首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 671 毫秒
1.
The analysis of long-term weather records and data on the water budget in a 3-m-deep layer of typical chernozems in the reserved steppe area has shown considerable changes in the soil hydrological regime under the impact of climatic fluctuations. In the past 34 years, the warm season has become more humid and the cold season has become warmer in comparison with the climatic norm. These changes have been accompanied by the settling of trees and shrubs on the reserved steppe territory; more frequent cases of water percolation throughout the entire profile of chernozems owing to the increased accumulation of water reserves in the fall, winter, and spring seasons; less active evapotranspiration of soil water during the growing season; and the smaller deficit of soil water in the fall. In general, the chernozems have become better moistened, which has led to certain changes in their genetic features.  相似文献   

2.
The reasons for the deterioration of the irrigation water quality and the alkaline degradation of chernozems in the Danube-Dnestr and Azov irrigation systems on the East-European Plain were studied. The water of the accumulation reservoirs in these systems is alkaline (pH up to 8.6), contains 1.5–2.5 g/l total dissolved salts, and is characterized by an increased content of magnesium (35% of the total cations). The irrigation of chernozems with such water results in the alkalinization of the soils and a decrease in the content of exchangeable calcium from 85–90 to 55–65% of the total exchangeable cations. The content of exchangeable magnesium increases to 30–40% and that of sodium to 3–5% of the total exchangeable cations. Problems of soil reclamation that have arisen during the functioning of irrigation systems without solving the main task (the improvement of the irrigation water’s quality) have been considered. Recommendations are given for the conservation of chernozems and the preservation of the quality of the irrigation water from the Kuban and Don rivers during its transportation to the irrigated fields.  相似文献   

3.
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.  相似文献   

4.
The trends of the soil-forming process and the changes in the main physicochemical properties of leached chernozems under different phytocenoses (virgin land, cereal-row crop rotation, and sown perennial grasses (Galega + Bromopsis)) were studied. In the cereal-row crop agrocenoses, as compared to the virgin land, the thickness of the humus horizon increased, and the depth of effervescence remained the same. The reaction of the leached chernozems in the phytocenoses did not change, and the sum of exchangeable bases increased in the following sequence: sown perennial grasses < cropland = virgin land. The humus content and its reserves in the 0- to 20-cm soil layer of all the agrophytocenoses were almost the same, and the total nitrogen content decreased in the following sequence: virgin land = cropland > perennial grasses. On the contrary, the total phosphorus content, its mobility, the phosphorus capacity and reserves, and the sum of the mineral phosphates increased in the same order. The highest content of exchangeable potassium was found in the soils of the virgin land and the lowest one, in the soils of the cereal-row crop agrocenosis. The perennial grasses consumed the greatest amounts of potassium and nitrogen and the spring wheat of the cereal-row crop rotation, those of nitrogen. The removal of nitrogen was 1.6–1.8 and 2.3 times greater than the losses of phosphorus and potassium, respectively.  相似文献   

5.
The results of long-term studies (1957–2007) of the changes in the morphology of soil profiles and in the reserves and fractional composition of the humus in the soils of the Ingulets irrigation system are discussed. After 50 years of irrigation, the boundaries of the genetic horizons shifted downward by 15–30 cm. The redistribution of the humus took place: its content decreased to a low level in the plow layer of the irrigated and rainfed soils and significantly increased in the layer of 60–100 cm so that the reserves of humus in the layer of 0–100 cm somewhat increased and corresponded to a moderate level. The distribution of humus in the soil profiles was characterized by the gradual lowering down the soil profile. The concentration of nitrogen in the humus of the irrigated southern chernozems was very low. The degree of humification of the soil organic matter was high. The humus was of the humate type in the upper horizons and of the fulvate-humate type in the lower horizons.  相似文献   

6.
Temporal changes of eroded soils in the southern Cis-Ural region (Republic of Bashkortostan) depending on their agricultural use during the period from 1975 to 2011 were studied. In the northern foreststeppe zone, the development of erosion processes was retarded upon the use of soil-saving management practices and grain-fallow-grass crop rotations. In slightly eroded light gray forest soils (Eutric Retisols (Cutanic)), the thickness of humus-accumulative horizons and the content of humus increased; the conversion of cropland into permanent fallow was found to be the most efficient measure to control soil erosion. In podzolized chernozems (Luvic Greyzemic Chernic Phaeozems) and typical chernozems (Haplic Chernozems) of the Cis-Ural steppe, the content of humus in the plow layer under grain-row crop rotation and classical soil management decreased, especially in moderately eroded soils. The development of water and wind erosion on slopes depended on the slope shape: the texture of soils at different degrees of erosion on slopes with free runoff became coarser by one gradation after 35 years; in the presence of linear obstacles in the lower part of slopes, the content of fine fractions in moderately and strongly eroded soils increased.  相似文献   

7.
A sequence of dark gray forest soils developing under a virgin broadleaved forest and under croplands used for 100 and 150 years was studied in the southern part of the forest-steppe zone on the Central Russian Upland. The application of multiple study methods for these objects made it possible to trace the evolutionary changes in the soil properties during the 150-year-long period of regular plowing. Several important trends in the soil development under the impact of the cultivation were revealed: (a) an increase in the thickness of the humus layer (according to the measurements at 20 points for each of the objects), (b) an increase in the amount of mole tunnels, (c) a decrease in the coefficient of the textural differentiation of the soil profile (with respect to the clay content), (d) an increase in the contents and reserves of the major nutrients upon a stable pool of humus in the upper meter, and (e) some alkalization and carbonization of the profile. Powdery accumulations of carbonates and whitish calcareous coatings on the faces of prismatic peds appeared at a depth of more than 130 cm. The plowed soils contained thin deep fissures, the surface of which was covered by dark-colored clayey-humus coatings at the depth of 50–110 cm. The radiocarbon age of the humus in these coatings was 500–1000 years younger than the age of the humus in the soil mass between the fissures. This set of features attests to the evolution of the plowed dark gray forest soils into chernozems under the impact of plowing.  相似文献   

8.
Soil organic matter dynamics after the conversion of arable land to pasture   总被引：4，自引：0，他引：4  
 Conversion of arable land (maize) to pasture will affect the soil organic matter (SOM) content. Changes in the SOM content were studied using a size- and density-fractionation method and 13C analysis. Twenty-six years of maize cropping had resulted in a depletion of carbon stored in the macro-organic fractions (>150 μm) and an increase in the <20 μm fraction. Maize-derived carbon in the upper 20 cm increased from 10% in the finest fraction (<20 μm) to 91% in the coarse (>250 μm), light (b.d. <1.13 g cm–3) fractions. Pasture installation resulted in a rapid recovery of the total SOM content. Up to 90% of the pasture-derived carbon that was mineralized during maize cropping was replaced within 9 years. Especially the medium and coarse size (>150 μm) and light (b.d. <1.13 g cm–3) fractions were almost completely regenerated by input of root-derived SOM. The amount of medium-weight and heavy macro-organic fractions (>150 μm; b.d. >1.13 g cm–3) in the 0- to 20-cm layer was still 40–50% lower than in the continuous pasture plots. Average half-life times calculated from 13C analyses ranged from 7 years in the light fractions to 56 years in heavy fractions. Fractionation results and 13C data indicated that mechanical disturbance (plowing) during maize cropping had resulted in vertical displacement of dispersed soil carbon from the 0- to 20-cm layer down to 60–80 cm. Conversion of arable land to pasture, therefore, not only causes a regeneration of the soil carbon content, it also reduces the risk of contaminant transport by dispersed soil carbon. Received: 10 March 1998  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
Experience in irrigation of chernozems in the steppe zone of Russia for a period from 1950 to 1990 is analyzed. By the end of this period and in the subsequent years, the areas under irrigation reduced considerably, and the soil productivity worsened. This was caused by the improper design of irrigation systems, on the one hand, and by the low tolerance of chernozems toward increased moistening upon irrigation, on the other hand. The analysis of the factors and regimes of soil formation under irrigation conditions shows that irrigation-induced changes in the soil hydrology also lead to changes in the soil physicochemical, biochemical, and other properties. In particular, changes in the composition of exchangeable cations lead to the development of solonetzic process. In many areas, irrigation of chernozems was accompanied by the appearance of solonetzic, vertic, saline, and eroded soils. The development of soil degradation processes is described. In general, the deterioration of irrigated chernozems was related to the absence of adequate experience in irrigation of steppe soils, unskilled personnel, improper regime of irrigation, and excessively high rates of watering. In some cases, the poor quality of irrigation water resulted in the development of soil salinization and alkalization. To improve the situation, the training of personnel is necessary; the strategy of continuous irrigation should be replaced by the strategy of supplementary irrigation in the critical periods of crop development.  相似文献   

12.
The effects of several dominant tillage and rotation systems on soil organic C content of different particle-size fractions were studied in Chernozemic soils from southwestern and east-central Saskatchewan, Canada. In an Orthic Brown Chernozem in southwestern Saskatchewan, 7 years of no-till cereal–fallow, imposed on a long-term tillage fallow–wheat rotation soil, resulted in 0.1 Mg C ha−1 more organic C mass in the sand + organic matter (OM) fraction of the 0- to 5-cm layer, whereas organic C associated with coarse silt (CS), fine silt (FS), coarse clay, and fine clay of 0- to 5- and 5- to 10-cm layers was less than that of the comparable tilled cereal–fallow system. Conversion of tilled fallow–wheat rotation soil to continuous cropping had a slight effect, whereas the organic C mass in all the size fractions was significantly increased in both 0- to 5- and 5- to 10-cm layers after alfalfa was introduced on tilled fallow–wheat as perennial forage for 10 years. In an Orthic Black Chernozem in east-central Saskatchewan that was cultivated and tilled using a cereal–fallow rotation for 62 years, organic C mass decreased in sand + OM, CS, and FS of 0- to 10-cm depth. Conversion of the tilled cereal–fallow cropland soil back to seeded grassland resulted in significantly more soil organic C in sand + OM fraction after 12 years of grass seed-down. The sand + OM fraction appears to be the size fraction pool initially most sensitive to adoption of management practices that are liable to sequester carbon in the soil.  相似文献   

13.
The effect of different land-use practices on the carbon budget in old arable gray forest soils of Russia was studied in field experiments. A short-term (for 6–7 years) cessation of mineral fertilization had no negative effects on the carbon budget in the agrocenoses studied. Only the combination of zero fertilization with the return to monoculture and the introduction of black fallows created a negative budget of humus in the soil. The regrassing of the eroded arable soil for 24 years increased the humus reserve in the 0- to 60-cm layer by a factor of 1.6–1.7. The average annual accumulation of carbon and nitrogen after the restoration of the perennial vegetation was 106–128 g C/m2 and 11–16 g N/m2, respectively.  相似文献   

14.
The long-term dynamics (1947–2006) of parameters characterizing the income and expenditure components of moisture balance in deep (3 m) chernozems of the reserved steppe area subject to annual hay cutting have been analyzed by methods of moving averages and resolution of data sets into time series. The results provide evidence for the cyclic patterns of these dynamics and their dependence on changes in weather conditions over the past few decades, referred to as recent climate warming. An increase is noted in the occurrence frequency of long time series (about 7 years) with parameters of soil moisture balance deviating (either positively or negatively) from long-term average values, during which changes in soil properties (in particular, carbonate status) may well leave their mark in the soil profile. The long-term dynamics of individual components of soil moisture balance have a specific pattern accounted for by the mutual influence of these components on each other as well as by the combined effect of changing environmental factors. An analysis of the moving-average curves of these components has revealed the tendency indicating that the period of increased moisture supply to chernozem soils (characteristic of the past few decades) is coming to an end.  相似文献   

15.
The contents of phospholipids and carbon of the total microbial biomass were determined in the modern chestnut soil and in the paleosols buried under mounds of the Bronze and Early Iron Ages (5000–1800 years ago) in the dry steppe of the Lower Volga River basin. Judging from data on the ratio between the contents of phospholipids and organic carbon in the microbial cells, the carbon content of the living microbial biomass was calculated and compared with the total microbial biomass and total organic carbon in the studied soils. In the background chestnut soil, the content of phospholipids in the A1, B1, and B2 horizons amounted to 452, 205, and 189 nmol/g, respectively; in the paleosols, it was 28–130% of the present-day level. The maximum content was measured in the paleosols buried 5000 and 2000 years ago, in the periods with an increased humidity of the climate. In the background chestnut soil, the total microbial biomass was estimated at 5680 (the A1 horizon), 3380 (B1), and 4250 (B2) μg C/g; in the paleosols, it was by 2.5–7.0 times lower. In the upper horizons of the background soil, the portion of the living microbial biomass in the total biomass was much less than that in the paleosols under the burial mounds; it varied within 8.5–15.3% and 15–81%, respectively. The portion of living microbial biomass in the total organic carbon content of the background chestnut soil was about 4–8%. In the paleosols buried in the Early Iron Age (2000 and 1800 years ago), this value did not exceed 3–8%; in the paleosols of the Bronze Age (5000–4000 years ago), it reached 40% of the total organic carbon.  相似文献   

16.
The soil cover pattern on a gentle watershed slope at the Kamennaya Steppe Experimental Farm consists of the areas of typical chernozems, zooturbated chernozems, and leached chernozems evolving into chernozemic-meadow soils; they are oriented along the slope. This soil combination is complicated by the presence of slightly eroded and slightly saline soils. The seasonal overwetting and inundation of the soils are favored by the discharge of the groundwater above the local aquiclude represented by the layer of dark brown calcareous clay at the depth of 1.0–2.2 m from the soil surface and by the concentration of snowmelt runoff in the concave parts of the slope. Seasonal overwetting of the soils leads to the appearance of olive tints and small iron concretions (quasigley features) in the lower horizons; in some cases, proper gley features (bluish coatings) appear in the chernozems. The veinlets of powdery gypsum are formed in the middle-profile horizons of some soils. Salt efflorescence on the surface in some places is also the result of the seasonal overwetting of the soils followed by their intense drying upon the hot and droughty weather conditions.  相似文献   

17.
The phenomenon of mineralization (biological mineralization) of organic matter in chernozems has been studied. A decrease in the content of Corg with time can be considered an index of the organic matter mineralization. It is suggested that the humus horizons of modern chernozems contain the pools of organic matter of different ages: easily decomposable organic matter, labile biologically active humus, stable biologically active humus, and relatively inert humus. The composition and mean residence times of these pools and their contribution to the total organic matter content have been estimated. The particular types of the biological mineralization have been determined on the basis of the comparison between the velocities of mineralization (M) and humification (H) processes: total unidirectional mineralization (M ≫ H), equilibrium mineralization (M ∼ H), nonequilibrium mineralization (M> <H), and zero mineralization. The separation of subtypes is based on data on the relative rates (%) of the organic matter mineralization. On the basis of available experimental data on chernozems buried under kurgans and in loess sediments (with the age of up to 800 ka), the quantitative relationship of the humus content in the buried soils on their age has been found; it has an exponential shape. During the first 100 ka after the soil burial, the soil humus content gradually (with a slowing intensity) decreases from 100–75 to 6.5% of its content in the virgin chernozems. Then, 100–1000 ka after the soil burial, the soil humus content remains approximately constant (6.5% of the initial level, or 0.3% of the soil mass). The rates of mineralization have been estimated. It is shown that the elemental composition (C, H, N, O) of humic acids remains relatively stable for a long time due to the regeneration of the chemical structure of humus (matric restoration of humus). It is suggested that several different forms of humus related to pedogenesis should be distinguished in the biosphere. The renewable humus in the equilibrium state with the environment is typical of the open biospheric (soil) systems. The fossil humus, whose content decreases with time, and whose composition remains stable, is typical of the semiclosed and closed systems. With time, it transforms into residual humus, whose content and composition remain stable. The fossilized organic matter in the fossil soils and sediments of the past geological epochs (Mesozoic and Paleozoic) considerably differs from the renewable, fossil, and residual humus.  相似文献   

18.
Seasonal changes in carbon availability and microbial biomass were studied in soil under an irrigated wheat-maize cropping system receiving different fertilizter treatments over the past 10 years. Treatments included N-100 and N-200 (urea at 100 and 200kgNha–1 year–1, respectively), FYM-16 and FYM-32 (farmyard manure at 16 and 32tha–1 year–1, respectively) and a control (unfertilized). Aerobically mineralizable carbon (AMC; C mineralized after 10 days aerobic incubation at 30°C) increased (13–16%) under wheat at both rates of urea whereas under maize it increased (22%) only with the lower rate of urea. Farmyard manure also increased the content of soil AMC under both crops, the effect being two- to threefold higher under wheat than under maize. Urea application caused an 32–78% increase in the specific respiratory activity (SRA) under wheat but caused an 11–50% decrease during the maize season. Farmyard manure also resulted in a higher SRA under both crops but only at the higher application rate. Under wheat, microbial biomass C (MBC) decreased in urea-treated plots but showed a slight increase at the higher rate of FYM. During the maize season, MBC was higher under both urea (42–46%) and FYM (36–47%) treatments as compared to the control. Microbial biomass turnover rate was highest for FYM-32 (2.08), followed by FYM-16 and urea treatments (1.35–1.49); control plots showed a turnover rate of 0.82. The higher AMC and SRA during the active growth period of wheat than that of maize indicated that root-derived C from wheat was higher in amount and more easily degradable. Received: 16 April 1996  相似文献   

19.
Hydraulic properties of a Walla Walla silt loam were significantly changed by 50 years or more of cultivation under either a wheat-peas rotation (tillage depth 30 cm) or a wheat-summerfallow rotation (tillage depth 15 cm) as compared with no cultivation. Soil pH was reduced to depths as great as 60 cm in the cultivated sites; dry bulk density was increased to depths as great as 40 cm. Expressions of these changes were greater in the wheat-peas rotation because tillage was deeper than in the wheat-summerfallow rotation. Small reductions in soil organic matter were also noted in the cultivated sites. In the 60- to 90-cm depth, all three sites had similar bulk density, pH, cation exchange capacity, soil texture, desorption water characteristic, and hydraulic conductivity. In the upper 40-cm layer the desorption water characteristic showed that cultivation produced more smaller pores at the expense of large pores; in the upper 30-cm layer of the cultivated soils hydraulic conductivity was reduced at least 10-fold for water potentials > −100 cm of H2O. Steady-state drainage profiles and associated assumptions suggest that long-term cultivation increased the hydraulic gradient in the upper 35 cm, and that the low saturated conductivity of the 0- to 15-cm layer had an overall drying effect on the 15- to 35-cm layer. In the cultivated soils increased runoff and denitrification in the plow layer should both be expected and water relations in the 15- to 35-cm layer should favor microorganisms sensitive to high water potentials. Simulations suggested that long-term cultivation decreased evaporation rates an estimated 40% and in wet soil, increased the drying time needed to attain optimum moisture for tillage.  相似文献   

20.
The hydrologic regimes of arable chernozems were simulated for two plots located within a watershed. For the last fifty years continuous corn monoculture was practiced in one plot, and permanent bare fallow was practiced in the other plot. Carbonates are detected from a depth of 140–160 cm under corn and from 70–80 cm under bare fallow. The objective of the simulation study was to test the validity of the hypothesis that the shallower depth to carbonates under bare fallow is related to carbonate rise due to changes in the hydrologic regime of bare soil compared to soil under vegetation. Mathematical modeling using the HYDRUS-1D software and the FAO56 method confirmed that the hydrologic regimes of arable chernozems within the two plots are different. The soil water content under bare fallow is generally higher than that under corn. The downward soil water fluxes for the two plots are comparable. The upward soil water fluxes under bare fallow significantly exceed those under corn and affect a thicker soil layer. The changes in the hydrologic regimes of chernozems under bare fallow favor the upward movement of carbonates through both the direct transfer by upward water fluxes and the diffusion of ions.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号