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1.
Methane production potentials of twenty-eight rice soils in China   总被引：5，自引：0，他引：5  
 Soil CH4 production potentials were investigated by incubating air-dried soils under anaerobic conditions in the laboratory. Twenty-eight soils from different fields and locations were collected for this study. Soil CH4 production during a 100-day incubation differed greatly and were significantly correlated with soil organic content (r=0.61, P<0.01). The statistical significance increased when soils were grouped according to soil reduction rates. A significant correlation was also found between CH4 production and total N content (r=0.64, P<0.01) and between CH4 production and soil particle sizes of 0.25–0.05 mm (r=0.48, P<0.05). A negative exponential correlation was found between CH4 production and aerobic soil pH (r=–0.74, P<0.01). The 28 soils were stratified into four groups on the basis of variation in CH4 production rates which were associated with the soil reduction rate and soil organic content. The faster the Eh of soil fell, the more CH4 was formed. Adding rice straw to Hangzhou and Beijing soils increased CH4 production. The increase in CH4 production was more pronounced in the soil with the lowest organic matter content and slowest reduction rate than in the soil with highest organic matter and fastest reduction rate. Inorganic fertilizer had no significant influence on CH4 production potentials of either type of soil. Received: 26 November 1997  相似文献   

2.
易利用态有机物质对水稻土甲烷排放的激发作用   总被引：1，自引：0，他引：1  
为探讨外源有机物质对淹水稻田土壤CH4排放的激发作用,对比不同外源有机物质对土壤CH4排放的贡献差别,本研究选取3种标记的易利用态有机物(葡萄糖、乙酸和草酸)分别加入水稻土,进行了为期1个月的培养。结果表明:培养30 d后不同处理CH4的累计排放量差异显著(P0.05),其中,乙酸葡萄糖草酸对照;双因素方差分析结果显示,外源有机物质的添加加速了土壤易利用态有机质的矿化(即产生正激发效应);不同处理条件下激发作用产生的CH4分别占各处理CH4总累计排放量的73.3%(葡萄糖处理)、71.5%(乙酸处理)和40.9%(草酸处理),且CH4排放量与CH4激发效应之间极显著正相关关系说明土壤CH4排放主要要来自于土壤原有机质的分解,外源有机物质可能主要对土壤微生物活性及代谢途径有影响。  相似文献   

3.
Methane and C02 production in flooded acid sulfate soils of Thailand were governed primarily by soil oxidation-reduction potential (Eh) and pH. The critical Eh and pH levels at which CH4 emission began was Eh-150 mV, and pH 6.1. Low soil pH limited soil reduction and subsequently CH4 production. Soil respiration (C02 production) was influenced by Eh-pH levels and organic matter content. Soils with higher C02 production rates produced greater amounts of CH4. Soil pH, however, was the dominant variable which influenced organic matter decomposition, low soil Eh conditions and subsequent CH4 and CO2 production. Curvilinear or log transformations of pH, Eh and organic matter content (OM) were used in explaining variables controlling CH4 and CO2 production; CH4 = ?2.359 ? 0.0001 Eh + 2.047 pH ? 3.019 (In pH)2 CO2 = ?5210 ? 1.6 Eh + 3144 (In pH) + 1011 (In OM).  相似文献   

4.
The nitrogen (N) requirement for paddy rice cultivated in Bangladesh amounts to approximately 80 kg N ha?1. Lack of knowledge on N mineralization from soil organic matter leads farmers to meet this N requirement exclusively by costly mineral fertilizers, which have typically an efficiency of less than 40%. We assessed to what extent routinely analysed soil properties (N and carbon (C), texture, pH, extractable iron (Fe), aluminium (Al) and manganese (Mn), soil mineralogy and length of the annual inundation period) are able to predict net aerobic and anaerobic N mineralization in paddy soils. Both soil N and C correlated positively with the aerobic but not with the anaerobic N mineralization rate. Instead, relative anaerobic N mineralization showed a significant negative correlation with soil N content. We observed no significant influence of clay mineralogy on soil N mineralization. Aerobic but not anaerobic N mineralization increased with length of the annual inundation period while the proportion of the soil N that was mineralized during 120 days decreased. The large clay content of fields that are inundated for 9–10 months annually explains the co‐occurrence of large soil N contents and relatively small N mineralization rates in these fields. However, variation in texture did not explain variation in N mineralization of soils with inundation periods of 3–8 months. Instead, the anaerobic N mineralization correlated positively with Na pyrophosphate‐extractable Fe and negatively with pH (both at P < 0.01). Thus, pH and Fe content, rather than soil N content, clay mineralogy or texture, explained the substantial variation in anaerobic N mineralization of paddy soils in Bangladesh inundated for 3–8 months. It is not known if these relationships between net evolution of ammonium in soil and pH and Fe content are causal or indirect. Elucidation of these mechanisms would greatly further our comprehension of the biochemistry of the young ‘floodplain soils' with relatively low content of pedogenic oxides throughout southeast Asia.  相似文献   

5.
异化铁还原是厌氧环境中有机物降解的重要微生物过程,不仅影响Cr、U等无机污染物在环境中的迁移,还与CH4、N2O、H2S等温室气体的释放关系密切.本文选择7个旱作褐土样品,采用泥浆厌氧恒温培养的方法,研究了旱作褐土中氧化铁的厌氧还原特征,结果表明旱作褐土在淹水条件下可以发生铁氧化物的异化还原,其还原潜势介于4.47～5.95 mg g-1之间,还原速率常数介于0.15 ～0.27 d-1之间.褐土中部分晶态铁氧化物可在这一过程中被还原,游离铁的平均还原率为41.95％.经过40 d厌氧培养后,99.26％的NO3-和88.82％的SO42-被还原.还原过程的速率常数κ、Vmax、Tmax随着土壤有机碳含量增加而增加,还原潜势与土壤SO42-含量呈显著负相关关系.  相似文献   

6.
Aerated forest soils are a significant sink for atmospheric methane (CH4). Soil properties, local climate and tree species can affect the soil CH4 sink. A two-year field study was conducted in a deciduous mixed forest in the Hainich National Park in Germany to quantify the sink strength of this forest for atmospheric CH4 and to determine the key factors that control the seasonal, annual and spatial variability of CH4 uptake by soils in this forest. Net exchange of CH4 was measured using closed chambers on 18 plots in three stands exhibiting different beech (Fagus sylvatica L.) abundance and which differed in soil acidity, soil texture, and organic layer thickness. The annual CH4 uptake ranged from 2.0 to 3.4 kg CH4-C ha−1. The variation of CH4 uptake over time could be explained to a large extent (R2 = 0.71, P < 0.001) by changes in soil moisture in the upper 5 cm of the mineral soil. Differences of the annual CH4 uptake between sites were primarily caused by the spatial variability of the soil clay content at a depth of 0-5 cm (R2 = 0.5, P < 0.01). The CH4 uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate. Low CH4 uptake activity during winter was further reduced by periods with soil frost and snow cover. There was no evidence of a significant effect of soil acidity, soil nutrient availability, thickness of the humus layer or abundance of beech on net-CH4 uptake in soils in this deciduous forest. The results show that detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary for a reliable larger scale estimate of the CH4 sink strength in this mixed deciduous forest. The results suggest that climate change will result in increasing CH4 uptake rates in this region because of the trend to drier summers and warmer winters.  相似文献   

7.
Decomposition of organic matter in inundated wetland soils requires a number of interdependent microbial processes that ultimately generate CO2 and CH4. Largely as the result of anaerobic decomposition, wetland soils store globally significant amounts of organic carbon and are currently net sources of CH4 to the atmosphere. Given the importance of wetlands in the global carbon cycle, it is important to understand controls on anaerobic decomposition in order to predict feedbacks between wetland soils and global climate change. One perplexing pattern observed in many wetland soils is the high proportion of CO2 resulting from anaerobic decomposition that cannot be explained by any measured pathway of microbial respiration. Recent studies have hypothesized that humic substances, and in particular solid-phase humic substances in wetland soils, can support anaerobic microbial respiration by acting as organic electron acceptors. Humic substances may thus account for much of the currently unexplained CO2 measured during decomposition in wetland soils. Here we demonstrate that humic acids extracted from a variety of wetland soils act as either electron donors or electron acceptors and alter the ratio of CO2:CH4 produced during anaerobic laboratory incubations. Our results suggest that soil-derived humic substances may play an important, and currently unexplored, role in anaerobic decomposition in wetland soils.  相似文献   

8.
Peatlands are important ecosystems in the global carbon cycle, serving as both the largest terrestrial soil carbon pool and a significant source of the greenhouse gas methane (CH4). In Sphagnum moss-dominated wetlands, anaerobic decomposition, and in particular the production of CH4, is highly variable and controlling factors are poorly understood. The main objective of this study was to determine if leachates of Sphagnum can explain differences in anaerobic decomposition and CH4 production from three Sphagnum-dominated peatlands.Soils from each peatland were incubated anaerobically for 40 days with Sphagnum-derived organic matter (S-DOM) extracted using distilled water at 25 or 60 °C in a fully-crossed experimental design. S-DOM extracted at 25 °C had a minimal effect on decomposition, but S-DOM extracted at 60 °C increased CO2 production in all soils. The magnitude of the increased CO2 production in response to S-DOM depended on the source site of the S-DOM. The response of CH4 production to additions of S-DOM extracted at 60 °C was more complex. Soils from one peatland produced no CH4 during the incubation, regardless of S-DOM source. The same S-DOM additions led to an increase in CH4 production in a second soil, but a decrease in CH4 production in the third soil. Stable isotopic evidence suggests that these patterns were driven by the selective inhibition or stimulation of acetoclastic methanogenesis. Taken together, these data suggest S-DOM alone does not explain differences in anaerobic decomposition in peatlands, but may play a role in regulating CO2 and CH4 production.  相似文献   

9.
Summary The CH4 flux from intact soil cores of a flooded rice field in Italy was measured under aerobic and anaerobic incubation conditions. The difference between the anaerobic and aerobic CH4 fluxes was apparently due to CH4 oxidation in the oxic soil surface layer. This conclusion was supported by measurements of the vertical CH4 profile in the upper 2-cm layer, and of the V max of CH4 oxidation in slurried samples of the soil surface layer. About 80% of the CH4 was oxidized during its passage through the soil surface layer. CH4 oxidation was apparently limited by the concentration of CH4 and/or O2 in the active surface layer. The addition of ammonium to the water layer on top of the soil core reversibly increased the aerobic CH4 fluxes due to inhibition of CH4 oxidation in the soil surface layer.  相似文献   

10.
We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO2, CH4 and N2O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH4 uptake rates (<1 kg C ha−1 yr−1) and, coinciding with WFPS values >70%, episodes of CH4 emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH4 (4.7 kg C ha−1 yr−1). The N2O releases at the cropland and pasture sites (2.7 and 4.8 kg N2O-N ha−1 yr−1) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N2O-N ha−1 yr−1). The highest N2O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH4 and N2O. On the contrary, afforestation resulted in increases in SOM content and CH4 uptake, as well as decreases in N2O emissions.  相似文献   

11.
Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H2O2 method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.  相似文献   

12.
14C-labelled cellulose and 15N-labelled (NH4)2SO4 were added to four soils with clay contents of 4, 11, 18 and 34%, respectively. Labelled cellulose was added to each soil in amounts corresponding to 1, 2 and 4 mg C g?1 soil, respectively, and labelled NH4+ at the rate of 1 mg N per 25 mg labelled C.After the first month of incubation at temperatures of 10, 20 and 30°C, respectively, from 38 to 65% of the labelled C added in cellulose had disappeared from the soils as CO2, and from 60 to nearly 100% of the labelled N added as NH4+ were incorporated into organic forms. The ratio of labelled C remaining in the soils to labelled N in organic forms was close to 25 after 10 days of incubation, decreasing to about 15 after 1 month and about 10 after 4 yr.The retention of total labelled C was largest in the soil with the highest content of clay where after 4 yr it was 25% of that added, compared to 12 in the soil with the lowest content of clay. The incorporation of labelled N in organic forms and its retention in these forms was not directly related to the content of clay in the soils, presumably because the two soils with the high content of clay had a relatively high content of available unlabelled soil-N which was used for synthesis of metabolic material.The proportionate retention of labelled C for a given soil was largely independent of the size of the amendments, whereas the proportionate amount of labelled N incorporated into organic forms increased in the clay-rich soils with increasing size of amendments. Presumably this is because the dilution with unlabelled soil-N was less with the large amendments.From 50 to 70% of the total labelled C remaining in the soils after the first month of incubation was acid hydrolyzable, as compared to 80–100% of the total remaining labelled organic N. This relationship held throughout the incubation and was independent of the size of the amendment and of the temperature of incubation.During the second, third and fourth year of incubation the half-life of labelled amino acid-N in the soils was longer than the half-life of labelled amino acid-C, presumably due to immobilization reactions. Some of the labelled organic N when mineralized was re-incorporated into organic compounds containing increasing proportions of native soil-C. whereas labelled C when mineralized as CO2 disappeared from the soils.In general, native C and native organic N were less acid hydrolyzable and were accounted for less in amino acid form than labelled C and N.The amount of labelled amino acid-C, formed during decomposition of the labelled cellulose, and retained in the soil, was proportional to the clay content. This amount was about three times as large in the soil with the highest content of clay as in the soil with the lowest content. This difference between the soils was established during the first 10 days of incubation when biological activity was most intense, and it held throughout the 4 yr of incubation; proportionally it was independent of the amount of cellulose added and the temperature.In contrast, the labelled amino acid-N content was not directly related to the amount of clay in the soil, presumably because more unlabelled soil-N was available for synthesis of metabolic material in the two clay-rich soils than in those soils with less clay. The wider ratio between labelled amino acid-C and labelled amino acid-N in the two clay-rich soils as compared with those obtained with the soils with less clay indicates this.The effect of clay in increasing the content of organic matter in soil is possibly caused by newly synthesized matter, extracellular metabolites, as well as cellular material, forming biostable complexes and aggregates with clay. The higher the concentration of clay the more readily the interactions take place. The presence of clay may also increase the efficiency of using substrate for synthesis.  相似文献   

13.
The reactions of methyl nitrite (CH3ONO), a gaseous product of NO?2 decomposition in soils, were studied by exposure of soils in closed vessels to the gas. The N transformations occurring in soils at different soil-water states were assessed by measuring CH3ONO and other gaseous forms of N in the gas space, soil inorganic N (NH4+, NO?2, NO3?) and incorporation of CH3O15NO into the soil organic N fraction. The initial rate of uptake of CH3ONO increased with decreasing soil-water content, but the rate of hydrolysis decreased as soil-water content decreased below – 33kPa matric potential. Uptake was not affected by y-irradiation of soils. Adsorption isotherms conformed to the Langmuir equation in each of 22 oven-dry soils studied. Langmuir adsorption maxima were positively correlated with the clay contents of the soils, and adsorption was reversible to some extent at all soil-water states. Small amounts of added CH3ONO were recovered as N2 and N2O and as 15NH4+ in γ-irradiated soils. From 60 to 72% of added CH3O15NO was recovered by Kjeldahl digestion; this was indicative of a chemical reaction with soil organic matter. The results suggest that the physical process of adsorption of CH3ONO by clay minerals and the chemical fixation of CH3ONO by soil organic matter are key factors controlling the atmospheric concentration of CH3ONO, and that the combined effect of these processes, together with hydrolysis in the soil solution, will inhibit the emission of CH3ONO formed in N-fertilized soils.  相似文献   

14.
In a field study, potassium (K) applied as muriate of potash (MOP) significantly reduced methane (CH4) emission from a flooded alluvial soil planted to rice. Cumulative emission was highest in control plots (125.34 kg CH4 ha−1), while the lowest emission was recorded in field plots receiving 30 kg K ha−1 (63.81 kg CH4 ha−1), with a 49% reduction in CH4 emission. Potassium application prevented a drop in the redox potential and reduced the contents of active reducing substances and Fe2+ content in the rhizosphere soil. Potassium amendment also inhibited methanogenic bacteria and stimulated methanotrophic bacterial population. Results suggest that, apart form producing higher plant biomass (both above- and underground) and grain yield, K amendment can effectively reduce CH4 emission from flooded soil and could be developed into an effective mitigation option, especially in K-deficient soils.  相似文献   

15.
徐勇贤  梁强  周勇  陈志清  王火焰  黄标 《土壤》2024,56(1):103-111
以云南抚仙湖北岸澄江市约1 130 hm2农田土壤为研究对象,通过调查分析土壤物理、化学性质,评价了研究区土壤质量状况,并进一步利用空间分析、相关分析与主成分分析对研究区烟草种植的主要土壤障碍因子进行了分析。结果表明:研究区土壤整体偏黏(平均黏粒含量496.7 g/kg)、偏碱(pH均值7.45)、有机质含量较高(均值28.55 g/kg)、大中微量营养元素有效态含量也整体偏高(水解性氮均值119.10 mg/kg、有效磷均值68.85 mg/kg、速效钾均值208.44 mg/kg、有效锰均值28.14 mg/kg),但各土壤性质在空间上变异较大。土壤基础地力、人为施肥管理、质地、酸碱性、有效锰是影响该地区土壤肥力的主要障碍因素,这些因素可通过有机质、速效钾、黏粒、pH、有效锰等指标进行评价,并指导烟草种植的土壤管理。烟草种植过程中应根据土壤性质、烟草养分需求,结合土壤养分空间变异采取相应的土壤改良措施。  相似文献   

16.
Based on a literature review including 201 surface soils from wet, mild, mid-latitude climates and 290 soils from the Lower Saxony soil monitoring programme (Germany), we investigated the relationship between soil clay content and soil organic matter turnover. The relationship was then used to evaluate the clay modifier for microbial decomposition in the organic matter module of the soil-plant-atmosphere model DAISY. A positive relationship was found between soil clay content and soil microbial biomass (SMB) C. Furthermore, a negative relationship was found between soil clay content and metabolic quotient (qCO2) as an indicator of specific microbial activity. Both findings support the hypothesis of a clay dependent capacity of soils to protect microbial biomass. Under the differing conditions of practical agriculture and forestry, no or only very weak relationships were found between soil clay content and non-living soil organic matter C (humus C). It is concluded that the stabilising effect of clay is much stronger for SMB than for humus. This is in contrast to the DAISY clay modifier assuming the same negative relationship between soil clay content, on the one hand, and turnover of SMB and turnover of soil humus on the other. There is a positive relationship between SMB and microbial decomposition activity under steady-state conditions (microbial growth≈microbial death). The original concept of a biomass-independent simulation of organic matter turnover in the DAISY model must therefore be rejected. In addition to the original modifiers of organic matter turnover, a modifier based on the pool size of decomposing organisms is suggested. Priming effects can be simulated by applying this modifier. When using this approach, the original modifiers are related to specific microbial activity. The DAISY clay modifier is a useful approximation of the relationship between the metabolic quotient (qCO2) as an indicator of specific microbial activity and soil clay content.  相似文献   

17.
The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K2SO4-extractable organic C and 33.3 mM KMnO4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation-extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation-incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO2 production rate, relative C mineralization rate (CO2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.  相似文献   

18.
Anaerobic decomposition in wetland soils is carried out by several interacting microbial processes that influence carbon storage and greenhouse gas emissions. To understand the role of wetlands in the global carbon cycle, it is critical to understand how differences in both electron donor (i.e., organic carbon) and terminal electron acceptor (TEA) availability influence anaerobic mineralization of soil organic matter. In this study we manipulated electron donors and acceptors to examine how these factors influence total rates of carbon mineralization and the pathways of microbial respiration (e.g., sulfate reduction versus methanogenesis). Using a field-based reciprocal transplant of soils from brackish and freshwater tidal marshes, in conjunction with laboratory amendments of TEAs, we examined how rates of organic carbon mineralization changed when soils with different carbon contents were exposed to different TEAs. Total mineralization (the sum of CO2 + CH4 produced) on a per gram soil basis was greater in the brackish marsh soils, which had higher soil organic matter content; however, on a per gram carbon basis, mineralization was greater in the freshwater soils, suggesting that the quality of carbon inputs from the freshwater plants was higher. Overall anaerobic metabolism was higher for both soil types incubated at the brackish site where SO42− was the dominant TEA. When soils were amended with TEAs in the laboratory, more thermodynamically favorable respiration pathways typically resulted in greater organic matter mineralization (Fe(III) respiration > SO42− reduction > methanogenesis). These results suggest that both electron donors and acceptors play important roles in regulating anaerobic microbial mineralization of soil organic matter.  相似文献   

19.
The sorption of zinc (Zn) by two acid tropical soils, Mazowe clay loam (kaolinitic, coarse, Rhodic Kandiustalf) and Bulawayo clay loam (coarse, kaolinitic, Lithic Rodustalf), was studied over a wide range of Zn solution concentrations. Samples of the two soils used in the experiments were collected at both uncleared, uncultivated (virgin) sites and cultivated sites. The two virgin soils showed similar abilities to bind Zn. Mazowe soil (40 g organic matter kg?1) presented the highest affinity for Zn. Yet, Bulawayo soil (23.5 g organic matter kg?1) sorbed almost the same amount. Bulawayo soil had higher pH and Fe and Mn-oxide content than Mazowe soil. Once cultivated, the two soils behaved quite differently. After 50 years, Mazowe soil had lost 60% of its organic matter and effective cation exchange capacity (ECEC). In this soil, Zn sorption capacity had also been decreased by 60%. Clearing and 10 years under cultivation had affected neither the organic matter content nor the ECEC of Bulawayo soil. For this soil, Zn sorption was even higher in the cultivated soil, presumably due to an increase in the amount of Fe and Mn oxide from subsoiling. Zinc sorption was dependent upon pH, with retention dramatically increasing in the pH range 6–7. Sorption occurred at pH values below the point of zero charge (PZC), indicating that the sorption reaction can proceed even in the presence of electrostatic repulsion between the positively charged soil surface and the cation. In the two soils, the reversibility of the sorption reaction was very low. More than 90% of the sorbed Zn was apparently strongly bonded.  相似文献   

20.
Fifty-five soil samples representing Egyptian alluvial and lacustrine soils were chemically analyzed for total Se which was found to vary from 0.18 to 0.85 ppm with an average of 0.45 ppm. These levels are positively correlated with organic matter, total carbonate and clay content of the soils. Minimum variation of total Se with soil depth was found. The chemical fractionation of soil Se, expressed as percent of the total, indicates that on the average about 25.4 % exists in 0.2 M K2SO4-extractable form, 18.5 % is extracted with 0.5 N NH4OH, 9.7 % as 6 N HCl-extractable form and 13.8 % as extractable with 9 N HNO3. Amounts of K2SO4-Se and HNO3-Se in soils correlated significantly with soil organic matter, total carbonate, free iron oxide and clay content. The NH4OH-Se and HCl-Se fractions correlated significantly only with organic matter and clay content. There is also significant correlation between total Se and the studied Se fractions. Specific adsorption of Se by soils was low as expressed by the Langmiur adsorption maximum values. The high soil pH has a reducing effect on Se adsorption.  相似文献   

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