Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Hydraulic properties, specifically the water holding capacity of soils, play a key role in the ability of soils to sustain plant growth. Additions of hydrophilic polymers (superabsorbents) can improve the water holding capacity of sandy soils. This has led to practical applications of these materials particularly in arid regions and countries, where water is the limiting factor for plant production. The objectives of this study are to investigate how effective hydraulic properties of polymer‐soil mixtures are affected by addition of absorbents in different concentrations. Novel aspects are the investigation of aging under repeated wetting–drying‐cycles over an appreciable time in the field and a systematic investigation of the salt influence on the water uptake of polymers. We added the polymer Super AB, A‐200 (Iran Polymer Institute), to dune sand in ratios of 0.3%, 0.6%, and 1% w/w. We found that the effective water retention characteristics of the soil–absorbent mixtures were improved with respect to plant‐available water compared to the pure sand, and the improvement was related to the respective amount of absorbent in the mixture. The plant available water content (PAW) increased from 0.005 for the untreated sand to 0.06, 0.20, and 0.28 g g^?1, respectively, for the sand with the three polymer additions. Due to aging of the polymers, PAW decreased after 6 months of cyclic drying and wetting to about half of the value immediately after the initial treatment. We attribute this to the effect of salts. This is corroborated by the results from water uptake experiments by the pure polymers. Repeated cycles of water uptake showed that salts in the water greatly reduced the uptake capacity of the polymers after few cycles. The effect was strong for bivalent cations and less pronounced for monovalent cations.     

不同土壤对Cr吸附的动力学特征

该文采用振荡平衡法比较了来自中国15 个省区16 种土壤对Cr（VI）的吸附及其动力学特性,并探讨了土壤pH值、阳离子交换量、黏粒含量和有机质对Cr（VI）吸附及其动力学参数的影响。结果表明：具有较低土壤pH值和较高物理黏粒含量的土壤对Cr（VI）具有较大的表观吸附量,而土壤阳离子交换量和有机质因素对土壤Cr（VI）的表观吸附量影响较小。酸性土壤对Cr（VI）吸附能力较强,可以采用一级动力学方程和抛物线方程描述Cr（VI）在酸性土壤中的动力学行为,且土壤的表观吸附速率和平衡时的吸附量与土壤的pH值呈显著（p＜0.05）负相关关系,而与物理黏粒含量呈显著（p＜0.01）正相关关系;而碱性土壤对Cr（VI）吸附能力较小,很难用动力学方程描述其吸附动力学特性。可见,土壤pH值不仅影响土壤对Cr（VI）的表观吸附量,并且对Cr（VI）表观吸附动力学特征产生了较大影响。     

手持式风送授粉机研制与试验

针对中国果树授粉大多采用人工点授、蜜蜂授粉等作业方式,迫切需要机械授粉机具的现状,研制了手持式风送授粉机。该机采用可变速的直流电机驱动离心风机,依照流体力学射流原理,计算授粉出口风速并设计了离心风机,叶片型式采用径向直板叶片,叶轮型式为平前盘,叶轮直径38 mm,叶片数为6,叶片宽度为18 mm。通过室内试验和样机田间试验分别测试了风机性能特性和气流速度对花粉分布的影响及猕猴桃柱头处的花粉覆盖率,试验结果表明:风机转速在8 000 r/min时风量为3.0×10-3 m3/s,满足风送授粉作业要求,风机转速9 000 r/min时全压效率较高,达到43%;花粉分布受风速影响较大,花粉竖直分布量以及喷粉量与出口风速成正比,且水平分布、竖直分布峰值随着风速的增加而后移,竖直分布峰值在距出口一定距离内保持稳定,显示花粉在一定速度的定向气流中能保持较好的直线传播;随着出口风速的增加,柱头处花粉覆盖率提高,当出口风速达到19.5 m/s时,花朵柱头平均有57.66%的花粉覆盖率。研究结果可为进一步研究风送授粉机的结构设计和作业参数优化提供依据。     

Chromium Speciation in Water by Sorption on Calcite and Determination by Electrothermal Atomic Absorption Spectrometry

Abstract

A rapid, sensitive, and accurate method for the separation and speciative determination of chromium (Cr)(VI) and Cr(III) in water samples has been developed using sorption as the separation technique in conjunction with final determination by electrothermal atomic absorption spectroscopy (ETAAS). The present method, where granular calcite is used as selective sorbent, separates Cr(III) with retention values up to 99%, resulting in high accuracy determination of Cr(VI). Total Cr was likewise determined by ETAAS after an efficient reduction of Cr(VI) to Cr(III) using ascorbic acid as reducing agent, deriving Cr(III) concentration from the difference between total Cr and Cr(VI). The parameters of the separation technique, solution pH (4.5–5.5), solution flow rate through the calcite column (0.14–0.42 mL min^?1), and calcite column internal diameter (1.5–3.0 cm), were evaluated. Best results were achieved with pH of 5.5, flow rate of 0.42 mL min^?1, and column internal diameter of 1.5 cm. Optimum determination conditions were found using magnesium nitrate [Mg(NO₃)₂] as chemical modifier, pyrolysis, and atomization temperatures of 1400 and 2200°C, respectively. In such conditions, the detection limits (n=10) were 1.5 and 0.8 µg L^?1 for Cr(III) and Cr(VI), respectively.     

4HLB-2型花生联合收获机起秧装置性能分析与试验

为了解4HLB-2型花生联合收获机起秧作业过程和作业性能,该文对起秧装置进行运动分析,研究各部件主要运动参数和位置配置参数对起秧效果的影响,并进行田间试验验证。运动分析表明,采用扶禾器倾角80°、夹持链倾角35°、扶禾速度比(扶禾链速度与机器前进速度的比值)1.5、夹持速度比(夹持输送速度与机器前进速度的比值)1.2等设计参数,起秧作业时花生秧蔓与夹持链呈近似垂直夹持状态,夹持链拔取作用力近似垂直向上;在解析花生秧蔓扶禾运动过程的基础上,确定了秧蔓扶禾次数和作用于单穴秧蔓最大拨指数的计算方法,优化扶禾器拨指间距为150mm;分析了扶禾器、挖掘铲、夹持链的位置关系对起秧作业的影响,确定3个部件侧视图方向的主要位置参数:拨禾指最低点距挖掘面的距离170mm;拨禾指最低点距夹持点所在铅锤面的距离325mm;夹持点距挖掘面的距离290mm;挖掘铲距夹持点所在铅锤面的最小距离25mm。田间试验表明,该起秧装置的运动参数及各部件位置配置能较好地满足起秧性能要求,起秧过程和状态与理论分析基本稳合。该研究为该类型花生起秧装置的结构完善设计和作业参数优化提供依据。     

苎麻机械剥制试验与工艺参数优化

苎麻剥制工艺参数是剥麻机设计与力学分析的基础。为提高剥麻机剥制质量和效率,论文针对剥麻机切削机构运动和力学特点,在自行设计的苎麻剥制机上进行了试验,对麻皮基本工艺参数、麻皮机械物理特性、切削机构动力参数对剥制质量和生产效率的影响关系进行了试验测定和优化分析。试验结果表明：随着正压力增大,纤维含杂率和含胶率降低,麻纤维质量得到提高,但损失率增加。麻皮切削速度加大有利于提高工效,但纤维质量有所下降,损失率增加。对剥制质量和工效的综合影响分析显示,切削机构刀具正压力和相对速度的最佳取值分别为220 N和 0.6 m/s,而滑动摩擦系数,麻壳剪切强度,麻壳及纤维的厚度压缩比等工艺参数可为剥麻机切削机构的设计提供重要依据。     

不同价态铬的土壤碱性磷酸酶效应模拟研究

铬是环境中四大污染元素之一,其不同价态间对生物的生态毒性差异较大。采用模拟方法对Cr3＋和Cr6＋的土壤碱性磷酸酶效应进行了研究。结果表明,铬显著抑制了土壤碱性磷酸酶活性,其中Cr3＋的抑制作用远强于Cr6＋,土壤轻度Cr3＋和Cr6＋污染时的临界浓度分别为151和1132mg·kg-1,二者相差6.5倍;碱性磷酸酶活性及动力学特征参数Vmax、k等与Cr浓度间达显著或极显著负相关,揭示土壤磷酸酶活性及Vmax、k可作为土壤Cr污染的监测指标之一;模型U=β0（/β1×C＋1）揭示酶与铬间的机理为完全抑制,动力学则进一步细化为非竞争性抑制;计算获得的抑制常数Ki为Cr3＋     

Detection of nitrate leaching through bypass flow using pan lysimeter,suction cup,and resin capsule

Abstract

We compared the use of mixed-bed ion exchange resin capsules (RC), suction cups (SC), pan lysimeters (PL), and subsurface drainage (DR) for the detection of nitrate movement through a clayey soil where onion (Allium cepa L.) had been cultivated over a period of seven months. At the topsoil level, solutions collected with SC showed higher concentrations of NO₃ ^? than the PL-collected samples. At 80-cm depth, however, the concentrations of NO₃ ^? were higher for the DR and PL samples than for the SC samples, suggesting that bypass or macropore flow was the primary mechanism of NO₃ ^? transport to subsurface drainage or groundwater, while solutions collected by SC mostly represented solutions inside soil aggregates. The use of the resin capsule method resulted in higher values of NO₃ ^? at 15- than at 50-cm depth initially but the trend was reversed after sufficient leaching and plant uptake. High and significant correlations were obtained between the amount of NO₃ ^? adsorbed on RC at 15-cm depth and the mean concentration of NO₃ ^? in the DR samples during the RC installation period and between the NO₃ ^? adsorbed on RC at 50-cm depth and the mean NO₃ ^? concentration of PL samples at 80-cm depth. Such results indicate that the RC method which enables the detection of nitrate transport via macropore flow is a promising technique for nitrate leaching measurements.     

铬在含水介质中的迁移及释放规律

根据天津某铬渣堆周边地区的污染情况和水文地质条件,选取该区域3种典型含水介质(黏土、粉质黏土、粉土)填充土柱,开展室内土柱淋滤实验,研究铬在含水介质中的迁移及释放规律。铬溶液淋滤实验表明,Cr(VI)在粉土中的迁移速率最快,粉质黏土中次之,黏土中最慢。清水淋滤实验表明,吸附在含水介质中的铬会在清水淋滤作用下解吸并重新释放到地下水中,从而造成地下水再次污染。根据土柱实验结果获得铬在黏土、粉质黏土和粉土中的弥散系数分别为1.87×10~(-4)m2d~(-1)、7.49×10~(-4)m2d~(-1)和1.17×10~(-4)m2d~(-1),渗透系数分别为8.60×10-6cm s~(-1)、2.14×10-5cm s~(-1)和1.34×10-5cm s~(-1),为模拟铬在含水介质中的迁移模型提供实测参数,进而为地下水中铬污染的控制与防治提供理论参考。     

岩土二元介质坡地非饱和渗流特征试验研究

为了研究岩土特性对坡地降水转化及再分布的影响,利用自行设计的大型渗透仪,对扰动组合岩土体天然降雨条件下的非饱和渗流特征进行了试验研究。结果表明：在进行岩土非饱和渗流计算时,岩体层应依据双重介质模型,并充分考虑岩块与裂隙填充物的不同,按照两者的体积含水率和体积大小分别计算其水分含量并求和得到岩体层的水分含量;下部相对弱透水层与相对高含水层的存在是壤中流发生的主要条件,在岩土水分含量较高的情况下,当降雨入渗到土壤与岩石交界面后,沿岩土界面产生侧向优先流,该优先流在水平和垂直方向交互作用引起水分在岩体裂隙中快速入渗;裂隙岩体的风化程度对非饱和渗流具有重要影响,在强风化的裂隙岩体中,水分不仅在裂隙网络中运动,同时由于岩块的风化分异,岩块的表层也参与了部分水分运动。     

2,4‐D Movement in Allophanic Soils from Two Contrasting Climatic Regions

Abstract

Allophanic top‐ and subsoils from the Mexican and Newzealand Central Volcanic Plateau, as well as a nonallophanic sandy loam soil, were sampled to study the impact of organic matter and allophane content on 2,4‐D fate. High sorption rates were found, especially in the two topsoils from Mexico and New Zealand, with distribution coefficient (K _d ) obtained from displacement experiments in packed columns equal to 7.61 and 8.43 L kg^?1 respectively. 2,4‐Dichlorophenoxyacetic acid transfer through the soil columns was found to be in chemical nonequilibrium and was well predicted using a two‐site sorption model. For the two allophanic top soils, K _d obtained from batch was very different to the K _d obtained from column experiments. Either the equilibrium could not be reached in batch or the two‐site model was not able to describe the wide range of sorption sites present in the highly reactive organic matter and allophane components.     

Cr^3＋对土壤脲酶活性特征的影响

采用模拟方法对Cr^3＋的土壤脲酶效应进行了研究,结果表明,土壤pH对Cr^3＋的生态毒性有重要影响;酸性土壤脲酶受到显著抑制,活性及动力学特征参数与Cr^3＋浓度间达显著或极显著负相关,而且模型U=β0（/β1×C＋1）揭示其间机理为完全抑制,动力学则进一步细化为非竞争性抑制;获得土壤轻微和中度污染时的生态剂量ED10和ED50分别为50.59和865.7 mg.kg^-1;酸性土壤中脲酶活性、Vmax、k可作为土壤Cr^3＋污染的监测指标之一,而碱性土壤则反应不敏感,其随铬浓度增加,脲酶活性及动力学参数呈先增加后降低的规律性变化,总体变幅较小;两类土壤的差别可能主要是由于土壤环境引起了不同价态铬转变的缘故。     

水稻秸秆纤维地膜制造工艺参数优化

为规模化生产与塑料地膜除草和保墒等同、价格相当的生物质基生物降解地膜提供技术支撑,该文对用水稻秸秆纤维制取地膜的工艺进行了探讨。以水稻秸秆纤维为主要原料,添加KP浆板（木材纤维）、湿强剂、松香以及矾土等环保助剂,利用常规抄纸工艺,采用五因素五水平1/2实施正交旋转中心组合试验设计的方法,以打浆度、混合比、定量、湿强剂、调节剂为影响因素,选取干抗张力、湿抗张力、施胶度为性能指标,进行了试验研究。研究结果表明：在定量90 g/m2,调节剂0.2%,湿强剂0.8%,混合比低于 68%,打浆度大于45°SR的参数组合下,水稻秸秆纤维地膜的干抗张力大于30 N,湿抗张力大于10 N,施胶度大于100 s。优化后的参数可满足地膜田间覆盖机械性能要求。     

新型异向流沉沙池泥沙沉降特性试验与机理分析

为了探明二级泥沙处理设施--新型异向流沉沙池的泥沙沉降特性及其沉沙机理,该研究开展了不同流量和不同含沙浓度的系列试验,并对泥沙运动过程进行了力学分析,建立并求解了新型异向流沉沙池双向倾斜薄板上泥沙运动的一阶非线性微分方程。研究结果表明,对于中值粒径为0.021 mm的细颗粒泥沙的含沙水流,长96 cm、宽10 cm、高110 cm的新型异向流沉沙池对流量为45～360 L/h的泥沙截除率为40%～88.53%,约为相同体积的底板倾斜和底板水平的条形沉沙池的1.2～2倍;单位时间沉降至集沙箱的泥沙量是底板倾斜条形沉沙池的1.3～2.3倍;不同时刻双向倾斜薄板上的泥沙运动速度和加速度均大于单向倾斜斜板,倾角为锐角时,角度越大,速度越大。工程设计时,若地形高差满足要求,双向倾斜薄板的倾角（<90°）越大越有利于提高沉降效率,若高差不满足,倾角应不小于泥沙休止角。研究结果可为新型异向流沉沙池结构优化及应用提供参考。