生物质炭结构性质及其对土壤有效养分和腐殖质组成的影响

生物质炭是具有高度热稳定性和较强吸附特性的含碳物质,不同来源生物质炭的结构性质可能存在着很大的差异。为此对2种自制的不同来源生物质炭和1种商业黑炭进行了结构表征,并研究了添加生物质炭对土壤有效养分和腐殖质组成的影响。结果表明,不同来源的生物质炭在结构上有明显区别：秸秆生物质炭的芳构化程度和热稳定性最低,脂族性最强;商业黑炭缩合程度和热稳定性最高,脂族性最弱;松枝生物质炭介于二者之间。向土壤中添加秸秆生物质炭和松枝生物质炭培养45d后,土壤有机碳含量、胡敏酸和富里酸含量、有效养分含量都有不同程度的增加,同时胡敏酸的色调系数ΔlgK降低,对土壤有机碳的长期保存有积极意义。     

K+浓度对潮土和褐土钾吸附动力学的影响

研究了潮土、褐土在五种Ｋ十浓度下吸附Ｋ＋的动力学，结果表明：不同浓度下的表观吸附过程均可用一级反应动力学方程描述；表观吸附速率常数ｋａ及其与表观平衡吸附量ｑ∞的乘积与淋洗液Ｋ＋浓度之间均表现为极显著的直线正相关；表观平衡吸附量与浓度之间的关系符合Ｌａｎｇｍｕｉｒ或Ｆｒｅｕｎｄｌｉｃｈ等温吸附公式。依据试验结果对土壤钾吸附动力学进行了讨论与推导，找到四个动力学参数ｎ、ｋ１、Ｋ２、ｑｍａｘ，通过这些动力学参数可以计算表观吸附动力学参数Ｋａ、ｑ∞和平衡常数Ｋ及吸附过程中的自由能变△Ｇ，在一定条件下，还可以用来判断等温吸附的类型、估算等温吸附参数。     

一个改进的土壤铵、磷和钾等温吸附新模型

土壤对养分的吸附特性是土壤化学和植物营养学的重要研究内容。9个供试土壤的NH4+、PO43-和K+吸附试验表明,Langmuir、Freundlish和Temkin等温吸附方程对其有较好的拟合效果,但亦有部分供试土壤的拟合精度不良。本文引进种群生态学的"形状因子d"概念,在Langmuir方程基础上构造了一个新的吸附模型。理论分析表明,新吸附模型综合反映了3个等温吸附方程所描述的吸附特征。模拟结果表明,等温吸附方程模拟不佳的供试土壤,用新模型模拟均能达到显著水平;新吸附模型的拟合精度(R2)高于3个等温吸附方程,且标准差最小。形状因子d的变化幅度在0.608 0～2.929 0,体现了土壤理化性质对NH4+、PO43-和K+等温吸附曲线形状的影响。新吸附模型和Langmuir方程的NH4+、PO43-和K+的qm值之间的线性相关系数分别为0.851 5**、0.825 8**和0.912 8**(n=9)。土壤理化性质分析表明,新吸附模型的PO43-和K+的qm值与土壤有机质之间、土壤NH4+和K+的qm值与CEC之间均有显著水平的线性正相关。NH4+的qm值与土壤碱解氮含量亦呈显著水平的线性正相关,而PO34-的qm值与土壤有效磷含量则呈显著水平的线性负相关。数学形式简洁的新等温吸附模型为采用统一模式定量处理土壤对NH4+、PO43-和K+的吸附特性提供了一条新途径。     

紫色土K+吸附解吸动力学研究

从国家紫色土肥力与肥料效益监测基地定位试验上 ,在第 10年水稻收获后从 0～ 30cm土层采取土壤样品 ,研究土壤K 吸附、解吸动力学过程。结果表明 ,不同施肥处理土壤K 吸附、解吸反应分别在2 4～ 32min和 4 6～ 6 4min达到平衡 ,吸附、解吸平衡量分别为 14 1～ 19 2cmolkg-1和 11 6～ 17 5cmolkg-1。相关分析说明 ,土壤阳离子交换量 (CEC)及粘粒含量是影响吸附平衡时间、吸附平衡量的重要因素 ;CEC、交换钾量是影响解吸平衡时间、解吸平衡量的重要因素。由此可见 ,长期不同施肥对土壤CEC、粘粒及交换钾量产生影响 ,从而影响了紫色土K 吸附、解吸平衡时间及吸附、解吸平衡量。平衡前钾离子的吸附、解吸速度及吸附、解吸率与反应时间lnt间存在良好的线性关系。其中反应速度直线和解吸率直线的斜率、初始反应速度及初始吸附率均与CEC、粘粒含量密切相关。Elovich方程和一级扩散方程分别为描述紫色土K 吸附、解吸反应的最优与最差模型 ,指数方程和抛物线扩散方程拟合性介于Elovich方程和一级扩散方程之间。由此可见 ,紫色土K 吸附、解吸过程不是一个单纯的过程 ,而是一个包括土体膨胀、吸附位活化、表面扩散等诸多因素的复杂过程。     

Column Holdup Formula of Soil Solute Transport

The shortcomings of the present two formulae for describing column holdup are analyzed and deductions are made to find a new formula. The column holdup, Hw, described by the new formula is dimensional,and related to soil solute transport kinesis and column physical properties. Compared with the other two column holdups, Hw is feasible to describe dimensional column holdup during solute transport process. The relationships between Hw and retardation factor, R, in different solute transport boundary conditions are established.     

Impact of soil texture on temporal and spatial development of osmotic‐potential gradients between bulk soil and rhizosphere

Solute transport from the bulk soil to the root surface is, apart from changes in soil moisture and plant nutrient uptake, a prerequisite for changes in soil osmotic potential (Ψ_o). According to the convection‐diffusion equation, solute transport depends on a number of parameters (soil moisture–release curve, hydraulic conductivity, tortuosity factor) which are functions of soil texture. It was thus hypothesized that soil texture should have an effect on the formation of Ψ_o gradients between bulk soil and the root surface. The knowledge about such gradients is important to evaluate water availability in the soil‐plant‐atmosphere continuum (SPAC). A linear compartment system with maize grown under controlled conditions in two texture treatments (T1, pure sand; T2, 80% sand, 20% silt) under low and high initial application of salts (S1, S2) was used to measure the development of Ψ_o gradients between bulk soil and the root surface by microscale soil‐solution sampling and TDR sensors. The differences in soil texture had a strong impact on the formation of Ψ_o gradients between bulk soil and the root surface at high and low initial salt application rate. At high initial salt application, a maximum osmotic‐potential gradient (ΔΨ_o) of –340 kPa was observed for the texture treatment T2 compared to ΔΨ_o of –180 in T1. The steeper gradients in osmotic potential in treatment T2 compared to T1 corresponded to higher cumulative water consumption in this treatment which can partly be explained by higher soil hydraulic conductivity in the range of soil matric potentials covered during the duration of the experiments. Differences between texture treatments in Ψ_o at the root surface did not result in differences in plant‐water relations measured as gas‐exchange parameters (transpiration rate, water‐use efficiency) and leaf osmotic potential. If soil osmotic and matric potential are regarded as additive in calculating the driving force for water movement from the soil into the root, the observed differences in water flux between treatments cannot be explained.     

盐胁迫下转Bt基因棉的K+、Na+转运及SOD活性的变化

通过对转Bt基因棉(苏抗103)和受体棉(苏棉12)在不同浓度盐胁迫条件下的钾钠离子的转运、累积分布以及它们SOD活性和H2O2含量变化的比较,证明了Bt抗虫基因的导入一方面导致棉花植株地上部钾累积增多,根部钾含量降低,从根往地上部的钾转运能力增强,而且根吸收能力也有增强趋势;然而另一方面,受盐胁迫时转Bt基因棉对钾的向上运输选择性减弱,地上部钠积累偏多,盐耐性减弱;SOD活性受盐胁迫影响,下降显著,超氧自由基的清除能力可能受到影响。结果表明,与常规棉有所不同,转Bt基因棉可能不太适宜在盐碱土壤上种植。     

铁铝氢氧化物对两种土壤和高岭石表面K+和NH4+解吸的影响

Potassium (K) and nitrogen (N) are essential nutrients for plants. Adsorption and desorption in soils affect K+ and NH + 4 availabilities to plants and can be affected by the interaction between the electrical double layers on oppositely charged particles because the interaction can decrease the surface charge density of the particles by neutralization of positive and negative charges. We studied the effect of iron (Fe)/aluminum (Al) hydroxides on desorption of K+ and NH + 4 from soils and kaolinite and proposed desorption mechanisms based on the overlapping of diffuse layers between negatively charged soils and mineral particles and the positively charged Fe/Al hydroxide particles. Our results indicated that the overlapping of diffuse layers of electrical double layers between positively charged Fe/Al hydroxides, as amorphous Al(OH) 3 or Fe(OH) 3 , and negatively charged surfaces from an Ultisol, an Alfisol, and a kaolinite standard caused the effective negative surface charge density on the soils and kaolinite to become less negative. Thus the adsorption affinity of these negatively charged surfaces for K+ and NH + 4 declined as a result of the incorporation of the Fe/Al hydroxides. Consequently, the release of exchangeable K+ and NH +4 from the surfaces of the soils and kaolinite increased with the amount of the Fe/Al hydroxides added. The greater the positive charge on the surfaces of Fe/Al hydroxides, the stronger was the interactive effect between the hydroxides and soils or kaolinite, and thus the more release of K+ and NH + 4 . A decrease in pH led to increased positive surface charge on the Fe/Al hydroxides and enhanced interactive effects between the hydroxides and soils/kaolinite. As a result, more K+ and NH + 4 were desorbed from the soils and kaolinite. This study suggests that the interaction between oppositely charged particles of variable charge soils can enhance the mobility of K+ and NH + 4 in the soils and thus increase their leaching loss.     

Impacts of Municipal Wastewater on The Transport Characteristics of Reactive Solutes Through Agricultural Soils

Reliable transport parameters of agrochemicals and soluble pollutants are crucial for modeling and management of soil and groundwater quality. This study investigated impacts of municipal wastewater on the transport parameters of five heavy metal/metalloid compounds (NaAsO₂, Cd(NO₃)₂, Pb(NO₃)₂, Ni(NO₃)₂ & ZnCl₂), two pesticides (cartap & carbendazim) and an inert salt (CaCl₂) in four agricultural soils of Bangladesh. Solute-breakthrough concentrations were measured in repacked soil columns with time-domain reflectometry (TDR) both before and after wastewater treatment. Transport velocity (V), dispersion coefficient (D), dispersivity (λ) and retardation factor (R) of the solutes, and pertinent soil properties were determined. Wastewater reduced bulk density (γ) of the soils (from 1.32–1.37 g/cm³ to 1.26–1.35 g/cm³) by increasing organic carbon (OC) (from 0.37%–0.84% to 0.40–0.93%), increased pore-size distribution index (n) (by 0.02 unit) and reduced soil pH (from 6.32–7.45 to 5.92–6.46). D and λ decreased while V and R increased after wastewater treatment; D decreased and R increased linearly with decreasing bulk density. The correlations of V, D, and R with n improved significantly (p < 0.05) after wastewater treatment. The correlation between λ and OC improved markedly for Ca, Pb, Ni, and cartap. The observed indicative results have practical implications in developing pedo-transfer functions for solute-transport parameters using basic soil properties, which are subject to progressive modification due to agrochemicals application and wastewater irrigation.     

低分子量有机酸对红壤和黄褐土K+吸附动力学的影响

采用连续流动法研究了低分子量有机酸影响下供试土壤的钾素吸附动力学特征,探讨了描述土壤K 吸附动力学的最优模型。结果发现,有机酸（苹果酸、柠檬酸）作用下,红壤吸附的K 量均低于对照（不加有机酸）处理,0.1 mmol/L草酸处理除外。黄褐土对K 的吸附因K 浓度的不同而差异明显。当K 浓度为0.1 mmol/L时,有机酸作用下黄褐土吸附的K 量低于对照,而当K 浓度为1.0 mmol/L时,有机酸作用下的黄褐土K 吸附量高于对照。K 吸附反应速度与时间的自然对数lnt间存在良好的线性关系（R0.05=0.754,R0.01=0.874）。1.0 mmol/L KCl处理的初始吸附速率较高,反应速度降低的较快。对红壤、黄褐土吸附K 的数据进行拟合,双常数方程、指数方程和Elovich方程拟合效果较好,都达到了极显著水平,一级动力学方程拟合效果不好。双常数方程的相关系数（R）高于Elovich方程和指数方程,双常数方程是描述红壤和黄褐土在有机酸作用下K 吸附动力学的最优模型。结果表明,有机酸对两种土壤吸附能力的影响均表现为草酸＞柠檬酸＞苹果酸。有机酸作用下红壤和黄褐土的K 吸附过程主要受土壤电荷的影响。