Phytolith transport in soil: a laboratory study on intact soil cores

Column experiments on phytolith transport were conducted to assess the partial contributions of water percolation and earthworm activity to phytolith transport in loamy and sandy soils. Six intact cores of a loamy sandy Haplic Cambisol and nine cores of a silty loamy Stagnic Luvisol were excavated. With the Luvisol, three treatments were perfomed: a percolation treatment with periodic irrigation, but without earthworms, a percolation and earthworm treatment with periodic irrigation and earthworms (Aporrectodea caliginosa) and a control. The Cambisol cores did not contain earthworms and hence only percolation and control treatments were tested. The phytoliths of common reed (Phragmites australis) were labelled with the fluorescent dye fluorescein isothiocyanate and applied to the soil surface of each core. Except for the control treatment, 3600 mm of water was applied over 6 months. In the Cambisol, the weighted mean transport distance of phytoliths was significantly greater with percolation (2.2 ± 0.1 cm) than in the control (0.9 ± 0.3 cm), indicating that water percolation is a driving mechanism of phytolith transport. In the Luvisol, the difference in mean transport depth between control and percolation treatments (1.0 ± 0.2 and 1.5 ± 0.3 cm) was not significant. The earthworms did not affect the mean transport distance of phytoliths in the Luvisol, but the phytolith concentrations in the leachates were significantly greater and their size distribution did not change with soil depth as observed in the percolation treatment without earthworms. Further studies are required to quantify the effect of earthworms on phytolith transport.     

光散射技术在土壤胶体颗粒相互作用研究中的应用

由于测试手段的限制,目前对土壤中粒径为0·001～1μm的"超微粒子"之间相互作用的微观效应研究还未引起足够的重视。本文从散射角和悬液颗粒密度两个方面讨论了光散射技术在土壤胶体研究中的应用条件,探讨了土壤胶体颗粒凝聚动力学机制及形成的聚合体结构特征。结果表明:(1)对于本实验所用黄壤悬液,应用光散射准确测定的散射角范围为90°～135°,初始颗粒密度范围为1·90×10-3～0·119gL-1。(2)在自相关曲线平滑地衰减至基线且散射光强保持不变的条件下,可以用光散射技术准确测定土壤胶体颗粒凝聚过程中有效直径、最可几粒径及粒径分布的变化,反映凝聚动力学规律。(3)在298K、90mmolL-1KNO3体系中用动态光散射测得黄壤胶体颗粒凝聚动力学为扩散控制团簇聚集机制,用静态光散射测得形成的聚合体分形维数为1·56±0·02。     

红壤复合胶体腐殖质的特性

对闽北6个样品测定结果表明,红壤复合胶体中C、N含量较高,其腐殖质的C/N和HA/FA、胡敏酸的芳构化度和腐殖质氧化稳定性系数均较重组小,而松结合态/紧结合态腐殖质的比值则较大.这些特性有利于土壤养分保存与供应和改善土壤结构.     

Studies on the organo-mineral colloidal complexes of paddy soil II

In the preceding paper (1) the authors reported the humus status in the organo-mineral colloidal complexes of the degraded paddy soils, which is characterized by the leaching of active iron, manganese and the other elements such as silica, magnesium and phosphoric acid from the furrow slice (2). And it was concluded that the organo-mineral colloidal complexes (Gl colloidal complexes) of the degraded paddy soil is characterized by the marked accumulation of humus, especially the readily soluble humus as compared with those of the normal.     

Studies on the organo-mineral colloidal complexes of paddy soil V

In the preceding paper (1), humus status in G 1 colloidal complexes of the high yield paddy soils was reported. This report describes the experimental results on the clay minerals contained in G 1 colloidal complexes of the same soils as above.     

Studies on the organo-mineral colloidal complexes of paddy soil IV

In Japan some of farmers are able to obtain a strikingly high yield of rice crop, i.e. over 8～9 tons of hulled rice per ha. on their paddy fields. Such fields are called the high yield paddy field.     

Interference of colloidal particles in the determination of orthophosphate concentrations in soil water extracts

Abstract

Accurate determination of orthophosphate (P) in soil solutions is a prerequisite for rigorously assessing soil P availability for plants as well as the potential risk of P transfer to water bodies. Although P is usually measured on extracts filtered at 0.45 μm, little is known on the potential interfences due to the presence of colloidal particles. This work was conducted to study the influence of colloidal particles on P concentration by measuring it both by the phosphoantimonylmolybdenum blue colorimetry and ion chromatography in soil water extracts filtered at 0.45, 0.2, or 0.025 μm. Results strongly suggest that direct measurements with colorimetry might lead to an overestimation of the P concentration due to the solubilization of P‐containing particles in the acid medium prevailing in the solution during colorimetric essay. In the present study, the largest overestimations were observed in soil extracts rich in iron (Fe) and aluminum (Al) that had been filtered at 0.45 μm, on the opposite this overestimation remained lower but constant for the three levels of filtration in the studied calcareous soil. Ion chromatography constantly underestimated P concentration especially when the solutions were rich in Al and Fe. This underestimation could not be related to the presence of dissolved polyvalent cations in the solution and, therefore, might be accounted for by the sorption of P at the surfaces of colloids. In order to limit these interferences, it is proposed to measure P concentration by colorimetry after a filtration of the solution through a 0.2‐ or 0.025‐um membrane, instead of a 0.45‐μm filter. In some cases for instance for soil solutions rich in calcium phosphate particles, it might be advisable to determine P concentration with ion chromatography.     

水铁矿对磷的吸附及胶体态磷迁移能力预测

土壤中流失的磷进入水体容易引起富营养化污染。目前对于铁矿物胶体结合态磷在土壤孔隙介质中的稳定性和迁移能力的认识还存在不足。本研究采用吸附试验,考察水铁矿对磷的吸附特征以及pH、离子强度和胡敏酸对磷在液相、水铁矿胶体和水铁矿固体上分布的影响;通过DLVO理论,预测水铁矿胶体结合态磷的稳定性和迁移能力。结果表明,假二级动力学模型(R~2=0.964)更适合用于描述磷在水铁矿上的吸附过程,磷在水铁矿上的吸附受液膜扩散、内部扩散和化学吸附等过程控制。Freundlich模型(R2=0.970)对等温吸附的拟合效果好,说明水铁矿对磷的吸附为多层吸附过程。从Langmuir模型参数可知,水铁矿对磷的最大理论吸附量为22.55mg·g~(-1)。水铁矿对磷的吸附能力随pH的升高而降低,随离子强度的升高而升高。然而,低离子强度和高pH有利于反应体系中水铁矿胶体的释放。无论胡敏酸是否存在,在碱性且离子强度不高(1～10mmol·L~(-1))的条件下,有约5%～20%的磷会与水铁矿胶体结合,且这些磷-水铁矿胶体之间的静电斥力较大。根据DLVO理论计算可知,这些带负电荷的胶体之间稳定性较好,在土壤中有一定迁移能力。在实际农业活动中,磷肥的过量施用可能会使大量的磷酸根离子吸附在铁矿物上,促进土壤孔隙水中形成稳定的、带负电的铁矿物胶体,这种磷-铁矿物复合胶体的迁移很可能成为磷迁移的另一种形式。本研究结果可为胶体促进下磷淋失风险评估提供理论和数据支撑。     

Current titles in soil science

Nine extraction procedures were tried on four calcareous soils containing very low to extremely high amounts of calcium carbonate. Correlation studies relating chemically extractable zinc to both concentration in and uptake of zinc by young sorghum and maize plants grown in the greenhouse indicated that five extraction methods exhibited a high degree of correlation. When the methods were compared among themselves, the highest correlation was obtained for dithizone and EDTA-ammonium-carbonate methods. The EDTA-ammonium-carbonate method seemed to reflect the available zinc status of the soils more accurately than other methods.