基于土壤导气率的燥红土孔隙结构及弯曲连通性研究

土壤气体传输高度依赖土壤孔隙结构,导气率的获取简单、快速、高效,且对土壤结构破坏小,利用PL-300土壤空气传导性测量系统分别对不同含水率、不同容重条件下的原状土与扰动土进行导气率测量,展开针对土壤孔隙结构与弯曲连通性的讨论。结果表明:(1)原状土样本孔隙弯曲连通性随气相饱和度增加而增加的程度较扰动土样本显著,两者相对导气率与饱和度的关系曲线变化走势差异不大,表明即便饱和度一样的条件下,孔隙弯曲连通程度仍然不同;(2)原状土导气率依赖于大孔隙的存在,扰动土导气率不仅依赖于孔隙连通的程度,还取决于孔隙弯曲程度。基于土壤导气率对土壤孔隙结构及弯曲连通性的讨论,在建立气体传输模型时应考虑孔隙尺寸分布对导气率的影响,就原状土与扰动土不同的弯曲连通系数加以区分与讨论,为进一步揭示土壤气体传输的内在机制提供参考。     

长武地区土壤导气率及其与导水率的关系

为了寻求快速、直接、耗资低并且可用于评估野外饱和导水率的量级和其空间变异性的方法,利用PL－300土壤导气率测量仪对长武小麦试验田不同含水率、体积质量、土层、取样方向、根系密度下的导气率,以及室内原状土壤样本（248 cm3）在田间持水率情况下的导气率及饱和导水率进行了研究。发现在不同的影响因素下导气率具有一定的变化规律;含水率接近田间持水率时的土壤导气率和饱和导水率之间存在对数线性关系。土壤导气率与饱和导水率的这种预测关系在早期的试验研究中也有所反映。将本试验结果与Loll、Iverson等人的研究成果进行对比论证,验证了通过测量土壤导气率预测田间饱和导水率的方法是可行的。     

滴灌条件下原状土与扰动土水分运动特性

为了分析土壤结构对土壤入渗规律的影响,通过研究云南红壤土滴灌条件下水分运动特征,采用室内外对比试验,试验共设计了3个滴头流量,分别为2.68,3.74,4.68L/h,土壤容重为1.2g/cm~3,分别进行了单、双点源滴灌入渗试验,着重分析了原状土与扰动土在一定的滴头流量下的湿润锋、湿润体变化特征,揭示区域土壤水分运移规律,进而为区域性作物灌水提供参考依据。结果表明:(1)原状土湿润锋运移速率比较快,原状土地表湿润比随交汇时间增加的速率快于扰动土,说明湿润锋的运移速率与土壤孔隙有关;(2)相同观测时间下,原状土湿润体变化比较快,原状土湿润体扁率α大于扰动土,原状土α=16.53%,扰动土α=45%;(3)原状土与扰动土含水率等值线变化有相同趋势,但不重合,疏密程度有差异;(4)原状土分形维数比扰动土的小,说明原状土孔隙分布差异大,扰动土的质地较均匀。研究结果揭示了该地区原状土与扰动土水分运动特征,为进一步的机理研究提供参考。     

设施栽培下原状土与扰动土水分特性的试验研究

以四川省双流县设施栽培土壤为研究对象,对其原状土与扰动土的土壤水分特征曲线、水分物理性质和比水容量等项目进行了研究。结果表明,扰动土水分特征曲线总体变化趋势与原状土较为一致。在低吸力阶段,相同吸力条件下扰动土含水量高于原状土,在高吸力阶段两者差异较小。扰动土毛管孔隙度、总孔度和凋萎含水量在剖面上的总体变化趋势与原状土较为一致。扰动土不同土层田间持水量和有效水含量差异较小,原状土的田间持水量和有效水含量均随土层加深而减少。在低吸力阶段,相同吸力条件下扰动土比水容量远高于原状土,但随土壤水吸力增加,扰动土比水容量变化趋势逐渐与原状土一致。     

原状土与装填土热特性的比较

土壤热特性是研究土壤—植物—大气系统中能量传输的必要参数。目前的研究集中在室内装填土柱上热特性与含水率、质地、温度和体积质量(容重)等因素的关系,田间条件下土壤结构对热特性影响的报道很少。该研究通过比较2种质地土壤田间原状土和室内装填土热特性的差异,初步探讨了不同含水率范围内结构形成对土壤热特性的影响。采集田间原状土,在室内利用热脉冲技术测定其热容量、热导率和热扩散率;然后将样品磨碎、过2mm土筛,填装后得到相同体积质量和含水率的装填土壤样品,并测定其热特性。结果表明,装填土和原状土的热容量基本一致;在中等含水率区域(砂壤土:0.07～0.24m3/m3;壤土:0.15～0.31m3/m3),重新装填后砂壤土和壤土的热导率分别降低了9.7%和9.8%。另外,结构形成增加了土壤热扩散率,在中等含水率区域尤其明显;在接近饱和区域,原状土与装填土的热扩散率趋于一致。因此,土壤结构形成对土壤热容量没有显著影响,但提高了中等含水率区域土壤的热导率和热扩散率。     

草原露天矿区劣质土壤水平扩散特征与模拟

为探究草原露天矿区不同类型土壤的水平扩散特征,以内蒙古鄂尔多斯市伊旗武家塔矿区的原状土、矿山堆积土和生态改造土3种不同立地类型的土壤为对象,通过土壤质地、扩散率、含水率等测试试验,采用HYDRUS-1D软件,对原状土、矿山堆积土和生态改造土入渗特性进行数值模拟,分析各因素对矿区土壤入渗规律的影响,探讨草原露天矿区不同类型土壤水平扩散过程的影响及变化规律。结果表明,在一维水平入渗运动条件下,原状土、堆积土、生态改造土3种不同粒径土壤的湿润锋运移距离与时间曲线整体呈现相似变化,随着入渗时间的增加,湿润锋运移距离呈现先快速增加,后缓慢推进趋势。同一种土壤类型条件下,土壤的湿润锋到达土柱最末端所需时间与土层深度呈反比关系,随着土层深度的增加,所需时间逐渐减少,且平均扩散速率更快;在同一入渗时间下,湿润锋运移距离与土层深度呈正比关系,随着土层深度增加,湿润锋运移距离也相应增大。Boltzmann参数(λ)随着土壤含水率的增加而逐渐减小,各土壤的λ～θ关系曲线随土壤含水率的增加呈现下降趋势。当θ达到某一临界值之后,λ急剧减少,原状土、堆积土和改造土各土层θ临界值略有差异,原状土各土层的θ临界值为0...     

煤矸石组分与表土质地对充填重构土壤导气率的影响

研究煤矸石组分及表土质地对煤矸石重构土壤导气率的影响,探讨重构土壤这种差异显著的非均质土壤导气内在机理,为进一步研究复杂的非均质土壤导气特性提供理论基础。通过在煤矸石中掺杂不同粒径碎石来改变其组分,并利用3种不同质地的土壤在土柱内进行土壤剖面重构,采用一维瞬态法测量其导气率。结果表明:(1)不同碎石粒径和质量分数对混合基质饱和含水量影响不同,掺杂2~5mm粒径碎石,随着质量分数的增加,饱和含水量逐渐增加,从7.29%增加到12.9%;掺杂5~10mm粒径碎石,饱和含水量随着质量分数的增加先增加后减少,分别为7.28%,8.5%,6.9%。(2)煤矸石的导气率远大于土壤,并且煤矸石的导气率对水分的敏感度随质量含水量的增加而增加,而土壤的导气率对水分变化的敏感度均随质量含水量的增加而降低。(3)碎石的存在为大孔隙的产生创造条件的同时也会减少了土壤通气断面,阻隔空气传输的通道。(4)重构土壤导气率受表土质地和底部填充介质的共同影响,覆土土壤导气率决定了重构土壤的导气率大小,而充填基质导气率决定了充填介质对重构土壤导气率影响的系数(Ska)。Ska与充填介质导气率呈显著相关,可以通过指数函数进行拟合(R2=0.93)。通过充填介质及覆土土壤的导气率可以对重构土壤导气率进行估算,简化了重构土壤导气率的测定过程。     

耕作与覆盖措施对黄土塬区春玉米田土壤水气传输的影响

  【目的】  良好的土壤物理和水力学性质是土壤肥力可持续的基础。研究黄土高原旱作农业区长期不同耕作、覆盖措施对土壤水气传输性质的影响,为黄土塬区可持续的农田管理提供参考。  【方法】  基于设在渭北旱塬始于2002年的田间定位试验,选取传统耕作 (CT)、传统耕作+秸秆覆盖 (TS)、传统耕作+地膜覆盖 (TP)、传统耕作+全膜覆盖 (TWP)、免耕 (NT)、免耕+秸秆覆盖 (NS)、免耕+地膜覆盖 (NP)、免耕+生草覆盖 (NG) 共8个处理。于2019年春玉米收获期采集剖面土样,对0—10、10—20、20—30和30—40 cm土层土壤质量含水量、容重、导气率、相对气体扩散率和饱和导水率进行测定与分析。  【结果】  与CT处理相比,TS处理显著增加了0—40 cm土壤平均质量含水量,降低了0—40 cm各层土壤导气率,增加了各层土壤相对气体扩散率,表层 (0—10 cm) 土壤饱和导水率显著降低了75.9%;TP处理收获期耕层 (0—20 cm) 土壤容重增加,土壤总孔隙度显著降低,在0—10 cm土层,土壤导气率显著提高了54.1%;TWP处理耕层土壤容重显著增加,土壤总孔隙度显著降低,剖面0—40 cm土壤导气率和饱和导水率分别平均增加了64.8%和111.2%,尤其是表层土壤导气率显著提高了99.5%。与NT处理相比,NS处理耕层土壤容重降低,总孔隙度增加,表层土壤质量含水量、相对气体扩散率和饱和导水率分别显著提高了14.8%、25.3%和446.4%;NP处理耕层土壤容重增加,总孔隙度降低,表层土壤质量含水量和饱和导水率分别显著增加3.5%和145.2%,土壤导气率显著降低33.7%;NG处理耕层土壤容重降低,总孔隙度增加,表层土壤质量含水量显著提高了11.3%,土壤相对气体扩散率显著降低了42.1%。相同覆盖条件下与传统耕作比较,免耕处理能够降低下层20—40 cm土壤容重,增加土壤总孔隙度,提高土壤持水性,虽然降低了表层0—10 cm土壤导气率,但提高了土壤相对气体扩散率和饱和导水率。  【结论】  免耕秸秆覆盖可降低耕层土壤容重,增加总孔隙度,并且显著提高耕层土壤相对气体扩散率和饱和导水率,增加下层土壤导气率,是免耕处理组中最佳处理。传统耕作全膜覆盖可提高耕层土壤导气率、相对气体扩散率和饱和导水率,是传统耕作组中最佳处理,可有效保持渭北旱塬良好的土壤水气传输能力。     

黄河三角洲滨海盐渍土饱和导水率的研究

通过对黄河三角洲滨海盐渍土饱和导水率的研究, 结果表明: 原状土的饱和导水率随着土壤剖面深度的增加呈现出表土层高、中间土层低、底土层又升高的趋势; 扰动土与原状土的饱和导水率差异较大, 土壤饱和导水率与土壤容重呈负相关、而与孔隙度、结构系数、团聚度等均呈正相关。原状土的饱和导水率能反映田间水分运动以及孔隙状况, 对研究土壤水量平衡和水土保持有重要的意义。扰动土的饱和导水率对于土壤理化性质的理论研究有一定参考价值。     

砾石对丘陵紫色砾质土持水性的影响

通过红棕紫泥、灰棕紫泥、棕紫泥原状土和扰动土的持水性实验,研究了砾石对丘陵紫色砾质土持水性的影响.结果表明,在考虑砾石的情况下,原状土饱和含水量减少0.70%～10.70%,田间持水量减少2.07%～4.33%;砾石含量＜10%,饱和含水量和田间持水量与砾石含量关系不明显;砾石含量＞10%,饱和含水量和田间持水量随砾石含量减少而增加;在0～30 kPa吸力段,原状土和扰动土的持水能力、幂函数拟合式的α值、原状土物理性黏粒含量、扰动土比水容量都随砾石含量减少而增大;原状土的比水容量随砾石含量减少而减小.     

扰动土与原状土侵蚀产沙规律研究

采用野外模拟降雨试验,对扰动土与原状土的土壤侵蚀规律进行了研究。结果表明,原状土坡面含沙量呈先下降后波动的过程,扰动土径流含沙量在坡度5°,11°时均呈上升-下降后波动的过程。在坡度相同,雨强相近的情况下,扰动土坡面径流含沙量大于原状土。前期原状土产沙量大于扰动土,后期扰动土产沙量大于原状土。扰动土产沙量大于原状土的时间点随着坡度的增加而提前。产沙速率达到稳定后,扰动土产沙速率大于原状土,差距随着坡度的增大而增大。     

基于水分和原位电导率的西宁盆地盐渍土含盐量估算模型

为了探讨西宁盆地黄土状盐渍土导电特性与土体本身含水率和含盐量之间的关系,该文在土体洗盐试验基础上,测得了不同含水率和含盐量条件下黄土状盐渍土电导率,分析了土体电导率与含水率、含盐量之间的相互关系和作用机理;在此基础上,建立了土体电导率与含水率、含盐量之间的多元回归模型。结果表明,在土体含盐量一定条件下随着土体含水率增加土体电导率呈逐渐增大的变化趋势,且二者之间符合幂函数关系;土体含盐量愈高条件下土体含水率增加对电导率的影响则愈为显著。在土体含水率一定的条件下,土体电导率随着含盐量增加呈逐渐增大的变化趋势,且二者之间符合线性函数关系;当土体含水率相对较高时,含盐量增加对电导率的影响程度亦较为显著。对建立的区内黄土状盐渍土电导率与含水率、含盐量之间的多元回归模型(R2=0.995)进行验证,相对误差在10%之内,表明模型可有效确定含水率大于5%且小于25%(?5.52%)及含盐量为0.18%～2.18%条件下黄土状盐渍土的含盐量。研究成果对研究区及其周边地区黄土状盐渍土其盐渍化程度划分、工程地质特性评价,以及土体盐渍化等地质灾害现象的科学防治具有理论研究价值和工程指导意义。     

Predicting soil workability and fragmentation in tillage: a review

Soil workability and friability are required parameters to consider when creating suitable seedbeds for crop establishment and growth. Knowledge of soil workability is important for scheduling tillage operations and for reducing the risk of tillage‐induced structural degradation of soils. A reliable evaluation of soil workability implies a distinctive definition of the critical water content (wet and dry limits) for tillage. In this review, we provide a comprehensive assessment of the methods for determining soil workability, and the effects of soil properties and tillage systems on soil workability and fragmentation. The strengths and limitations of the different methods for evaluating the water content for soil workability, such as the plastic limit, soil water retention curve (SWRC), standard Proctor compaction test, field assessment, moisture‐pressure‐volume diagram, air permeability and drop‐shatter tests are discussed. Our review reveals that there is limited information on the dry limit and the range of water content for soil workability for different textured soils. We identify the need for further research to evaluate soil workability on undisturbed soils using a combination of SWRC and the drop‐shatter tests or tensile strength; (i) to quantify the effects of soil texture, organic matter and compaction on soil workability; and (ii) to compare soil water content for workability in the field with theoretical soil workability, thereby improving the prediction of soil workability as part of a decision support system for tillage operations.     

Soil degradation and desertification induced by vegetation removal in a semiarid environment

Abstract. The fragile soils at the transition between semiarid and arid areas are continuously threatened by human activity, which frequently involves the elimination of plant cover. We studied the impact of vegetation removal on soil characteristics in senmiarid Mediterranean Spain using two plots (15 m ± 5 m), installed on a north facing slope of 23%. Vegetation was removed from one of the plots (disturbed plot), and changes in the soil characteristics were compared with an undisturbed control plot. Fifty-five months after vegetation removal the organic carbon content decreased by 35%, the percentage of stable aggregates by 31% and soil bulk density increased by 8%. The models that best represented the changes of these parameters with time were linear equations. There were no significant differences between the water retention capacity or saturated hydraulic conductivity of the treatments. The rapid loss of soil organic matter and the consequences in terms of physical soil properties were considered to be the main factors in soil degradation. No symptoms of natural recovery were observed in the disturbed plot and the tendency was for a steady deterioration in soil behaviour. This means that human activity or climatic change leading to less vegetation could result in irreversible soil degradation in semiarid areas.     

Estimation of clay content from easily measurable water content of air‐dried soil

Soil texture is one of the main factors controlling soil organic carbon (SOC) storage. Accurate soil‐texture analysis is costly and time‐consuming. Therefore, the clay content is frequently not determined within the scope of regional and plot‐scale studies with high sample numbers. Yet it is well known that the clay content strongly affects soil water content. The objective of our study was to evaluate if the clay content can be estimated by a simple and fast measure like the water content of air‐dried soil. The soil samples used for this study originated from four different European regions (Hainich‐Dün, Germany; Schwäbische Alb, Germany; Hesse, France; Bugac, Hungary) and were collected from topsoils and subsoils in forests, grasslands, and croplands. Clay content, water content of air‐dried soil, and SOC content were measured. Clay content was determined either by the Pipette method or by the Sedigraph method. The water content of air‐dried soil samples ranged from 2.8 g kg^–1 to 63.3 g kg^–1 and the corresponding clay contents from 60.0 g kg^–1 to 815.7 g kg^–1. A significant linear relationship was found between clay content and water content. The scaled mean absolute error (SMAE) of the clay estimation from the water content of air‐dried soil was 20% for the dataset using the Pipette method and 28% for the Sedigraph method. The estimation of the clay content was more accurate in fine‐textured than in coarse‐textured soils. In this study, organic‐C content played a subordinate role next to the clay content in explaining the variance of the water content. The water retention of coarse‐textured soils was more sensitive to the amount of organic C than that of fine‐textured soils. The results indicate that in our study the water content of air‐dried soil samples was a good quantitative proxy of clay contents, especially useful for fine‐textured soils.     

Slurry-application implement tine modification of soil hydraulic properties under different soil water content conditions for silt–clay loam soils

Tillage action associated with liquid slurry application systems/management practices can modify soil infiltration properties. The degree or nature of such modification will depend largely on the type of tillage implement used, and the soil conditions at time of tillage activity. The specific objective of this study is to evaluate differences in soil infiltration properties, as measured using pressure infiltrometers and Guelph permeameters, resulting from the immediate tine action of two commonly used slurry application tillage implements (Kongskilde Vibro-Flex (S-tine) and the AerWay SSD (rolling aerator-type tine)) over a variety of silt–clay loam soil water content conditions. The results indicated that there were consistent negative correlations between field saturated hydraulic conductivity and soil water content for all tine-disturbed and undisturbed soil treatments. For Kongskilde, field-saturated hydraulic conductivity was, on average, lower in tine-influenced furrow bottoms, relative to those measured in undisturbed conditions at similar depths for most water content conditions. Generally, the Kongskilde tine-action reduced macropore-based infiltration in the bottom of the furrow for most soil conditions, albeit, this effect was most pronounced at the higher soil water contents. For AerWay, the tine-disturbed soils had generally higher field saturated hydraulic conductivities than undisturbed soil treatments over the observed water content range. This effect was manifested to a greater degree at higher, relative to lower observed water contents.