长期传统耕作对土壤团聚体稳定性及有机碳分布的影响

通过野外调查取样,并结合室内实验分析,对甘肃会宁县丘陵地区不同耕作年限黄绵土耕地不同土层(0～ 20 cm,20～40 cm)土壤团聚体分布及稳定性和水稳性团聚体有机碳含量进行研究.结果表明:未经开垦土壤团聚体稳定性最好,耕作明显地破坏土壤团聚体,降低其稳定性;经过70 a以上时间开垦,0～ 20 cm和20～40 cm土层≥0.25 mm直径水稳性团聚体含量分别下降了40.5％和12.5％.耕作层水稳性团聚体平均重量直径和几何均重直径比亚表层平均大了10％,两土层之间的差异随着耕作年限变小.0～20 cm土层,＞2mm和0.25～0.106mm直径水稳性团聚体有机碳含量较高;20 ～ 40 cm土壤各直径水稳性团聚体有机碳含量差异不明显,耕作层以及亚表层水稳性团聚体有机碳含量整体表现出不断下降的趋势.平均重量直径和几何均重直径与土壤有机碳之间很好的相关性表明团聚体对于有机碳的保持作用关键.     

黄土丘陵沟壑区不同年限苜蓿地土壤水稳性团聚体分布特征及稳定性研究

为了探索种植苜蓿对土壤质量的影响,选取黄土高原丘陵沟壑区3、7、12 a和18 a生苜蓿草地0～60 cm土层土壤为研究对象,以农田为对照(CK),采用湿筛法研究了不同种植年限苜蓿草地土壤团聚体分布特征及其稳定性。结果表明:黄土丘陵沟壑区土壤水稳性团聚体组成随着粒径减小呈阶梯式递增态势,增幅为1.22%～61.43%,以<0.25 mm的微团聚体占据优势级别,其比例达60.83%～79.72%。当农田更替为苜蓿草地后,在0～20 cm土层,随种植年限增加至12 a,土壤团聚化递增趋势明显,>2 mm、1～2 mm、0.5～1 mm和0.25～0.5 mm粒径的土壤水稳性团聚体分别为农田对照的2.03～2.75倍、1.98～2.72倍、1.31～1.65倍和1.15～1.36倍;平均重量直径(MWD)、几何平均直径(GMD)在0～20 cm土层均表现为12 a>18 a>7 a>3 a>CK,变化范围分别为0.34～0.70和0.18～0.26;分形维数(D)变化虽然较小,但在0～20 cm土层也呈现出了不同年限苜蓿草地均小于农田的规律性,变化范围为2...     

黄土丘陵沟壑区退耕地人工林的土壤环境效应

根据延安、安塞和吴旗退耕20年以上人工林地、自然恢复草地和坡耕地的调查与分析资料,分析了人工林相对于坡耕地、自然恢复草地、次生林的土壤环境效应,包括土壤有机质的积累、土壤氮磷钾素的变化、土壤水分效应和水稳性团聚体的特征。结果表明:人工林可明显地提高土壤有机质、全氮、有效氮和速效钾的含量,特别是0~20cm土层,但这些土壤肥力指标仍处于低或中等水平;同时人工林地土壤的水稳性团聚体含量较高,增强了土壤的抗侵蚀能力;但人工林对土壤水分的消耗却远远大于坡耕地和自然恢复的草地,在安塞和吴旗表现得更为明显。综合分析结果和黄土丘陵沟壑区特殊的自然环境特征,认为在黄土高原丘陵沟壑区,退耕地的植被恢复宜采取先封禁牧,然后补种部分适宜的牧草、灌木和乔木,逐步实现良好的乔灌草植被结构特征和其生态环境功能。     

冻融对五台山典型林线植被土壤水稳性大团聚体的影响

以五台山林线附近3种典型植被(亚高山草甸CD、华北落叶松林HL和云杉×华北落叶松混交林YH)土壤为研究对象,采用土柱野外原位培养法,通过对各时期土壤水稳性大团聚体含量、平均重量直径(MWD)和几何平均直径(GMD)的测定与分析,研究季节性冻融对土壤水稳性大团聚体的影响。结果表明:培养期内,3种植被土壤5～10mm和2～5mm水稳性团聚体含量与其余粒级呈现相反的波动变化趋势。深冻期,CD土壤5～10mm水稳性团聚体含量显著减小(p<0.05),MWD显著减小(p<0.05);YH土壤2～5mm水稳性团聚体含量显著增加(p<0.05),GMD显著增加(p<0.05)。融化期,HL土壤2～5mm和1～2mm水稳性团聚体含量显著增加(p<0.05),MWD和GMD显著增加(p<0.05)。不同植被覆盖下土壤水稳性大团聚体含量的差异主要体现在CD土壤水稳性大团聚体含量与HL、YH差异显著(p<0.05)。因此,季节性冻融对3种植被土壤水稳性大团聚体都具有显著影响,而且3种植被覆盖下土壤团聚体水稳定性对季节性冻融的响应也明显不同,主要发生在深冻期和融化期。...     

渭北旱塬植被恢复对土壤有机质和水稳性团聚体含量的影响

植被恢复可改变土壤水稳性团聚体的形成及其对土壤有机质的保护。通过对渭北旱塬礼泉县北部不同土地利用类型下土壤水稳性壤团聚体和有机质含量的分析,探讨了两者之间的关系。结果表明：＞0.25 mm土壤水稳性团聚体百分含量,平均质量直径和土壤有机质（SOM）含量在林地和永久性荒地中较农地大,而农地土壤水稳性团聚体的分形维数较大。矩法参数（Cs）在农地和一年荒地中为负值,而在林地和永久性荒地为正值。土壤有机质与水稳性团聚体平均质量直径线性正相关,粒级小于0.25 mm的水稳性团聚体中有机质含量最小,随粒级的增加,有机质线性增加,表明存在于水稳性团聚体内部的有机质矿化程度降低,同时也表明有机质为水稳性大团聚体的形成提供了良好的物质基础。渭北旱塬植被恢复可提高土壤有机质和水稳性团聚体含量。     

退耕年限与方式对土壤团聚体稳定性及有机碳分布的影响

以黄土高原南部退耕还林年限6 a(FL06)和15 a(FL15)刺槐林地、退耕还草年限6 a(GL06)和15 a(GL15)紫花苜蓿草地为研究对象,以临近长期耕作坡耕地(CK)作为对照,采用湿筛法,分离出2 mm、1~2 mm、0.5~1 mm、0.25~0.5 mm和0.25 mm 5个粒级的水稳性团聚体,研究了退耕年限与方式对团聚体稳定性和不同粒径团聚体有机碳分布的影响。结果表明:在0~20 cm土层,退耕还林还草与未退耕相比能显著提高2 mm和1~2 mm粒径团聚体含量,显著减少0.25 mm粒径团聚体含量,其中对于2 mm和1~2 mm粒径团聚体在不同退耕年限与方式下含量表现为GL15GL06FL06FL15CK和GL15FL06GL06FL15CK;退耕还林和还草增加了两个土层的团聚体稳定性,GL15的平均重量直径(MWD)值和几何平均直径(GMD)值均最大,土壤结构最稳定,其次为GL06;不同退耕年限,2 mm粒径下退耕还林地和还草地、1~2 mm粒径下退耕还草地团聚体有机碳含量均随退耕年限的延长而增加。20~40 cm土层中,团聚体含量均值随粒径的减小而增加;MWD和GMD值均小于0~20 cm层;各粒径范围内退耕还林与还草后的团聚体有机碳含量与坡耕地相比总体表现出减小的趋势。研究结果表明,退耕改善了土壤结构,对各粒径团聚体有机碳含量分布的影响随退耕年限与方式不同效应各异,且GL15相较于其它退耕年限和方式下的样地有更好的土壤团聚体稳定性和更多的团聚体有机碳积累。     

无定河流域植被恢复对土壤团聚体及碳固定的影响

对无定河流域坡耕地和4、5、10、30、50年植被恢复样地土壤水稳性团聚体含量,全土样及不同直径水稳性团聚体中的有机质、速效磷含量进行了测定分析,计算了土壤有机碳密度,旨在评价植被恢复对土壤结构、养分及土壤固定的影响。结果表明:各样地全土样有机质和速效磷含量分别介于6.73~31.83 g·kg-1和1.93~14.72 mg·kg-1之间,不同直径团聚体有机质和速效磷含量分别介于7.15~26.03 g·kg-1和3.71~16.64 mg·kg-1之间。相对农地,植被恢复能明显增加表层土壤有机质含量和有机碳密度,杜梨群落增加幅度最高,增加值分别为24.93 g·kg-1和91.98 mg·cm-2;水稳性团聚体以0.05 mm和0.05~0.1 mm为主,含量分别在37.06%~57.22%和21.71%~29.76%之间;不同直径水稳性团聚体中有机质含量表现为2 mm至0.2~0.5 mm之间,直径愈小,有机质含量愈高,0.2~0.5 mm至0.05 mm之间,粒径愈小,有机质含量愈低;除1~2 mm团聚体中的速效磷含量最高外,2 mm至0.05 mm团聚体之间,粒径愈小,速效磷含量愈低。土壤有机碳密度与植被恢复年限呈线性正相关关系。相对于土壤碳固定,土壤抵抗水力侵蚀的能力需更长时间才能显著提高。相对慢速湿润,快速湿润条件下各直径水稳性团聚体有机质含量均较高。研究区大雨或暴雨是造成该区域土壤结构恶化和有机碳损耗的主要原因。     

土地利用方式对东祁连山土壤表层有机碳的影响

在祁连山东段高寒地区,选取天然草地、退耕自然恢复地、坡耕地和人工草地4种土地利用方式,研究了土地利用方式对土壤表层有机碳含量和有机碳密度的影响.结果表明:在4种土地利用方式中天然草地土壤表层有机碳含量最高,坡耕地和退耕自然恢复地土壤表层有机碳含量较低;土壤表层有机碳密度整体上随着土层加深而逐渐降低,在0～30cm土层土...     

秸秆还田与长期连作棉田土壤水稳性团聚体特征

以棉花长期连作定点试验田为研究对象,研究秸秆还田对长期棉花连作土壤水稳性团聚体及有机碳分布的影响。试验设长期连作5、10、20 a和30 a的秸秆还田小区及长期棉花连作5、10 a和20 a无秸秆还田小区,共计7个处理,每个处理3个重复。结果显示:无秸秆还田条件下,随着连作年限的增加,土壤1~0.25 mm水稳性团聚体含量和团聚体中有机碳含量逐渐降低,0.053 mm水稳性团聚体含量逐渐增加;而秸秆还田可以显著提高长期连作棉田土壤中1~0.25 mm水稳性团聚体含量、团聚体平均重量直径(MWD)、几何平均直径(GMD)值及团聚体中有机碳含量;秸秆还田条件下随着连作年限的增加,土壤1~0.25 mm水稳性团聚体含量逐渐增加,0.053mm水稳性团聚体含量逐渐降低,且对0~30 cm耕作层土壤影响较大;与无秸秆还田相比,秸秆还田长期连作棉田,随着连作年限的增加,团聚体分形维数(D)逐渐降低,而无秸秆还田分形维数(D)逐渐增加,团聚体分形维数表现为随土层加深而增大,最后在20~30 cm处趋于稳定。说明秸秆还田显著提高长期连作棉田水稳性团聚体的稳定性,对改善土壤结构、提升土壤的肥力具有积极作用,能够缓解长期连作对土壤物理性状产生的不利影响。     

基于LB法不同植被类型下土壤团聚体水稳性研究

土壤团聚体与土壤侵蚀和径流密切相关,本试验用Le Bissonnais法中的快速处理测定黄土丘陵区纸坊沟流域土壤水稳性团聚体含量,计算团聚体平均质量直径(MWD)、几何平均直径(GMD)和质量分形维数(D),比较几种水稳性团聚体指标之间的相关性,确定植被类型对土壤水稳性团聚体含量的影响。结果表明,大于0.2 mm的土壤团聚体含量在1978年油松林地的0~5 cm层最大,为54.95%,在1990年刺槐林地和荒地的20~40 cm层最小,为3.20%;MWD(mm)和GMD(mm)在1978年油松林地的0~5 cm层最大,分别为1.66和0.46,在荒地的20~40cm层最小,分别为0.09和0.05;表层(0~5 cm)土壤D在2.71~2.84之间,表下层在2.74~2.91之间。土壤有机质与D,MWD,GMD和0.2 mm显著相关,表明增加土壤有机质含量有利于土壤团聚体形成和水稳定性提高。D,MWD,GMD和0.2 mm都可用于表征土壤团聚体水稳定性,作为土壤抗侵蚀性指标。     

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

Soil organic matter content in water-stable aggregates(WSA) in the arid ecosystems(abandoned agricultural lands especially) of China is poorly understood. In this study, we examined the WSA sizes and stability, and soil organic carbon(OC) and nitrogen(N) contents in agricultural lands with abandonment ages of 0, 3, 12, 20, 30 and 40 years, respectively, in the Minqin Oasis of Northwest China. The total soil OC and N contents at depths of 0–20, 20–40 and 40–60 cm in abandoned agricultural lands were compared to those in cultivated land(the control). Agricultural land abandonment significantly(P0.05) influenced the distribution of MWD(mean weight diameter), and OC and N contents. There were significant increases in MWD and the proportion of macroaggregates(sizes 0.25 mm) as the age of agricultural land abandonment increased. The effect of abandonment ages of agricultural lands on MWD was determined by the changes of OC and N accumulation in WSA sizes 2 mm. The total OC and N contents presented a stratification phenomenon across soil depths in this arid ecosystem. That is, both of them decreased significantly at depths of 0–20 and 40–60 cm while increased at the depth of 20–40 cm. The WSA sizes 0.053 mm had the highest soil OC and N contents(accounting for 51.41%–55.59% and 42.61%–48.94% of their total, respectively). Soil OC and N contents in microaggregates(sizes 0.053–0.25 mm) were the dominant factors that influenced the variations of total OC and N contents in abandoned agricultural lands. The results of this study suggested that agricultural land abandonment may result in the recovery of WSA stability and the shifting of soil organic matter from the silt+clay(0.053 mm) and microaggregate fractions to the macroaggregate fractions. However, agricultural land abandonment did not increase total soil OC and N contents in the short-term.     

黄土坡面土壤性质随退耕时间的动态变化研究

退耕还林还草是控制水土流失和防治土壤退化的关键措施,黄土高原退耕还林还草从试验到推广已有几十年历史。该文通过对黄土高原地区退耕区的实地调查,测定不同地区不同退耕年限植被恢复区表层土壤的理化性质,分析黄土坡面土壤理化性质随退耕时间的动态变化规律。结果表明:随着退耕植被恢复时间的增长,土壤物理结构将日趋改善,土壤养分含量水平将逐渐的提高,并主要集中在植被恢复10~20年期间,20年后,尤其是30年后,土壤理化性质较为稳定,而且,植被维护的好坏往往影响其稳定性。同时,水热条件较好的安塞地区土壤理化性质随退耕时间的改善程度更明显,而水热条件较差的皇甫川流域土壤理化性质随植被类型和植被恢复程度的影响更为显著。结果可为退耕的环境影响评价预测以及土地利用的调控提供科学依据。     

Dynamics of ecosystem carbon stocks during vegetation restoration on the Loess Plateau of China

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil(0–100 cm), plant biomass and the ecosystem(plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation(natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0–100 cm. Moreover, there was a time lag of about 15–30 years between biomass production and soil carbon sequestration in 0–100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.     

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau,China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term(2004―2016) experimental data in the northern Loess Plateau region, China. Soil bulk density(BD), saturated soil hydraulic conductivity(Ks), field capacity(FC) and soil organic carbon(SOC) in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland(korshinsk peashrub), artificial grassland(alfalfa), fallow land and cropland(millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage(SWS) significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland(alfalfa) and shrubland(peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.     

黄土丘陵沟壑区植被自然恢复过程中土壤种子库特征

采用野外调查取样和室内实验相结合的方法,研究了黄土丘陵沟壑区植被自然恢复过程中土壤种子库的物种组成、密度、物种多样性以及相似性特征.结果表明:阴、阳坡10个样地中,共萌发了55种2203株幼苗,隶属于23科48属;总密度达到5 505±625.537粒/m2,且0～5 cm土层远远大于5～10 cm土层的土壤种子库密度,约是其4.6倍;丰富度、多样性、均匀度指数均未与恢复年限达到显著相关水平,但生态优势度随恢复年限的增加呈上升趋势,且阳坡上升的趋势比阴坡明显;组成成分相似性系数变化范围为0.0952～0.7143,恢复年限相距越大,其相似性越小,说明植被恢复演替的过程也是土壤种子库空间异质性加大的过程.     

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau,China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types(5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics(including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process(8–50 years).     

杨凌区浅层土壤水分与深层土壤水分的关系研究

通过测定陕西杨凌区不同灌水条件下冬小麦的土壤水分变化,研究了浅层土壤水分与深层土壤水分的关系。结果表明:土壤含水量随土层深度的加深,呈先上升,后下降,又上升的变化趋势。在自然降水或灌溉条件下,土壤水分的变化程度随土层深度的增加,呈剧烈—缓和—剧烈—缓和的趋势。表层20、30、40、50 cm各土层含水量分别与0~150 cm各土层含水量的相关性较好,并且土层相邻越近,其相关性越好,说明由表层土壤含水量来推算深层土壤含水量是可行的。基于Biswas土壤水分估算模式,由表层30~40 cm的含水量来推算0~100 cm各土层含水量的精度较高,由表层20 cm的含水量来推算100~150 cm各土层含水量的精度较高。总灌水量及灌水次数对含水量的影响,直接影响到估算模式参数的取值及估算精度。     

Spatio-temporal variations of soil water content and salinity around individual Tamarix ramosissima in a semi-arid saline region of the upper Yellow River,Northwest China

Ecological restoration by Tamarix plants on semi-arid saline lands affects the accumulation, distribution patterns and related mechanisms of soil water content and salinity. In this study, spatio-temporal variations of soil water content and salinity around natural individual Tamarix ramosissima Ledeb. were invetigated in a semi-arid saline region of the upper Yellow River, Northwest China. Specifically, soil water content, electrical conductivity(EC_e), sodium adsorption ratio(SAR_e), and salt ions(including Na~+, K~+, Ca~(2+), Mg~(2+) and SO_4~(2–)) were measured at different soil depths and at different distances from the trunk of T. ramosissima in May, July, and September 2016. The soil water content at the 20–80 cm depth was significantly lower in July and September than in May, indicating that T. ramosissima plants absorb a large amount of water through the roots during the growing period, leading to the decreasing of soil water content in the deep soil layer. At the 0–20 cm depth, there was a salt island effect around individual T. ramosissima, and the EC_e differed significantly inside and outside the canopy of T. ramosissima in May and July. Salt bioaccumulation and stemflow were two major contributing factors to this difference. The SAR_e at the 0–20 cm depth was significantly different inside and outside the canopy of T. ramosissima in the three sampling months. The values of SAR_e at the 60–80 cm depth in May and July were significantly higher than those at the 0–60 cm depth and higher than that at the corresponding depth in September. The distribution of Na~+ in the soil was similar to that of the SAR_e, while the concentrations of K~+, Ca~(2+), and Mg~(2+) showed significant differences among the sampling months and soil depths. Both season and soil depth had highly significant effects on soil water content, EC_e and SAR_e, whereas distance from the trunk of T. ramosissima only significantly affected EC_e. Based on these results, we recommend co-planting of shallow-rooted salt-tolerant species near the Tamarix plants and avoiding planting herbaceous plants inside the canopy of T. ramosissima for afforestation in this semi-arid saline region. The results of this study may provide a reference for appropriate restoration in the semi-arid saline regions of the upper Yellow River.