content in the soil increased by 1.1–1.3 times in comparison with the control. The changes in the content of the mobile strontium compounds were statistically insignificant. The strontium accumulation in the vetch and oats grown on the plot with the P_ds application was 1.4–2.4 times greater than that in the control and in the NK variant. The strontium content in the plants was maximum on the nonlimed plots. Liming, especially in combination with application of organic fertilizers, led to changes in the soil chemical properties controlling the strontium mobility, which resulted in the lower uptake of strontium by the plants. However, the same factors predetermined an increase in the yield of the crops and a more active removal of strontium with the harvested plants. Ten years after the cessation of the fertilization, no increase in the concentration of the strontium in the perennial grasses grown on the plots with the former P_ds application was registered.