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1.

Purpose

The impacts of land-use change on dynamics of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the subsoil (>?30 cm) are poorly understood. This study aims to investigate whether the effects of land-use change on stocks and stoichiometric ratios (RCN, RCP, and RNP) of SOC, TN, and TP can be different between topsoil (0–30 cm) and subsoil (30–60 cm) in the Ili River Valley, northwest China.

Materials and methods

Soil samples (0–10, 10–20, 20–30, 30–40, 40–50, and 50–60 cm) were collected from a pasture (PT), a 27-year-old cropland (CL) converted from PT, and a 13-year-old poplar (Populus tomentosa Carr.) plantation (PP) converted from CL. SOC, TN, and TP concentrations and soil bulk density were determined to calculate stocks and stoichiometric ratios (molar ratios) of SOC, TN, and TP.

Results and discussion

Conversion from PT to CL led to substantial losses in SOC, TN, and TP pools in both topsoil and subsoil, and the reduction rates in subsoil (13.8–24.7%) were higher than those in topsoil (8.5–17.3%), indicating that C, N, and P pools in subsoil could also be depleted by cultivation. Similar to topsoil, significant increases in SOC, TN, and TP stocks were detected after afforestation on CL in subsoil, although the increase rates (31.2–56.2%) were lower than those in topsoil (47.8–69.1%). Soil pH and electrical conductivity (EC), which generally increased after conversion from PT to CL while decreased after CL afforestation, showed significant negative correlations with SOC, TN, and TP, suggesting that cultivation might lead to soil degradation, whereas afforestation contributed to soil restoration in this area. Significant changes in C:N:P ratios in topsoil were only detected for RNP after conversion from CL to PP. By contrast, land-use change significantly altered both RCN and RNP in the subsoil, demonstrating that the impacts of land-use change on RCN and RNP were different between topsoil and subsoil. The significant relationship between soil EC and RNP suggested that RNP might be a useful indicator of soil salinization.

Conclusions

Stocks of SOC, TN, and TP as well as RCN and RNP in subsoil showed different responses to land-use change compared to those in topsoil in this typical agro-pastoral region. Therefore, it is suggested that the effects of land-use change on dynamics of SOC, TN, and TP in subsoil should also be evaluated to better understand the role of land-use change in global biogeochemical cycles.
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2.
Abstract

A study of the electrical charge distribution of selected Venezuelan soils (two Oxisols, two Ultisols, and one Alfisol) by potentiometric titration (PT) and ion adsorption (IA) procedures, showed that all soils have a predominance of negative charge at their natural pH level and within the experimental pH range used (3.5–7.5). The only exception was the Amazonas 2 soil, which has a point of zero net charge (PZNC) at pH 3.5. Potentiometric titration (PT) results allowed us to find the point of zero salt effect (PZSE) of these soils, which is related to their pedogenetic development. The order found, from older to younger, was: Guanipa (Oxisol) > Amazonas (Oxisol) > Lomas de Cubiro (Ultisol) > Altos de Pipe (Ultisol) > Barinas (Alfisol). The Stoop's method, used to determine the PZSE of the soils, was found to be a more efficient and shorter way than PT for this purpose. Ion adsorption (IA) was a more realistic way than PT to determine charge distribution for the studied soils. The soils were classified according to their charge distribution, following Gillman and Sinclair (4), as type 1 (Barinas, Lomas de Cubiro, Altos de Pipe, Amazonas 1) and type 2 (Amazonas 2 and Guanipa). This classification has agrotechnological and management implications related to the effect of added amendments, fertilizer and pollutants that would interact as ions in these soils. The low anion exchange capacity (AEC) of all these soils means low absorption capacity for non‐specifically adsorbed anions, and therefore, their probable ease of leaching down through the soil profile.  相似文献   

3.
Among factors controlling decomposition and retention of residue C in soil, effect of initial soil organic C (SOC) concentration remains unclear. We evaluated, under controlled conditions, short-term retention of corn residue C and total soil CO2 production in C-rich topsoil and C-poor subsoil samples of heavy clay. Topsoil (0–20 cm deep, 31.3 g SOC kg?1 soil) and subsoil (30–70 cm deep, 4.5 g SOC kg?1 soil) were mixed separately with 13C–15N-labeled corn (Zea mays L.) residue at rates of 0 to 40 g residue C kg?1 soil and incubated for 51 days. We measured soil CO2–C production and the retention of residue C in the whole soil and the fine particle-size fraction (<50 μm). Cumulative C mineralization was always greater in topsoil than subsoil. Whole-soil residue C retention was similar in topsoil and subsoil at rates up to 20 g residue C kg?1. There was more residue C retained in the fine fraction of topsoil than subsoil at low residue input levels (2.5 and 5 g residue C kg?1), but the trend was reversed with high residue inputs (20 and 40 g residue C kg?1). Initial SOC concentration affected residue C retention in the fine fraction but not in the whole soil. At low residue input levels, greater microbial activity in topsoil resulted in greater residue fragmentation and more residue C retained in the fine fraction, compared to the subsoil. At high residue input levels, less residue C accumulated in the fine fraction of topsoil than subsoil likely due to greater C saturation in the topsoil. We conclude that SOC-poor soils receiving high C inputs have greater potential to accumulate C in stable forms than SOC-rich soils.  相似文献   

4.
The worldwide production of rice husk, a by‐product and agrowaste that causes serious environmental problems, may reach 116 million t y?1. The objectives of this study were (i) to determine the physicochemical changes of rice husk and its structural chemistry during composting using 13carbon nuclear magnetic resonance (13C NMR) and (ii) to determine the effect of the composted rice husk (CRH) on the properties of Oxisol and cocoa (Theobroma cacao L.) growth under glasshouse conditions. Results showed an active composting phase occurred at the first 53 days as revealed by high carbon dioxide (CO2)‐C (40–71 µg g?1 h?1) production, followed by a matured composting phase occurring at 54–116 days as revealed by decreasing in CO2‐C production (10 µg g?1 h?1). The active composting was accompanied by increases in electrical conductivity (EC), pH, ammonium (NH4 +), and nitrate (NO3), whereas during the matured composting phase, the EC and cation exchange capacity increased but pH, NH4 +, and NO3 ?1 decreased. The ash of the produced compost contains mainly calcium (Ca), potassium (K), sulfur (S), magnesium (Mg), and phosphorus (P) as essential nutrients. The CP/MAS 13C NMR spectra before and after various composting times indicated the dominance of sharp and well‐resolved signal peaks at O‐alkyl C and di‐O‐alkyl C regions (67–73%), which are characteristic of cellulose. The percentage of N‐alky/methoxyl was 23–26% whereas phenolic, carboxyl, and alkyl C types were less than 3% each. The application of the CRH to an Oxisol significantly increased soil pH and Ca, Mg, K, sodium (Na), and silicon (Si) ions of in situ soil solution but decreased the amounts of toxic ions [aluminum (Al), manganese (Mn), and iron (Fe)]. The CRH was found to increase cocoa growth up to 37%.  相似文献   

5.
We examined the potential of a subsoil to denitrify nitrate under optimal anaerobic conditions in a laboratory-based incubation when supplied with a range of C substrates of increasing recalcitrance. Both topsoil and its associated subsoil were supplied with nitrate and either glucose, starch or cellulose. Microbial respiration and the evolution of N2O and N2 were measured. The subsoil supported low amounts of microbial activity and responded only to the glucose treatment; with less than one-fifth of the N2O production measured in the top soil. Overall, our findings demonstrated that the denitrification potential of this particular subsoil is relatively low and that only simple carbohydrates could be utilised readily by the resident microorganisms.  相似文献   

6.
Soil erosion has significant impacts on terrestrial carbon (C) dynamics. It removes C‐rich topsoil and deposits it in lower areas, which might result in its stabilization against microbial decay. Subsequently, C‐poor deeper horizons will be exposed, which also affects C stabilization. We analysed factors governing soil organic C (SOC) mineralization in topsoil (5–10 cm) and subsoil (75–100 and 160–200 cm) horizons from two contrasting sites (up‐slope compared with down‐slope) in the Belgian Loess Belt; we refer to these as eroding and depositional sites, respectively. Deposition of eroded soil material resulted in significantly increased SOC contents throughout the entire soil profile (2 m) and microbial biomass C in the topsoil. In a 28‐day incubation experiment we studied effects of O2 concentrations (0, 5 and 20%) and substrate (glucose) availability on C mineralization, soil microbial biomass and CaCl2‐extractable C. Carbon enrichment at the depositional site was accompanied by weak mineralization rates and small contents of water‐extractable organic C. Addition of glucose stimulated microbial growth and enhanced respiration, particularly in the subsoil of the depositional site. Availability of O2 showed the expected positive relationship with C mineralization in topsoils only. However, small O2 concentrations did not decrease C mineralization in subsoils, indicating that controls on C dynamics were different in top‐ and subsoils. We conclude that reduced C mineralization contributed to C accumulation as observed at depositional sites, probably because of poor availability of C in subsoil horizons. Limited availability of O2 in subsoils can be excluded as an important control of soil C accumulation. We hypothesize that the composition of the microbial community after burial of the organic‐rich material might play a decisive role.  相似文献   

7.
ABSTRACT

A field study was conducted with the objective of determining response of dry bean (Phaseolus vulgaris L.) to liming and copper (Cu) fertilization applied to an Oxisol. The lime rates used were 0, 12, and 24 Mg ha?1 and Cu rates were 0, 2.5, 5, 10, 20, and 40 kg Cu ha?1. Liming significantly increased common bean grain yield. Liming also significantly influenced soil chemical properties in the top (0–10 cm) as well as in the sub (10–20 cm) soil layer in favor of higher bean yield. Application of Cu did not influence yield of bean significantly. Average soil chemical properties across two soil layers (0–10 and 10–20 cm) for maximum bean yield were pH 6.4, calcium (Ca), 4.2 cmolc kg?1, magnesium (Mg) 1.0 cmolc kg?1, H+Al 3.2 cmolc kg?1, acidity saturation 40.4%, cation exchange capacity (CEC) 8.9 cmolc kg?1, base saturation 63.1%, Ca saturation 45.7%, Mg saturation 18.0%, and Potassium (K) saturation 2.9.  相似文献   

8.

Purpose

Soil temperature is a fundamental parameter affecting not only microbial activity but also manganese (MnIII,IV) and iron (FeIII) oxide reduction rates. The relationship between MnIII,IV oxide removal from oxide-coated redox bars is missing at present. This study investigated the effect of variable soil temperatures on oxide removal by MnIII,IV and FeIII oxide-coated redox bars in water-saturated soil columns in the laboratory.

Materials and methods

The Mn coatings contained the mineral birnessite, whereas the Fe coatings contained a mixture of ferrihydrite and goethite. Additionally, platinum (Pt) electrodes designed to measure the redox potential (EH) were installed in the soil columns, which were filled with either a humic topsoil with an organic carbon (Corg) content of 85 g kg?1 (pH 5.8) or a subsoil containing 2 g Corg kg?1 (pH 7.5). Experiments were performed at 5, 15, and 25 °C.

Results and discussion

Although elevated soil temperatures accelerated the decrease in EH after water saturation in the topsoil, no EH decreases regardless of soil temperature occurred in the subsoil. Besides soil temperature, the importance of soil organic matter as an electron donor is highlighted in this case. Complete removal of the MnIII,IV oxide coating was observed after 28, 14, and 7 days in the soil columns filled with topsoil at 5, 15, and 25 °C, respectively. Along the Fe redox bars, FeIII reducing conditions first appeared at 15 °C and oxide removal was enhanced at 25 °C because of lower EH, with the preferential dissolution of ferrihydrite over goethite as revealed by visual differences in the FeIII oxide coating. Oxide removal along redox bars followed the thermodynamics of the applied minerals in the order birnessite > ferrihydrite > goethite.

Conclusions

In line with Van’t Hoff’s rule, turnover rates of MnIII,IV and FeIII oxide reduction increased as a result of increased soil temperatures. Taking into account the stability lines of the designated minerals, EH-pH conditions were in accordance with oxide removal. Soil temperature must therefore be considered a master variable when evaluating the oxide removal of redox bars employed for the monitoring of soil redox status.
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9.
Three Oxisols, developed from serpentinite (Sungai Mas Series), basalt (Kuantan Series) and andesite (Segamat Series), selected to represent the most common Oxisols in Malaysia were sampled and studied. The objectives of this study were: (i) to determine mineralogical composition and factors responsible for changes in point of zero charge (pH0) of the variable charge component of three Oxisols; (ii) to use pH0 values to assess degree of chemical weathering; and (iii) to determine the magnitude of variable charge using corrected back-titration technique. The mineralogical composition was determined by X-ray diffraction analysis (XRD). The pH0 was determined by potentiometric titration in different electrolyte strengths. The magnitude of variable charge generation as a function of soil pH was measured using corrected back-titration to allow elimination of charge overestimation caused by solid dissolution and hydrolysis reactions. The results showed that the mineralogical composition were similar (kaolinite, goethite, hematite and gibbsite) between profiles but different in proportion, except for gibbsite which was absent in the andesite-derived soil. The sequential removal of soil organic matter (SOM), iron oxides and SOM together with iron oxides resulted in the changes of pH0 from 3.9–5.7 to 5.3–6.7, 2.6–3.7 and 3.3–4.5, respectively. These pH0 changes indicate SOM and sesquioxides are masking mineral surfaces and are factors responsible for lowering and increasing pH0 values, respectively. Regression correlation (R2 = 0.87??) showed that for every 1% organic C may decrease 1.0 unit of pH0 value. The pH0 values, after SOM removal, are in the order of Sungai Mas ~ Segamat > Kuantan Series. This suggests that the serpentinite and andesite-derived soils have achieved a relatively similar degree of chemical weathering and they are more weathered than the basalt-derived soil. The charge measured by corrected back-titration is 1.5–3.8 cmolc kg? 1 at pH 4.5 and increases to 4.2–10.8 cmolc kg? 1 at pH 6.5, indicating that the three Oxisols mainly bear variable charge. Charge overestimation resulted from dissolution and hydrolysis reactions during potentiometric titration ranges from 36 to 160%, depending on pH values (the lower the pH the higher is the overestimation). Hence, back-titration is a reliable technique to correct charge overestimation when using the traditional potentiometric titration for highly weathered tropical soils.  相似文献   

10.
Abstract

The interacting effects between topsoil water supply, nitrogen (N) placement and subsoil aluminum (Al) toxicity on wheat growth were studied in two split‐root pot experiments. The native nitrate‐N (NO3‐N) in the topsoil used in each experiment differed and were designated as high (3706 μM) and low (687 μM) for experiments one and two, respectively. Wheat was grown in pots that enabled the root system to be split so that half of the roots were in topsoil and the other half were in subsoils containing varying concentrations of soluble Al. Treatments were imposed which varied the supply of water to the topsoil (either ‘wet’ or ‘dry'). Placement of applied N in either the topsoil or subsoil had little effect on either shoot or root fresh weight, or on the length of roots produced in the subsoil section of the split pots. When water supply to the topsoil was decreased, both shoot and root growth of wheat declined and the yield decrease increased with subsoil Al. In the high‐N experiment, wheat grown in the low Al subsoil with the high native soluble subsoil (NO3 (3002 μM) was able to exploit the N and subsoil water, hence both shoot and root growth increased considerably in comparison to shoot and root growth of wheat grown in soils containing higher concentrations of subsoil Al. When the native NO3 was lower (i.e. the low‐N experiment) inadequate root proliferation restricted the ability of plants to use subsoil N and water irrespective of subsoil Al. The results from this study suggest that wheat, grown on yellow earths with Al‐toxic subsoils, will suffer yield reductions when the topsoil dries out (e.g. in the spring when winter rainfall ceases) because subsoil reserves of water and nitrogen are under utilised.  相似文献   

11.
In Saxony‐Anhalt, Germany, an area of about 6000 ha is covered by lignite‐ash‐derived substrates. In some cases, pollutants like heavy metals or toxic organic compounds had been disposed of together with the lignite ashes. For this reason, we assessed factors influencing the cation exchange capacity (CEC) of lignite‐ash substrates exposed to natural weathering. We chose four research sites reflecting the different methods of disposal: two dumped landfills and two lagooned ashes of different ages. After determining the CEC at pH 8.1 (CECpot), we evaluated the influence of the content of silt and clay and the content of total organic C. As lignite‐ash‐derived substrates are rich in oxalate‐extractable Si, Al, and Fe, we performed an oxalate extraction and determined afterwards the CECpot to assess the contribution of oxalate‐soluble compounds to the CECpot. Moreover, we determined the variable charge of selected samples at pH values ranging from 4 to 7. The lignite‐ash‐derived soils had a high CECpot with means ranging from 25.1 cmolc kg–1 to 88.8 cmolc kg–1. The influence of the parent material was more important than the degree of weathering. The content of total organic C consisting of pedogenic organic matter and coked lignite particles together with the content of silt and clay played a statistically significant role in determining the CEC. Another property that influenced the amount of CEC in medium textured lignite ashes was the content of oxalate‐soluble silica and aluminum. After oxalate extraction, they lost about 30% of their CEC due to the dissolution of oxalate‐soluble compounds. In coarse textured lignite ashes, oxalate extraction led to higher amounts of CEC, probably due to an increase of surface area resulting either from the disintegration of particles or from etching caused by insufficient dissolution of magnetite and maghemite. Moreover, lignite‐ash‐derived substrates exhibit a high amount of pH‐dependent charge. The CEC decreased by 40% in a topsoil sample and by 51% in a subsoil sample as the pH declined from 7 to 4.  相似文献   

12.
Abstract

Colloidal mineralogy is one of the main characteristics of the steady state reached in developed soils. Surface charge and other chemical and physical properties of the soil depend on colloidal mineralogy. It is, therefore, very important to further investigate the clay mineralogy of acidic variable charge subsoils in order to understand better their unusual chemical behavior. The objective of this investigation was to characterize the inorganic colloid mineralogy, chemical (subsoil solution pH and electrical conductivity), and charge properties (PZNC and PZSE) in some variable charge subsoils. Subsoil materials were collected from the southeastern United States and other tropical and subtropical areas around the world. The clay fraction mineralogy in the majority of the subsoils was dominated by the quartet kaolinite, gibbsite, goethite, and hematite. They manifested, however, a significant diversity in their charge and other chemical characteristics because the proportions and contents of mineralogical constituents, particle size distributions, and specific surface areas were very different. The pHKCl values ranged from 3.69 to 5.91. Under such conditions, pure kaolinite and aluminum/iron (Al/Fe) oxides have opposite net surface charges, and acidic subsoils are mixed charge colloidal systems. They have extremely low EC values, varying from 9.9 to 132 μS cm‐1, with corresponding ionic strengths between 0.14 and 1.86 mmol L‐1. They develop towards a “no or little charge state”; and the native pH is near the PZNC or PZSE. The overall charge characteristics and adsorption properties in these heterogenous colloidal systems are clearly a direct function of the relative contents, interactions, and surface reactivity of mineralogical soil constituents in the subsoils.  相似文献   

13.
Chickpea (Cicer arietinum L.) roots exude carboxylates. While chickpea commonly grows where the topsoil dries out during crop growth, the importance of carboxylate exudation by the roots and mobilization of soil P from below the dry topsoil has not been examined. The study investigates the response of carboxylate exudation and soil P mobilization by this crop to subsoil P fertilizer rate. In constructed soil columns in the glasshouse, the P levels (high, low, and nil P) were varied in the well‐watered subsoil (10–30 cm), while a low level of P in the dry topsoil (0–10 cm) was maintained. At flowering, rhizosphere carboxylates and rhizosphere soil from topsoil and subsoil roots were collected separately and analyzed. The concentration of total carboxylates per unit rhizosphere mass in the subsoil was nearly double that of the topsoil. Plants depleted sparingly soluble inorganic P (Pi), NaOH‐Pi, and HCl‐Pi, along with the labile Pi (water soluble and NaHCO3‐Pi). The P depletion by plants was greater from the subsoil than the topsoil. The study concluded that depletion of sparingly soluble P from the chickpea rhizosphere in the subsoil was linked with the greater levels of carboxylates in the rhizosphere. These findings indicate that chickpea, with its deep rooting pattern, can increase its access to subsoil P when the topsoil dries out during crop growth by subsoil rhizosphere modification.  相似文献   

14.
Recent studies have shown both increased (positive priming) and decreased (negative priming) mineralisation of native soil organic carbon (SOC) with biochar addition. However, there is only limited understanding of biochar priming effects and its C mineralisation in contrasting soils at different temperatures, particularly over a longer period. To address this knowledge gap, two wood biochars (450 and 550 °C; δ13C −36.4‰) were incubated in four soils (Inceptisol, Entisol, Oxisol and Vertisol; δ13C −17.3 to −28.2‰) at 20, 40 and 60 °C in the laboratory. The proportions of biochar- and soil-derived CO2–C were quantified using a two-pool C-isotopic model.Both biochars caused mainly positive priming of native SOC (up to +47 mg CO2–C g−1 SOC) in the Inceptisol and negative priming (up to −22 mg CO2–C g−1 SOC) in the other soils, which increased with increasing temperature from 20 to 40 °C. In general, positive or no priming occurred during the first few months, which remained positive in the Inceptisol, but shifted to negative priming with time in the other soils. The 550 °C biochar (cf. 450 °C) caused smaller positive priming in the Inceptisol or greater negative priming in the Entisol, Oxisol and Vertisol at 20 and 40 °C. At 60 °C, biochar caused positive priming of native SOC only in the first 6 months in the Inceptisol. Whereas, in the other soils, the native SOC mineralisation was increased (Entisol and Oxisol) and decreased (Vertisol) only after 6 months, relative to the control. At 20 °C, the mean residence time (MRT) of 450 °C and 550 °C biochars in the four soils ranged from 341 to 454 and 732−1061 years, respectively. At 40 and 60 °C, the MRT of both 450 °C biochar (25−134 years) and 550 °C biochar (93−451 years) decreased substantially across the four soils. Our results show that biochar causes positive priming in the clay-poor soil (Inceptisol) and negative priming in the clay-rich soils, particularly with biochar ageing at a higher incubation temperature (e.g. 40 °C) and for a high-temperature (550 °C) biochar. Furthermore, the 550 °C wood biochar has been shown to persist in soil over a century or more even at elevated temperatures (40 or 60 °C).  相似文献   

15.
Water extracts from fresh wheat and barley straw, straw incubated with Pleurotus ostreatus, and straw compost were studied by IR, 1H NMR, and 13C NMR spectroscopy. During incubation lignin was degraded, water extractability increased, and water extracts were rich in polysaccharides. After composting solubility decreased and the water extracts were rich in aromatic, methoxyl, and carboxyl C, but poor in O-alkyl C indicating that during composting mainly polysaccharides had been mineralized. GPC revealed that water extracts from straw compost contained polysaccharides, peptides, C- and O-substituted aromatics, and alkyl compounds.  相似文献   

16.
Batch adsorption experiments were conducted to assess the effects of pH and ionic strength (I) on cadmium (Cd) adsorption by two Brazilian Oxisols. Adsorption envelopes were constructed through soil sample reactions with 0.01, 0.1, and 1 mol L?1 calcium nitrate [Ca(NO3)2] solutions containing 5 mg L?1 of Cd, with an increasing pH value from 3 to 8. The adsorption increased drastically with increasing pH, varying from 20 to 90% in a narrow pH range (4–6 in topsoil and 5–6 in subsoil). Gibbs energy (ΔG) for Cd adsorption was negative, and the phenomenon became more thermodynamically spontaneous with an increase in pH. Under the standard 0.01 mol L?1 I and at pH close to natural, the ΔG values ranged from ?796 to ?3427 J mol?1. No effect of I was observed on the ΔG values for Cd adsorption at pH values less than 6. At values greater than pH 6, sharp changes in the Cd adsorption pattern were observed on subsoil samples. The only soil attribute significantly correlated with the spontaneity of Cd adsorption was the effective cation exchange capacity, ECEC (r = 0.97; p < 0.1).  相似文献   

17.
Microbial biomass C and soil respiration measurements were made in 17–20 yr old soils developed on sluiced and tipped coal‐combustion ashes. Topsoil (0–30 cm) and subsoil (30–100 cm) samples were collected from three soil profiles at two abandoned disposal sites located in the city area of Halle, Saxony‐Anhalt. Selected soil physical (bulk density and texture) and chemical (pH, organic C, total N, CEC, plant available K and P, and total Cd and Cu) properties were measured. pH values were significantly lower while organic C and total N contents and the C : N ratio were significantly higher in the topsoil than in the subsoil indicating the effects of substrate weathering and pedogenic C accumulation. Likewise, microbial biomass C, K2SO4‐extractable C, and soil respiration with median values of 786 μg biomass C g–1, 262 μg K2SO4‐C g–1, and 6.05 μg CO2‐C g–1 h–1, respectively, were significantly higher in the topsoil than in the subsoil. However, no significant difference was observed in metabolic quotient between the topsoil and the subsoil. Metabolic quotient with median values of 5.98 and 8.54 mg CO2‐C (g biomass C)–1 h–1 for the 0–30 cm and 30–100 cm depths, respectively, was higher than the data reported in the literature for arable and forest soils. Microbial biomass C correlated significantly with extractable C but no relationship was observed between it and total N, Cd, and Cu contents, as well as plant‐available K and P. We conclude that the presence of the remarkable concentration of extractable C in the weathered lignite ashes allowed the establishment of microbial populations with high biomass. The high metabolic quotients observed might be attributed to the heavy‐metal contamination and to the microbial communities specific to ash soils.  相似文献   

18.
Carbohydrates are an important component of soil organic matter, and a method is needed to quantify them, which would be efficient in terms of time and cost. Different extractants and methods were examined in this work for their efficiency to extract carbohydrate C from four calcareous soils. Four extractants (distilled water, 0.5 M potassium sulfate (K2SO4), and 0.25 and 0.5 M sulfuric acid (H2SO4)) and three incubation methods (shaking for 16 h, heating in an oven (85 °C) for 16 h, and heating in a water bath (85 °C) for 2.5 h) were compared. The results show that significantly more carbohydrate C was extracted from all four soils with oven and water bath heating of the soil–extractant suspensions than with shaking them at room temperature. The efficiency of the extractants decreased in this order: 0.5 M H2SO4 > 0.25 M H2SO4 > 0.5 M K2SO4. The combination of the heated–water bath incubation method with 0.5 M H2SO4 as extractant was the most efficient method.  相似文献   

19.
Soybean is one of the most important legume crops in the world. Two greenhouse experiments were conducted to determine the influence of liming and gypsum application on yield and yield components of soybean and changes in soil chemical properties of an Oxisol. Lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg?1 soil. Gypsum rates applied were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg?1 soil. Lime as well as gypsum significantly increased grain yield in a quadratic fashion. Maximum grain yield was achieved with the application of 1.57 g lime per kg soil, whereas the gypsum requirement for maximum grain yield was 1.43 g per kg of soil. Lime significantly improved soil pH, exchangeable soil calcium (Ca) and magnesium (Mg) contents, base saturation, and effective cation exchange capacity (ECEC). However, lime application significantly decreased total acidity [hydrogen (H) + aluminum (Al)], zinc (Zn), and iron (Fe) contents of the soil. The decrease in these soil properties was associated with increase in soil pH. Gypsum application significantly increased exchangeable soil Ca, base saturation, and ECEC. However, gypsum did not change pH and total acidity (H + Al) significantly. Adequate soil acidity indices established for maximum grain yield with the application of lime were pH 5.5, Ca 1.8 cmolc kg?1, Mg 0.66 cmolc kg?1, base saturation 53%, Ca saturation 35%, and Mg saturation 13%. Soybean plants tolerated acidity (H + Al) up to 2.26 cmolc kg?1 soil. In the case of gypsum, maximum grain yield was obtained at exchangeable Ca content of 2.12 cmolc kg?1, base saturation of 56%, and Ca saturation of 41%.  相似文献   

20.
Abstract

Potassium‐retention characteristics of the topsoil and subsoil of a medial over thixotropic, isomesic, Typic Hydrandept (Puaulu series) was investigated under moist conditions. This soil occurs in high rainfall areas where important losses of K are likely. Exchangeable cations were extracted with 1M NH4OAc pH 7 and Potassium Retention (Kr) was calculated by the difference between initial K (exchangeable, soluble, and added K) and final K. The results indicated that for any given K solution concentration, the amount of K held by the subsoil was twice that retained by the topsoil. The relationship between Kr and Potassium Adsorption Ratio (PAR) was nonlinear. The Gapon selectivity coefficient (KG) sharply decreased with increasing Potassium Saturation (Ep) and then leveled off to an almost constant value at Ep values of 0.25 for the topsoil and 0.15 (mmol‐1L for the subsoil. This constant value of =KG was reached when 5 and 10% of the initial exchange sites were occupied by K retained in the topsoil and subsoil, respectively.  相似文献   

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