Wet aggregate stability as affected by excess carbonate and other soil properties

Aggregate stability is a fundamental property influencing soil erodibility and hydraulic characteristics. Knowledge of soil components controlling aggregate stability is very important to soil structure conservation. The objective of this study, which was carried out in surface soils from central Greece, was to relate wet aggregate stability to selected soil properties, with emphasis on excessive free carbonate content. The wet‐sieving technique of air‐dried aggregates was used for structural stability evaluation, according to a test that calculates an instability index. The soils studied were developed on Tertiary marly parent material and ranged in calcium carbonate content from 5 to 641 g kg⁻¹. From the texture analysis before and after removal of carbonates, it was concluded that carbonates mainly contributed to total silt and sand fractions, that is to the mechanical fractions which, as a rule, negatively affect aggregate stability. The results of the correlation analysis showed that aggregate stability was positively affected by aluminosilicate clay content, cation exchange capacity (CEC) and Al‐containing sesquioxides. Clay fraction from carbonates and total sand and silt negatively affected aggregate stability. CEC has been proved a very significant determinant of aggregate stability, which in a hyperbolic form relationship with instability index explained 78·9 per cent of aggregate stability variation. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation of regenerated cellulose fiber via carbonation. I. Carbonation and dissolution in an aqueous NaOH solution

Cellulose carbonate was prepared by the reaction of cellulose pulp and CO₂ with treatment reagents, such as aqueous ZnCl₂ (20–40 wt%) solution, acetone or ethyl acetate, at −5–0°C and 30–40 bar (CO₂) for 2 hr. Among the treatment reagents, ethyl acetate was the most effective. Cellulose carbonate was dissolved in 10% sodium hydroxide solution containing zinc oxide up to 3 wt% at −5–0°C. Intrinsic viscosities of raw cellulose and cellulose carbonate were measured with an Ubbelohde viscometer using 0.5 M cupriethylenediamine hydroxide (cuen) as a solvent at 20°C according to ASTM D1795 method. The molecular weight of cellulose was rarely changed by carbonation. Solubility of cellulose carbonate was tested by optical microscopic observation, UV absorbance and viscosity measurement. Phase diagram of cellulose carbonate was obtained by combining the results of solubility evaluation. Maximum concentration of cellulose carbonate for soluble zone was increased with increasing zinc oxide content. Cellulose carbonate solution in good soluble zone was transparent and showed the lowest absorbance and the highest viscosity. The cellulose carbonate and its solution were stable in refrigerator (−5°C and atmospheric pressure).     

Comparison of sulfurous acid generator and alternate amendments to improve the quality of saline-sodic water for sustainable rice yields

The prolonged irrigation with marginal quality water can cause secondary salinization of soils, which necessitates for better understanding of water management alternatives. Relative performance of sulfuric acid and gypsum is still controversial to counter sodium hazards in soil/water system. As an alternative, sulfurous acid generators (SAG) are also being marketed. But up-till-now, there is not even a single field study published in scientific journals about their efficiency and economical viability for the treatment of saline-sodic water. Therefore, a field study was carried out to compare the effectiveness of SAG and alternate amendments applied on an equivalent basis to grow rice crop. SAG treatment of saline-sodic tube well water decreased only residual sodium carbonate (RSC) from 5.4 to 3.6 mmol_c l⁻¹, and had no beneficial effect on its sodium adsorption ratio (SAR) or electrical conductivity (EC). All the treatments kept soil EC and SAR around their respective threshold levels. For paddy yield, SAG, sulfuric acid, and gypsum treatments depicted nonsignificant differences. SAG and sulfuric acid treatments of water were about six times expensive than that of gypsum. It was concluded that soil-applied gypsum, to counter sodic hazards of irrigation water, is economical to sustain irrigated rice in dry regions.     

中国西南薄层砾石土喀斯特坡地土壤的137Cs分布特点

The fallout radionuclide cesium-137(137 Cs) has been widely employed as a tracer for assessment of soil loss from thick uniform soils;however,few studies have been conducted on thin stony soils on slopes underlain by carbonate rocks which are widely distributed in karst areas.Information derived from 137 Cs measurement of soil samples collected along a carbonate rock slope with thin stony soil where neither soil erosion nor deposition occurred was used to investigate the characteristics of 137 Cs redistribution in a karst area of Southwest China.The results indicated that the 137 Cs inventories of the surface soil on the slope studied were much lower than that of the local 137 Cs reference inventory and the 137 Cs activities were much higher than those on slopes with thick uniform soils.The spatial distribution of 137 Cs inventories was characterized by considerable variation.The high 137 Cs depletion in the stony soil of the slope studied was mainly because a considerable proportion of the fallout input of 137 Cs could be lost with runoff and the dissolution of carbonate particles in the soil promoted the loss of 137 Cs.These demonstrated that the rates of soil loss could not be estimated from the degree of depletion of the 137 Cs inventory relative to the local reference inventory for the thin stony soil of the rocky slope underlain by carbonate rocks in the study area in the way that has been widely used in areas with thick uniform soils.     

Pedogenic carbonate recrystallization assessed by isotopic labeling: a comparison of 13C and 14C tracers

The C isotopic composition (δ¹³C) of pedogenic carbonates reflects the photosynthetic pathway of the predominant local vegetation because pedogenic (secondary) CaCO₃ is formed in isotopic equilibrium with soil CO₂ released by root and rhizomicrobial respiration. Numerous studies show the importance of pedogenic carbonates as a tool for reconstructing paleoecological conditions in arid and semiarid regions. The methodological resolution of these studies strongly depends on the time scale of pedogenic carbonate formation, which remains unknown. The initial formation rate can be assessed by ¹⁴C labeling of plants grown on loess and subsequent incorporation of ¹⁴C from rhizosphere CO₂ into newly formed carbonate by recrystallization of loess CaCO₃. We tested the feasibility of ¹⁴C and ¹³C tracers for estimating CaCO₃ recrystallization rates by simultaneous ¹⁴C and ¹³C labeling and comparison with literature data. ¹⁴C labeling was more efficient and precise in assessing recrystallization rates than ¹³C labeling. This is connected with higher sensitivity of ¹⁴C liquid scintillation counting when compared with δ¹³C measurement by IRMS. Further, assessment of very low amounts of incorporated tracer is more precise with low background signal (natural abundance), which is true for ¹⁴C, but is rather high for ¹³C. Together, we obtained better reproducibility, higher methodological precision, and better plausibility of recrystallization rates calculated based on ¹⁴C labeling. Periods for complete CaCO₃ recrystallization, extrapolated from rates based on ¹⁴C labeling, ranged from 130 (125–140) to 240 (225–255) y, while it was ≈ 600 (365–1600) y based on the ¹³C approach. In terms of magnitude, data from late‐Holocene soil profiles of known age provide better fit with modeled recrystallization periods based on the ¹⁴C approach.     

水流近壁面水力剪切力对滴灌系统碳酸钙污垢的影响

针对目前水动力学条件对滴灌系统碳酸钙污垢形成的影响及适宜的污垢控制阈值尚不明确的问题,该研究对不同近壁面水力剪切力(0～0.70 Pa)下的滴灌系统附着碳酸钙污垢总量、晶相组成及表观形貌进行了分析。结果表明：不同剪切力显著(P<0.05)影响了碳酸钙污垢的形成,随着剪切力的增大碳酸钙污垢的总量呈现先增高后降低的趋势,最大碳酸钙污垢形成量的剪切力为(0.42±0.02)Pa。剪切力较低(0～0.42 Pa)时,随着剪切力的增大碳酸钙晶体的尺寸逐渐变大,Ca²⁺和CO₃^2-的碰撞几率增加且晶体成核效率提高,使得碳酸钙污垢总量呈现增加趋势;剪切力较高(0.42～0.70 Pa)时,随着剪切力的增大碳酸钙晶体大小逐渐减小,且晶体由于高剪切力的作用发生破碎和脱落,使得碳酸钙污垢总量呈现下降趋势。建议灌水器流道近壁面水力剪切力控制在0～0.24 Pa和0.65～0.70 Pa,以减少碳酸钙污垢的形成。该研究结果可为高抗堵塞灌水器的研发以及劣质水滴灌技术的应用和推广提供支撑。     

Biomass,Mineral Accumulation,and Calcium Crystals in Trema micrantha (L.) Blume as a Function of Calcium Carbonate Addition

Trema micrantha (L.) Blume is a neotropical multipurpose tree species, which could be used in forest restoration and agroforestry. Several cultures, however, require liming to satisfactory yields in acid soils. Therefore, it is important to determine the effect of liming to this native species, in order to include it in agroforestry associations. The aim of this work was to evaluate the morphological changes of T. micrantha, including the calcium oxalate (druses) and cystolith density, as caused by the calcium carbonate (CaCO₃) addition. The assay included three treatments: control, pH 5.3; treatment 1, pH 5.5; treatment 2, pH 6.0. The liming reduced the root biomass and increased the shoot biomass. The leaf specific mass and nutrients concentration were not changed. The leaves presented higher density of druses in treatment 2. The cystolith density was not modified, but the cystolith size was increased by the liming. The results indicate liming tolerance in this species.     

The effect of slag on paddy rice

To raise more rice in Japan we have placed much fertilizers in the fields, thus the soils often have been degraded by the leaching of essential elements including Fe to such a extent as rice roots are injured by the H₂S produced by the reduction of sulphates. It has been encouraged by law to place non-sulphate fertilizers and iron compounds in these fields.     

环氧化天然橡胶包覆CaCO3填充LDPE的技术

选用环氧化程度摩尔分数为25%的环氧化天然橡胶胶乳(ENRL-25)包覆轻质CaCO3,研究了处理方法、ENRL-25用量和CaCO3填充量对CaCO3 /LDPE(低密度聚乙烯)复合材料结构与性能的影响,并与钛酸酯偶联剂NDZ-201处理CaCO3进行了对比。结果表明:ENRL-25和NDZ-201湿法包覆CaCO3效果较好,使CaCO3 /LDPE材料在拉伸强度保持较高的情况下,拉伸弹性模量、撕裂强度和扯断伸长率得到有效的提高;在采用最佳改性剂用量时,ENRL-25改性CaCO3/LDPE复合材料的撕裂强度和扯断伸长率较优,而NDZ-201改性CaCO3/LDPE复合材料的拉伸强度和拉伸弹性模量较优。SEM的分析结果表明,包覆CaCO3与LDPE的界面作用强度提高,材料的破坏不是始于CaCO3粒子脱粘,而是始于基质的变形破坏。