城市土壤压实对土壤水分特征的影响——以南京市为例

通过对南京市不同土地利用下的土壤容重、孔隙度和土壤水分特征曲线的测定，研究了压实对土壤水分特征参数的影响。结果表明城市土壤存在严重的压实退化现象，土壤容重和孔隙度能够很好地反映土壤的压实程度。随着压实程度的增加，土壤的田间持水量增加，萎蔫点含水量增加，而土壤的最大有效水含量却明显减少。所以，压实土壤对水分的调节能力下降，使其上生长的植物更不容易获得水分供应。     

深松与压实对红壤坡耕地土壤物理性质的影响

以红壤坡耕地为研究对象,研究了深松和机械压实对土壤物理性质的影响。结果表明:深松改善了除土壤最小持水量和毛管孔隙度外的土壤物理性质,并对表层土壤的改善效果较好,进而提高了红薯产量;机械压实则对除土壤紧实度和最小持水量外的土壤物理性质产生了负面影响,影响深度达30 cm左右,造成红薯产量降低。0~20 cm土层土壤容重、土壤孔隙度及土壤持水量之间呈显著或极显著相关;20~40 cm土层土壤容重、毛管孔隙度与土壤紧实度分别呈极显著和显著相关性,土壤持水量与土壤非毛管孔隙度、总孔隙度呈显著或极显著正相关。可见,避免机械压实并对深松耕作管理模式进行优化,是缓解红壤坡耕地农业生产与生态破坏的突破口之一。     

渭北果园土壤物理退化特征及其机理研究

【目的】针对我国渭北苹果主产区出现的随植果年限增加,果园土壤质量严重退化,树势衰弱、树体过早衰老、抗性降低、腐烂病及早期落叶病频繁发生,果品产量与品质下降等问题,开展了渭北苹果园土壤物理质量退化特征、退化机理及危害程度等问题的研究,以期查明制约果业可持续发展的因素,为果园土壤科学管理提供依据。【方法】在渭北黄土塬区选取了10 a、10 20 a、20 a 3个园龄段果园各4个,并以土壤条件相同的农田作对照,在果树冠层投影范围内距树干2/3处采取土样,测定土壤剖面不同层次容重、紧实度、孔隙度、饱和导水率、粘粒含量等物理性指标。【结果】渭北果园土壤容重和紧实度随园龄和土层深度的增加而增大,尤其在表层(20 cm)以下,土壤容重已经达到了1.45 1.61 g/cm3,紧实度达到933 2433 k Pa,严重超出果树健康生长的阈值。土壤孔隙度仅在0—20 cm土层能够保持在50%以上,属于良好状态,而20—60 cm土层维持在40%46%,已处于紧实和严重紧实状态。土壤饱和导水率在果园表层和紧实层均表现出随植果园龄的增大而减小的趋势,尤其是10 20 a和20 a的果园亚表层土壤饱和导水率低至46.88 cm/d和20.89 cm/d,制约着降水入渗和土壤蓄墒。3个园龄段果园土壤剖面上粘粒含量随土层深度呈递增趋势,且在0—30 cm土层随园龄的增加而明显减少,而在30 cm以下则随园龄的增加而呈递增趋势。进一步分析发现,粘粒含量与土壤容重、紧实度以及孔隙度之间呈极显著的相关关系。以压实密度(PD)为指标,对渭北果园土壤压实程度进行评估,发现渭北果园20 cm土层以下的土壤压实密度都在1.40 g/cm3以上,均达到了中度压实的程度,严重影响果树根系的健康生长及对养分的吸收。【结论】渭北果园20 cm以下的亚表层土壤孔隙密实、容重和紧实度增大,土壤饱和导水率递减是其土壤物理性质退化的主要特征,表层土壤粘粒的深层移动与淀积是土壤物理退化的主要过程和机理,果园土壤翻耕扰动少、对物理退化干预少是其土壤物理退化程度逐渐加剧的外在原因,土壤团聚体稳定性差是土壤物理状态退化的根本原因。     

城市功能区、植被类型和利用年限对土壤压实的影响

土地利用会对土壤压实产生影响。本文通过对南京市不同功能区、植被类型和利用年限的土壤进行调查研究,了解这些利用情况对土壤压实的影响程度。结果表明:城郊菜地土壤没有被压实,而城区土壤存在不同程度的压实退化现象;城区内部只有公园土壤与道路绿化带土壤之间的通气孔隙度指标差异显著,其他功能区土壤之间压实指标差异不显著。所以,就压实状况而言,城区内并不存在所谓的功能区之间的差异。植被类型和利用年限对城市土壤的压实都有显著的影响。蔬菜地土壤与自然土壤体积质量和孔隙度相近,为无压实土壤,城区除了树下灌木土壤无压实外,其他植被类型下的土壤均有不同程度的压实退化现象,草坪和裸地土壤压实最为严重。从利用年限看,利用时间少于5年的新土压实程度远远大于利用时间在20年以上老土的压实程度。土壤压实严重与城市建设时的机械压实和草坪建成后的人为践踏密切相关,利用较久的老土壤压实较轻,主要是在无进一步人为践踏情况下,植被生长后根系和土壤生物活动有一定的修复作用。乔木和灌木搭配的修复效果最好。     

基于修正介电常数模型的煤矿区复垦土壤压实评价

模拟复垦机械对试验区土壤进行不同程度的压实,在探地雷达获取土壤介电常数的基础上,检验并修正了4种经典复合介电常数模型,并结合野外试验对修正后的模型通用性进行了验证。结果表明,土壤介电常数与土壤压实指标(土壤紧实度、容重、孔隙率等)相关系数89%,可以表征土壤压实状况;原有复合介电常数模型虽然存在误差不能直接使用,但模型计算值与实测值相关系数0.99,修正后二者拟合误差1%;在野外试验中,基于修正后的介电常数模型反算的土壤压实指标(容重、孔隙率)与实验室测量值误差率5%,通用性较好。表明在科学布设测线以保证探地雷达准确获取土壤介电常数的前提下,可以通过修正后的复合介电常数模型对煤矿区复垦土壤压实状况进行全面客观的评价。     

紫色土坡地土壤性质对耕作侵蚀的影响

[目的]揭示土壤性质对耕作侵蚀土壤的敏感性,为紫色土区域采取适宜的耕作措施提供依据。[方法]利用磁性示踪技术定量旋耕机上下耕作和等高耕作的土壤耕作位移和土壤位移量,选取土壤容重、土壤含水量、土壤有机质、土壤全氮、土壤有效磷、土壤抗剪强度和土壤紧实度等土壤理化性质和力学性质指标,研究土壤性质对旋耕机上下耕作和等高耕作的耕作侵蚀的影响特征。[结果]旋耕机上下耕作和等高耕作的土壤净位移和净位移量不仅受坡度影响,也受土壤性质的影响。土壤力学性质和土壤物理性质对旋耕机耕作侵蚀有显著影响,对于上下耕作的土壤抗剪强度、土壤紧实度和土壤容重与土壤净位移量呈显著正相关。对于等高耕作措施的土壤抗剪强度、土壤紧实度、土壤容重和土壤含水量与土壤净位移量呈显著正相关,其他指标关系不显著。[结论]土壤抗剪强度、土壤紧实度和土壤容重可以作为评价耕作侵蚀的土壤可蚀性指标。     

机械压实过程中复垦土壤紧实度影响因素的模拟分析

机械碾压造成的土壤压实是土地复垦中面临的主要问题之一,影响土壤压实程度的因素很多,除土壤自身的因素以外,还包括压实机械、压实次数以及土层厚度等。该文基于统计学的理论,采用2×5×4的混合试验设计并建立模拟实验区,使用重锤模拟分析了2种压实机械、不同压实次数(1、3、5、7、9次)和不同土层厚度(0~10cm、10~20cm、20~30cm、30~40 cm)上土壤紧实度的变化情况,并在SPSS中进行变量的方差分析和多重比较,试图找到机械压实过程中影响土壤紧实度的因素及其变化水平。结果表明:增加压实机械的承重轮面积能够有效降低对土壤的压实作用;压实机械、土层厚度和压实次数都是影响土壤紧实度的显著性因素且各因素的贡献率(97%)远高于随机误差;自卸汽车在第5次压实之后就已经使上层土壤紧实度达到最大值,而履带式推土机需要压实7次,土地复垦中应尽量选择履带型机械,碾压次数控制在5~7之内;机械压实的过程中,各土层厚度之间土壤紧实度的大小关系并不是一成不变的,中间层次(10~30 cm)的土壤由于同时受到来自上下2个方向的作用力,紧实度相对较高;不同次数的压实对土壤紧实度的影响深度和程度不同,在一定范围内,随着压实次数的增加,单次压实对土壤紧实度的影响逐渐减小。     

多年固定道保护性耕作对土壤结构的影响

为了解决拖拉机作业机组作业时造成的土壤普遍压实,在10a连续固定道保护性耕作试验基础上,研究了固定道保护性耕作对土壤容重、孔隙度、紧实度、水分以及冬小麦产量的影响。试验结果表明,对于作物生长带,固定道保护性耕作可以降低0～20cm土层的容重6.8%,提高0～40cm土层土壤总孔隙度4.6%,降低0～30cm土层土壤紧实度31.5%,提高0～1m土层蓄水能力,在固定道占地20%的情况下,仍能提高冬小麦产量10.8%。因此,固定道保护性耕作是减少土壤压实、改善土壤结构、提高小麦产量的有效耕作方式。     

石匣小流域整地措施对土壤剪切性质的影响

为了解坡面整地措施对坡体稳定性的影响和土壤物理性质对土壤抗剪强度的差异性,选取石匣小流域4个标准样地,通过测量多个土壤物理性质指标(土壤容重、土壤含水率、总孔隙度、毛管孔隙度、非毛管孔隙度、紧实度和液限),研究不同坡面整地措施的土壤临界剪切力随深度的变化,以及土壤抗剪切破坏能力的强弱关系和影响因素。结果表明:原状土的临界剪切力随深度的增加而增加;通过库伦公式得出的土壤抗剪强度与土壤临界剪切力的回归方程为σ=0.0123τf+0.6308。土壤物理性质对抗剪强度的影响不同,紧实度、容重与含水率对抗剪强度的影响相对较大。对于不同的坡面整地措施,土壤抗剪切能力强弱顺序为梯田水平条裸地,其中,在水平条上种植针叶树,土壤抗剪切能力优于种植阔叶树。在北京石匣地区,布设坡面整地措施时,需因地制宜地增加田面宽度,并种植针阔混交林以增加土壤抗剪强度。     

微观尺度上土壤孔隙及其分维数的SEM分析

对两类不同质地土壤的SEM图像,利用数字图像技术分析孔隙的大小、数量及其分布规律,由测量数据给出了微观尺度上土壤孔隙的质量分维数Dm和表面分维数Ds。结果表明:Dm与土壤质地、容重、孔隙度、孔径分布等之间存在一定的相关关系,土壤质地越细、容重越大、孔隙度越低、小孔隙越多,Dm越大,Dm与土壤容重和孔隙度均存在显著线性回归关系;Ds反映了土壤孔隙轮廓边界的曲折程度,孔隙轮廓越不规则,Ds越大,土壤中各孔隙的Ds分布符合总体正态分布形式。Dm和Ds的数值大小对不同利用方式和耕作制度下的土壤较为敏感,分维数可为土壤科学管理提供依据。     

城市“土壤水库”库容的萎缩及其环境效应

"土壤水库"具有容纳和调节水分的功能,不仅能供给植物生长所需的水分,而且具有防洪减灾的作用。城市土壤的水分储蓄和调节功能对于城市生态环境具有非常重要的作用。城市化造成了大量的封闭地表,使得土壤的功能几乎完全丧失。本文以南京市为例,选择不同压实程度的土壤,根据其饱和含水量、田间持水量和萎蔫点含水量计算土壤的总库容、有效库容、滞洪库容和死库容。结果表明,随着城市土壤压实程度的增加,土壤水库的总库容、有效库容和滞洪库容萎缩也越严重,而死库容却明显增加。城市土壤普遍存在压实现象,使城市土壤疏导和容纳水分的能力减弱,城市里出现瞬时洪涝的几率增加,强度加大。因此,良好的城市环境需要有更多的绿地和良好的土壤条件。     

生物炭添加对矿区压实土壤水力特性的影响

中国黄土高原大型露天煤矿开采导致土壤质量下降,生物炭作为环境友好型土壤改良剂,在改善农田土壤质量中应用广泛,但在有关矿区压实土壤改良的研究中不够深入。为此,该研究通过室内试验分析不同粒径的生物炭在不同添加量下对矿区排土场压实土壤水力特性的影响。试验采用4种粒径（>1～2、>0.25～1、0.10～0.25、<0.10 mm）与4种添加量（0、4、8、16 g/kg）的生物炭,设计5种压实条件（容重分别为1.3、1.4、1.5、1.6、1.7 g/cm3）,并利用van Genuchten模型（VG模型）拟合土壤水分特征曲线。结果表明,添加生物炭后土壤水分特征曲线的相关系数均在0.960以上,标准差均小于0.015,说明VG模型适用于拟合添加生物炭后的土壤水分特征曲线。随着生物炭添加量的增加,土壤孔隙分布明显改变,形成了大量大孔隙和中孔隙,土壤的持水能力提高。在低容重（1.3、1.4 g/cm3）条件下,生物炭粒径越大（0.25～2 mm）添加量越高（8、16 g/kg）,土壤持水、保水效果越明显;在高容重（1.5、1.6、1.7 g/cm3）条件下,小粒径（<0.25 mm）和较低的生物炭添加量（4、8 g/kg）则表现出较好的持水能力。对于不同压实条件的排土场土壤,有针对性地施用生物炭,将有效提高土壤持水保水能力,提高土壤中植物的有效利用水分。     

阳泉矿区自燃煤矸石山绿化中覆盖层碾压效果试验

自燃煤矸石山是矿区环境主要的污染源之一,对其实施封闭并绿化,需要构建具备一定阻隔空气能力的覆盖层,而覆盖层多为土质材料经碾压构成,空气阻隔性受其碾压质量的影响。结合阳泉三矿煤矸石山治理现场进行野外碾压试验,研究了煤矸石山现场碾压工具及碾压条件下的压实效果。通过对不同铺土厚度的黄土进行碾压,测定紧实度和干密度来表征碾压效果,分析以压实度(85%)作为压实质量控制标准的条件下合理的碾压工程参数。结果表明,利用现场自制碾磙(4t)进行平碾碾压,浅部土层受到碾压遍数的影响较大,深部土层受到碾压遍数的影响较小,其特征深度在15—25cm;建议的施工方案及碾压参数为:含水量接近最优含水率(相差不超过±2%),松铺厚度20~40cm,碾压3~5遍。     

压实对矿区废弃土壤含水量及植物生长的影响

[目的]探究不同压实处理对矿区废弃土壤含水量及植物生长的影响,为有效利用采石场废弃物和城市固体废弃物、改善矿区立地条件、进行植被修复提供依据。[方法]将砾石和城市固体废弃物按体积8∶2混合后进行不同程度压实处理,进行小区试验。[结果]压实显著提高基质含水量,减小各层含水量差异。随着压实程度增加,植物主要耗水层上移。不同植物受到压实的影响不同,刺槐和苜蓿在重度压实条件下生长明显受阻,侧柏生长量增加。植物在中等强度的压实条件下,能够通过调节自身,适应环境。[结论]一定程度的压实能获得理想的植物保存率和生长量,压实技术可以运用在废弃采石场植被修复工作中。     

Anwendbarkeit geophysikalischer Prospektionsmethoden zur Bestimmung von Bodenverdichtungen und Substratheterogenitäten landwirtschaftlich genutzter Flächen

Applicability of geophysical prospecting methods for mapping of soil compaction and variability of soil texture on farm land The increasing degree of mechanization in agriculture has resulted in the use of more powerful and heavier tractors and machines. Consequently, mechanical burden to soils has increased, too, which can lead to persistent subsoil compaction at depths below 30 cm. In soils damaged by compaction soil functions like transportation of water and air decrease. Because of that, conditions for plant growth are getting worse and the soils' natural regulation functions could be impaired. In order to take counteractive measures, it is necessary to get information about the status of soil compaction. Up to now, the status of soil compaction can only be determined at single points in laboratory measurements or with less accuracy in field measurements. Therefore, the demand for an efficient planar‐mapping system arises. The applicability of different geophysical prospecting methods with regard to this problem has been examined. For this purpose, geophysical and soil measurements were performed in a field with conventional agricultural land use in Schleswig‐Holstein (Germany) on a young moraine site. We applied GPR (Ground Penetrating Radar) with main frequencies 500 MHz and 900 MHz, supplemented by inductive electromagnetic technique (EM) using the Ground Conductivity Meter EM38 and high‐resolution refraction seismic using compressional and shear waves. Differences in soil type were found by all these geophysical methods and confirmed by soil measurements, therefore, locations with higher risk for compaction (loamy soils) could be distinguished from locations with lower risk (sandy soils). Under humid conditions, radar data showed strong reflections at a depth of approx. 30 cm. During summer, under dry conditions, these reflections did not occur. This temporal variation of radar reflections can be explained by variable water layers inside the soil, which can be regarded as an indicator for compacted soil. The seismic investigation was performed along short (12 m) profiles with dense (20 cm) sensor spacing. Excellent data quality showed that this sort of measurement, known from engineering geophysics, is also feasible for soil investigations. We performed both compressional‐ (P‐) and shear‐(SH‐) wave refraction studies. Differences in soil type of subsoil affected especially seismic velocities of P‐waves. Whether or not areas of compacted soil can be detected is still unknown, because deeper soil horizons of our test area showed only uniformly strong compaction with little contrasts.     

Effects of compaction on soil surface water repellency

Water repellency can reduce the infiltration capacity of soils over timescales similar to those of precipitation events. Compaction can also reduce infiltration capacity by decreasing soil hydraulic conductivity, but the effect of compaction on soil water repellency is unknown. This study explores the effect of compaction on the wettability of water repellent soil. Three air‐dry (water content ～4 g 100 g^?1) silt loam samples of contrasting wettability (non‐repellent, strongly and severely water repellent) were homogenized and subjected to various pressures in the range 0–1570 kPa in an odeometer for 24 h. Following removal, sample surface water repellency was reassessed using the water drop penetration time method and surface roughness using white light interferometry. An increase in compaction pressure caused a significant reduction in soil surface water repellency, which in turn increases the soil's initial infiltration capacity. The difference in surface roughness of soils compacted at the lowest and highest pressures was significant (at P > 0.2) suggesting an increase in the contact area between sessile water drops and soil surfaces was providing increased opportunities for surface wetting mechanisms to proceed. This suggests that compaction of a water repellent soil may lead to an increased rate of surface wetting, which is a precursor to successful infiltration of water into bulk soil. Although there may be a reduction in soil conductivity upon compaction, the more rapid initiation of infiltration may, in some circumstances, lead to an overall increase in the proportion of rain or irrigation water infiltrating water repellent soil, rather than contributing to surface run‐off or evaporation.     

Do effects of soil compaction persist after ploughing? Results from 21 long-term field experiments in Sweden

The extent and persistence of the effect of soil compaction in a system with annual ploughing were investigated in 21 long-term field experiments in Sweden with a total of 259 location-years. Crop yield, soil physical properties and plant establishment were determined. All experiments had two common treatments: control (no extra traffic) and compacted (350 Mg km ha⁻¹ of experimental traffic in the autumn prior to ploughing), using a tractor and trailer with traditional wheel equipment and an axle load restricted to 4 Mg. During the rest of the year, both treatments were conventionally and equally tilled. The compaction was repeated each autumn for at least 7 years, and the yield was determined each year until 5 years after the termination of the compaction treatment.

Compaction decreased the porosity and the proportion of large pores and increased the tensile strength of dry aggregates. On clay and loam soils, it decreased the proportion of fine aggregates in the seedbed and the gravimetric soil water content in the seedbed.

The yield in the compacted treatment declined compared with the control during the first 4 years, after which it reached steady state. During this steady state, the compaction treatment caused a yield loss of 11.4%, averaged over 107 location-years. Within 4–5 years after the termination of the compaction treatment, the yield returned to the control level. The average yield loss at individual sites increased with increasing clay content.

Results from additional treatments indicated that yield loss was linearly correlated with the amount of traffic up to 300–400 Mg km ha⁻¹. With greater ground contact pressure or a greater soil water content at time of traffic, there was a greater yield loss.

Soil compaction effects on yield were similar for all spring-sown crops, and the percentage yield loss seemed to be independent of the yield. In a few location-years with winter wheat there was on average no yield decrease.

There were 5.1% less plants in the compacted treatment than in the control. The yield decrease was significantly correlated with the number of plants.

Between years results were highly variable, and no consistent correlations between yield loss and soil water content at the time of traffic or the weather conditions during the growing period were found. Soil compaction affected yield during years with good as well as poor conditions for crop growth.     

Mechanisms of soil vulnerability to compaction of homogenized and recompacted Ultisols

Soil compaction is a main cause of soil degradation in the world and the information of soil compaction in subtropical China is limited. Three main Ultisols (quaternary red clay, sandstone and granite) in subtropical China were homogenized to pass through 2 mm sieve and recompacted into soil cores at two bulk densities (1.25 and 1.45 g cm⁻³). The soil cores were equilibrated at different matric potential values (−3, −6 and −30 kPa) before subjected to multi-step compaction tests. Objectives of this study were to determine how different initial soil conditions and loading time intervals influence pre-compression stress and to evaluate an easy measure to determine soil vulnerability to compaction. It became evident that the soil strength indicator, pre-compression stress, was affected by soil texture, initial soil bulk density and matric potential. The coarser the soil texture, the lower the bulk density and the higher the matric potential, the lower was the pre-compression stress. The pre-compression stress decreased exponentially with increasing initial soil water content. Soil water content and air permeability decreased after compaction. The amount of water loss was affected not only by soil texture, bulk density and initial water content but also by loading time interval. These results indicate soil pore structure and hydraulic conductivity changed during compactions. The applied stress corresponding to the highest changes of pore water pressure during compaction had a significant linear relationship with the pre-compression stress (R=0.88, P<0.001). The correlation was ascribed to that the changes in pore water pressure describe the dynamics of the interactive effects of soil pore characters and soil water movement during compaction. The results suggested the evaluation of soil vulnerability to compaction have to consider the initial soil condition and an easy method to measure the changes in pore water pressure can be applied to compare soil strength and soil vulnerability to compaction.