OCHRE FORMATION IN FIELD DRAINS IN PYRITIC SOILS

Two distinct forms of ochre are known to occur in field drains. One form, which is most common in wet peaty areas, is caused by the growth of filamentous iron bacteria. The second form is associated with Thiobacillus ferrooxidans, and occurs where the soil contains pyrite. Contrary to previous reports, liming decreases the rate at which pyrite is oxidized in soil and, by decreasing the amount of iron entering the drains in a given period, should significantly increase the active life of the drainage system. Regular liming is probably preferable to a single large initial dressing.     

THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOILS. VIII —A THEORY FOR THE PROPAGATION OF CHANGES OF pH IN SOILS

The way pH changes in soil are propagated by movement of acids and bases is described. In acid soils the H₃O⁺-H₂O acid-base pair is most important, while in alkaline soils the H₂CO₃-HCO₃^? pair is always dominant, its effect depending directly on the pressure of CO₂. In neutral and slightly acid soils, soluble organic matter and the H₂PO₄^?-HPO²₄^? pair may also contribute. A soil acidity diffusion coefficient is derived, and defined as: where v_l= the volume fraction of the soil solution, f_l= the impedance factor for the liquid diffusion pathway, b_HS= the pH buffer capacity of the soil, b _HB= the pH buffer capacity of each mobile acid-base pair, Dl _HB= the diffusion coefficient of each mobile acid-base pair in free solution, and the sum is taken over all mobile acid-base pairs. The soil acidity diffusion coefficient may be used to predict the course of pH equilibration in practical situations. It is high in acid and alkaline soil, and at a minimum in slightly acid soil. It is little affected by variation of the ionic strength of the soil solution at concentrations less than 0.01M. When the pH buffer capacity of the soil is constant, and only the H₃O⁺-H₂O and H₂CO₃-HCO₃^? pairs are important, the soil acidity diffusion coefficient varies as cosh{2.303(pH—pH₀)}, where pH₀ is the pH at which the soil-acidity diffusion coefficient is a minimum.     

石灰性土壤施磷、铁对柠条生长及根际土壤环境的影响

采用随机区组和裂区设计,通过盆栽和根箱模拟试验研究了石灰性土壤,在水分充足的条件下施磷及磷、铁对柠条生长发育及根际土壤养分有效性的影响。盆栽试验结果表明,柠条的生物产量随着施磷水平的增加而增加;在低磷或磷胁迫条件下,柠条的地上部生长受到抑制,根冠比增大,土壤pH值迅速降低。根箱模拟试验发现,不同的铁、磷施肥配比对柠条生物产量的影响不同,当磷和铁的施用量分别为P2O50.15 g kg-1 和FeSO4·7H2O0.03g kg-1时能明显提高柠条的生物量。不同铁、磷配比对柠条根际土壤有效磷含量影响的根际范围是0-6 mm之间,在此范围内供试土壤有效磷含量随距离快速下降,并与根际土壤pH值呈反比。柠条对根际土壤pH的调控主要受磷水平的影响,而施铁水平对根际和根外土壤pH值的影响比较小。     

Association of soil properties and soil and plant iron to iron deficiency response in rice (Oryza Sativa L.)

Abstract

Problems are invariably encountered when attempts are made to explain the variability in Bray percent yields or plant response in terms of soil or plant iron (Fe). To resolve this inconsistency, the present investigation was initiated to identify a combination of soil extractable Fe, soil properties and form of plant Fe that may be used as a measure of Fe deficiency. The study involved 16 diverse soils, using upland rice (Oryza sativa L.) as the test crop and Fe‐EDDHA [ferric ethylenediamine di (o‐hydroxyl‐phenyl acetic acid)] as source of Fe. The results showed that Bray percent yields were neither related to DTPA (diethylenetriamine pentaacetic acid) or EDTA (ethylenediamine tetraacetic acid) extractable Fe nor with total plant Fe. Even the inclusion of pH, lime, organic carbon and clay data in the regression equations was of no value. However, Bray percent yields were significantly and positively (r = 0.57* ) associated with ferrous Fe (Fe²⁺) in 40‐day‐old rice plants. The explanation concerning variability in Bray percent yields obtained on diverse soils could be increased about one and half 2 times (R²= 0.59*) if the contribution of lime and soil pH was also incorporated in the stepwise regression analysis. The individual contribution to R of lime, pi respectively. Thus, it appears that Fe²⁺ concentration in plants (along with soil pH) may identify Fe deficiency. The critical limit to separate Fe deficient from green rice plants was set at 45 ug Fe²⁺/g in the leaves.     

THE EQUILIBRIA OF K:Al EXCHANGE IN CLAY MINERALS AND ACID SOILS1

Conventional K: Al exchange isotherms for montmorillonite showed that Al³⁺ was strongly preferred to K⁺ in o-oin solutions. The exchange coefficient, K', calculated using the isotopically exchangeable K, was greater than unity and did not vary with the Al-saturation or with the initial pH of the AlCl₃ solutions. Isotherms for vermiculite, illite, and soils in o·oin solutions also showed Al³⁺-preference but unlike those for montmorillonite were not asymptotic to q_Al/q_o= 1, q_Al being the amount of adsorbed Al and q_o the total adsorbed (Al + K), indicating that some of the isotopically exchangeable K could not easily be exchanged by Al³⁺ ions; this difficultly exchangeable K (DEK) was estimated for each exchanger. K' values for vermiculite, illite, and soils were less than unity and did not vary with Al-saturation or initial pH if the isotopically exchangeable K was corrected for DEK. This showed that K⁺ was adsorbed more strongly than Al³⁺. Strengths of K⁺ adsorption referred to Al³⁺ as the counter-cation were in order: soils > vermiculite, illite > montmorillonite.     

SOLUBLE ALUMINIUM AND CALCIUM-ALUMINIUM EXCHANGE IN RELATION TO THE pH OF DILUTE CALCIUM CHLORIDE SUSPENSIONS OF ACID SOILS

Measurements of pH and A1 concentration were made on 10^-2 M CaCl₂, suspensions of a number of acid soils that had been limed to give 3 range of pH values, and exchangeable A1 and Ca+Mg were determined in 1.0 M NH₄Cl extracts. The variation of pH with A1 concentration did not support the theory that pH is controlled by the solubility of Al(OH)₃. For some of the soils, proton release on hydrolysis of A1₃₊ions in solution accounted for the pH values, and explained quantitatively the variation of pH with the Ca:Al balance of the exchange complex, taking account of the selectivity coefficient for exchange, K_ca→A1 Although K_ca→A1 was smaller for soils containing more humus, their pH values were also less than those predicted by the hydrolysis of A1³⁺ in solution, indicating that they contained other sources of protons, presumably the carboxyl groups in humus.     

pH对酸性土壤中铝的溶出和铝离子形态分布的影响

ＰＨ对酸性土壤中铝的溶出和土壤溶液中铝离子形态分布的影响的研究结果表明,土壤中铝的溶出量随ＰＨ降低而增加,ＰＨ对不同土壤中铝的溶出的影响不同,三种土壤中铝的溶出量受ＰＨ影响的大小顺序是：红壤〉赤红壤〉砖红壤,说明不同类型土壤中铝的溶出对外来酸的敏感和程度不同。     

Iron Toxicity in Lowland Rice

Lowland rice is a staple food for more than 50% world population. Iron toxicity is one of the main nutritional disorders, which limits yield of lowland rice in various parts of the world. The toxicity of iron is associated with reduced soil condition of submerged or flooded soils, which increases concentration and uptake of iron (Fe^{2 +}). Higher concentration of Fe^{2 +} in the rhizosphere also has antagonistic effects on the uptake of many essential nutrients and consequently yields reduction. In addition to reduced condition, increase in concentration of Fe^{2 +} in submerged soils of lowland rice is associated with iron content of parent material, oxidation-reduction potential, soil pH, ionic concentration, fertility level, and lowland rice genotypes. Oxidation-reduction potential of highly reduced soil is in the range of –100 to –300 mV. Iron toxicity has been observed in flooded soils with a pH below 5.8 when aerobic and pH below 6.5 when anaerobic. Visual toxicity symptoms on plants, soil and plant tissue test are major diagnostic techniques for identifying iron toxicity. Appropriate management practices like liming acid soils, improving soil fertility, soil drainage at certain growth stage of crop, use of manganese as antagonistic element in the uptake of Fe^{2 +} and planting Fe^{2 +} resistant rice cultivars can reduce problem of iron toxicity.     

THE POTASSIUM STATUS OF MALAWI SOILS

Twenty surface soils from four main Soil Groups in Malawi and their sub-soils were divided into three groups based on cation exchange capacity (group I, CEC < 50; group II, 50–100; and group III > 100μeq g^–1). In each soil group the maximum amounts of K removed by successive extraction with 0.005 M CaCl₂ solution were well related to the potassium potential pK–0.5p(Ca + Mg), exchangeable K, ‘step K’, and the quotient ‘step K’/CR.K, where CR.K is ‘constant-rate’potassium. In Group III soils only, ‘step K’/CR.K values were significantly correlated with pH, clay, and CEC, and this suggested that the soils were relatively rich in K⁺ specific binding sites. In 27 soils from an NPK factorial experiment on tea, the rate of depletion of extractable K reserve increased with ammonium sulphate treatment, whereas K fertilizers tended to off-set significantly (P= 0.001) the depletion of K reserve. The values for the change in free energy ΔG =RT In a_K/ (a_(Ca+Mg)) ^½, ranged from –12 to –16 kJ mol^–1, and field observations showed that tea plants growing on soils having ΔG values less than –15 kJ mol^–1 responded to K fertilizers. The investigation has indicated that heavily cropped soils are likely to show crop responses if the intensive cropping system does not include supplementation of K.     

应用穆斯堡尔(Mössbauer)谱学方法研究Fe+++, Fe++与胡敏酸结合的性质

本文应用穆斯堡尔谱学方法,研究了在不同pH条件下Fe⁺⁺⁺,Fe⁺⁺与胡敏酸结合的性质。计算机拟合的pH3.0⁵⁷Fe-胡敏酸络合物泥浆的穆斯堡尔谱和参数表明,三对四极双峰(图1,AA',BB',CC')是合理的。在pH3.0 Fe⁺⁺⁺以高自旋态存在,它和胡敏酸的结合多于一种环境类型。在pH1.0的⁵⁷Fe-胡敏酸络合物中,观察到了Fe⁺⁺⁺的穆斯堡尔谱信号,但没有Fe⁺⁺的信号,在这个样品离心分离出的液体部分检测到了加入量的59.7%的铁,表明在pH1.0时相当数量的Fe⁺⁺⁺被胡敏酸还原成Fe⁺⁺,Fe⁺⁺并不与胡敏酸牢固结合。在30伏电析过的⁵⁷Fe-胡敏酸络合物样品中(pH2.8)出现了Fe⁺⁺⁺,Fe⁺⁺的穆斯堡尔谱,这一结果指示出,在电析过程中由于⁵⁷Fe⁺⁺⁺-胡敏酸络合物悬浮液pH的降低,一部分Fe⁺⁺⁺还原成Fe⁺⁺,在pH2.8相当数量的Fe⁺⁺与胡敏酸牢固结合。根据在80K记录的穆斯堡尔谱,在pH1—3的范围出现了磁有序成份,但在室温记录的穆斯堡尔谱没有磁分裂。     

THE CONTENTS AND SORPTION OF CADMIUM IN SOME AGRICULTURAL SOILS OF ENGLAND AND WALES

Cadmium sorption was measured in 10 agricultural soils with pH ranging from 4.5 to 7.9, and total Cd content from 0.27 to 1.04 μg g^?1 dry soil. With initial Cd concentrations of 0.5 to 100.0 μM, sorption from 0.002 M CaCl₂ was described by the Freundlich adsorption equation but the gradients of the isotherms increased when the initial concentrations were below 0.5 μm. This indicates that there are specific sites of differing sorption energy; differences between soils in the gradients of the isotherms at low initial concentration could largely be accounted for by their contents of ‘free’ Fe₂O₃. When initial concentrations were below 0.5 μm there was a linear relationship between the quantity of Cd sorbed and the final concentration in solution. This relationship held with all soils except that of lowest pH from which there was a net loss of Cd to the solutions. Desorption was measured from three soils with contrasting pH. With the soil of lowest pH, over 80 per cent of sorbed Cd was desorbed to 0.002 m CaCl₂ and up to 30 per cent to 100 or 500 μm solutions of heavy metal chlorides. In contrast, only very small proportions (<1.25 per cent) were desorbed from the other soils with pH 6.7 and 7.8. The results indicate that Cd is strongly sorbed by soils of pH of above 6.0 when added in amounts comparable to additions in sewage sludges or phosphatic fertilizers, and illustrate the importance of liming as a means of reducing the mobility of this metal in soils.     

磷肥肥粒对周围微域土壤pH的影响

本文报告了常用的三种国产磷肥的饱和溶液的性质、组成及其施入土壤后对肥粒周围微域土壤pH的影响。普钙饱和溶液是强酸性的,pH为2.5左右,施入土壤后降低了所有供试土壤之微域pH值。钙镁磷肥饱和溶液则是强碱性的,pH为9.7左右,施入土壤后提高了所有供试土壤的微域pH值。而磷铵肥料的饱和溶液是中性的,pH为7.5左右,施入土壤后使黄土性土壤的微域pH下降但使中性水稻土和酸性红壤的微域pH上升。无论何种磷肥、何种土壤,其施肥前后微域pH变化值(△pH)之大小与土壤质地、缓冲性能及原来土壤pH值的高低有关。     

陕西地区土壤中的硒

硒是人和动物体必需的微量元素之一,早已证明,土壤和饲草中过量的硒会导致牲畜中毒而罹患“碱质病”和“盲跚症”,而土壤和饲草硒含量过低则会引起牲畜白肌病等多种缺硒病^[9]。近年来国外又有资料报道食物和饮水中的低硒容易使人体产生癌症、心血管病、关节炎、婴幼儿碎死症等多种疾病^[6]。鉴于在土壤一植物一动物和人的生态系统中,土壤是最基本的因素,因此对土壤硒的研究在许多国家早已受到人们的重视。国内对土壤硒的研究,始于七十年代对人体地方性疾病的研究,现已证实,地方性克山病、大骨节病的发生与环境和机体缺乏硒有密切关系^[1,3,11]。     

EVALUATION OF DIFFERENT IRON SOURCES FOR IRON CHLOROSIS RECOVERY IN LOW-CHILL PEACH CULTIVARS

An experiment was conducted with iron chlorosis affected low-chill peach cultivars such as ‘Shaharanpur Prabhat’, ‘Shan-e-Punjab’, and ‘Pratap’ to examine the recovery upon foliar application of three iron sources namely iron (Fe)-sulfate, Fe-citrate and Fe ethylenediaminetetraacetic acid (EDTA). All the iron sources significantly increased the SPAD meter value, physiologically active (Fe²⁺) iron and total iron content of the leaves over control. However, highest values were noted with foliar spray of 1.0% Fe-sulfate. The low-chill peach cultivar ‘Saharanpur Prabhat’ responded best with iron resupply treatment. Significant correlations (at P ≤ 0.01) were obtained between SPAD meter readings with both physiologically active iron (Fe²⁺) and total iron content of leaves in all peach cultivars. Among the sources, the correlations between SPAD meter readings, physiologically active iron (Fe²⁺) and total iron contents were significant at P ≤ 0.01 for only Fe-sulfate and Fe-citrate. The regression analysis showed that the SPAD meter reading accounted 78.2 to 88.0% variation in physiologically active iron (Fe²⁺) and 65.0 to 73.7% variation in the total iron content in the low-chill peach cultivars. The SPAD readings could be used for management of iron chlorosis in peach orchard.     

SANDSTONE-DERIVED SOILS OF A CATENA AT IPERU, NIGERIA

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe₂O₃:Al₂O₃ ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.     

除草剂咪草烟在土壤上吸附-脱附过程及作用机理

本文研究了咪唑啉酮类除草剂咪草烟在不同土壤固－液相间的分配及与土壤组分作用的定量相关性。结论指出：咪草烟在土壤固－液相的分配主要受土壤粘粒,有机质及土壤ｐＨ的影响。它们在土壤上的吸附－脱除均可用Ｆｒｅｕｎｄｌｉｃｈ方程描述;通过运用红外及Ｘ－衍射技术,从分子水平研究了咪草烟与蒙脱石的作用机理,发现咪草烟与蒙脱的作用不仅发生在表面,而且咪草烟还能进入蒙脱石内层与其层间阳离子形成配合物。     

MICROMORPHOLOGY OF SOME TROPICAL ALLUVIAL CLAY SOILS

The micromorphological properties of some marine and estuarine tropical clays from Holocene coastal plain soils of Surinam and Thailand have been explained against the background of sedimentation and initial soil formation. During geogenesis stratified sediments are formed, above which are sediments with slightly disturbed stratification, with or without matric faecal pellets. Pedogenesis during the sedimentation phase included development of channels in the sediment, formation of channel neostrians, biological homogenization, possibly pyrite accumulation, and partial oxidation and precipitation of iron as ferric hydroxide. During the brackish water phase pyrite accumulates in various amounts, mass illuviation may occur, part of the iron may oxidize and precipitate and part of the pyrite may be oxidized. During and after the swamp phase further oxidation and precipitation of iron as ferric hydroxide occurs, ferric hydroxide crystallizes into goethite. Pyrite becomes oxidized, resulting in the formation of jarosite, gypsum, silica, and ferric hydroxide.     

南方水稻土中的磷酸铁对水稻磷素营养的意义

研究了我国南方18个不同类型水稻土标本的无机磷的形态。结果表明,非闭蓄态的磷酸盐,包括磷酸铝、磷酸铁和磷酸钙三种形态,一般占土壤无机磷总量的30—60%,其中磷酸铁一极占非闭蓄态总量的50—80%。土壤无机磷中另外的40-70%主要是被氧化铁胶膜包蔽的磷酸铁和磷酸铝。应用同位素P³²示踪法进行的水稻盆栽试验表明:在水稻不同生育期,土壤有效磷量“A”值与水稻土中非闭蓄态的磷酸铁化合物具有极显著的相关性(成熟期的r=0.95)。用P³²人工合成的两种不同晶形的磷酸铁进行了水稻盆栽试验;进一步指出:在水稻土的条件下,晶形的粉红磷铁矿对水稻具有良好的磷素供应能力。这些结果说明,水稻土中非闭蓄态的磷酸铁化合物,即使是以比较稳定的结晶状态存在,但却有可能作为水稻磷素营养的重要给源。室内试验表明,粉红磷铁矿所以对水稻磷素营养具有良好供应能力,以及酸性和中性水稻土中的非闭蓄态磷酸铁化合物,所以能作为水稻磷素营养的重要给源,主要是受渍水还原过程的影响,这一过程,使原来晶形的磷酸铁化合物转化为无定形的状态。     

苏南水稻土对铜离子专性吸附的初步研究

六十年代以来,土壤对多价离子特别是重金属离子的专性吸附,已日益成为土壤化学领域中一个受人注意的问题。土壤胶体中铁、锰、铝、硅等氧化物及其水合物和土壤有机质是专性吸附的主要载体^{[12,16,17,19,20,21]},它们对许多重金属元素的专性吸附所引起的富集过程,起着控制这些金属元素在土壤溶液和海水中浓度的作用^[9,15,18];一些微盒营养元素在土壤中的移动及其对植物的有效性,也深受土壤中氧化物胶体的专性吸附的影响^[11,14,21]。因此,铁、锰等水合氧化物对重金属离子的专性吸附的研究,不仅是土壤化学领域,而且也是土壤环境保护和地球化学等领域中的重要研究课题。     

土壤中可变电荷表面磷的解吸特性

本文研究了土壤中可变电荷表面磷的解吸特性。结果表明,磷解吸量与吸附量成正相关,并与直线方程和指数方程拟合。其平均解吸百分数依次为:高岭石(66%)>无定形硅酸铝(60%)>砖红壤粘粒(55%)>>无定形氧化铁(29%)>三水铝石(23%)>>火山灰粘粒(9%)。解吸体系的pH是借对磷酸根质子的解离和表面电荷的影响而制约解吸量。F^-和OH^-离子对磷酸盐化的三水铝石连续解吸的结果表明,磷酸根和氟离子在三水铝石表面的吸附量或剩余量之和均较为接近,这揭示了H₂PO₄^-和F^-离子之间既竞争又相互补充表面空位。它可作为一种区分磷吸附形态和沉淀的定量方法来进一步研究。