水稻土中氧化还原过程的研究Ⅸ.水溶态亚铁的存在形态

水溶态亚铁是亚铁中最活泼的部分,对一系列的土壤性质和水稻生长具有直接影响.有相当多的材料(彭拉姆帕鲁马,1955;于天仁、刘碗兰,1957)表明,当土壤中亚铁量过多时,可使水稻的生长受阻,并且亚铁的出现可以改变交换性养分离子在固液相之间的平衡(保学明等,1964).但是水溶态亚铁的形态甚为复杂,各种形态的亚铁在土壤肥力上的意义也应该不同,因此关于水溶态亚铁的存在形态的研究,具有实际意义.     

Comparison of several methods for determining free iron in soils

In the previous paper (1), for determining free iron in paddy soils the writers proposed a new method in which free iron was removed by reduction with sodium hydrosulfite in disodium ethylendiamine tetraacetate solution. As described in that paper, many methods have been proposed up to the present time. In this paper the writers are to compare their method with some of those methods, especially with both methods using sodium hydrosulfite and dilute hydrochloric acid and using hydrogen sulfide and dilute hydrochloric acid. The latter method has generally been employed for free iron determination of paddy soils in Japan.     

水稻土中氧化还原过程的研究 ⅤⅡ.亚铁的存在形态

水稻土在渍水时,合有大量的亚跌;在较为张烈的还原条件下,可以达每百克土中四、五百毫克^[1,2]。这样大量的亚铁的存在,应该具有一定的土壤学意义。     

Light inhibition of carbon mineralization associated with iron redox processes in calcareous paddy soil

Purpose

The iron redox cycle is closely tied to the fate of carbon in terrestrial ecosystems, especially paddy soils. Varies diurnally and seasonally, light—the crucial environmental factor—may be a fundamental factor elucidating temporal and spatial variabilities of carbon-containing gases emission. The role of sunlight in the iron-mediated carbon cycle, however, has not been fully elucidated. We conduct this study to test the role of light in the iron-mediated carbon cycling.

Materials and methods

In this study, we conducted anaerobic incubation experiments of a calcareous paddy soil in serum vials under alternating dark and light conditions. The dynamic evolution of the carbon and iron contents was evaluated by measuring the CO₂, CH₄, and O₂ concentrations in the headspace of the vials, as well as the water-soluble inorganic carbon, microbial biomass carbon, and HCl-extractable ferrous iron contents in soil slurries. We also analyzed the soil microbial community structure by high-throughput 16S rRNA gene sequencing.

Results and discussion

The results highlighted the positive correlation between carbon mineralization and ferric iron reduction under dark conditions. Under light conditions, however, ferrous iron was oxidized by the O₂ generated via oxygenic photosynthesis of phototrophic bacteria such as Cyanobacteria, along with a decreased production of CO₂, CH₄, and water-soluble inorganic carbon. The abundance of Cyanobacteria positively correlated to O₂ levels and MBC content significantly. Light-induced periodic variations in the redox conditions facilitated carbon fixation in microbial biomass and up to 31.79 μmol g^?1 carbon was sequestrated during 30 days light incubation.

Conclusions

These results indicate that light inhibits the emission of carbon-containing greenhouse gases associated with the iron redox cycle in calcareous paddy soil. Assimilation of inorganic carbon by phototrophs may responsible for the inhibition of carbon mineralization. Our study suggests that procedures allowing more light to reach the soil surface, for instance, reducing the planting density, may mitigate greenhouse gas emissions and promote carbon sequestration in paddy soils.

     

Evaluation of slag application to decrease methane emission from paddy soil and fate of iron

Abstract

Organic carbon in paddy soil is oxidized to carbon dioxide by reducing electron acceptors for a certain period after submerging. Methane production commences after the reduction of iron oxide which is the most important electron acceptor in the soil. We aimed to study the long-term suppression of the methane emission from the paddy soil by single application of iron slag. A revolving furnace slag (RFS; 248 g Fe kg^?1) was applied to the potted soil at the rate of 0 (control) or 20 ton ha^?1 in 2000. Rice plants were successively cultivated on the potted soils for 3 years without further application of the RFS. Methane emissions from the potted soils with rice plants were measured by the closed chamber method during these cultivation periods. Total flux of CH₄ emission from the pot applied with ,FS decreased by 5–30% compared with the control. The RFS supplied free iron oxide to the potted soil, and its iron acted as the oxidizing agent as evidenced by the increase in ferrous iron content in the soil. The amount of iron lost from leaching at the bottom of the pots was estimated as 54–59 kg Fe ha^?1 year^?1 at the percolation rate of 20 mm d^?1. Accordingly, half-life of the iron in the applied RFS was calculated as 42–46 years. Therefore, there is a possibility that the suppressing effect of RFS on CH₄ emission is sustained for a half-century, Contents of heavy metals (Cd, Cu, and Zn) in the brown rice harvested from the pot applied with RFS were not significantly different with those from the control pot.     

不同开垦年限水稻土还原性物质含量及其分布

以辽宁省各地棕壤型、草甸土型水稻土为研究对象,探讨了不同开垦年限的棕壤型、草甸土型水稻土中还原性物质总量、活性还原性物质、络合态铁、水溶性亚铁、水溶性亚锰含量及其分布状况。结果表明,不同开垦年限供试水稻土随着开垦年限增加表层还原性物质总量、活性还原性物质、络合态铁、水溶性亚铁和水溶性亚锰含量明显增加,且均随土壤深度增加而减少,其积累主要集中在土壤上层。土壤络合态铁与还原性物质总量和活性还原性物质均呈极显著正相关,表层土壤有机质对铁、锰的络合减少了铁、锰元素向剖面下层的迁移数量。开垦10年以上,水稻土耕层中还原性物质就明显积累,直至60年,其积累量仍不断增加,因此生产上必须采取措施抑制水稻土中还原性物质的累积。     

Effect of Organic Matters on the Formation of Ferrous Iron in Soils

Under the condition of flooded irrigation, it has been confirmed that ferric iron compounds existing mostly in insoluble forms in soils were appropriately reduced to more soluble ferrous forms, and that the application of organic matters brought about favorable circumstances for the development of the reducing state induced by activated microbes^{1 2}) and consequently the formation of active ferrous iron in soils resulted.     

水稻土中氧化还原过程的研究——Ⅷ.水溶态亚铁的区分

在上一工作(保学明等,1964)中,已证明当土壤中加入大量有机质并溃水时,水溶态亚铁可以高达每100克土数十毫克,占亚铁总量的10-25%,水溶液中的亚铁浓度达百万分之一二百甚至更高.由于水溶态亚铁是亚铁中最活泼的部分,对于土壤性质和水稻生长具有直接影响,所以关于水溶态亚铁的性质的研究,应该具有重要意义.     

Characteristics of ferrous iron forms in paddy soil with reference to development of the soil profile

It is considered that transformation of iron compounds owing to alternation of submergence and drainage exert a complicated influence on physico-chemical properties of paddy soils and that subsequent changes in physicochemical properties play an important role in the development of paddy soil profile, for example gley formation, occurrence of iron mottling etc. Ferrous iron in waterlogged condition, however, exists in many complex forms, and is under physico-chemical equilibrium in conjunction with the environmental soil condition. In the previous paper, the authors have suggested that ferrous iron status in submerged condition is closely related to the characteristics of genetic soil types from their experiment on fractionation of inorganic ferrous iron (8).     

Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. I. Effect of iron oxides on ammonium fixation

Experiments were conducted with two typical paddy soils from China and a vermiculite to study the influence of iron oxides on the fixation and release of ammonium. Removing iron oxides, especially amorphous iron oxides, from the soils favoured the release of non-exchangeable NH₄-N and stimulated the fixation of NH₄-N in the presence of added (NH₄)₂SO₄. Addition of artificial goethite and hematite to the original soils or to the soils free of iron oxides reduced the fixation of NH₄⁺-ions. This effect was also observed with vermiculite. We conclude that the coating of clay minerals with iron oxides has an impact on the diffusion of NH₄⁺-ions into and out of the interlayers of the clay minerals. The reduction and dissolution of iron oxides induced by low redox potential (E_h) after flooding of paddy soils is assumed to be an important mechanism controlling NH₄⁺-fixation in paddy fields.     

Surface-water gley soils in Bangladesh: Genesis

Extensive areas of periodically wet, acid soils in Bangladesh have a seasonally fluctuating pH of the surface horizon and evidence for net clay loss. Morphological, chemical, mineralogical and other data mainly on a typical profile of these surface-water gley soils indicate a clay loss of some 1.5 kg/dm' ; alteration of smectite to a soil chlorite, interlayered material with trapped ferrous iron; the consequent drop in C.E.C. of the clay fraction; and the presence of amorphous silica. The data were used to reconstruct a sequence of three soil forming processes: Vertisol formation, then argilluviation, followed by ferrolysis.Ferrolysis involves, in the wet season: reduction producing ferrous iron, which displaces part of the exchangeable basic cations and aluminium; leaching of bases and part of the aluminium; and interlayer formation by the remaining aluminium while some exchangeable ferrous iron is trapped in the interlayers. In the dry season, oxidation of exchangeable ferrous iron produces exchangeable hydrogen, part of which attacks the clay minerals and is neutralized by liberation of Al, Mg and other ions from the clay structure. Part of the silica remaining from the clay structure is leached out in the next wet season, part accumulates in amorphous form. In soils long used for paddy cultivation, man has concentrated the ferrolysis process in the ploughed layer by the formation of a slowly permeable ploughpan causing strong reduction only in the surface horizon.The hydromorphic albic horizon over more clayey material is indicative of the dominant process in surface-water gley soils. This sequum could usefully have a more important place in soil classification than it has at present, e.g. at great group level.     

江西低丘红壤性水稻土的主要化学特性研究

三个红壤性水稻土的有机质和腐殖质的含量由淹育型水稻土→潴育型水稻土→潜育型水稻土依次逐渐增加,其C/N和H/P比值也顺次增大。它们的粘土矿物组成无明显差异。铁、锰物质在潴育型水稻土剖面中分异最明显,其次为淹育型水稻土;而无定形氧化铁在剖面中变幅最大却是潜育型水稻土;结晶态铁在土壤剖面中分异亦有一定规律,其中潴育型水稻土的指示性土层(W层)的晶胶率(结晶铁/无定形铁)远较其它土层为高,这种变化特性的差异,对区分不同水分作用的水稻土发育类型有一定的特殊意义;土壤络合态铁与土壤有机质含量有关。土壤氧化锰与土壤氧化铁相比虽然含量低,但对土壤氧化还原条件反应更加敏感,所以在土壤剖面中淋移趋势更加明显。     

聚合氨基酸对北方水稻土中氧化铁存在形态的影响

为了解不同类型水稻土中氧化铁含量特征,探明添加外源聚合氨基酸对水稻土中氧化铁形态变化的影响,本研究以中国北方不同类型水稻土(棕壤型、草甸土型和滨海盐渍型)为研究对象,设置添加占供试土壤干重0.05%的γ-聚谷氨酸和聚天冬氨酸处理,以不添加氨基酸作为对照。通过室内恒温厌氧培养30 d后,测定各水稻土全铁、游离氧化铁、无定形氧化铁和络合态铁含量及氧化铁的活化和络合程度。结果表明:供试的北方3种典型水稻土中,游离氧化铁含量为滨海盐渍型草甸土型≥棕壤型,络合态铁含量为棕壤型滨海盐渍型≥草甸土型,而无定形氧化铁含量为棕壤型滨海盐渍型草甸土型。两种外源聚合氨基酸对不同类型水稻土氧化铁形态转化能力影响存在差异,与不添加氨基酸的对照相比,添加γ-聚谷氨酸的棕壤型水稻土无定形氧化铁和络合态铁含量分别增加27.72%和32.25%,聚天冬氨酸对无定形氧化铁和络合态铁含量无显著促进作用;在草甸土型水稻土中,γ-聚谷氨酸和聚天冬氨酸均能显著增加无定形氧化铁含量,且与对照相比,络合态铁含量分别增加136.24%和12.00%;γ-聚谷氨酸能有效促进滨海盐渍型水稻土中无定形氧化铁和络合态铁的生成。总之,添加γ-聚谷氨酸和聚天冬氨酸对水稻土游离氧化铁的含量没有明显影响;而添加γ-聚谷氨酸能有效增加水稻土中无定形氧化铁和络合态铁含量,降低晶胶率,有利于提高土壤中有效铁含量,显著活化铁氧化物,抑制各类型水稻土中铁的结晶老化;而聚天冬氨酸对水稻土无定形氧化铁和络合态铁没有明显的激发效应。     

Coupled diffusion and oxidation of ferrous iron in soils. I. Kinetics of oxygenation of ferrous iron in soil suspension

The kinetics of oxidation of iron in an aqueous suspension of a thoroughly reduced low-humus tropical rice paddy soil were followed by measuring the extractable ferrous iron in the whole suspension and in the solution. Three-quarters of the initial ferrous iron was oxidized rapidly (first-order rate constant = 9.2 × 10^?5 s^?1). The subsequent reaction was slow (first-order rate constant = 9.4 × 10^?7 S^?1) and was not studied in detail. The pH fell from 6.6 to 4.9 over the course of the fast reaction. In further experiments the rate of oxidation was followed at constant pH values in the range 6.5 to 4.5. It was concluded that the oxidation of adsorbed iron was much faster than solution iron, and that the adsorbed iron was oxidized at a rate that was nearly independent of the pH. During the reaction some ferrous iron is adsorbed on the ferric hydroxide formed. The proportion of the remaining ferrous iron adsorbed on ferric hydroxide rather than the original exchange surfaces was high at pH > 6.0 and low at pH < 5.0. The rate of oxidation of the ferrous iron was similar whether it was adsorbed on exchange sites or on the ferric hydroxide formed. Since the rate of oxidation of the iron adsorbed on ferric hydroxide was very much slower than that on ferric hydroxide formed in the absence of soil, it is suggested that the rate in soil may be controlled by diffusion of oxygen to the adsorption sites.     

Studies on soils of Peaty paddy fields II

Chemical changes ordinarily occuring in flooded paddy soils in Japan had been investigated in detail by Dr. SHIOIRI and his coworkers (1). The problem of degraded paddy soils had also been discussed by them on the basis of the experimental results on the deficiency of free iron oxides which affect the root of rice plant. As described in the previous report (2), causes for low rice production in the peaty Paddy fields seemed to be different from those in the degraded paddy ones. Thereupon, for a comprehensive understanding of the properties of peaty paddy soils, many important aspects such as the nature and role of each soil layer, and the behaviour of iron and nitrogen in soil Will have to be studied.     

Bonding and oxidation state of iron in humic complexes extracted from some Greek soils

Electron spin resonance and Mössbauer spectroscopy were used to obtain information on the nature of the bonding and of the oxidation state of iron in complexes of iron-humic substances, some prepared in the laboratory and others extracted from samples of Greek soils developed under different vegetative covers. In the synthetic FeHA complexes prepared at pH 2.8, iron was found to be both in trivalent and bivalent states. At pH 4.0, iron was in the trivalent state and only traces of Fe²⁺ were found.The ESR spectra of the natural HA's and FA's indicated that iron forms complexes with both of them. The Mössbauer spectra, however, did not provide verification for existence of Fe³⁺ organically bound to the humic acids. All the Mössbauer spectra of the natural humic acids showed minute quantities of iron in the ferrous state. The respective parameters indicated that the Fe²⁺ is directly bound to HA's. The ferrous iron probably resulted from the reduction of Fe³⁺ during the humification process. The Mössbauer spectrum of an FeFA complex prepared in the laboratory with a fulvic acid: metal ratio of (1:1) at pH 4.0 showed that iron occurred in both trivalent and bivalent states.Differences in the vegetative cover and in the taxonomic category of the soils studied did not have any effect on the Mössbauer parameters of the natural HA's, but differences were reflected in the ESR spectra of the FA's.     

土壤组分对广东省酸性水稻土磷吸附参数的影响

Soil components affecting phosphate sorption parameters were studied using acid paddy soils derived from basalt, granite, sand-shale and the Pearl River Delta sediments, respectively, in Guangdong Province.For each soil, seven 2.50 g subsamples were equilibrated with 50 mL 0.02 mol L-1 (pH=7.0) of KCl containing 0, 5, 10, 15, 25, 50 and 100 ng P kg-1, respectively, in order to derive P sorption parameters (P sorption maximum, P sorption intensity factor and maximum buffer capacity) by Langmuir isotherm equation. It was shown that the main soil components influencing phosphate sorption maximum (Xm) included soil clay, pH,amorphous iron oxide (Feo) and amorphous aluminum oxide (Alo), with their effects in the order of Alo ＞Feo ＞ pH ＞ clay. Among these components, pH had a negative effect, and the others had a positive effect.Organic matter (OM) was the only soil component influencing P sorption intensity factor (K). The main components influencing maximum phosphate buffer capacity (MBC) consisted of soil clay, OM, pH, Feo and Alo, with their effects in the order of Alo ＞ OM ＞ pH ＞ Feo ＞ clay. Path analysis indicated that among the components with positive effects on maximum phosphate buffer capacity (MBC), the effect was in the order of Alo ＞ Feo ＞ Clay, while among the components with negative effects, OM ＞ pH. OM played an important role in mobilizing phosphate in acid paddy soils mainly through decreasing the sorption intensity of phosphate by soil particles.     

Adsorption and Desorption of Cry1Ab Proteins on Differently Textured Paddy Soils

In recent years, selected cry genes from Bacillus thuringiensis (Bt) encoding the production of Cry proteins (Bt toxins) have been engineered into crop plants (Bt-crops). Through the cultivation of Bt crops and the application of Bt pesticides, Cry proteins could be introduced into arable soils. The interaction between the proteins and soils was analyzed in this study to investigate the affinity of Cry proteins in paddy soil ecosystems. Four Paddy soils were selected to represent different soil textures. Cry proteins were spiked in soils, and the amount of protein adsorbed was measured over 24 h. Desorption of Cry1Ab proteins from paddy soils was performed by washing with sterile Milli-Q water (H₂O_MQ), and subsequently extracted with an extraction buffer. The paddy soils had a strong affinity for Cry1Ab proteins. Most of the Cry1Ab proteins added (> 98%) were rapidly adsorbed on the paddy soils tested. More Cry1Ab proteins were adsorbed on non-sterile soils than on sterile soils. Less than 2% of the adsorbed Cry1Ab proteins were desorbed using H₂O_MQ, while a considerable proportion of the adsorbed proteins could be desorbed with the buffer, ranging from 20% to 40%. The amount of proteins desorbed increased with the increases in the initial amount of Cry1Ab proteins added to the paddy soils. The concentration of Cry1Ab proteins desorbed from the paddy soils was higher for sterile soils than non-sterile ones. Our results indicate that Bt toxins released via the cultivation of Bt crops, the application of Bt pesticides can be adsorbed on paddy soils, and soil texture could impose an impact on the adsorption capability.     

长江中游水稻土潜育作用的特点

The gleyization of representative paddy soils in the middle reaches of the Yangtze River was characterized, taking oxidation-reduction potential(Eh), the amount of active reducing substances and the forms of iron and manganese as the parameters. The Eh value was linearly related with the logarithm of the amount of active reducing substances, which was contributed by ferrous iron by 83% on an average. The degree of gleyization of different horizons was graded as ungleyed, slightly gleyed, mildly gleyed and gleyed. The Eh of the four grades was > 500, 300-500, 100-300 and < 100 mV, respectively, and the corresponding amount of active reducing substances was < 1, 1-7, 7-30 and > 30 mmol_c kg^-1, respectively. The amount of ferrous iron of the four grades was < 0.5, 0.5-5, 5-25 and > 25 mmol kg^-1, respectively. The extent of gleyization of a soil was classified as upper-gleyed, middle-gleyed and lower-gleyed, depending on whether the depth of the gley horizon was less than 30 cm, 30-60 cm or more than 60 cm.     

Evaluation of available silicon content and its determining factors of agricultural soils in Japan

To evaluate the available silicon (Si) content in agricultural soils in Japan and to investigate the determining factors of this content, we collected 180 soil samples from the surface layer of paddies and upland fields in Japan and determined their available Si contents. A phosphate buffer (PB; 0.02 M, pH 6.9) or an acetate buffer (AB; 0.1 M, pH 4.0) was used to extract available Si from the soil samples, and the Si concentrations in the extracts were determined by inductively coupled plasma-atomic emissions spectroscopy (ICP-AES). The total Si content and selected physicochemical properties were also determined for the soil samples. The median values of the available Si contents by the PB and AB methods were 48.8 and 79.7 mg kg^?1 and corresponded to 0.017% and 0.027% of the total Si content, respectively. The overall data showed log-normal distributions. The available Si content of the upland soils was significantly higher than that of the paddy soils by both the PB (p < 0.01) and AB methods (p < 0.05). The available Si contents by the PB and AB methods had a significant positive correlation (p < 0.01) and they had significant negative correlation with the total Si content (p < 0.01). The values of the available Si contents by the PB and AB methods correlated positively with the pH, total carbon (C) content, and dithionite-citrate bicarbonate extractable iron (Fed) and aluminum (Ald), acid oxalate extractable iron (Feo) and aluminum (Alo), Fed-Feo and Alo+1/2Feo values (p < 0.01). A multi-regression analysis indicated that pH, amorphous minerals and crystalline iron (Fe) oxides were the dominant determining factors of available Si in the soils, and these three variables explained approximately two thirds of the variation of available Si content in agricultural soils in Japan. In terms of soil type, Terrestrial Regosols, Dark Red soils and Andosols had relatively high available Si contents, whereas Sand-dune Regosols, Red soils and Gray Lowland soils had relatively low contents. In terms of region, the soils in the Kanto and Okinawa regions had relatively high available Si contents and those in the Kinki, Shikoku and Chugoku regions had relatively low contents. In conclusion, the available Si content and its determining factors for agricultural soils in Japan were quantitatively elucidated, and this will contribute to the establishment of rational soil management?—including the application of silicate materials, taking into account the Si-supplying power of the relevant soils—for sustainable and productive agriculture in Japan.