用悬液Wien效应研究阳离子与土壤粘粒间的能量关系

从能量关系研究土壤带电粘粒与电解质离子间的相互作用一直是土壤化学家希望解决的课题。本文介绍阳离子与带电粘粒间的平均结合自由能和平均吸附自由能的计算公式,并用悬液Wien效应法研究K 、NH4 、Ca2 和Cd2 与黄棕壤、棕壤和黑土粘粒间的能量关系。研究结果表明:K 和NH4 的平均结合自由能范围为6.3~7.1kJmol-1,K 的结合能稍大于NH4 的;Ca2 和Cd2 的结合能范围为7.2~9.4kJmol-1。同一阳离子与不同土壤的结合能顺序如下:黄棕壤<棕壤<黑土。它们在同一高场强(如150kVcm-1)下的平均吸附能ΔGad值:K 和NH4 在黄棕壤和棕壤粘粒上的很接近,分别为0.9和0.8kJmol-1,而在黑土粘粒上,NH4 的较K 的大0.1kJmol-1;Ca2 在黄棕壤和黑土上的吸附能较Cd2 的分别大0.3和0.6kJmol-1;二价阳离子的平均吸附自由能约为一价阳离子的2~2.5倍。     

用悬液Wien效应研究Na+、K+、NH4+、Ca2+、Zn2+和Cd2+阳离子与红壤黏粒间的相互作用及能量关系

采用悬液Wien效应法研究了Na+、K+、NH4+、Ca2+、Zn2+和Cd2+阳离子与红壤黏粒间的相互作用及能量关系。结果表明,在试验条件下,红壤黏粒与阳离子Na+、K+、NH4+、Ca2+、Zn2+和Cd2+的平均结合自由能分别为:4.50、7.35、7.15、9.12、9.84和9.63 kJ mol-1。含Ca2+悬液的电导率随场强增加而递增最快,含Na+和NH4+悬液的电导率随场强增加而增加最慢,而含K+、Zn2+和Cd2+的悬液电导率的增速相近、介于其间。红壤悬液中不同阳离子的解离速率顺序为Ca2+>K+>Zn2+=Cd2+>Na+=NH4+。在低场强(15～80 kV cm-1)下,不同阳离子的平均吸附自由能ΔGad没有差异。在场强100 kV cm-1以上,二价阳离子的ΔGad明显大于单价阳离子,不同阳离子间ΔGad的大小顺序为NH4+≤Na+>K+=NH4+>Ca2+>Zn2+=Cd2+,Na+离子平均解离度的递增速率(场强增加1kV cm-1所引起的解离度增量)最大,为0.000 427 cm kV-1,其次是Ca2+离子,为0.000 221 cm kV-1,其余阳离子为0.000 12～0.000 14 cm kV-1。     

用Wien效应研究土壤有机质对阳离子与黄棕壤型水稻土黏粒相互作用的影响

选择富含有机质的黄棕壤型水稻土,提取小于2μm的黏粒,将其中1/2黏粒去除有机质,分别制成为不同阳离子(Na+、K+、NH4+、Ca2+、Cd2+和La3+)饱和的土样,用Wien效应法研究土壤有机质对阳离子与土壤黏粒相互作用的影响。研究结果表明:原土悬液的起始电导率大于去有机质土者;除含Na+悬液外,去有机质土悬液的电导率随场强而增加的速率在50～100 kV cm-1以上,明显大于原土。有机质会使Na+以外的阳离子的平均结合自由能增大,Ca2+的结合能增加最大(增量为0.57 kJ mol-1),而Cd2+的结合能增加最小(增量为0.03 kJ mol-1)。对于供试土壤悬液,不同阳离子的结合能顺序均为Na+相似文献   

不同土壤对钾的选择吸附特性

用K Ca交换平衡法对砖红壤、红壤、土、黑土和水稻土K的选择吸附特性研究结果表明 :KG 和KV 系数随着K Ca平衡体系中吸附相中钾与钙比率的变化而改变 ,其曲线特征说明土壤胶体存在着对K亲和力不同的吸附点位。在低钾饱和度时 ,土壤对K的高选择吸附主要归于粘粒矿物楔形区域电荷点位吸附 ,五种土壤楔形区域相对吸附点位顺序为 :黑土 >土 >水稻土 >红壤 >砖红壤 ,该相对吸附点位顺序与土壤含有风化云母和蛭石有关。在高钾饱和度时 ,五种土壤对K的吸附主要发生于粘粒矿物的晶层表面电荷点位 ,粘粒矿物的晶层表面电荷起源也许起决定作用 ,此时KG 选择系数的大小顺序为 :砖红壤 >红壤 >黑土 >土 >水稻土     

几种有机酸对恒电荷和可变电荷土壤吸附Cu2+的影响

以恒电荷土壤(黄褐土和黄棕壤)和可变电荷土壤(红壤和砖红壤)为供试材料,研究了乙酸、草酸、酒石酸和柠檬酸对土壤吸附重金属铜离子(Cu2 )的影响。结果表明,在相同酒石酸浓度下,土壤对酒石酸的吸附量依次为黄棕壤(2 1 8mmolkg-1) >红壤(15 4mmolkg-1) >砖红壤(9 5mmolkg-1) ,土壤吸附有机酸后负电荷量增加,相同条件下增幅为砖红壤>红壤>黄棕壤;无有机酸配体时,供试土壤对Cu2 的吸附量为黄褐土>黄棕壤>砖红壤>红壤;加入有机酸时,随有机酸浓度增高,土壤对Cu2 的吸附一般表现为“峰”形曲线,峰所对应的有机酸浓度因有机酸类型而异,且随土壤可变电荷性质增强而增高;土壤吸附有机酸后对Cu2 的次级吸附不同于有机酸与铜共存时的竞争吸附,且因土壤性质表现迥异。这些结果意味着在存在有机酸配体的根际环境中,恒电荷土壤与可变电荷土壤对Cu2 的吸附明显不同,并将影响重金属离子在根际的转化与有效性     

应用Multi-Langmuir模型评价土壤的表面电荷特性

用返滴定技术测定土壤的可变电荷量(Qv),应用Muti-Langmuir模型评价土壤的表面电荷特性。结果表明,黄壤和黄棕壤可变电荷量的变化范围在0～45cmolkg-1,红壤为0～21cmolkg-1,砖红壤和赤红壤为0～14cmolkg-1。可变电荷量(Qv)依赖土壤悬液的pH,3点位模型能很好地描述6种土壤的可变电荷量随pH的变化关系;黄壤、黄棕壤、湖南红壤、江西红壤、赤红壤和砖红壤的pK1分别为4.45、4.46、4.76、4.62、4.66和4.74,可变电荷量Qv1分别为11.7、9.64、9.31、7.14、4.86和5.95cmolkg-1。黄壤和黄棕壤pK1较红壤、砖红壤和赤红壤约低0.3。pK1与ZPC呈现极显著的线性关系,可变电荷量(Qv(i))与有机质含量呈极显著的正相关。     

土壤—水体系中离子反应平衡时间的电导法检测

采用电导法检测了土壤—水体系中离子反应达到平衡所需的时间。5种土壤和硝酸盐溶液(10-4/3z mol L-1)配制的20种悬液(30 g kg-1)的电导率时间变化曲线表明,所有悬液的电导率均呈下降趋势,在平衡100~300 h后不再变化。含Cu(NO3)2和Pb(NO3)2溶液(10-4mol L-1)的黄棕壤悬液(10 g kg-1)的Wien效应曲线的位置和形状随平衡时间而变,但当平衡时间≥480 h,曲线出现重叠。含NaNO3和KNO3溶液(2×10-4mol L-1)的黄棕壤悬液(10 g kg-1)的电导率与离心清液中Na 和K 离子浓度随平衡时间呈同步变化趋势,平衡初期均不断下降,分别在平衡70 h和30 h后趋达稳定。这些实验结果表明,电导法确是一种检测土壤—水体系中离子反应平衡时间的简易手段。     

用电导频散法研究Cl-、SO2-4和H2PO-4阴离子与土壤的相互作用

本文介绍了采用电导频散装置测量分别含有10-4mol/L HCl、5×10-5mol/LH2SO4和10-4mol/L H3PO4的黄棕壤、棕壤、黑土和砖红壤悬液(20-30g/kg)的电导频散曲线,频散曲线上均呈现频率范围相当宽的坪区.频散曲线的特性分析结果表明,黄棕壤和棕壤在3种酸溶液中的始散频率(0.6-1kHz)低于黑土悬液(16-28kHz),而砖红壤的始散频率最高(25-47kHz);Cl-、SO2-4和H2PO-4离子与4种土壤的相对亲合力(REC1.5/REC2-1)顺序为Cl-＜SO2-4＜H2PO-4,在不同土壤之间的顺序则随酸溶液而异.     

硫酸根离子添加顺序对可变电荷土壤吸附铜离子的影响

研究了SO2-4添加顺序对三种可变电荷土壤(昆明铁质砖红壤、徐闻砖红壤和江西红壤)吸附Cu2+的影响,作为对照,也研究了其对恒电荷土壤(黄棕壤、棕壤)以及两种不同矿物(高岭石与针铁矿)吸附铜离子的影响。实验结果表明,在同等条件下,SO2-4添加顺序对两类表面性质不同的土壤吸附Cu2+有着不同的影响。对于恒电荷土壤,SO2-4添加顺序对土壤吸附Cu2+几乎没有影响。同等pH条件下,对可变电荷表面而言,加入CuSO4者具有最高的Cu2+吸附率;对昆明砖红壤、徐闻砖红壤以及针铁矿和高岭石而言,先加入Cu2+者相对先加入SO2-4者Cu2+吸附率更高;对江西红壤而言,上述这个次序则刚好相反。SO2-4浓度和有机质去除对同等pH条件下铜离子吸附率高低的排序并无实质性影响。     

Cs离子吸附法测定土壤和矿物的永久负电荷

离子吸附法是测定土壤表面电荷最常用的方法,由于吸附离子选择的限制,长期以来用这一方法得到的结果偏低。Cs+的水合离子半径在元素周期表第一主族中最小,用其作为吸附离子测定土壤表面电荷有诸多优点。研究结果表明,Mehlich法得到的CEC8.2小于NH4OAC法得到的CEC,由该方法获得的土壤永久负电荷数据也小于Cs+吸附法测定的结果,Cs+吸附法获得的土壤永久负电荷数据更符合实际。Cs+吸附法得到的几种土壤永久负电荷量由小到大的顺序为:海南澄迈砖红壤(50~80cm)<广西柳州红壤(60~160 cm)<江西进贤红壤(80~150 cm)<安徽宣城红壤(0~20 cm)<江苏南京黄棕壤(20~40cm),表明随着纬度的增加,土壤永久负电荷量逐渐增加,CEC表现为相似的趋势。     

Interactions between Oat beta-Glucan and calcofluor characterized by spectroscopic method

This paper describes the binding of Calcofluor, a fluorescent probe, to oat beta-glucan in buffer solutions. The binding equilibrium constant (K), the total number of binding sites per beta-glucan molecule (N), and the average binding number of Calcofluor per beta-glucan molecule (n) were determined by UV spectroscopic method. The results indicate that the association of Calcofluor and beta-glucan is driven by both enthalpy and entropy and that the process involves hydrogen bonding, van der Waals forces, and hydrophobic interaction. Higher buffer concentration and NaCl facilitate the binding of Calcofluor to beta-glucan. The adsorption isotherm fits a Langmuir model quite well.     

Soil particle size range correction for improved calibration relationship between the laser-diffraction method and sieve-pipette method

Particle size fraction(clay, silt, and sand) is an important characteristic that influences several soil functions. The laser-diffraction method(LDM) provides a fast and cost-effective measurement of particle size distribution, but the results usually differ from those obtained by the traditional sieve-pipette method(SPM). This difference can persist even when calibration is applied between the two methods. This partly relates to the different size ranges of particles measured by the two methods as a result of different operational principles, i.e., particle sedimentation according to Stokes’ Law vs. Mie theory for laser beam scattering. The objective of this study was to identify particle size ranges of LDM equivalent to those measured by SPM and evaluate whether new calibration models based on size range correction can be used to improve LDM-estimated particle size fractions, using 51 soil samples with various texture collected from five soil orders in New Zealand. Particle size distribution was determined using both LDM and SPM. Compared with SPM, original data from LDM underestimated the clay fraction(< 2 μm), overestimated the silt fraction(2–53 μm), but provided a good estimation of the sand fraction(53–2 000 μm).Results from three statistical indices, including Pearson’s correlation coefficient, slope, and Lin’s concordance correlation coefficient, showed that the size ranges of < 2 and 2–53 μm defined by SPM corresponded with the < 5 and 5–53 μm size ranges by LDM, respectively. Compared with the traditional calibration(based on the same particle size ranges), new calibration models(based on the corrected size ranges of these two methods) improved the estimation of clay and silt contents by LDM. Compared with soil-specific models(i.e., different models were developed for different soils), a universal model may be more parsimonious for estimating particle size fractions if the samples to be assessed represent multiple soil orders.     

扩散率与吸水率关系的解析方法

A simple method was developed to relate soil sorptivity to hydraulic diffusivity and water absorption experiments were conducted utilizing one-dimensional horizontal soil columns to validate the relationship. In addition, an estimation method for hydraulic diffusivity with disc infiltrometer was developed. The results indicated a favorable fit of the theoretical relation to the experimental data. Also, the experiment with disc infiltrometer for estimating the diffusivity showed that the new method was feasible.     

水稻籽粒流对承载板冲击过程离散元分析

为了提高谷物流量测量精度,基于软球模型的离散元法,采用Hertz-Mindlin(无滑移)接触力学模型模拟水稻籽粒流与承载板冲击过程,在升运器线速度分别为0.5、1.0、1.5m/s时分析水稻质量与平均法向冲击力变化规律。结果表明:水稻籽粒流对承载板冲击过程的离散元模型参数选用合理,具有工程应用价值;去除水稻籽粒在承载板上的滑落阶段,3种线速度下水稻质量与平均法向力的线性相关系数由0.8062,0.9082,0.9891分别增大到0.9144,0.9630,0.9944。在设计冲量式谷物质量流量测量装置时应考虑如何减少谷物在测量装置上的滑落阶段,从而提高测量精度。为谷物流量测量装置的开发提供技术支持。     

Relationship between granitic soil particle-size distribution and shrinkage properties based on multifractal method

The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by weathering. The purpose of this study was to relate the spatial variation of particle-size distribution (PSD) of granitic soils with soil shrinkage parameters using multifractal theory. The heterogeneity of PSD and pedogenic processes were depicted in detail by multifractal dimensions. The PSD generally increased with the increase of profile depth in accordance with the variation of single fractal dimension (D) ranging from 2.45 to 2.65. The shrinkage limit was greatly influenced by the multifractal dimension parameters, including information dimension (D₁) and capacity dimension (D₀) (Adjusted R²=0.998, P < 0.01), and the maximum linear extensibility (κ_v) was determined by spectral width (△α) and bulk density, with the latter explaining 89% of the total variance of κ_v (P < 0.01). Soil shrinkage characteristic curve was fitted by the modified logistic model (R² > 0.97, root sum of squares < 0.1), and the water variation corresponding to the maximum change rate of linear extensibility was determined by the silt content (R²=0.81, P < 0.01). Overall, the shrinkage of granitic soils was primarily influenced by PSD and soil compactness.     

果园行间3D LiDAR导航方法

为克服二维激光扫描仪在果园导航中感知信息少、无法有效应对树冠茂密、树干被遮挡等复杂三维果园场景,该研究提出一种基于3D LiDAR的果园行间导航方法。以3D LiDAR为检测设备实时采集果园信息,使用挖空打断后的树墙体心等效树干位置,根据左右树行的最佳平行度对随机采样一致性算法与最小二乘法拟合的树行进行互补融合并求其中心线得到导航线;对纯跟踪算法进行改进,实现差速运动机器人对树行的跟踪。结果表明:系统在篱壁式仿真果园环境下以0.33 m/s的速度沿中心线行走时,绝对航向定位偏差在1.65°以内,绝对横向定位偏差在6.1 cm以内;以0.43 m/s的速度跟踪树行的绝对横向偏差在15 cm以内。在真实梨园下,系统分别以0.68与1.35 m/s的速度跟踪树行,绝对横向偏差分别不超过21.3与22.1 cm。本系统可广泛用于标准果园与复杂三维果园机械的自主导航,具有可靠的稳定性。     

Reaction between albumen and 3,3',5,5'-tetramethylbenzidine as a method to evaluate egg freshness

The 3,3',5,5'-tetramethylbenzidine colorimetric test is proposed as a method for the evaluation of shell egg freshness. A simplification of the original method was tested on albumen, and the modified method was used to study the development of albumen-tetramethylbenzidine reaction in eggs stored at three temperatures for different times. The stability of the reagent solution and the repeatability of the analytical method were also studied. The reaction mechanism showed the predominant role of iron ions on the colorimetric response, and the secondary role of copper ions added to the reaction mix in order to enhance the response. The response coefficient of variation, due to the natural variability in eggs laid by hens of two breeds and different ages, was 10.3%, which is similar to the value obtained for furosine, but lower than those previously observed for other egg freshness indices such as Haugh Unit and air-cell height.     

Surface-bound phosphatase activity in ectomycorrhizal fungi: a comparative study between a colorimetric and a microscope-based method

For the quantification of surface-bound phosphomonoesterase activity (SBPA) of fungi, roots, or mycorrhiza, a colorimetric method based on p-nitrophenyl phosphate (pNPP) is widely used. Unfortunately, this method does not reveal information about the localization of the surface-bound phosphomonoesterase (SBP). We introduce a method that localizes and quantifies SBPA in living hyphae of ectomycorrhizal fungi using confocal laser scanning microscopy of the hydrophilic substrate enzyme-labelled fluorescence (ELF-97) and compare it to the pNPP assay. ELF-97 turns into a strongly fluorescent precipitate upon activation by SBPA and forms bright fluorescent centres on the outer cell wall of the hyphae. Our data show that the enzymatic reaction is not substrate-limited during an incubation period of 15 min in fungal hyphae of Pisolithus tinctorius, Cenococcum geophilum, and Paxillus involutus. Image-processing routines determined the total intensity and the average number of the fluorescent ELF-97 centres per micrometre fungal hyphae of C. geophilum and Paxillus involutus. ELF-97 and pNPP detected similar variations of the SBPA at different pH values (3–7) during the measurement and different phosphorus (P) concentrations during the growth period of the fungi. The ELF-97 method revealed that C. geophilum and Paxillus involutus adapt in different ways to the variation of the P concentrations during the growth period by varying the number, the activity, or both properties of the SBP centres. The phosphatases show peak activities at different pH values, so the response of the fungal mycelium to varying P concentrations in soils is pH selective. In conclusion, ELF-97 is a promising substrate to reveal SBPA and adaptation strategies on a structural–physiological level.     

A method of selective inhibition to distinguish between nitrification and denitrification as sources of nitrous oxide in soil

Summary Nitrapyrin and C₂H₂ were evaluated as nitrification inhibitors in soil to determine the relative contributions of denitrification and nitrification to total N₂O production. In laboratory experiments nitrapyrin, or its solvent xylene, stimulated denitrification directly or indirectly and was therefore considered unsuitable. Low partial pressures of C₂H₂ (2.5–5.0 Pa) inhibited nitrification and had only a small effect on denitrification, which made it possible to estimate the contribution of denitrification. The contribution of nitrification was estimated by subtracting the denitrification value from total N₂O production (samples without C₂H₂). The critical C₂H₂ concentrations needed to achieve inhibition of nitrification, without affecting the N₂O reductase in denitrifiers, must be individually determined for each set of experimental conditions.