黄土高原土壤干层评定指标的改进及分级标准

土壤干层是黄土高原普遍存在的特殊土壤水文现象,研究其现状、成因、防治、调控措施等对科学认识区域植被承载力、土地生产力以及低效林草改造和可持续植被建设等有重要理论与生产指导意义,而合理通用评判指标与分级标准是开展土壤干层研究的基础。目前黄土高原土壤干层尚无统一评判指标与分级标准,给区域土壤干层研究带来困难。本文在已有研究成果的基础上,提出用土壤有效水饱和度/不饱和度作为土壤干层评判指标,并给出其分级标准。该评判指标计算简单,具通用性和可比性,可望成为土壤干层的通用评判指标。     

土壤干层量化指标初探

土壤干层是黄土高原一种常见的土训物理现象。近年来,以林草地地力衰退为特征的人工林草地土壤干化日益严重,其直接后果就是形成土壤干层,导致土地退化,植被生长速率减缓,群落衰败以至大片死亡,严重地威胁到我国北方地区特别是黄土高原地区的生态环境建设,由此土壤干层及其危害才逐渐受到了人们的重视。根据影响水分性质地因素及水分动脉分布规律,初步探讨了土壤干怪的量化指标和分级,以便今后系统深入研究和解决黄土高原的土壤干层问题。     

黄土高原土壤干层研究述评

从土壤干层的定义及土壤干层形成的气候、土壤、植被和人为因素等4个方面综述了黄土高原土壤干层研究的现状和问题,并指出了需要进一步加强的研究领域.     

黄土高原人工林草地“土壤干层”问题初探

“土壤干层”是黄土高原一种特殊的土壤水文现象。依据调查资料,分析了“土壤干层”特征、成因、危害和树草种特点,认为“土壤干层”不是黄土高原恢复植被的必然产物,但是“土壤干层”的不良影响是严重而持久的,应给予高度重视。现有人工植被虽然有“土壤干层”,但在保持水土、促进天然植被恢复和演替方面仍然具有极为重要的意义。     

略论土壤干化层的判定问题

针对干旱半干旱地区广泛存在的土壤干化问题,在深入分析植物萎蔫过程及其与土壤干化之间关系的基础上,提出了初始萎蔫湿度(IWP)的概念,作为界定土壤干化层的定量判定指标。以该指标为基础,提出了土壤干化层发生与否及其发生类型的判定方法,并就指标的实验测定等问题进行了探讨。最后以黄土高原为例,应用该判定系统对黄土高原典型地区的土壤干化层分布情况进行了研究。研究成果对干旱半干旱地区土壤干化层的识别、类型判定、评价及其数量描述以及植被建设具有重要的指导意义。     

吴旗县不同植被类型土壤干层特征分析

吴旗县位于黄土高原暖温带半干旱地区,由于降雨量较少以及地表的蒸发和植物的蒸腾,使土壤水亏损严重,部分植被下的土壤中出现了土壤干层。为了系统比较不同植被类型下土壤干层特点,通过对吴旗不同植被0～9．0m土壤水分的实地测量和分析,得出以下结论：除农地外,其它植被类型下都不同程度的存在着土壤干层,干层严重程度,林地大于灌木林地,灌木林地大于草地;草地存在临时干层和永久干层,永久干层深度可以达到4．0m。测量当时,灌木林没有临时干层,存在永久干层,深度3．0～8．4m;杏树林不存在临时干层,油松林临时干层则很严重．杏树林和油松林永久干层深度分别在8．0m和9．0m以上。临时干层的出现取决于降水的补充．因此可能与采样时间有关。通过对吴旗县土壤干层的分析可以为进一步研究土壤干层和植被建设提供借鉴。     

延安试区土壤干层现状分析

近年来,以林草地地力衰退为特征的人工林草地土壤退化日趋严重,其中以土壤水分严重亏缺为特征的土壤干化现象愈益引起了人们的重视。土壤干化的直接后果是形成土壤干层,导致土壤退化,植物生长速率减缓,群落衰败以至大片死亡,严重地威胁到中国中北方地区特别是黄土高原地区生态环境的建设。因此,研究和解决土壤干层问题已成为黄土高原植被建设的迫切任务。根据现有土壤水分资料,初步分析了延安试区植被下的土壤干层现状,对不     

黄土高原生物利用型土壤干层的水文生态效应研究

对黄土高原高产农、林、草、灌、果5种植被1000cm土层土壤剖面含水量多点测定结果表明,各植被类型均存在不同程度的生物利用型土壤干层,该土壤干层的水文作用表现为增强土壤-植被-大气间垂直水分交换,阻碍入渗降雨转化为地下径流,削弱植被对枯水季节低径流量的补偿能力,其生态效应是恶化植物生长的土壤水分环境,削弱土壤水库对年际干旱的调节能力。     

黄土高原坡地土壤干层形成机理及补水途径研究

对黄土高原坡地林地土壤干层形成原因进行研究,指出降水较少和下渗困难是本区干层形成的两个直接因素,大鱼鳞坑内打孔覆草拦蓄径流、强制下渗是缓解干层形成的最佳途径,同时指出在黄土高原植被建设中应注意树种的选择和搭配,避免种植蒸腾量大、根系吸水强的树种,在工程措施的基础上多种草是生态效益和经济效益双赢的最佳途径。     

2000—2019年黄土高原地区土壤保持时空变化及影响因素分析

为揭示全球气候变化背景下黄土高原的生态建设成效,以土壤保持量为评估指标,应用美国修正通用土壤流失方程,评估了黄土高原土壤保持服务功能以及植被、气象等因素对其影响,分析了2000年以来植被和气候变化影响下黄土高原土壤保持量时空动态变化特征。结果表明:2000—2019年黄土高原土壤保持量平均值为109.5 t/hm²,并呈增加趋势,平均每年增加2.0 t/hm²,空间分布黄土高原中部和东部土壤保持量增加较明显。2000年以来黄土高原地区植被NPP呈增加趋势,年平均值为330.5 gC/m²,且平均每年增加7.2 gC/m²; 2000年以来植被覆盖度年平均值为29.2%,且以平均每年0.52%的趋势增加。黄土高原地区2000年以来气温和降水量均显著增加,平均年降水量为469.1 mm,且呈增加趋势,平均每年增加3.1 mm,年平均气温为10.2℃,平均每年增加0.03℃。黄土高原生态恢复措施加强,加之区域“暖湿化”有利气候条件,促进了区域生态建设成效显现,成为黄土高原生态恢复、功能提升的重要因素之一。     

陕西省延川县孙家塬经济林土壤水分和水分平衡

对陕西省延川县孙家塬枣树林和苹果林4m深度土层水分的变化进行了研究,并对土壤水分有效性、土壤干层及其水循环等方面进行了分析。结果表明,枣树林地含水量平均为10.6%,还有4.5%的土壤水资源可以利用。苹果林地4m深度范围内平均含水量为7.4%,2.0—4.0m深度范围内土壤水资源基本耗尽。苹果林地土壤含水量自上向下呈现高—低—高分层变化特点,枣树林地土壤水分剖面垂向分层不明显。枣树林地和苹果林地土壤水分基本都呈难效水状态,但枣树林土壤水分接近中效水,土壤水分对苹果林生长具有严重的抑制作用,对枣树林的生长基本没有抑制作用。枣树林地2.0—4.0m深度范围仅有轻度干层发育,苹果林地土层2.0—4.0m深度范围有轻度干层、中度干层和重度干层发育。苹果林地和枣树林地土壤干层切断了深层水分与上层的联系。水循环主要表现为地表水循环,基本不存在地下水循环,形成了土壤—植物—大气的水分循环模式,属于异常水分循环类型。干层长期发展会导致该区地下水位的持续下降和地下水资源减少。该区土壤水分条件更适于发展枣树经济林。     

陕西省靖边县不同土层含水量与干层差异研究

根据野外考察和土层含水量的测定，研究了靖边县沙地土层和黄土层土壤含水量。结果表明，靖边几个研究点的沙地土层平均含水量小于3%，杨树林地黄土层平均含水量为7％左右；沙地土层含水量远低于黄土层含水量，杨树林沙地和沙柳沙地已经出现了严重的土壤干层，杨树林地黄土层出现了发育中等的土壤干层，干层发育深度都已超过6m。干旱气候是引起干层发生的主要因素，人工灌木和树种消耗水分较多也促进了干层的发育。沙地区应以发展耐旱草灌为主的植被，黄土分布区也应发展草灌为主的植被，但在黄土分布的洼地区和有外来水源的地区可以发展耐旱的乔、灌、草相结合的植被。在靖边县这一土壤干层发育较严重的地区，造林一般不能带来良好的环境效益与经济效益，反而会导致深部土壤水分的过量消耗等不良后果，因此该区是不适于造林的地区。     

黄土高原土壤干层减缓方法初探

针对黄土高原长期种植苜蓿会导致深层土壤的干层化现象，在陕北黄土丘陵沟壑区的苜蓿种植区采用侧膜种植、播量减半种植、间作种植、常规种植4种种植模式来分析土壤水分环境。研究表明：侧膜种植年内贮水量在各个时期较其它3种模式高，各种植模式有效降雨量与土壤水分补给量之间关系呈线性相关，侧膜种植提高0～180cm土层土壤水分补给量更为突出。有效降雨对4种种植模式活跃层的贮水补偿作用极显著。春夏失墒期各种模式土壤相对稳定层对活跃层的补偿作用显著，各处理的相对稳定对活跃层补给量之间呈直线正相关，但补给量存在一定差异。     

露天煤矿排土场覆土厚度对土壤水分入渗及植物水分利用的影响

表土回覆是露天煤矿排土场生态修复的关键步骤，覆土厚度直接影响植物生长和复垦成本，为研究露天煤矿排土场不同覆土厚度对土壤水分入渗及植物水分利用的影响，采用室内土柱模拟试验，设置10,20,30,40,50 cm共5个覆土厚度，分别进行垂直入渗试验和室内盆栽试验(玉米),并结合氢氧同位素稳定示踪技术，研究不同覆土厚度土壤入渗和玉米水分利用特征，筛选研究区排土场最佳覆土厚度。结果表明：覆土厚度为10～30 cm(27.05～33.02 mm/min)的初始入渗速率显著高于40～50 cm(21.59～24.89 mm/min)的初始入渗速率(p<0.05),稳定入渗速率随覆土厚度的增加而增大，当覆土厚度高于40 cm后，随着覆土厚度的增加稳定入渗速率维持在3 mm/min左右。矸石层入渗过程受覆土层的影响较大，覆土厚度高于40 cm后，矸石层入渗速率基本稳定在土层连接面的入渗速率上。不同覆土厚度下玉米木质部水氢氧同位素值与土壤水氢氧同位素随土层变化曲线交点主要集中在覆土层，因此，玉米生长水分主要来源于覆土层。覆土厚度越大，2条线交点增多、交点分布范围增大，玉米对土壤水分的利用范围越大，...     

Least limiting water range indicators of soil quality and corn production, eastern Ontario, Canada

The least limiting water range (LLWR) attempts to incorporate crop-limiting values of soil strength, aeration, and water supply to plant roots into one effective parameter (on the basis of soil water content). The LLWR can be a useful indicator of soil quality and soil physical constraints on crop production. This study focused on assessing dynamic cultivation zone LLWR parameters between different cropping/tillage/trafficked clay loam plots at Winchester, Ont., to identify potential management impact on surficial soil physical conditions for contrasting growing seasons. This study also evaluated dynamic cultivation layer LLWR variables as indicators of corn (Zea mays L.) plant establishment and corn yield. The results suggest that no-till soils had lower average air-filled porosities (AFP) and O₂ concentrations than respectively managed tilled plots for both years of study. Potential trafficking effects on aeration properties were most evident in no-till relative to till; preferentially trafficked no-tilled plots had lower AFP and O₂ concentrations than respective non-preferentially trafficked no-till plots for both years of study. Corn establishment and yield variability were principally explained by cumulative differences between daily AFP and aeration threshold values, and the cumulative number of days daily AFP was below an AFP aeration threshold for specific corn growth stage periods. Lower AFP was linked to lower yields and plant establishments. Soil strength, as measured by cone penetration resistance, was important over certain sites, but not as important globally as AFP in predicting crop properties. Overall, conventional tilled soils that were not preferentially trafficked had most favorable aeration properties, and subsequently, greatest corn populations and yields. No-till soils were at greater risk of aeration limiting conditions, especially those in continuous corn and preferentially trafficked.     

天津滨海盐渍土客土改良后的土壤理化性质与持水特性

为了解天津滨海新区盐渍土采用客土法改良后的土壤理化性质的变化情况,该研究选取滨海新区汉沽区的滨海盐渍土以及采用客土改良后历经5 a的土壤(配制客土)作为研究对象,测定分析这2种土壤0~60 cm不同土层土样的基本理化性质、土壤水分特征曲线,探讨了理化性质和土壤水分参数的差异。结果表明:客土改良后历经5 a的配制客土电导率远低于未改良的滨海盐渍土,降幅约为97%,有效含水量以及田间持水量明显低于滨海盐渍土。有机质质量分数和阳离子交换量分别增加了29.65%和8.36%,pH值和容重变化不大。综合分析后认为,滨海盐渍土经配制的客土改良后,盐渍化程度减弱,有机质增大,但持水特性和物理性质却没有明显的改善。土壤质地黏重是影响该地区土地资源开发利用的主要因素之一。     

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.     

Using Static and Dynamic Indicators to Evaluate Soil Physical Quality in a Sicilian Area

Both capacitive indicators derived from the water retention curve and dynamic measurements of the flow‐weighted mean pore radius, R₀, were used to assess the soil physical quality of two agricultural areas (cropland and olive orchard) and two natural areas (grassland and managed woodlot plantation) potentially subject to soil degradation. The overall idea of the study was to investigate whether a dynamic indicator quantitatively derived from hydraulic conductivity measurements could be used to supplement the traditionally applied capacitive indicators retrieved from water retention measurements. According to the available criteria, only the surface layer of the cropland site showed optimal soil physical quality. In the grassland and woodlot sites, the physical quality was deteriorated also as a consequence of compaction because of grazing. Overall, the physical quality was better in tilled than nontilled soils. The optimal soil in terms of capacitive indicators had hydraulic conductivity close to saturation that was intermediate among the different land uses, and it remained 1·3–1·9 times higher than that observed in the natural sites even when the largest pores emptied. A depth effect on R₀ was observed only when larger macropores were activated. It was suggested that water transmission parameters are more affected by changes in large pore domain. The plant available water content and Dexter's S‐index showed inverse statistically significant regressions with R₀. The empirical relationships were physically convincing given that, at increasing R₀, the contribution of macropores increases, water is transmitted faster below the root zone and the soil's ability to store water is reduced. Copyright © 2013 John Wiley & Sons, Ltd.     

红壤干旱过程中剖面水分特征与土层干旱指标

农田水分管理以及产量评估都需要对土壤作物受旱状况定量化和指标化。干旱强度和干旱程度结合才能完整地描述土壤作物干旱状况，土壤干旱强度I是土壤剖面失水速率的函数，干旱影响逐渐累积并增强就构成干旱程度D，据此提出了包含I和D二个指数的土层干旱指标表达模式。通过红壤小区种植玉米并在抽穗期开始设置连续干旱12～36 d等6个不同的处理，研究了红壤干旱过程中剖面水分特征和干旱指标。结果表明：供试红壤干旱过程中剖面40 cm以下含水率下降幅度很小，玉米主要利用了0～40 cm土层的水分，监测30～40 cm土层含水率的变化情况可以指示玉米受到干旱胁迫的程度。连续干旱25 d后40 cm以下土层含水率明显降低，玉米产量也显著下降，此时0～60 cm土层和30～40 cm土层的干旱程度D均为0.55，可用此指标作为灌溉的依据。