土壤中黑碳对农药敌草隆的吸附-解吸迟滞行为研究

采用批处理振荡法和连续稀释法分别测定了敌草隆在人工添加黑碳土壤和自然形成的不同有机质和黑碳含量的土壤中的吸附一解吸行为。吸附结果表明，人工添加黑碳的土壤对敌草隆的吸附强度和吸附容量以及吸附等温线的非线性均随土壤黑碳添加浓度的增加而逐步增大；自然土壤的吸附容量和吸附强度随土壤总有机质含量增加而增加，但吸附等温线的非线性则与土壤中黑碳对有机质的相对含量有关，黑碳比例越高，等温线非线性越大。解吸实验结果表明，无论是人工添加黑碳的土壤还是自然土壤，对敌草隆的解吸迟滞作用均随土壤黑碳含量增高而愈明显。     

Effects of hysteresis on redistribution of soil moisture and deep percolation at continuous and pulse drip irrigation

The infiltration and redistribution of soil moisture under surface drip irrigation considering hysteresis were investigated in two soils (loamy sand and silt loam) of different texture. The effect of continuous versus intermittent application of 1, 2 and 4 l/h to the soils was evaluated in terms of wetting front advance patterns and deep percolation under the root zone. For this purpose, a cylindrical flow model incorporating hysteresis in the soil water retention characteristic curve, evaporation from the soil surface, and water extraction by roots was used. The results show that, compared with continuous irrigation, pulse irrigation slightly reduces the water losses under the root zone in both cases (with and without hysteresis). Also, at the total simulation time, in both types of irrigation, hysteresis reduces significantly the water losses under the root zone. Finally, the effect of hysteresis was found to be greater at higher discharge rate (4 l/h) and consequently at higher water content at the soil surface.     

镉在土壤中吸附的能量特征和解吸滞后效应研究

[目的]为了研究吸附-解吸反应对重金属生物有效性的影响.[方法]以我国12种典型农田土壤为试验材料,采用批次平衡法,研究重金属镉在农田土壤中吸附的能量特征和解吸滞后效应.[结果]供试土壤对镉的吸附均为自发反应,温度的升高有利于促进土壤对镉的吸附.土壤镉吸附的吉布斯自由能变（△G°）可以用来预测土壤镉的解吸能力.土壤对重金属镉吸附的主要机理为化学键力.镉在土壤中的解吸过程存在滞后现象,随着镉平衡液浓度的增加,各供试土壤中镉解吸的滞后效应增强.供试土壤pH和碳酸钙含量越高,滞后系数越大.这可能与土壤pH和碳酸钙含量较高时,镉在土壤中形成难解吸的内圈配合物和碳酸镉沉淀有关.[结论]该研究结果可以为防治土壤重金属污染和修复研究提供参考依据.     

Carbon dioxide fluxes in corn-soybean rotation in the midwestern U.S.: Inter- and intra-annual variations, and biophysical controls

Quantifying carbon dioxide (CO₂) fluxes in terrestrial ecosystems is critical for better understanding of global carbon cycling and observed changes in climate. This study examined year-round temporal variations of CO₂ fluxes in two biennial crop rotations during 4 year of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production. We monitored CO₂ fluxes using eddy-covariance (EC) and soil chambers in adjacent production fields near Ames, Iowa. Under the non-limiting soil water availability conditions predominant in these fields, diel and seasonal variations of CO₂ fluxes were mostly controlled by ambient temperature and available light. Air temperature explained up to 81% of the variability of soil respiratory losses during fallow periods. In contrast, with full-developed canopies, available light was the main driver of daytime CO₂ uptake for both crops. Furthermore, a combined additive effect of both available light and temperature on enhanced CO₂ uptake was identified only for corn. Moreover, diurnal hysteresis of net CO₂ uptake with available light was also found for both crops with consistently greater CO₂ uptake in the mornings than afternoons perhaps primarily owing to delay in peak of soil respiration relative to the time of maximum plant photosynthesis. Annual cumulative CO₂ exchange was mainly determined by crop species with consistently greater net uptake for corn and near neutral exchange for soybean (−466 ± 38 and −13 ± 39 g C m⁻² year⁻¹). Concomitantly, within growing seasons, CO₂ sink periods were approximately 106 days for corn and 90 days for soybean, and peak rates of CO₂ uptake were roughly 1.7-fold higher for corn than soybean. Apparent changes in soil organic carbon estimated after accounting for grain carbon removal suggested soil carbon depletion following soybean years and neutral carbon balance for corn. Overall, results suggest changes in land use and cropping systems have a substantial impact on dynamics of CO₂ exchange.     

加载/卸载作用次数对水稻谷粒机械损伤的影响

水稻谷粒在收获、加工、储运过程中的损伤不仅与其所受载荷的大小有关，也与载荷作用次数有关。对水稻谷粒进行多次加载、卸载作用下的压缩试验，研究了水稻谷粒的滞回耗能特性，分析了水稻谷粒的机械损伤机理。通过试验建立了载荷、加载循环次数对水稻谷粒损伤率影响规律的数学模型，并对模型进行了F检验。通过该模型导出了水稻谷粒损伤率为1％时载荷与加载次数间的关系曲线。     

土壤不同粒径组分对菲的吸附解吸行为的研究

有机污染物在土壤环境中的行为主要取决于它们与土壤不同组分之间的相互作用,土壤不同粒径组分中有机质的含量和结构特征以及矿物组成不同,它们对有机污染物的环境行为影响也不同。本研究用物理方法将两种不同类型土壤水稻土(SEBC-07)和红壤(SEBC-13)分成粒径大小不同的土壤组分(<2μm、2~20μm、20~54μm、54~105μm、105~280μm、>280μm),研究了它们对菲的吸附解吸行为。SEBC-07土样不同粒径组分对菲的吸附容量(Kf)从大到小顺序为:2~20μm、20~54μm、54~105μm、<2μm、>105μm;SEBC-13土样不同粒径组分的Kf值从大到小顺序为:20~54μm、<2μm、2~20μm、54~105μm、105~280μm、>280μm。除<2μm和20~54μm的粒径组分外,有机质含量较高的水稻土不同粒径组分对菲的吸附容量都明显高于有机质含量较低的红壤。两种土壤20~54μm组分的Koc值都最大,然后向粒径增大和减小的方向都逐渐降低。不同粒径组分的Kf和Koc值与它们的理化性质(有机碳含量、比表面积)都没有显著的相关性。两种土壤的不同粒径组分对菲的解吸都有不同程度的滞后现象。     

Sorption–desorption of phenolic acids as affected by soil properties

Phenolic acids have been implicated in the process of allelopathy and are, therefore, of interest in plant management as a basis for new herbicide structures. The potential bioavailability of phenolic acids is controlled by sorption–desorption processes in soil. Sorption–desorption of p-coumaric acid (4-hydroxycinnamic acid), ferulic acid (3-methoxy-4-hydroxycinnamic acid), veratric acid (3,4-dimethoxybenzoic acid), vanillic acid (3-methoxy-4-hydroxybenzoic acid), and p-hydroxybenzoic acid (4-hydroxybenzoic acid) was characterized on soils with varying physicochemical properties. The phenolic acids sorbed quickly (<8 h) and in high proportions to the amount applied (average 84% of applied was sorbed). Sorption was irreversible with the batch desorption method used (0.01 N CaCl₂ extraction). Pretreatment of soils to remove organic matter and free metal oxides from the soils decreased sorption, particularly in soils with free oxides removed. Statistical analysis suggested that sorption of p-coumaric and ferulic acids was correlated with soil clay content and veratric acid sorption was correlated with several soil factors. In contrast, no consistent relationship between soil characteristics and vanillic and p-hydroxybenzoic acid sorption was found. Based on the results of these experiments, i.e. the high reactivity of the phenolic acids, it is unlikely that these chemicals would be transported far from their point of origin, limiting their range of influence. It appears that, for phenolic acids to have allelopathic effects on plants, they would have to persist in the soil for long periods, resulting in a buildup of the chemical to high enough levels so that sufficient chemical would be in solution to cause the allelopathic effects, even though they may be strongly sorbed at lower concentrations.     

塿土表面铜吸附解吸的动力学特征及滞后效应

采用间歇法发现土娄土及不同处理土样对铜离子的吸附过程遵循二级反应动力学方程 ,吸附速率常数ka 呈 :土娄土 >去OM土娄土 >去Ca土娄土 >去Ca、OM土娄土 ;解吸过程符合两点位一级动力学方程 ,第一点位解吸速率常数kd1大于第二点位解吸速率常数kd2 ;各土样解吸速率常数的大小顺序与ka相反 ;吸附 解吸之间的滞后效应用ka/kd来衡量 ,滞后程度大小与ka大小顺序一致     

超磁致伸缩执行器率相关迟滞混合模型研究

超磁致伸缩执行器的迟滞具有率相关特性。提出一种混合建模方法用于率相关迟滞建模。首先,在低频激励下,建立系统的率不相关PI迟滞模型;其次,在高频激励下,提出率不相关PI迟滞模型求逆与拟合相结合的方法,将系统响应解耦,进而建立系统线性环节模型;然后,在上述基础上,提出并建立系统迟滞环节的率相关PI迟滞模型;最后,通过系统线性环节模型和率相关PI迟滞模型串联得到率相关迟滞混合模型。实验结果显示:相对于率不相关迟滞模型或率不相关迟滞混合模型,率相关迟滞混合模型具有更高的精度,从而验证了所提模型的有效性和精确性。