近地表水文条件对横坡垄作坡面褐土团聚体流失的影响

以横垄褐土坡面为研究对象,基于室内模拟降雨试验,就3种近地表水文条件下(自由入渗、土壤饱和与渗流)团聚体(≥5、2～5、1～2、0.5～1、0.25～0.5、<0.25 mm)在不同雨强(30,60,和90 mm·h–1)下的流失规律进行了探究。结果表明:(1)团聚体流失量的差异表现为:渗流>土壤饱和>自由入渗,且随雨强变化土壤水分饱和与渗流对团聚体流失的贡献较水势差分别显著增加2.02倍～3.71倍和1.28倍～2.51倍;(2)土壤饱和与渗流的存在致使2～5、1～2、0.5～1 mm团聚体的流失比例增加46.74%～121.19%,而削弱了90%以上0.25～0.5 mm团聚体的流失;(3)土壤饱和与渗流使>0.5 mm团聚体的富集率增加了23.77%～215.80%,但导致0.25～0.5 mm团聚体的富集率减少45.07%～68.90%,主要是因为0.25～0.5mm团聚体在侵蚀过程中发生了团聚;(4)平均重量直径是反映自由入渗与土壤饱和条件下团聚体流失的重要指标,而渗流条件下则为分形维数;(5)雨强对团聚体流失的影响在自由入渗条件下表现最明显,尤其是对...     

植物篱对紫色土坡面侵蚀泥沙粒径分布特征的影响

为探究植物篱对紫色土坡面侵蚀泥沙粒径分布特征的影响,该研究以三峡库区紫色土为研究对象,在3种坡面条件下（裸坡对照组CK、植物篱组P和仅地下根系组R）以不同降雨强度（60、90 mm/h）进行人工模拟降雨试验。结果表明：与CK相比,R坡面条件下侵蚀泥沙中黏粒和粉粒含量减少了0.25%～5.48%,而P坡面条件侵蚀泥沙中砂粒含量减少了30.75%～47.28%。CK坡面条件下,泥沙分选现象主要出现在降雨前期,R坡面条件只影响降雨初期的泥沙分选,而P坡面条件对降雨全程均具有分选拦截砂粒的作用,但分选拦截效果随降雨时间的增加而渐趋稳定。R坡面条件下更多团聚体被雨滴击打破碎而分散为单粒,而P坡面条件则使更多细颗粒聚集形成团聚体,但松散的团聚体在降雨中后期倾向于分散为单粒。该研究结果可深入理解植物篱对紫色土坡面侵蚀泥沙分选的影响,并为区域土壤侵蚀模型构建和水土资源高效利用提供科学依据和数据支持。     

北方土石山区横坡垄作坡面土壤氮的空间分布特征

横坡垄作是坡耕地广泛采用的水土保持措施,垄沟内雨水的汇聚和泥沙沉积,使得土壤氮的空间分布特征明显有别于传统耕作坡面。以北方土石山区横坡垄作坡面为研究对象,样带法采集土壤样品,基于经典统计、地统计学、Kriging插值等方法,分析垄面、垄沟等特征点位全氮(TN)、硝态氮(NO^3--N)、铵态氮(NH4+-N)含量沿坡位变化及其剖面分布,明晰横坡垄作坡面土壤氮的空间分布特征。结果表明:北方土石山区土壤氮含量属于中低水平,变异系数介于17.64%～33.60%,但垄面土壤氮的变异水平高于垄沟。TN含量沿坡位的变异最为显著,表现为坡下>坡脚>坡中>坡上;仅垄沟NO^3--N、NH4+-N含量沿坡位存在显著变化,坡脚NO^3--N、NH4+-N含量较其他坡位显著增加66.30%～83.85%。垄面与垄沟间氮含量的差异在坡上、坡下和坡脚体现的较为明显;与垄沟相比,垄面坡上TN含量减少21.34%,坡脚NO^3--N和NH4+-N含量减少17.42%～37.47%,坡下土壤氮含量增加21.56%～38.16%。TN剖面分布与坡位和特征点位有关,NO^3--N、NH4+-N的剖面分布主要受控于特征点位,但氮含量剖面分布符合指数函数关系。综上,横坡垄作坡面土壤氮空间异质性明显,且主要受控于特征点位和坡位。研究结果可为提高横坡垄作措施下氮肥利用效率、精准农业的顺利推广提供技术支撑。     

耕作对东北黑土团聚体粒级分布及其稳定性的短期影响

土壤团聚体粒级分布是作物发芽和出苗以及根系发展的重要影响因子,其团聚作用在土壤固碳过程中具有不可或缺的贡献,团聚体的结构性破坏将导致土壤有机质的流失,而团聚体稳定性直接影响着土壤侵蚀程度[1]。常规耕作表层土壤易受外界因素(如温度和水分条件)的影响。这不仅使土壤团聚体经常受到干扰,而且释放了受团聚体保护的免遭矿化的土壤有机质,同时也使团聚体稳定胶结剂(如碳水化合物)减少,严重降低了农田土壤结构的稳定性[2]。广义上看,土壤团聚体被划分为大团聚体(>0.25mm)和微团聚体(<0.25mm)[3],湿筛法往往被用于对土壤团聚体进行分级,从而得到土壤团聚体的质量分数以及评价团聚体稳定性的参数(平均     

用激光法和吸管法测定东北黑土区侵蚀泥沙颗粒组成的差异分析

吸管法是测定颗粒组成的经典方法,激光法作为一种新兴的方法,近年被广泛应用于土壤和河流泥沙颗粒组成的分析中,并逐步应用到侵蚀泥沙粒径分析.为获取激光法与吸管法测定侵蚀泥沙特性指标和不同粒径的差异以及二者之间的转换关系,对18个黑土区侵蚀泥沙样品颗粒组成进行了测定和分析.采用中值粒径D50和平均质量直径MWD进行侵蚀泥沙样品特性分析,激光法比吸管法测定结果明显偏低;但2种方法测定D50和MWD具有很好的线性转换关系(R＞0.9,P ＜0.001).激光法测定的砂粒和黏粒质量分数低于吸管法测定值,测定粉粒质量分数明显高于吸管法测定值.测得砂粒、粉粒和黏粒含量在2种方法间,均具有很好的线性转换关系(R＞0.8,P ＜0.001).进一步细分泥沙颗粒为大于中砂、细砂、极细砂、粗粉和细粉这5个粒级时,2种方法间除极细砂(R=0.764,P＜0.001)外,其余粒级均具有很好的线性转换关系(R＞0.8,P＜0.001).     

黑土区坡耕地横坡垄作措施防治土壤侵蚀的土槽试验

为了研究黑土区坡耕地横坡垄作防治坡面土壤侵蚀的效应,该文利用8 m×1.5 m的试验土槽,设计3个降雨强度(50、75和100 mm/h)、1个典型坡度(5°)以及横坡垄作和无垄作(平坡裸地对照试验)的试验处理进行模拟降雨试验,研究东北黑土区横坡垄作坡面在不同降雨强度下的防治坡面侵蚀效应。结果表明:横坡垄作在50 mm/h降雨强度下坡面基本不发生土壤侵蚀,但在75和100 mm/h降雨强度下会发生断垄,造成防蚀效应急剧降低。横坡垄作坡面的径流和侵蚀过程均明显存在以断垄时间为界的突变,在3个降雨强度下,横坡垄作断垄前可使坡面径流量和侵蚀量分别减少97.7%和99.1%以上,坡面蓄渗率达到97.2%以上;而断垄后坡面径流量和侵蚀量分别增加23.3~25.9倍和136.8~171.5倍,蓄渗率下降至50%以下。试验研究表明横坡垄作在≤50 mm/h的降雨强度下具有很好的坡面防治侵蚀效应,但当遇到强降雨时易发生断垄,防蚀效应急剧降低。     

团聚体大小分布对孔隙结构和土壤有机碳矿化的影响

土壤团聚体在外部和内部因素影响下发生团聚和破碎过程,形成不同大小分布的团聚体。团聚体大小分布的变化会改变土壤孔隙结构,影响各种土壤物理、化学和生物学过程,进而影响土壤有机碳(SOC)的周转。选择三种长期施用不同量有机肥的红壤(不施肥,CK;施低量有机肥,LM;施高量有机肥,HM),过不同大小孔径筛(5 mm,S₅;2 mm,S₂;0.5 mm,S_0.5)改变团聚体的大小分布,然后填装土柱(直径2.9 cm、高度4 cm),填装容重为1.3 g·cm^-3。利用X射线显微CT(Computed Tomography)成像技术分析土壤的孔隙结构,采用室内培养法测定土壤有机碳矿化量。结果表明,团聚体大小对孔隙结构有极显著的影响。相较于S₅和S₂处理,S_0.5处理土壤的大孔隙度(>16μm)降低了83.0%～93.9%,孔隙连通性降低了95%以上。而S₅和S₂处理的大孔隙度和孔隙连通性只在HM土...     

Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development

Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 × 40 × 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m⁻³; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures.     

雨滴击溅对耕作层土壤团聚体粒径分布的影响

为研究不同雨滴直径的降雨对耕作层团聚体的破碎及其粒径分布特征的影响,该文选取4个雨滴直径(2.67~3.79 mm)对耕层土壤(0~20 cm)团聚体进行雨滴击溅试验,每次试验各滴5 000滴,每1 000滴收集1次溅蚀团聚体。结果表明:1)所有收集次序中雨滴直径3.79 mm溅蚀量最大,累积雨滴数为2 000、3 000和4 000时,溅蚀量与雨滴直径均呈显著的指数函数关系。2)各雨滴直径的溅蚀量随粒径减小呈增大-减小-增大趋势,2 mm粒径的溅蚀量几乎为0,0.053 mm粒径的溅蚀量随雨滴直径增大而增大。3)相同雨滴直径不同累积雨滴数之间平均重量直径值差异不显著,相同累积雨滴数不同雨滴直径之间平均重量直径值差异不显著(P0.05)。4)不同雨滴直径溅蚀团聚体富集率随粒径变化一致,1 mm粒径溅蚀量团聚体富集率值接近0,0.053~1 mm粒径团聚体富集,1 mm粒径团聚体主要破碎成0.053~1 mm粒径团聚体,且粒级越小,富集率越高。研究可为黄土高原地区水土保持提供理论依据。     

Influence of soil tillage systems on aggregate stability and the distribution of C and N in different aggregate fractions

Soil aggregation is influenced by the tillage system used, which in turn affects the amount of C and N in the different aggregate fractions. This study assessed the impact of different tillage systems on soil aggregates by measuring the aggregate stability, the organic carbon (C_org) and the total nitrogen (N_tot) contents within different aggregate fractions, and their release of dissolved organic carbon (DOC). Soil samples were collected from the top 0 to 10 cm of a long-term tillage experiment at Fuchsenbigl (Marchfeld, Austria) where conventional tillage (CT), reduced tillage (RT), and minimum tillage (MT) treatments were applied to a Chernozem fine sandy loam. The stable aggregates (1000–2000 μm) were subject to dispersion by the soil aggregate stability (SAS or wet sieving) method after Kemper and Rosenau (1986), and the ultrasonic method of Mayer et al. (2002). Chemical analysis of the soil was obtained for the aggregate fractions 630–1000, 250–630 and 63–250 μm gathered from the ultrasonic method. Using the SAS method, CT and RT had the least amounts of stable aggregates (18.2% and 18.9%, respectively), whereas MT had twice as much stable aggregates (37.6%). Using the ultrasonic method, MT also had the highest amount of water stable aggregates in all three fractions (1.5%, 3.7%, and 35%, respectively), followed by RT (1%, 2.3%, 32.3%), and CT (0.8%, 1.7%, 29.1%). For comparison, a reference soil, EUROSOIL 7 (ES-7) was also analysed (40%, 6.7%, and 12.1%). The highest amounts of C_org and N_tot were measured under MT in all three fractions, with 8.9%, 3.8%, and 1.3% for C_org, and 0.4%, 0.3%, and 0.1% for N_tot. Apart from the fraction 630–1000 μm, the aggregates of RT and CT contained <50% of the C_org and N_tot values of MT. The C/N ratio was least favourable for CT (42.6) in the aggregate fraction 630–1000 μm. The DOC release from stable aggregates after 10 min of ultrasonic dispersion was highest from MT soil (86.7 mg l⁻¹). The values for RT and CT were 21% and 25% below this value. The results demonstrate that tillage type influences both aggregate stability and aggregate chemical composition. This research confirms that CT interferes more with the natural soil properties than RT and MT. Furthermore, MT has the highest potential to sequester C and N in this agriculturally used soil.     

垄作与垄向区田技术对黑土区坡耕地土壤侵蚀影响的研究进展

东北黑土区在中国粮食安全与可持续发展中占据重要地位,但过度开发利用导致该区土壤侵蚀问题严峻。耕作方式的差异直接影响黑土区坡耕地土壤侵蚀特征,相关研究的开展对于准确评价水土保持措施的适宜性具有重要意义。该研究通过系统梳理文献资料,总结了垄向、垄规格以及垄向区田技术的内涵及应用条件,分别综述了其对黑土区坡耕地土壤侵蚀的影响;指出了目前研究中还存在垄作与垄向区田技术对坡耕地土壤侵蚀影响的机理研究不深、垄向与垄规格之间的耦合关系分析不细、垄向区田垄沟土埂优化设计不足、土壤侵蚀综合影响因素探索不全等方面主要问题;明确了未来研究中应加强量化垄向、垄规格、垄向区田技术与其他水土保持措施相结合对黑土区坡耕地土壤侵蚀影响的过程与机理,为筛选适宜的水土保持耕作措施提供科学依据。     

Effects of soil depth and aggregate size on weed seed distribution and viability in a silt loam soil

The position of weed seeds within the soil matrix plays an important role in seedling emergence and seed survival. The relationship of weed seeds with soil aggregates and soil depth was evaluated in a Waukegon silt loam soil that had been under a long-term, conventional tillage, annual crop management system. Soil aggregates were separated and classified into eight size classes from ≤5 to >12 mm and weed seeds were extracted from the aggregates. Amaranthus spp., Chenopodium album L. (common lambsquarters), Polygonum pensylvanicum L. (Pennsylvania smartweed), Setaria faberi Herrm. (giant foxtail), and Solanum ptycanthum Dun. (eastern black nightshade) accounted for the majority of seeds recovered. In general, seed viability declined from April to June, but increased in October following seed deposition. Seeds of individual species were most abundant in the aggregate size class most closely matching its seed size. However, seeds were commonly found associated with aggregates larger than 9 mm. Highest seed viability was found in the aggregate fraction closest to the seed size, however, S. faberi viability was also high in the >12 mm aggregate size class. Regardless of aggregate size, seed numbers were generally greatest in the upper 5 cm of soil. The results of this research were species-dependent and variable and demonstrated the complexity of weed seed/soil aggregate associations. However, they did show that seed placement within the soil matrix may play an important role in weed population dynamics.     

降雨类型对褐土横垄坡面土壤侵蚀过程的影响

雨型是影响土壤侵蚀过程的重要因子之一,而影响效应与耕作措施密切相关。目前,雨型对横垄坡面土壤侵蚀过程的影响机制尚不清楚。该文以褐土横垄坡面为研究对象,设计了平均雨强和降雨量相同的4种雨型(增加、减弱、增加-减弱和减弱-增加型),采用可同时调节垄向和坡面坡度的土槽进行模拟降雨,研究各个雨型下不同侵蚀阶段的产流产沙特征。结果表明:雨型间的径流量和侵蚀量在细沟间和细沟侵蚀阶段均差异显著,且差异在细沟阶段体现的更为明显。雨型间径流量的大小顺序为增加-减弱型减弱型减弱-增加型增加型,侵蚀量则为增加-减弱型减弱-增加型减弱型增加型。给定雨强下(30、60或90 mm/h),径流量、径流贡献率和侵蚀量贡献率均随降雨过程中雨强发生时序的延迟而增加,而单位径流侵蚀量呈相反趋势;雨型间给定雨强同一发生时序下的径流量和侵蚀量及其它们对总径流量和总侵蚀量的贡献率均差异显著。4种雨型下,幂函数均能很好的描述细沟间和细沟侵蚀阶段内产沙率与径流率间的关系,且方程中的指数均低于2,但雨型间幂函数方程中的指数存在明显差异。以上研究结果有助于深入理解褐土垄作系统下的土壤侵蚀机理,并为横坡垄作的合理利用提供科学指导。     

黄土高原坡沟系统侵蚀泥沙来源模拟试验

为了进一步明确黄土高原坡沟系统侵蚀泥沙主要来源及其动态变化过程,该文利用室内概化坡沟系统模型,结合稀土元素（REE）示踪技术,采用放水冲刷试验,对黄土高原的坡沟系统侵蚀泥沙来源问题进行了研究。结果表明,在该试验的坡沟系统中,侵蚀泥沙主要来自坡沟系统的坡面,距离坡面顶端2 m的侵蚀产沙量占到坡面总侵蚀量的57%～74%,沟坡部分的侵蚀产沙量较少;坡面部分的4种示踪元素侵蚀带,在流量为6、8、10和14 L/min时,各个侵蚀带的侵蚀量大小依次为La元素示踪带＞Ce元素示踪带＞Tb元素示踪带＞Sm元素示踪带,但在流量为12 L/min时,侵蚀量大小依次为La元素示踪带＞Ce元素示踪带＞Sm元素示踪带＞Tb元素示踪带;坡面侵蚀产沙泥沙百分比随着冲刷历时的增长,总体上呈现出波动式的递增趋势,25 min以后又开始减小,沟坡侵蚀产沙量的变化趋势与坡面相反。研究为黄土高原小流域坡沟的治理提供了科学依据。     

土壤水稳性大团聚体测定方法综述

 湿筛法是测定土壤团聚体粒径分布和稳定性的经典方法。土样在湿润过程中,同时发生了崩解、差异膨胀和物理化学分散作用。已有的湿润方法按湿润速度可分为快速湿润和慢速湿润,按土样所处的气压条件可分为常压湿润和高真空湿润。常压快速湿润过程中,水分沿毛管快速渗入土体,土壤内部封闭的空气被压缩,产生微型爆炸,对团聚体破坏较大;慢速湿润和真空湿润能使团聚体稳定性显著增大。如果是为全面了解土壤团聚体稳定性及粒径分布的信息,可对土样采用常压快速湿润和常压慢速湿润（或真空湿润）2种预湿润。湿筛的作用在于区分不同粒级的土壤颗粒,应尽量减小对团聚体颗粒进一步的磨蚀作用,因此湿筛过程中振动速度不能太快。筛目可以根据实验目的选择。     

Investigating the effects of wettability and pore size distribution on aggregate stability: the role of soil organic matter and the humic fraction

Soil organic matter (SOM) is an important factor influencing aggregate stability. Interactions between SOM and soil structure are widely studied, although the subtle relationship between SOM content, pore size distribution and aggregate stability is not fully known. Here we investigate such a relationship by means of a long‐term experiment established in 1962 in northeastern Italy, which considers different fertilizer practices (organic, mineral and mixed) applied to a continuous maize crop rotation. We measured wet stability of 1–2 mm aggregates subjected to different pretreatments. Both soil physical properties (such as pore size distribution and hydrophobicity) and chemical properties (soil organic and humic carbon content) affecting aggregate stability were considered. The chemical structure of humic substances was characterized by thermal and spectroscopic analyses (TG‐DTA, DRIFT and ¹H HR MAS NMR). The Pore‐Cor network model was then applied to evaluate the contribution of hydrophobicity and porosity to aggregate wetting. Our study suggests that SOM and its humic fraction can affect aggregate wetting and consequently slaking by modifying the pore size distribution with a shift from micropores (5–30 µm) and mesopores (30–75 µm) to ultramicropores (0.1–5 µm); hydrophobicity was also increased as a result of different humic composition. Spectroscopic analysis showed that hydrophobic compounds were mostly associated with complex humic molecules. Models of fast wetting dynamics, however, suggest that the contribution that hydrophobicity makes to aggregate stability, especially to soils with large carbon inputs, may not be the most significant factor.     

垄作免耕影响冷浸田水稻产量及土壤温度和团聚体分布

研究垄作免耕对冷浸田水稻产量及其构成因子的影响,同时,观察其耕层土壤温度和土壤团聚体结构的变化,旨在为冷浸田的综合治理技术提供科学依据。该研究以湖北省冷泉烂泥型冷浸田为对象,采用垄作免耕栽培田间定位试验方法,设计垄高10(LG10)、15(LG15)、20 cm(LG20)和平作(CK)4个处理种植中稻。研究结果表明,起垄(垄高10和15 cm)能显著(P0.05)提高冷浸田水稻产量,2011年和2012年垄高15 cm较CK分别增产10.95%和18.51%;与CK处理相比,垄作土壤平均增温范围为0.4~1.2℃,在0~5 cm土层内,垄作处理的土壤大团聚体(1 mm)含量明显提高;在5~25 cm土层内,土壤大团聚体含量LG15最高、CK最低、而LG20和LG10处于两者之间。垄高15 cm对大团聚体形成的影响大于垄高10和20 cm。垄作对冷浸田表层(0~5 cm)和下层(5~25 cm)土壤团聚体形成的影响存在差异,起垄后表层土壤大团聚体数量高于下层。但是,不同起垄高度与土壤温度和土壤大团聚体的变化不存在对应的数学正相关。综上所述,冷浸田合适的免耕起垄高度为15 cm。     

前期含水量对机械压实后黑土团聚体特征的影响

以东北典型黑土区耕地土壤为研究对象,通过对不同前期含水量下机械碾压处理后土壤干筛团聚体和水稳性团聚体粒级分布、破坏率(PAD0.25)、分形维数(D)、平均重量直径(MWD)、平均重量比表面积(MWSSA)等特征指标的测定和分析,对比研究了干湿处理条件下模拟机械作业过程中土壤团聚体特征的变化。结果表明:黑土耕作区0～30 cm范围内团聚体组成上干筛团聚体以>2 mm粒级的团聚体比例最高,而水稳性团聚体则随着粒级的减小,比例逐渐增加。不同前期土壤含水量能够对机械压实黑土的团聚体组成分布、分形等特征产生影响,低含水量时,机械碾压在一定程度上能够促进土壤团聚体的团聚,但同等负荷下多次积累压实会削弱土壤的水稳定性和机械稳定性;而在高含水量时,机械碾压相对更易对黑土团聚体产生负效应,加剧破坏、抑制团聚,降低其水稳定性和机械稳定性。同时发现,MWSSA与其他常用团聚体特征值PA0.25、MWD、D、PAD0.25的线性关系达到了极显著水平,说明MWSSA同样可以作为分析和研究土壤团聚体特征的有效指标。研究结果可为科学指导大机械作业提供理论依据。     

The effect of successive wet/dry cycles on aggregate size distribution in a clay texture soil

Aggregates of a fine textured (61% clay, 33% silt) soil with a high coefficient of linear expansion (20%) were exposed to successive wet/dry cycles in their natural state and after mechanical reworking. In both cases aggregate size decreased; the reworked sample initially consisted of larger aggregates, but their size fell more rapidly, and after four cycles both the reworked and natural aggregates had a similar size distribution. A model was developed which successfully predicts the proportion of aggregates in each size grade at the n th cycle from that present at the outset. The rate of decrease in aggregates size declined with aggregate size and on both reworked and natural samples the dispersion ratio was low (≤5%).     

The distribution of nematodes and soil microbial communities across soil aggregate fractions and farm management systems

We hypothesized that nematode and microbial communities vary between soil aggregate fractions due to variations in physical and/or resource constraints associated with each fraction and that this, in turn, contributes to management impacts on whole soil food webs. Nematode and microbial communities were examined within three soil fractions: large macroaggregates (LM; >1000 μm), small macroaggregates (SM; 250-1000 μm) and inter-aggregate soil and space (IS; <250 μm) isolated from soils of four agricultural management systems: conventional tomato (CON), organic tomato (ORG), a minimum till grain-legume intercrop with continuous cover (CC) and an unmanaged riparian corridor (RC). Aggregate fractions appeared to influence nematode assemblages more than did management system. In general the IS and LM fractions contained higher densities of all nematode trophic groups than did SM. Management × fraction interactions for bacterivores and fungivores, however; suggested a non uniform trend across management systems. The IS fraction exhibited stronger trophic links, per the nematode structure index (SI), while the LM and SM fractions had more active fungal decomposition channels as indicated by the channel index (CI). Higher adult to juvenile ratios in the LM and IS than the SM fraction, and a positive correlation between nematode density in the IS fraction and the proportion of macroaggregates in the soil, indicated an association between soil structure and nematode distribution. Microbial communities varied across both aggregate fractions and management systems. Phospholipid fatty acid (PLFA) analysis suggested that the LM fraction contained greater microbial biomass, gram positive bacteria, and eukaryotes than the IS fraction, while SM contained intermediate PLFA associated with these groups. Total PLFA was greater under RC and ORG than under CC or CON. Total PLFA was positively correlated with % C in soil fractions while nematode abundance exhibited no such relationship. Our findings suggest that microbial communities are more limited by resource availability than by habitable pore space or predation, while nematode communities, although clearly resource-dependent, are better associated with habitable pore space for the soil fractions studied here.