砂粒含量对土壤水分蓄持能力影响模拟试验研究

通过人工配制不同质地土壤,测定土壤水分特征曲线,研究了土壤中砂粒含量对其水分蓄持能力的定量影响.结果表明:(1)砂粒含量对土壤水分蓄持能力有较大影响.土壤持水能力随砂粒含量增加递减,表征土壤持水能力的水分特征曲线Gardner模型参数及表征土壤饱和含水量的Van Genuchten模型参数均随砂粒含量增加逐渐减小.(2)砂粒含量对土壤比水容量有较大影响,试验土壤在任一吸力水平下的比水容量值均随其砂粒含量增加递减.(3)试验土壤饱和含水量与砂粒含量呈线性关系,田间持水量、凋菱系数与砂粒含量都呈开口向下抛物线右半段的关系.(4)试验土壤有效水、迟效水含量随砂粒含量增加递减,二者与砂粒含量均呈开口向下抛物线右半段的关系.易效水含量与砂粒含量呈开口向上抛物线关系.     

黏粒质量分数对土壤水分蓄持能力影响的模拟试验

通过人工配制不同质地土壤,测定土壤水分特征参数,研究土壤中黏粒质量分数对其水分蓄持能力的定量影响。结果表明：1）黏粒质量分数对土壤水分蓄持能力有较大影响,土壤持水能力随黏粒质量分数增加而递增。2个水分特征曲线模型——Gardner模型及van Genuchten模型中,表征土壤持水能力的参数均随黏粒质量分数增加而增大。2）黏粒质量分数对土壤比水容量有较大影响,试验土壤在任一水吸力水平下的比水容量值均随其黏粒质量分数增大而增大。3）试验土壤饱和含水量、田间持水量分别与黏粒质量分数呈指数、对数正相关,凋萎系数与黏粒质量分数呈指数正相关。4）试验土壤有效水、迟效水含量随黏粒质量分数增加呈先升高后降低趋势,二者与黏粒质量分数均呈抛物线关系,最高点分别出现在黏粒质量分数为35.9%和35.8%处,易效水含量与黏粒质量分数相关性不显著。研究结果可为黄土区土壤水分蓄持机制进一步研究提供一定理论依据。     

崩岗不同土层土壤水力学特性差异性分析

为研究崩岗不同土层土壤水力学特性的差异性,采用离心法测定不同土层土壤水分特征曲线,筛选出适合的土壤水分特征曲线拟合模型,结合统计模型,推求土壤的当量孔径分布、比水容量、非饱和导水率和扩散率,分析崩岗不同土层土壤水力学参数的变化规律。结果表明,崩岗土层从红土层到砂土层的变化过程中,土壤质地由黏土向砂土变化;Fredlund&Xing模型对崩岗土壤土水特征曲线拟合效果最好;参数θs、α、n随着质地变黏重逐渐减小;随着土层深度的增加,土壤的持水性能降低;土壤比水容量、非饱和导水率和扩散率受土壤质地和基质吸力的共同影响。在低吸力阶段,3个指标随基质吸力变化比较平缓,砂土层土壤比水容量和非饱和导水率最大,扩散率最小;而在高吸力阶段,砂土层土壤的这些指标降低较快,且低于其他土层,各层土壤间导水率和扩散率差异随着基质吸力的增加而增大。     

容重对土壤水分蓄持能力影响模拟试验研究

通过人工改变土壤颗粒级配,并设置不同容重水平,测定土壤水分特征参数,研究了容重对土壤水分蓄持能力的定量影响。结果表明:(1)容重对土壤水分特征曲线、比水容量有较大影响,试验土壤各吸力段水分蓄持能力均随容重增大递减,比水容量也随容重增大递减。(2)容重对试验土壤饱和含水量、田间持水量、凋萎系数有较大影响,此3个水分参数均随容重增大递减。饱和含水量与容重呈幂函数负相关关系,田间持水量及凋萎系数均与容重呈指数负相关关系。(3)容重对试验土壤有效水、易效水、迟效水含量有较大影响,此3水分参数均随容重增大递减,分别与容重呈指数、幂函数、对数负相关关系。     

再生水水质对斥水和亲水土壤水分特征曲线的影响

为探求再生水灌溉对斥水和亲水土壤水力特性的影响,该文选用有代表性的斥水黏壤土和亲水黏壤土、斥水砂土和亲水砂土,测定其在自来水、再生水和其他4种生活污水条件下的土壤水分特征曲线,采用主成分分析法得到不同水质综合指标,分析水质综合指标对不同土壤水分特征曲线的影响,采用van Genuchten-Mualem模型对黏壤土土-水曲线的参数进行拟合,并分析水质综合指标对黏壤土累积当量孔径分布、比水容量和水分常数的影响。结果表明:在相同基质吸力情况下,黏壤土含水率随水质综合指标增加(水质变差)而减小,砂土的含水率随水质变化不大;在低吸力段,斥水和亲水黏壤土的比水容量随水质综合指标的增加而增加;土壤进气值与水质综合指标呈显著负线性相关关系(R~2分别为0.94和0.78);相同水质条件下,斥水土壤的进气值比亲水土壤小;随着水质综合指标的增加,斥水和亲水黏壤土的极微孔隙降低,而中等孔隙和大孔隙增加,小于某当量孔径的累积百分比增加;随着水质综合指标的增加,斥水和亲水黏壤土的田间持水率、凋萎系数、有效水和易利用水比例均减小,但再生水对田间持水率和易利用水比例降低作用不显著。研究结果可为大面积再生水灌溉及其管理提供一定的理论依据。     

晋中东山地区褐土土壤水分特征的测定与应用

利用压力膜方法测定晋中东山地区褐土的土壤水分，并分析了土壤水分及其能态特征。结果表明：本区土壤水吸力与土壤含水量之间呈明显的幂函数关系，可以用幂函数方程模拟；土壤的当量孔径分布大致随土壤水吸力的增加而减小；土壤的结构性能良好，通气孔隙、毛管孔隙、无效孔隙的当量孔径分布分别占土壤总孔隙度的１８．３％、５１．２％和３０．５％，尤其是毛管孔隙的分布占土壤总孔隙度的一半以上；土壤的比水容量随吸力的增大而迅速减小．当吸力为０．１×１０￣５～０．３×１０￣５ｐａ时，其比水容量的量级为１０￣（－１）［ｍ１／（１０￣５ｐａ·ｇ）］，而当吸力达３×１０￣５～１５×１０￣５ｐａ时，其比水容量的量级下降了１００倍，为１０￣（－３）［ｍｌ／（１０￣５Ｐａ·ｇ）］。表层土壤水分对于作物吸收利用比心土层和底土层更为有效，但深层土壤的持水性能比表层士壤要好。为此，必须提高作物对土壤深层储水的利用。     

北京西山侧柏林和刺槐林土壤水分研究

为了解不同人工林树种对土壤的改良情况,探究北京西山地区不同林分下土壤水分状况,通过对原状土样土壤水分特征曲线的拟合,分析刺槐林下和侧柏林土壤的水分状况.研究表明:该区土壤质地较粗,植物利用水分困难,侧柏林下土壤持水性要比刺槐好,侧柏和刺槐对土壤上层和下层改良作用不同;在刺槐林下,上层土壤持水性好于下层;而在侧柏林下,下层土壤持水性则好于上层;在供水性方面,刺槐林较侧柏林好,且同一立地条件下表层优于底层.刺槐林和侧柏林下土壤易效水和难效水的吸力界点都在0.3 MPa左右.     

黄河下游不同质地潮土孔隙形态特征

土壤颗粒排列及形成的团聚结构是影响孔隙形态的基本因素,为直观观察与定量测算不同质地土壤的孔隙形态及其变化特征,于山东省东昌府区采集壤土、粘壤土、砂壤土样品,通过常规方法和土壤薄片,研究了土壤孔隙形态特征。结果表明:(1)土壤容重均随深度增加而增加。土壤孔隙度均为表层向下逐渐减少且10月份低于6月份。(2)砂质壤土孔隙形状均以简单堆集孔隙为主。而粘壤土、壤土则以复合堆积孔隙为主,且土壤团聚作用较强。(3)砂质壤土的孔隙平均当量直径(ED)及孔隙形状系数(S)明显高于粘壤土及壤土,而砂质壤土的孔隙复杂度(D)明显低于粘壤土及壤土。且ED及S值分别与土壤砂粒含量呈显著正相关,与粉、粘粒含量呈显著负相关;D值与砂粒含量呈显著负相关,而与粉、粘粒含量呈显著正相关。综上,土壤质地(即砂、粉、粘粒含量)能够影响土壤孔隙形态。     

北疆典型土壤反射光谱特征研究

针对新疆玛纳斯河流域中下游冲洪积扇平原绿洲的农田土壤的室内光谱分析,研究在不同质地及水盐条件下土壤光谱反射率的变化。结果表明:不同质地土壤光谱反射率表现为粘土>粉粘壤土>砂壤土;不同盐分含量的土壤光谱曲线变化趋势基本一致,利用BP神经网络能够很好地反映土壤含盐量与其反射率间的非线性映射关系。各种质地土壤含水量反射光谱曲线以田间持水量为临界值,在高于田间持水量时,随土壤含水量增加反射率升高;在低于田间持水量时,随土壤水分含量增加反射率减小。在土壤含水量的反射率特征波段内,构建了土壤含水量预测模型。     

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.     

中国几种主要土壤的持水性质

土壤的持水性是指土壤吸持水分的能力。在对植物的有效范围内,土壤所吸持的水分是由土壤孔隙的毛管引力和土壤颗粒的分子引力所引起的,这两种力现在统称为土壤吸力,或基质吸力,它相当于土壤总水势中的基质势。     

TOWARDS AN OBJECTIVE CLASSIFICATION OF SOIL STRUCTURE

A classification of structural condition in surface soils is proposed, based on the volumes of two categories of pore size, termed air capacity (pores greater than 60 μm diameter) and available water (pores of 60 to 0.2 μm diameter. Relationships of pore volumes to particle size class, organic carbon content and soil water regime are examined. Soil structural conditions are mainly affected by water regime and organic carbon and, apart from the extremes of sandy or clayey textures, less influenced by particle size distribution.     

南京近郊不同质地黄棕壤水分动态及其与杉木生长的关系

土壤水作为一个肥力因素,与林业生产有着密切的关系,许多国家的土壤学者都把它作为评价森林土壤生产力的关键因素之一^[6]。Zahner对于水分张力与林木生长曾作过详述^[7];而对于土壤有效水与杉木生长的关系,我国也曾有过报道^[3]为了进一步研究不同质地土壤的水分动态,近年来我们在南京近郊东善桥吉山附近本所幼龄杉木试验林,选择不同土壤质地的标准地,进行土壤含水量和杉木生长量的定位观察研究,以探索不同质地土壤水分动态与衫木生长的关系。现将试验结果叙述如下。     

THE RELATION BETWEEN BULK DENSITY, AVAILABLE WATER CAPACITY, AND AIR CAPACITY OF SOILS

The effect of bulk density on moisture content at 50 mb tension in four soils of different textures was studied. The volumetric water content increased linearly with bulk density over a wide range of densities. Depending on texture, a maximum bulk density was reached above which continued compaction decreased the water content. This is shown to be the point at which the air capacity of the soil at this tension approaches zero. Accepting that the gravimetric wilting point depends mainly on texture, the available water capacity varies in a manner similar to the 50 mb water content. If the relationships described are valid in the field, the available water capacity and air capacity may be optimized using cultivation techniques to adjust the bulk density. The available water capacity of coarse-textured droughty soils may be increased by increasing the bulk density provided that the air capacity remains above acceptable lower limits (10–15 per cent). Conversely, the air capacity of compacted soils with large available-water capacities could be increased by reducing the bulk density to a value corresponding to an acceptable available-water capacity. In very compacted soils a decrease in bulk density will benefit both available-water capacity and air capacity.     

上海地区土壤持水特性研究

土壤水的研究,从Henri Darcy(1856)提出达西定律算起,已有一百多年历史.经历了由经验到理论、由静态到动态、由定性到定量、由宏观到微观逐步深入发展的过程^[1].1877年Briggs L.J.提出毛管假说,将土壤孔隙组成的孔道看成是一些大小不同的毛细管,认为表面张力是土壤保持水分的主要原因.     

红壤的物理性质及其生产意义

热带和亚热带地区广泛分布着红壤性土壤。由于该地带水热条件十分优越,促进了土壤矿物组成的强烈风化和生物物质的迅速循环,从而构成了红壤性土壤所具有的独特的化学性质和物理行为。晚近的研究表明,红壤性土壤中大量存在的高岭类粘土矿物和三二氧化物不仅决定了土壤中一系列的化学环境,而且也影响着土壤中的物理过程和力学性质的变化^[13,18],而后者的控制和改善又往往是红壤开发利用成败的关键之一^[17]。     

Biochars improve aggregate stability,water retention,and pore‐space properties of clayey soil

The influence of biochar amendments on the physical quality of a clayey soil (Vertisol) was evaluated by aggregate‐size distribution and stability, water retention, and pore‐space structure of biochar‐amended soils. Clayey soil was treated with three kinds of biochars (straw biochar, woodchips biochar, and wastewater‐sludge biochar) at the rate of 0, 20, 40, and 60 g biochar (kg soil)^–1 and incubated for 180 d in glasshouse. The application of straw biochar (SB) and wastewater‐sludge biochar (WSB) significantly enhanced the formation of 5–2 and 0.25–0.5 mm macroaggregates in the clayey soil relative to the control treatment, while the < 0.25‐cm microaggregate decreased with biochar additions. However, woodchips biochar (WCB) had no obvious effect on the formation of macroaggregate. The application of SB and WSB increased the mean weight diameter (MWD) and geometric mean diameter (GMD) of clayey soil, implying that biochar increased the aggregate stability. They improved the aggregate stability through an enhanced resistance to slaking and increased interparticular cohesion. The SB‐amended soils exhibited significant increases in the available water contents of soils. The application of SB significantly increased pore volume in the macropore (> 75 μm) and mesopore (30–75 μm) ranges, which may be the result of the reorganization of pore‐size distribution and aggregation processes induced by the addition of biochar. Results indicated that biochar had the potential to improve the physical quality and pore‐space status of clayey soil. It is suggested that biochar may be considered as a soil amendment for improving poor physical characteristics of clayey soil.     

The effect of soil texture and organic amendment on the hydrological behaviour of coarse-textured soils

To gain more insight into the hydrological behaviour of coarse-textured soils, the physical properties of artificially created soil mixtures with different texture were determined. The mixtures were prepared according to the specifications of the United States Golf Association (USGA) for constructing putting greens. In addition, the effect of 10 vol.% organic matter addition was studied. The soil moisture retention and hydraulic conductivity relationships of the different mixtures were determined and their hydrological behaviour was studied using the numerical model SoWaM. Both texture and organic matter addition substantially affected the hydraulic properties. Hydraulic conductivity significantly increased with increasing coarseness while moisture retention decreased. On the other hand, organic matter addition reduced saturated hydraulic conductivity by a factor of 10 to 100 and distinctly increased moisture retention capacity. The amounts of total available water were increased by the addition of organic matter between 144% (slightly coarse texture) and 434% (very coarse texture). Results indicate that the mixtures can contain only 2–16% plant available water and therefore need frequent irrigation to maintain plant growth. Addition of organic matter seems a good solution to reduce the irrigation water requirements but it increases the risk of ponding or runoff because of large reductions in the saturated hydraulic conductivity sometimes to below the rate of 3.6 m/day recommended by the USGA.     

Kinetics of nitrification under upland and flooded soils of varying texture

Abstract

Higher rates of nitrification often reported in fine than in coarse textured soils may not be a direct effect of soil texture because in most of the earlier studies, soil water content has been usually expressed as gravimetric, volumetric or soil's water‐holding capacity without consideration of differences in density/ porosity for soils of varying texture. The same water content in texturally different soils could provide very different conditions of soil aeration and associated nitrifying activity. Effects of soil texture on nitrification was studied by incubating three semiarid subtropical soils having sandy loam, loam, and silty clay textures at 35°C for 30 days using water‐filled pore space (WFPS) as the criterion of soil aeration. Upland or aerobic soil conditions, simulated by incubating soil at 60% WFPS, exhibited very fast nitrification of added fertilizer nitrogen (N) and most of the applied 100 mg of ammonium‐nitrogen (NH₄+‐N/kg soil) was nitrified within 10 days of incubation in all three soils irrespective of the differences in texture. Under flooded soil conditions (120% WFPS), nitrification was slow and only 84 to 92% of the applied NH₄+‐N was nitrified even after 30 days. Nitrification could be described by first‐order kinetics for both the upland and flooded moisture regimes, thus nitrification rate depended upon NH₄+ concentration. At similar gravimetric water contents, rates of nitrification differed greatly in soils of varying texture, but when varying water‐holding capacity and bulk density were accounted for using WFPS, all the soils behaved similarly at 60% WFPS. Under impeded aeration (flooded conditions), however, substantial differences were observed in nitrification in soils of varying texture, the largest in fine‐textured Chamror silty clay followed by Habowal loam and the smallest in Tolewal sandy loam soil. These results illustrate the utility of WFPS, compared with soil water content, and its reliability as an indicator of aeration dependent nitrification for soils of varying texture.