土壤中游离铁和络合态铁的测定

土壤中不属于层状硅酸盐组成部分的其它形态的铁,统称为游离铁(Fe_d),主要是氧化铁及其水合物。土壤(或粘粒)中游离铁占全铁的(Fe_T)的百分比称为铁的游离度(Fe_d×100/Fe_T),它反映成土过程的特点,常用作为风化度的指标之一。     

有机覆盖对城市森林土壤有机碳矿化及其氧化稳定性特征的影响

为探究有机覆盖对城市森林土壤有机碳矿化及其氧化稳定性特征的影响，采集北京市鹫峰国家森林公园土壤，进行室内培养，研究不覆盖(CK)、木片覆盖(M_w)、堆肥覆盖(M_c)、上层木片覆盖+下层堆肥覆盖(M_w+c) 4种条件下土壤有机碳矿化特征及氧化稳定组分变化。结果表明，不同有机覆盖方式均显著影响了土壤有机碳(SOC)矿化(P<0.05)，M_c、M_w+c、M_w处理的有机碳累积矿化量分别是CK的1.77倍、2.93倍和3.98倍，M_w处理累积矿化量分配比和Cp/SOC值(土壤有机碳矿化潜能占土壤有机碳含量的比重)显著高于M_c和M_w+c处理(P<0.05)，说明M_c和M_w+c处理的固碳潜力好于M_w处理。不同有机覆盖方式显著提升了土壤有机碳及其氧化稳定组分含量(P<0.05)，M_w+c处理的增幅最明显，土壤有机碳含量比CK提高了29.14%；高活性有机碳组分和低活性有机碳组分含量较CK分别提高了20% 和37.14%。有机覆盖提高了土壤有机碳稳定指数，降低了活性指数，表明有机覆盖增强了土壤有机碳稳定性。有机碳累积矿化量与高活性有机碳组分呈极显著正相关(P<0.01)，与土壤有机碳和低活性有机碳组分呈显著正相关(P<0.05)。综合土壤有机碳矿化特征及其氧化稳定组分的变化来看，上层木片+下层堆肥的覆盖模式，既能提高土壤的固碳潜力，又能协调有机碳矿化与稳定性特征。     

不同结皮类型对植被混凝土基材团聚体及有机碳的影响

[目的] 分析土壤团聚体分布和有机碳含量特征,揭示生物结皮对边坡稳定和养分固持的影响,为生物结皮在修复工程中的运用提供参考和指导意见。[方法] 以植被混凝土基材修复边坡为例,运用土壤干筛法、土壤湿筛法分别对结皮覆盖和无结皮覆盖坡面土壤的结皮层(0—2 cm)和结皮下层(2—7 cm)团聚体和有机碳特征进行研究。[结果] ①生物结皮的存在明显影响了土壤团聚体分布、机械稳定性及R_0.25含量。结皮覆盖层较CK(无结皮覆盖坡面)稳定性指标分别增加27.42%~33.51%(MWD),21.66%~28.88%(GMD),大团聚体含量(R_0.25)增加10.68%,且苔藓类结皮影响最为显著。②湿筛法测定的不同结皮类型土壤团聚体均以＞0.25 mm粒径为主,其中结皮覆盖边坡的团聚体水稳性参数MWD,GMD,R_0.25分别介于1.93~5.33 mm,0.85~3.16 mm,70.97%~87.50%,以苔藓覆盖边坡最大,D_d值介于2.48~2.74间,以苔藓类值最小。团聚体水稳定性表现为苔藓覆盖边坡最好,裸坡最差。③结皮的存在促进了土壤有机碳累积,有机碳含量是CK组的两倍以上。其中对表层土壤有机碳水平提升作用明显,对下层土壤作用较低。④土壤有机碳含量与土壤水稳性参数MWD,GMD,R_0.25呈显著正相关性(p＜0.05),有机碳水平和团聚体稳定性联系密切,相互影响,有机碳水平的提高对增加团聚体稳定性具有重要作用。[结论] 生物结皮的存在对修复边坡团聚体稳定和有机碳累积具有促进作用,结皮对生态修复边坡稳定和养分固持有一定的作用,且不同结皮类型作用强度不一,其中苔藓类和混生结皮固土和固碳效果最优。     

中国下蜀黄土发育的土壤表层及典型剖面的硫状况

Studies were conducted to examine factors which might influence the status and distribution of S in some surface horizons and typical profiles of soils derived from Xiashu loess on the upper slope (US), middle slope (MS) and lower slope (LS) of Nanjing-Zhenjiang-Yangzhou hilly zone. The total S contents varied from 70.30 to 350.21 mg/kg, and the average for all surface soils was 218.3 mg/kg. The average S contents in the profiles followed the sequence: USo) and the ratio of amorphous iron oxide to free iron oxide (Fe_o/Fe_a), but no significant relationship was found between total S and the ratio of free iron oxide to total iron (Fe_d/Fe_t). Inorganic sulphate in paddy soils (MS and LS) was nearly higher in surface soil than in subsurface soil and subsoil, it, however, remained relatively unchanged with increasing depth for the original soil profile (US). The average organic S accounted for 94% of the total S in the surface soils, but the percentage decreased with depth in the profiles. Like the total S, the organic and inorganic S contents were highly significantly correlated with organic matter, total N, Fe_o and Fe_o/Fe_d ratio, but they were insignificantly related to Fe_d/Fe_t ratio. The C/S and N/S ratios in this study were somewhat lower than the results reported by others. The C/N/S ratios varied considerably within the same profile and among different soils but they fell within the range of values reported worldwide.     

向家坝水电站生态修复边坡土壤团聚体及有机碳含量特征

[目的] 分析生态工程修复技术对土壤团聚体稳定性及有机碳分布的影响,为向家坝水电站不同生态修复边坡土壤结构稳定及碳汇功能的提升提供科学依据。[方法] 以向家坝水电站4种不同生态修复边坡：植被混凝土(CBS)、厚层基材喷播(TB)、框格梁覆土(FB)、客土喷播(SS)表层土壤为研究对象,并以天然林(NF)和弃渣地(AS)两种自然恢复边坡为对照,采用湿筛法研究土壤团聚体分布和稳定性及其有机碳含量特征。[结果] ①各边坡土壤均以＞0.25 mm的大团聚体粒径为主;其中天然林大团聚体含量最高,为81.83%;植被混凝土和厚层基材边坡次之,弃渣地含量最低,仅占55.19%。4个人工生态修复边坡的MWD和GMD均低于天然林高于弃渣地,其中厚层基材边坡的值最高,分别为2.96 mm和1.47 mm。客土喷播和弃渣地的分形维数(D)显著高于(p＜0.05)其余4个边坡。②各生态修复边坡措施均以＞0.25 mm粒径的大团聚体有机碳含量最高;除客土喷播和弃渣地外,其他修复措施和天然林均以＞2 mm粒级土壤团聚体贡献率最大。③相关性分析表明土壤SOC与MWD,GMD和R_0.25呈极显著正相关(p＜0.01),＞5 mm和5～2 mm粒级团聚体数量与土壤MWD,GMD,R_0.25和土壤SOC均呈极显著正相关(p＜0.01),与D呈极显著负相关(p＜0.01)。[结论] 向家坝水电站研究区内厚层基材喷播技术和植被混凝土生态修复技术对土壤结构和有机碳库的改善效果比较接近天然林,客土喷播技术改善效果较差。     

黔中石漠化地区水土保持措施对土壤有机碳的影响

土地石漠化是中国西南喀斯特地区的重大生态问题,石漠化治理引发土壤碳转变并对陆地碳循环产生影响。然而,石漠化地区水土保持措施对土壤有机碳的影响机制还不明确。选取典型石漠化区梯田嵌套鱼鳞坑(NL)、鱼鳞坑(FSP)、梯田(TR) 3种水土保持措施作为研究对象,以无任何水土保持措施的退耕还林地(CK)作为对照,研究不同水土保持措施土壤有机碳含量分布规律。结果表明:鱼鳞坑土壤有机碳含量分别是梯田嵌套鱼鳞坑和梯田的1.4,6.2倍,有机碳储量分别比梯田嵌套鱼鳞坑和梯田提高30.78%和444.44%,活性有机碳含量也显著大于其他2种水土保持措施,因此固碳效果最好。土壤有机碳储量与活性有机碳组分易氧化碳、可溶性碳、微生物量碳呈极显著相关(p<0.01),易氧化碳与可溶性碳、微生物量碳呈极显著相关(p<0.01),可溶性碳与微生物量碳呈显著相关(p<0.05),因此土壤活性有机碳组分能在一定程度上反映土壤质量变化情况。鱼鳞坑和梯田措施土壤全氮含量和碳氮比的增加会促进土壤有机碳固存。鱼鳞坑可作为石漠化地区生态恢复中优先考虑的治理措施。     

中国黄土高原黄土-古土壤序列的红度对古气候的指示意义

Comparisons of red ratings (RR) with Fe_d, Fe_d/Fe_t, clay content, and magnetic susceptibility (x) of two loess-paleosol sequences at Luochuan and Lingtai on China's Loess Plateau were conducted to study the possible relationship between RR and pedogenic degrees of the two loess-paleosol sequences, and to discuss whether the RR could become new paleo-climatic indicators. Results showed that the RR of the two loess-paleosol sequences had positive, highly significant (P < 0.01) correlations with: 1) citrate-bicarbonate-dithionite (CBD) extracted iron (Fe_d), 2) ratios of CBD extracted iron to total iron (Fe_d/Fe_t), 3) clay (< 2 μm), and 4) magnetic susceptibility (x). This suggested that the RR of these loess-paleosol sequences could indicate degrees of loess weathering and pedogenesis and were potential paleo-climatic proxies. The strong correlations of RR to Fe_d and x also implied that during pedogenic processes, pedogenic hematite in loess and paleosols were closely related to the amount of total secondary iron oxides and pedogenic ferrimagnetic minerals (predominantly maghemite).     

凋落物输入改变对慈竹林土壤有机碳的影响

通过野外试验,研究了凋落物输入改变对慈竹林土壤有机碳的影响。设置10%,50%和70%这3种去除凋落物量和分别添加15%,25%的绵竹、杉木凋落物处理及对照。结果发现,去除凋落后慈竹林土壤有机碳含量明显减少(p<0.05),而且去除量越大,有机碳含量减少越大。添加外源凋落物显著提高了慈竹林土壤有机碳含量(p<0.05),其中,15%的添加比例比25%更有利于土壤有机碳的积累,添加绵竹凋落物对土壤有机碳增加的效应高于添加杉木凋落物。研究表明,选择适合的树种和恰当的混交比例以及加强对凋落物层的保护,对维持慈竹林土壤有机碳具有重要的意义。     

红壤侵蚀区不同植被类型土壤磷垂直分布特征及影响因素研究

为探讨红壤侵蚀区不同植被类型下土壤磷素有效性,选取福建长汀红壤丘陵生态系统国家定位观测研究站的裸地(CK)、针叶林(CF)、针阔混交林(CB)以及阔叶林(BF)4种植被类型,分别测定其铁氧化物、各级磷素形态,并采用高通量测序技术对解磷菌(PSM)进行测定。结果表明:随着植被类型的转变,中等活性磷含量增加,低活性磷含量总体上减少,游离态氧化铁(Fe_d)含量逐渐减少。土壤中解磷菌的丰富度和多样性随植被类型的转变增加。在门分类水平上,优势类群主要有变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、异常球菌—栖热菌门(Deinococcus-Thermus)等。变形菌门和酸性磷酸酶的含量随植被类型的转变总体呈现出增加趋势,变形菌门与ACP呈极显著正相关。综上所述,随着植被类型转变,稳定态磷逐渐向可利用态磷转化,土壤潜在磷源增加;游离态氧化铁含量的减少有利于有机磷的解吸和矿化,进而增加磷的有效性;解磷菌群落结构与多样性变化会受到土壤理化性质的影响,解磷微生物可通过分泌酸性磷酸酶的方式水解有机化合物并降解固定在土壤的无机磷,进而提高磷的有效性。     

坡面片蚀泥沙有机碳组分及13C同位素不均匀富集对水动力学参数的响应

[目的] 探究片蚀泥沙轻组有机碳(LF_OC)和重组有机碳(HF_OC)不均匀富集的水动力学和碳同位素特征,为正确理解水蚀作用下土壤有机碳库变化提供理论与技术支撑。[方法] 以陕西省咸阳市杨凌区土为研究对象,采用改进"三区"移动式变坡钢制土槽,结合人工模拟降雨技术,测定径流水动力学参数和泥沙各粒径团聚体有机碳组成及其δ¹³C值,并辅以棕壤侵蚀泥沙有机碳δ¹³C值和水力参数,验证土试验结果的准确性。[结果] ①雨强和坡度较小时,侵蚀泥沙LF_OC和HF_OC易发生富集,且相较黏粉粒和微团聚体,大团聚体LF_OC与HF_OC含量受雨强和坡度的影响更大; ②侵蚀泥沙黏粉粒中有机碳δ¹³C值与其有机碳活跃分数(λ)呈负相关,而其他粒径团聚体有机碳δ¹³C值与其λ呈显著正相关(p<0.05); ③流速与黏粉粒λ显著正相关(p<0.05),雷诺数与各粒径团聚体有机碳δ¹³C值均呈显著负相关(p<0.01),片蚀过程中流速越大,黏粉粒中LF_OC越易于优先输移,而紊流加剧则促进低δ¹³C值团聚体有机碳的优先输移; ④对于侵蚀泥沙黏粉粒,流速和雷诺数越大,其有机碳δ¹³C值越小,λ越大;对于微团聚体和大团聚体,雷诺数越小,其有机碳δ¹³C值与λ越大。[结论] 片蚀过程中轻重组有机碳流失与流速和雷诺数密切相关。并进一步验证了¹³C同位素对侵蚀泥沙有机碳示踪的有效性。     

Soil Erodibility and Physicochemical Properties of Collapsing Gully Alluvial Fans in Southern China

In southern China, collapsing gully erosion produces massive deposits of sediment on the plough layer of alluvial fan farmland, leading to reduced nutrients, increased erodibility, and even desertification. The aim of this study was to investigate soil erodibility (the factor K in the universal Soil Loss Equation, USLE) and physicochemical properties of the alluvial fans of the most severe collapsing gully erosion areas (Hubei, Jiangxi, Fujian, and Guangdong provinces) in southern China. The soils of the collapsing gully alluvial fans had a higher bulk density, but a lower total porosity, saturated water content, and silt and clay fractions than the control (CK) soils from the farmland without desertification. Soil quality gradually decreased from fan edge to fanhead. Significant decreases were found in soil pH, organic matter, cation exchange capacity, and total potassium, nitrogen, and phosphorus, as well as available nitrogen, phosphorus, and potassium, resulting in a gradual decrease in soil nutrients from the fanedge to the fanhead. Soil erodibility was greatest in the fanhead, and soil erodibility K values of the alluvial fans were 53.71%, 66.28%, 67.53%, and 71.68 % greater than that in those of the CK soils of Hubei, Jiangxi, Fujian, and Guangdong, respectively, indicating a significant correlation between the soil erodibility K values and physicochemical properties, particularly sand fraction and organic matter content. The results provide new insights into the relationship between soil physicochemical properties and erodibility of alluvial fans, and suggest that improving soil structure might increase soil fertility in the collapsing gully alluvial fan farmland.     

东北黑土区土壤退化及水土流失研究现状

东北黑土区严重的水土流失破坏了宝贵的黑土资源,危及当地群众的生产生活条件,恶化了生态环境,制约了当地经济社会的可持续发展,对我国的粮食安全构成了严重威胁。当前黑土区土壤退化及水土流失研究的领域主要集中在:现状研究、影响因素研究以及土壤侵蚀研究。在概述当前黑土区土壤退化及水土流失研究概况的基础上,指出应该加强研究的领域在于综合性的水土流失研究,融雪侵蚀模拟,先进的土壤侵蚀预报模型应用等方面。     

长期化肥有机替代对黑土颜色及腐殖物质的影响

基于30年长期定位试验,通过测定黑土光谱反射率和不同腐殖质组分含量,探究了不同施肥对黑土土壤腐殖质含量、土壤颜色及二者之间的关系。试验设置5个处理:(1)休耕(Fallow);(2)不施肥处理(CK);(3)单施化肥(NPK);(4)有机肥部分替代化肥(NPKM);(5)秸秆部分替代化肥处理(NPKS)。结果表明:与NPK处理相比,Fallow、NPKS、NPKM分别显著提高49.7%,74.3%,27.0%的土壤有机碳含量(p<0.05)。NPKM处理中胡敏酸(HA)含量最高为3.9 g/kg,随后依次为CK、NPKS、NPK、Fallow。NPKM、NPKS和Fallow处理中土壤富里酸(FA)含量为2.2~2.3 g/kg,显著高于NPK和CK。NPKM处理中胡敏素(HM)含量为18.6 g/kg,显著高于其他处理(p<0.05)。不同处理间土壤光谱反射率由高到低依次为NPK>Fallow、CK>NPKS>NPKM,与CK处理相比,NPK土壤光谱反射率在平均提高6.5%,NPKS和NPKM则分别降低11.1%和15.1%。根据线性相关分析结果,黑土土壤光谱反射率与土壤HAHM均呈显著负相关关系(p<0.01),相关系数(r)分别为-0.858,-0.681。综合上述结果,长期有机物料投入可以显著提高黑土腐殖物质含量,降低黑土光谱反射率,使黑土颜色加深,而长期化肥施入则使黑土光谱反射率提高,出现"褪色"现象,有机粪肥在黑土中对土壤有机质和腐殖质含量的提升效果优于秸秆。     

土壤培肥过程中氯离子累积与分布规律研究

以陕西杨凌杜寨村为中心,沿南、西、北3条辐射线分别采取耕层和剖面土样,探讨土壤中Cl^-的累积与垂直分布情况,揭示受人类生活影响历史较长的杜寨村农田土壤中Cl^-的累积状况与迁移规律。结果表明,在半干旱偏湿润气候地区,由于受自然环境因素和人为因素的强烈影响,Cl^-在村庄附近的土壤耕层呈现出累积趋势,随着离村庄距离的增加而明显减少;土壤剖面上Cl^-的含量随着土壤深度的增加也逐渐减少;Cl^-在土壤耕层虽然表现出一定的累积趋势,但累积量并不高,暂时不会影响作物的产量和品质。     

土壤可蚀性研究现状及展望

<正> 土壤可蚀性(soil erodibility)是指土壤是否易受侵蚀破坏的性能,也就是土壤对侵蚀介质剥蚀和搬运的敏感性。与侵蚀营力一样,土壤可蚀性是影响土壤侵蚀量大小的又一个重要因子。在水土保持学科中,我国习惯上把“水”和“土”并列使用,而国际上则用“soil loss”、“soil erosion”、“soil conservation”或“soil and water conservation”等术语。显然,土壤是水土保持学科的重点。另一方面,土壤侵蚀营力等是土壤流失过程中的外部因素,而土壤性质才是内在因素,因此,水土保持学科中核心的也是重要的问题,应该是土壤保护。土壤可蚀性研究在水土保持研究工作中具有重要意义,国际上把土壤可蚀性研究一直作为水土保持学科研究的重要内容之一。     

Responses of Soil Microbial Community Structure and Activity to Incorporation of Straws and Straw Biochars and Their Effects on Soil Respiration and Soil Organic Carbon Turnover

Like straw, biochar incorporation can influence soil microorganisms and enzyme activities and soil carbon(C) responses; however,few studies have compared the various effects of straw and biochar and the underlying mechanisms. An experiment was performed to study the changes in soil respiration(SR) and soil organic C(SOC) fluxes in response to the incorporation of three kinds of straw(reed, smooth cordgrass, and rice) and their pyrolyzed products(biochars) at Chongming Island, China. In addition, the microbial activity and community structure of some amended soils were also analyzed to clarify the mechanisms of these responses. The results showed that all biochar incorporation(BC) induced lower SR than the corresponding unpyrolyzed straw incorporation(ST), and the average SR in the soils following BC and ST during the experimental periods was 21.69 and 65.32 μmol CO_2 m~(-2)s~(-1), respectively.Furthermore, the average SOC content was 16.97 g kg~(-1) following BC, which was higher than that(13.71 g kg~(-1)) following ST,indicating that compared to ST, BC was a low-C strategy, even after accounting for the C loss during biochar production. Among the BC treatments, reed-BC induced the lowest SR(17.04 μmol CO_2 m~(-2)s~(-1)), whereas smooth cordgrass-BC induced the highest SR(27.02 μmol CO_2 m~(-2)s~(-1)). Furthermore, in contrast with ST, BC significantly increased the abundance of some bacteria with poorer mineralization or better humification ability, which led to lower SR. The lower easily oxidizable C(EOC) and higher total C contents of biochars induced lower SR and higher SOC in the soil following BC compared to that following ST. Among the BC treatments,the higher total nitrogen content of rice biochar led to significantly higher soil microbial biomass, and the lower EOC content of reed biochar led to lower soil microbial activity and SR.     

土壤抗蚀抗冲性研究综述

该文是对土壤抗蚀抗冲性与其内在性质研究历史和特点的综述,并提出了今后研究的方向。     

植被恢复下土壤结构与功能的关系

通过查阅有关土壤结构和土壤功能的国内外文献,对土壤结构和土壤功能的研究进展、土壤结构稳定性指标以及土壤结构的研究方法进行了阐述;讨论了土壤结构与土壤的作物生产功能、土壤水库功能、土壤碳库功能、土壤基因库功能等的关系;并对激光共聚焦扫描技术在土壤结构与孔隙特征分析中的应用及数字图像处理技术的应用如何反映土壤孔隙的真实状况,加强对土壤结构及其功能的定量关系研究等方面提出了展望。     

土壤水分和氮添加对3种质地紫色土氮矿化及土壤pH的影响

为正确认识土壤水分、质地和外源氮添加对紫色土氮矿化作用和土壤pH的影响,以西南地区典型的紫色土为研究对象,通过90d的室内恒温(25℃)好气培养,研究了3种质地(粘土、粉粘壤土和砂土)紫色土在不同含水量(55%,65%和75%田间持水量)和尿素氮添加水平(0mg/kg土和250mg/kg土.)条件下,土壤氮矿化作用和pH的变化。结果表明:前30d的累积矿化氮量可占培养期间(90d)的78.48%~91.55%,且各处理的土壤累积矿化氮量和净矿化速率均随着培养时间的延长而快速增加;第30~90d,土壤累积矿化氮量增长缓慢,净矿化速率迅速下降并趋于稳定。土壤累积矿化氮量和净矿化速率在各培养阶段均随土壤水分含量的增加而逐渐增大,其中75%WHC(75%田间持水量)和75%WHC+U(75%田间持水量+尿素)处理的矿化作用最强。土壤质地从一定程度上对土壤的矿化产生影响,但其影响并不显著。外源氮添加能促进土壤氮矿化,其净氮矿化量和净矿化速率在各培养阶段均极显著(p0.01)高于未加氮处理,分别为未施氮处理的1.68~4.56倍,0.60~6.47倍。外源氮添加使土壤pH显著下降,55%WHC+U、65%WHC+U和75%WHC+U处理分别下降了0.57,0.66,0.72个pH单位,土壤有酸化趋势。土壤pH值与土壤氮素净矿化速率呈极显著线性相关,净矿化速率对pH变化贡献巨大。总之,土壤含水量增加和外源氮添加均促进了土壤氮矿化,增加了土壤矿质氮含量,同时外源氮添加也加速了土壤pH下降,土壤有酸化趋势。     

土壤干密度和含水率对2种紫色土抗剪强度的影响

选择广泛分布于重庆丘陵山区的钙质紫色土和中性紫色土2种土壤,通过室内三轴剪切试验测定含水率和干密度交互作用对土壤抗剪强度指标的影响。结果表明:(1)在相同干密度情况下,2种土壤粘聚力(c)随着含水率增加呈现出先增加后减小的趋势,在相同土壤含水率水平下,土壤粘聚力(c)随干密度增大而增大;2种土壤内摩擦角(φ)在各干密度条件下均随着含水率增加呈明显减小的趋势。(2)含水率和干密度的交互作用对粘聚力(c)有显著影响,粘聚力(c)随着干密度的增大而增大,且每一个干密度都有一个含水率与之对应,并在此交互条件下c达到最大。钙质紫色土粘聚力(c)在干密度为1.7g/cm3,含水率为11%时达到极大值,此时粘聚力(c)为154.59kPa,中性紫色土粘聚力(c)在干密度为1.6g/cm3,含水率为8%时达到极大值,此时粘聚力(c)为126.38kPa。(3)含水率和干密度的交互作用对内摩擦角(φ)影响相对较小,同一干密度下,其φ值差异不大,随干密度的增大缓慢增大,相对而言,含水率对内摩擦角(φ)的影响更明显。钙质紫色土内摩擦角(φ)随含水率的增大呈曲线下降,中性紫色土内摩擦角(φ)随含水率增大有一个短暂的增大过程,而后随之迅速减小。