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1.
The stable desorption parts of soil Quantity/Intensity isotherms were used to determine the contributions of initially exchangeable and non-exchangeable potassium to plant uptake from ten soils. The activity ratio, ARK= aK/√aCa, Mg at which K was first taken up from non-exchangeable sources varied from 3 × 10?3 to 8 × 10?3 M1/2 depending on the soil. Uptake rates of two categories of initially non-exchangeable K were linearly related to √times;. The first category appeared to be close to equilibrium with the initially exchangeable K, and gave effective diffusion coefficients of 10?7 cm2 s?1 for four soils. The second category gave diffusion coefficients from 10?20 to 10?22 cm2 s?1, probably came from internal surfaces of micaceous clays, and began to be released at activity ratios below 3 × 10?4 to 6 × 10?4 M1/2 depending on soil type. The soils fell into three groups, broadly consistent with soil series, on their ability to release the second category of potassium.  相似文献   

2.
Summary Soil texture affects pore space, and bacterial and protozoan populations in soil. In the present study we tested the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils because they have a larger volume of protected pore space available to them. The experiment consisted of three sterilized Orthic Black Chernozemic soils (silty clay, clay loam, and sandy loam) inoculated with bacteria, two treatments (with and without protozoa), and five sampling dates. The soils were amended with glucose and mineral N on day 0. On day 4 bacterial numbers in all three soils were approximately 3×109 g–1 soil. The greatest reduction in bacteria due to protozoan grazing occurred between day 4 and day 7. Compared to the treatment without protozoa, bacteria in the treatment with protozoa were reduced by 68, 50, and 75% in the silty clay, clay loam, and sandy loam, respectively. On day 4, 2 days after the protozoan inoculation, all protozoa were active. The numbers were 10330, 4760, and 15 380 g–1 soil for the silty clay, clay loam, and sandy loam, respectively. Between day 4 and day 7, the period of greatest bacterial decline, total protozoa increased greatly to 150480, 96160, and 192100 g–1 soil for the three soils, respectively. Most protozoa encysted by day 7. In all soils the addition of protozoa significantly increased CO2–C evolution per g soil relative to the treatment without protozoa. Our results support the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils.  相似文献   

3.
The carbon pool and its fluxes were studied in Karelian pine forests of automorphic sites for the characterization of the regional carbon cycle. On the permanent sample plots arranged in pine stands (dominant forest types) of the middle and northern taiga, the structure and dynamics of the phytomass, as well as the composition of the soil organic matter, were investigated. The contribution of different components of the forest ecosystems to the regional carbon budget was studied. The carbon pools in the soils of the middle and northern taiga subzones were 330–440 × 102 and 440–550 × 102 kg/ha, respectively. The share of soil carbon in the total carbon pool of the forest biogeocenoses studied amounted to 46–35 and 33–24%, respectively. The period of considerable carbon fixation in the pine ecosystem (nearly 20 × 102 kg/ha/yr) turned out to be limited to the middle-aged stands. In the mature and overmature pine forests, only 4 × 102 kg of C/ha/yr were fixed. The main part of carbon in the soil (65–75%) was contained in the illuvial horizons, although its content there was less that 1% as compared to 30–50% in the forest litters. On industrial harvesting of wood, the main reserves of soil carbon are not spent; only the fund of mobile carbon in organic horizons of poor soils is exhausted or carbon accumulates intensely due to the development of continuous plant cover on fertile soils.  相似文献   

4.
The communities of soil algae in saltwort ecosystems of the Transural part of Bashkiria were studied. The impact of salinization on the soil alga Xanthonema exile (Klebs) Silva (section Xanthophyta) was specially investigated. Sodium chloride and sodium carbonate were applied as salinization agents in the following concentrations: NaCl—2 × 10−1; 3.5 × 10−1; 5 × 10−1; 7 × 10−1; 1, and 1.5 M/l (11.7, 20.5, 29.3, 41.0, 58.5, and 87.8 mg/l); Na2CO3—5 × 10−4, 1 × 10−3, 5 × 10−3, 1 × 10−2, and 5 × 10−2, M/l (0.053, 0.106, 0.53, 1.06, and 5.3 mg/l). Algae in the natural salt-affected soils of the studied region were represented by 83 species belonging to 5 divisions, 11 orders, 23 families, and 24 genera. The genera Phormidium, Navicula, and Oscillatoria were represented by the maximum numbers of species. The ecological groups of soil algae relative to the soil salinization were distinguished. The study of the impact of salinization with NaCl and Na2CO3 on X. exile demonstrated a reliable change in the size of algal cells. Upon the high concentration of salts, changes in the size of the algal cells were also accompanied by their morphological disturbances. Sodium carbonate proved to be more toxic than sodium chloride. The minimal salt concentrations upon which changes in the cell morphology took place were 5 × 10−2 M/l Na2CO3 (1.06 mg/l) and 1 M/l NaCl (58.5 mg/l). Original Russian Text × L.S. Khaibullina, L.A. Gaisina, 2008, published in Pochvovedenie, 2008, No. 2, pp. 241–247.  相似文献   

5.
Abstract

Changes in pH values during 12 weeks incubation in soils treated with acidified sawdust (ACD‐SD)‐treated soils ranged from 5.03 to 5.89, from 9.88 to 10.35 in soil treated with alkalized sawdust (ALK‐SD), and ranged from pH 6.88 to 7.35 in untreated sawdust‐amended soil. In unamended soil, pH values were 6.80 to 7.35. Bacterial populations over the 12 weeks in ACD‐SD‐treated soils increased from 5×106 to 167×106 colonies while bacterial populations in ALK‐SD‐treated soils increased from 2×106 to 54×106. Fungal populations increased from 6×104 to 11,333×104 colonies per gram soil in ACD‐SD treated soils over the 12 week incubation. Untreated sawdust and control soil did not result in any significant changes in the fungal populations.  相似文献   

6.

Purpose

Hoop pine (Araucaria cunninghamii) is a nitrogen (N)-demanding native Australian softwood plantation species. Litter quality and its effects on soil mineral N and 15N transformations have not been well studied in the hoop pine plantation and adjacent native forest. The present study was conducted to determine the impact of 15N injection depth and litter additions on the dynamics and fate of mineral 15N and also to compare the difference in litter quality, 15N dynamics, and fate between the hoop pine plantation (HP) and the adjacent native forest (NF).

Materials and methods

The experiments were done in the Yarraman State Forest (26°52′ S, 151°51′ E), southeastern Queensland. Materials of litter addition were prepared on the basis of ten random samples of litters taken from the NF and HP sites using a 1?×?1-m quadrat. Litter additions were defined as: SL represented the average condition of forest floor in the forest ecosystems and DL represented the double average amount of litters in the forest ecosystem. Experiment 1 covered 2 forest types (NF and HP)?×?3 litter rates (nil litter, SL, and DL)?×?3 15N injection depths (0, 2.5, and 5.0 cm). Experiment 2 included 2 forest types (NF and HP)?×?2 litter rates (nil litter and SL)?×?3 injection depths (0, 2.5, and 5.0 cm) of distilled water. The in situ core incubation method was used with an incubation period of 28 days. The isotope ratio of mineral N or/and total N (soil and litter) were analyzed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer (Isoprime-EuroEA 3000).

Results

Total N and δ 15N were significantly higher, and C/N ratios and δ 13C were significantly lower in the NF litters than in the HP litters. The NF litters had significantly lower total 15N and total 15N recovery than the HP litters after 15N addition. Litter addition had no significant effect on mineral 15N transformations and δ 15N in the NF soil, but decreased 15NO 3 ? –N, mineral 15N, and δ 15N and increased immobilized 15N in the HP soil. The depth of added 15NH 4 + significantly altered total 15N, δ 15N, and total 15N recovery in the litters, whereas it did not influence 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, or immobilized 15N in soils in the two forest ecosystems.

Discussion

The NF litters had significantly higher δ 15N than the HP litters, indicating that the NF soil had a higher rate of nitrification than the HP soil. Higher litter quality in the NF was an important driving force for N cycling to promote strong N dynamics in the NF soil over the HP soil. The HP litters had significantly higher total 15N than the NF litters after 15N addition, implying that soil mineral N was relatively deficient in the HP in comparison with the NF. Litters decreased nitrification and increased immobilization in the HP soil, showing forest litters resulted in more N immobilization to prevent the loss of substantial quantities of NO 3 ? through leaching or denitrification. The depth of 15N injection did not significantly alter concentrations of 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, and immobilized 15N in the NF and HP soils, suggesting that the depth of 15N injection had no significant influence on the evaluation of soil N transformations.

Conclusions

The NF litters had significantly higher total N and δ 15N and lower C/N ratios and δ 13C than the HP litters. Mineral N was relatively insufficient in the HP soil relative to the NF soil. The HP litters facilitated more N immobilization in the soil to reduce the loss of substantial quantities of NO 3 ? through leaching or denitrification. The depth of 15N added did not significantly alter concentrations of 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, and immobilized 15N in the NF and HP soils. The application of 15N solution by uniform sprinkling onto the soil surface can be used to study in situ field N (including mineral 15N) transformations in the 10-cm depth soils of both forest ecosystems.  相似文献   

7.
Sixteen soils and 4 soil preparations were cropped exhaustively with ryegrass in the glasshouse and monocalcium phosphate potentials (½pCa+pH2PO4=1) were measured after each of 6 consecutive harvests. The amounts of phosphorus (Q) removed from the soils by ryegrass accounted for 95·1–96·6 per cent of the variance in 1 for 3 soils and 2 soil preparations (P < 0·001), for 88·4–93·7 Per cent of the variance for 6 soils and 2 soil preparations (0·001 < P < 0·01), for 71·6–82·6 per cent of the variance for 3 soils (0·01 < P < 0·05) and for insignificant amounts of the variance for 4 soils. Values of ΔI/ΔQ ranged from 7 × 10–4 to 431 × 10–4½pCa+pH2PO4/ppm P removed from soil. ΔI/ΔQ tended to decrease (i.e. the soils were more buffered) with increasing clay contents and with increasing amounts of NaHCO3-soluble P and to increase (i.e. the soils were less buffered) with increasing amounts of CaCO3. Variations in organic C did not significantly affect ΔI/ΔQ. The following equation accounts for 81 per cent of the variance in ΔI/ΔQ for all soils except those in equilibrium with octacalcium phosphate: ΔI/ΔQ× (104) = 225·9–4·17(% clay)+8·01(% CaCO3)–1·38(ppm NaHCO3-soluble P).  相似文献   

8.
Abstract

Characterization of methanotrophs isolated from paddy soils and rice (Oryza sativa) roots was investigated in the present study. The number of methanotrophs in root homogenates of the rice cultivar Mutsuhomare was 4.9 × 107 most-probable-number (MPN) g?1 dry roots, in Yumeakari it was 2.0 × 108 MPN g?1 dry roots and in Kirara it was 4.6 × 107 MPN g?1 dry roots. Although bacterial cells were observed infrequently on the surface and in the interiors of roots before incubation, a large number of colonies, measuring 0.5–5 mm in diameter, were observed on the sterilized roots after incubation on nitrate mineral agar plates under methane in air. In particular, a large number of colonies were observed at the emergence sites of lateral roots and root hairs. Strains MD5-1 and M1 were isolated from the roots of Mutsuhomare and strain R62 was isolated from the root homogenate of Yumeakari. All isolates were catalase-positive and oxidase-positive, Gram-negative, straight-rod-shaped and curved-rod-shaped bacteria, and formed exospores. The isolates were able to fix nitrogen and grew in the absence of copper. In addition, all were found to be positive for naphthalene-oxidizing activities (corresponding to soluble methane mono-oxygenase activities). Strains MD5-1, M1 and R62 were closely related to Methylosinus sporium. Methanotrophic strains W3-6, SD3-5 and 2-19, isolated previously from paddy field soils, were classified into Methylosinus (W3-6) and Methylocystis (SD3-5 and 2-19) type II methanotrophs. Isolates from the rice roots (MD5-1, R62 and M1) grew logarithmically when casamino acid was used as the nitrogen source; however, the growth of these strains was reduced on the nitrate medium. These strains preferred amino acids over inorganic nitrogen as a nitrogen source for growth.  相似文献   

9.
Tetrahymena pyriformis cultures were maintained when transferred serially in solutions containing 105 to 107Klebsiella pneumoniae cells.ml?1, bacterial numbers that were observed to persist in the presence of protozoa. The number of cells of one strain of K. pneumoniae surviving predation in solution was essentially the same in the absence of an alternative prey as in the presence of a second K. pneumoniae strain. Toxins deleterious to protozoa did not appear as the animal consumed the bacteria. T. pyriformis reduced the abundance of Escherichia coli from about 108 to 106.ml?1. but the latter number persisted for 15 days; however, in solutions containing chloramphenicol, the abundance of E. coli fell to 590 cells. ml?1 in 15 days. In solutions containing the antibiotic, T. pyriformis reduced the Rhizobium sp. population from more than 106 to less than 103 cells in 10 days and K. pneumoniae from more than 108.ml?1 to zero in 18 days. An appreciable decline in abundance of these bacteria did not occur in the antibiotic-amended liquid free of protozoa. T. pyriformis did not greatly reduce Rhizobium sp. numbers when both were added to irradiated soil, but the predator caused the bacterial population to decline from 4 × 108 to fewer than 105.g?1 in 16 days in chloramphenicol-treated soil. Colpoda sp. inoculated with Rhizobium sp. into soil sterilized by autoclaving only reduced the prey abundance from 109 to 108.g?1, but the protozoan caused the bacterial population to fall to about 100.g?1 in 15 days in the presence of the antibiotic. The population of Rhizobium sp. added to nonsterile soil dropped from in excess of 108 to 6 × 106.g?1 in 29 days. but it declined to 550. g?1 in the same period when chloramphenicol was also introduced. It is concluded that the ability of these bacteria to maintain themselves in solution and in soil is governed by their capacity to reproduce and replace the cells consumed by predation.  相似文献   

10.
Arid soils where water and nutrients are scarce occupy over 30% of the Earth's total surface. However, the microbial autotrophy in the harsh environments remains largely unexplored. In this study, the abundance and diversity of autotrophic bacteria were investigated, by quantifying and profiling the large subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase(Ru Bis CO) form I(cbb L) responsible for CO2 fixation, in the arid soils under three typical plant types(Haloxylon ammodendron, Cleistogenes chinensis,and Reaumuria soongorica) in Northwest China. The bacterial communities in the soils were also characterized using the 16 S r RNA gene. Abundance of red-like autotrophic bacteria ranged from 3.94 × 105 to 1.51 × 106 copies g-1dry soil and those of green-like autotrophic bacteria ranged from 1.15 × 106 to 2.08 × 106 copies g-1dry soil. Abundance of both red- and green-like autotrophic bacteria did not significantly differ among the soils under different plant types. The autotrophic bacteria identified with the cbb L gene primer were mainly affiliated with Alphaproteobacteria, Betaproteobacteria and an uncultured bacterial group, which were not detected in the 16 S r RNA library. In addition, 25.9% and 8.1% of the 16 S r RNA genes were affiliated with Cyanobacteria in the soils under H. ammodendron and R. soongorica, respectively. However, no Cyanobacteria-affiliated cbb L genes were detected in the same soils. The results suggested that microbial autotrophic CO2 fixation might be significant in the carbon cycling of arid soils, which warrants further exploration.  相似文献   

11.
The EPIC model was used to simulate soil erosion and soil C content at 100 randomly selected sites in the US corn belt. Four management scenarios were run for 100 years: (1) current mix of tillage practices maintained; (2) current trend of conversion to mulch-till and no-till maintained; (3) trend to increased no-till; (4) trend to increased no-till with addition of winter wheat cover crop. As expected, the three alternative scenarios resulted in substantial decreases in soil erosion compared to the current mix of tillage practices. C content of the top 15 cm of soil increased for the alternative scenarios, while remaining approximately constant for the current tillage mix. However, total soil C to a depth of 1 m from the original surface decreased for all scenarios except for the no-till plus winter wheat cover crop scenario. Extrapolated to the entire US corn belt, the model results suggest that, under the current mix of tillage practices, soils used for corn and/or soybean production will lose 3.2 × 106 tons of C per year for the next 100 years. About 21% of this loss will be C transported off-site by soil erosion; an unknown fraction of this C will be released to the atmosphere. For the base trend and increased no-till trend, these soils are projected to lose 2.2 × 106 t-C yr?1 and 1.0 × 106 t-C yr?1, respectively. Under the increased no-till plus cover crop scenario, these soils become a small sink of 0.1 × 106 t-C yr?1. Thus, a shift from current tillage practices to widespread use of no-till plus winter cover could conserve and sequester a total of 3.3 × 106 t-C yr?1 in the soil for the next 100 years.  相似文献   

12.

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 ?) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g?1 soil) and biomass N (63 to 28 μg N g?1), protease (361 to 694 μg tyrosine g?1 soil h?1) and deaminase (4.3 to 5.6 μg NH4 + g?1 soil h?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?109 to 2.77?×?109 g?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?107 to 3.01?×?108 g?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.  相似文献   

13.
Thermal diffusivity and heat capacity of virgin and plowed heavy loamy typical chernozems of Kursk oblast were studied. Thermal diffusivity was determined in the course of step-by-step drying of the initially capillary-saturated samples to the air-dry state. Specific heat capacity was determined for absolutely dry samples. Volumetric heat capacity was calculated according to the de Vries equation. Thermal diffusivity varied within the ranges of (1.15–3.46) × 10–7 m2/s in the Ap horizon, (1.14–3.35) × 10–7 m2/s in the А1 horizon, (1.49–3.70) × 10–7 m2/s in the АВ horizon, (1.49–3.91) × 10–7 m2/s in the В1 horizon, and (1.60–3.80) × 10–7 m2/s in the Вса horizon. The thermal diffusivity vs. water content dependencies had distinct maximums and were flattened in the range of low water contents. The maximums were most pronounced for the mineral B1 and Bca horizons; for the A1 and Ap horizons, the curves were rather S-shaped. Volumetric heat capacity of the air-dry soils varied from 0.96 J/(cm3 K) in the A1 horizon to 1.31 J/(cm3 K) in the Bca horizon; in the state of capillary saturation, it varied from 2.79 J/(cm3 K) in the А1 horizon to 3.28 J/(cm3 K) in the Вса horizon. Thermal properties of topsoil horizons were higher in the plowed chernozem compared with the virgin chernozem, which is explained by an increase in the bulk density and a decrease in the organic matter content in the plowed soil.  相似文献   

14.
Employing four mathematical models (first-order, parabolic-diffusion, Elovich and zero-order), kinetics of potassium desorption from eight soils with and without cropping were studied to evaluate their ability in explaining K release from soils. The decline in the soil test K in cropped soils over original soils was drastic in easily desorbable forms compared to that of strongly held forms like 3 M H2SO4 K. Results showed that parabolic diffusion as well as first-order kinetic equation explained the K release data well for both original and K depleted (cropped) soils. Elovich and zero-order equations were not suitable to describe the kinetic data. However, zero-order equation explained K release data better in case of K-depleted soils as compared to original soils. Soils with higher initial K contents registered higher release rate constants. Over the entire period of cropping the range of release rate (b) decreased from 1.26 to 1.53 × 10?2 to values ranging from 1.12 to 1.30 × 10?2 h?1. In contrast, the first-order equation, parabolic diffusion showed higher b values for cropped soils as they represent the diffusion gradient. Mica and its biotite content in both silt and clay fractions showed significant correlation (r) with b values. Similarly with the rate of K release, clay content of soils maintained significant r whereas the silt content did not.  相似文献   

15.
LU XIAO-NAN  LU YUN-FU 《土壤圈》1992,2(3):201-208
Kdesorption from soils in a constant electric field (field strength:44.5Vcm-1) by means of electro-ultrafil-tration (EUF) followed second-order kinetics and could be described by the equation dd/dt=k(D-d)2. From theequation, such kinetic parameters relating to K desorption from soils as the maximum desorbable quantity D, quantity of K desorbed within 40 minutes d40, initial desorption rate Vo, desorption rate constant k and half-time t1/2 could be calculated. An expression which describes the relationships between the kinetic parameters on the one hand and the responses of barley to fertilizer-K in the field experiments in different sites and the potassium-supplying power of soils on the other was established. Vo, D and d40 were significantly correlated with barley relative yield, K uptake by barley and the content of soil available potassium. The rate constants of K desorption varied between 4.42×10-4-1.80×10-3kg mg-1 min-1 and highly correlated with the relative yield of barley.  相似文献   

16.
The apparent diffusion coefficients, Dp/b+ø, of Zn and ZnEDTA were linear functions of added Zn, and were related to the adsorption and fixation capacities of soils rather than their pH. Lower apparent diffusion coefficient values were found in an Haplustoll soil that had higher clay and humus contents inspite of its lower pH. At comparable rates of added Zn, the apparent diffusion of ZnEDTA was 930–1010 (Bakyria), 700–1330 (Dirab), and 730–1880 (Baha) times that of Zn in the soils. The adsorbed Zn per cm3 of soil/Zn per cm3 of the equilibrium solution at the water content existing in the diffusion experiment approximated the capacity factor and was determined by extrapolation. The self-diffusion coefficient of Zn in Baha soil (5 × 10?7 cm2sec?1) of higher clay and water content was higher than in Bakyria or Dirab soil (2 × 10?7 cm2sec?1). These values were similar to the self-diffusion coefficient of P in soils of similar texture at similar water content.  相似文献   

17.
Cd adsorption isotherms were measured on five Israeli soils ranging in specific surface area from 65 to 315m2/g. Retention capacity of Cd ranged from 4.7 × 103 to 10 × 103μg/g soil (8.4 to 17.9 mequiv/100 g soil) and was correlated with the specific surface area. Almost all the adsorbed Cd was exchangeable with 0.5 M CaCl2 and the remaining fraction was extractable in 0.5 M HCl. Plots of Kd, the distribution coefficient of Cd between the solid and solution phases, vs. Γ, the surface density of adsorbed Cd, showed that all soils behave similarly, Kd sharply diminishing with Γ. It was suggested, based on comparison with literature data on Cd adsorption on montmorillonite, that below γ s 0. 5 × 1017 ions/m2, specific adsorption mechanisms prevail whereas above it the adsorption is mainly due to electrostatic interactions and ion exchange.  相似文献   

18.
Rotary tillage experiments were carried out under laboratory conditions in 3 types of Dutch soil. The moisture contents were set at 6 levels. Two tools were used; a knife blade and a tine. The energy required to work the soil was assessed with a pendulum.The specific energy requirement was expressed in units per volume of loosened soil, EV (kJ m?3) and also in units per surface area of loosened soil, EA (kJ m?2). In silty clay loam EV ranged between 153 and 160 kJ m?3 for the knife blade, and increased from 170 to 280 kJ m?3 for the tine, when the moisture content increased from 17 to 22%. EA increased from 2.5 to 9 kJ m?2 × 10?1 for the knife blade and from 3.8 to 10.5 kJ m?2 × 10?1 for the tine, when the moisture content increased from 17 to 22%.In sandy loam EV decreased from 110 to 75 kJ m?3 for the knife blade and from 165 to 130 kJ m?3 for the tine, when the moisture content increased from 9.5 to 17% EA increased from 1 to 2.5 kJ m?2 × 10?1 for the knife blade and increased from 2.7 to 2 kJ m?2 × 10?1 for the tine, when the moisture content increased from 9.5 to 17%.In silty loam EV decreased from 117 to 95 kJ m?3 for the knife blade and from 170 to 137 kJ m?3 for the tine, when the moisture content increased from 17 to 22%. EA increased from 3.7 to 5 kJ mm?2 × 10?1 for the knife blade, and from 3 to 5.5 kJ m?2 × 10?1 for the tine, when the moisture content increased from 17 to 22%.The energy requirement was related to penetration resistance, shearing resistance and modulus of elasticity. In silty clay loam the penetration resistance decreased from 3.9 to 2.6 MPa × 10?1, the shear resistance hardly changed and ranged between 0.8 and 0.9 MPa × 10?1, and the modulus of elasticity decreased from 46 to 23 MPa × 10?1, when the moisture content increased from 17 to 22%.In sandy loam the penetration resistance decreased from 5.5 to 1.9 MPa × 10?1, the shear resistance decreased from 0.6 to 0.4 MPa × 10?1 and the modulus of elasticity decreased from 84 to 15 MPa × 10?1, when the moisture content increased from 9.5 to 17%. In silty loam, the penetration resistance decreased from 3.6 to 1.7 MPa × 10?1, the shear resistance decreased from 0.6 to 0.4 MPa × 10?1 and the modulus of elasticity decreased from 58 to 11 MPa × 10?1 when the moisture content increased from 17.5 to 22%.  相似文献   

19.
The thermal diffusivity of the upper horizons of model soddy-podzolic soils in the lysimeters depends on their water contents and varies within 2.1?4.32 × 10?7 m2/s in the Ap horizon, 1.59?3.99 × 10?7 m2/s in the B1 horizon, 1.28?3.74 × 10?7 m2/s in the plowed B2 horizon, and 1.12?4.10 × 10?7 m2/s in the B2 horizon. The dependence of the thermal diffusivity on the soil water content is described by an inverted parabolic curve for the Ap horizon, an S-shaped curve for the B1 and B2 horizons, and by a curve of transitional type for the plowed B2 horizon. The temperature regimes of model soils with different morphologies of the profile do not differ much and are close to the soil temperature regime under natural conditions on the plots of the weather station of Moscow State University.  相似文献   

20.
Antarctic sediments, clays and rock fines collected on Ross Island and in the Wright Valley (L. Vanda, Don Juan Pond) are depleted in Hg relative to Fe. Average Fe/Hg values ofca 9 to 48 × 106 were found. These abundance ratios compare with general terrestrial values of 0.03 to 2.32 × 106 for sedimentary and residual materials andca 3 × 106 for igneous surfaces. Lowest ratios were found in New Zealand clays and mud and in volcanic soils. Algal mats from the Wright and Taylor Valleys averagedca 5 × 106 in Fe/Hg value whereas those from Hawaii and Iceland were < 0.2 × 106. Algal abundance ratios may reflect both exceptionally high Fe content and bio-volatilization of Hg, but sediments, fines and soils with more or less normal Fe content may have lost Hg by leaching as well as evaporation.  相似文献   

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