Quantification and correlation of vesicular-arbuscular mycorrhizal propagules with soil properties of some mollisols of northern India

The populations of vesicular-arbuscular mycorrhizae (VAM) propagules by the most probable number method in some mollisols and their correlations with some important soil properties were determined. On average, the six soils, Phoolbagh clay loam, Beni silty clay loam, Haldi loam, Nagla loam, Khamia sandy loam and Patherchatta sandy loam contained 4.9, 4.0, 7.9, 7.9, 3.3 and 13.0 propagules/g soil, respectively, i.e. none of the soils was found to be high in VAM. The size of the VAM population was compared to soil properties such as pH, organic carbon, sand content, available phosphorus and available potassium, cation-exchange capacity, silt and clay contents. A significant positive correlation (r=0.586) was only found with available soil phosphorus (P<0.05) and a significant negative correlation (r=-0.555) with soil clay content (P<0.05).Directorate research paper series No. 7862     

Local environmental correlates of variability in the organic soils of moorland and alpine vegetation,Mt Sprent,Tasmania

Abstract Data on soils, vegetation and environment were collected between 510 and 1050m a. s. l. on Mt Sprent, southwestern Tasmania, traversing the Gymnoschoenus sphaerocephalus sedgeland-alpine vegetation boundary. One or more of the following horizons were found in almost all soil pits (downwards from the surface to the bed rock) fibric peat, hemic peat, sapric peat, organic sand, sand and clay. Mean total soil depth, mean organic soil depth, mean humification of the soil surface horizon, pH and mean organic content of the surface horizon all decline with altitude, while the redness of the soil and the mean depth of the mineral and gravel layers increase. At four intensively studied sites at 620, 850, 930 and 1040 m the relationships between phytosociological, topographic and water-table variables, and soil characteristics were determined. The pH of the topsoil was significantly positively related to water-table depth at three sites, but there were no other relationships between local environmental variation and soil characteristics that were consistent between most of the four sites, despite a large number of locally significant relationships. The alpine and sedgeland soils differ most markedly in colour, number of horizons and degree of humification of the surface horizon. The vegetation at each site was separated into communities along a drainage gradient. The mesoscale differences in soils seem most likely to be attributable to a vegetation productivity gradient.     

不同母岩发育土壤的可氧化态有机碳

采用KMnO4氧化法测定了8种不同母岩发育形成的土壤的可氧化态有机碳含量,结果表明,发育母岩不同,土壤可氧化态有机碳含量显著不同。通过对土壤养分、土壤颗粒组成、容重与可氧化态有机碳含量的相关性分析表明,土壤可氧化态有机碳与土壤的速效磷、全氮、速效钾、砂粒、粉粒的含量存在着极显著负相关关系;与土壤容重存在着极显著的正相关关系;与土壤的有机质、碱解氮、粗砂、细砂、粘粒、pH值、石砾含量无相关关系。     

Determining the important environmental variables controlling plant species community composition in mesotrophic grasslands in Great Britain

Question: What is the relative importance of local site effects and selected important environmental variables in determining plant species composition? How do species respond to these environmental variables? Location: Ten mesotrophic grassland sites of high conservation value in southern England. Methods: Species cover was assessed in between 10 and 25 randomly selected 1‐m² quadrats at each site. At each quadrat degree of waterlogging (W), soil Olsen extractable phosphorus (P) and soil pH were measured. Variation partitioning was used to separate site and soil effects, and HOF (Huisman, Olff & Fresco) modelling was used to produce response curves for the major species on soil gradients, based on coenoclines derived from partial canonical correspondence analysis (pCCA). Results: Variation partitioning identified Site as the most important environmental variable (34.6%). Only 18.7% was accounted for by the three soil variables together; W (degree of waterlogging), P and pH accounted for 11.1%, 5.7% and 4.3%, respectively in raw form with 2.4% shared. However, when Site and the other soil variables were removed the variation explained reduced to 2.3% for W, 1.1% for P and 1.0% for pH. The species responses to each of these soil environmental factors could be separated into four types on each gradient. Most species were abundant at low W, low soil P and intermediate pH. Conclusions: Site‐based factors were more important than the three soil variables, which were assumed to be directly or indirectly associated with productivity. This implies that each site has unique properties that are more important than the soil variables. The three soil factors were, however, significant and the groups of the most common species, based on significant response curves, can be used as a first approximation of indicators of environmental conditions in British mesotrophic grasslands for conservation. However, W accounted for most variation, and the current reliance on soil available P and soil pH for assessing conservation/restoration potential should be viewed with caution.     

长白山苔原草本植物入侵与土壤环境的关系

在对长白山高山苔原西坡样带内132个样方进行植被调查和土壤取样分析的基础上,应用冗余分析(RDA)和典型相关分析方法,探讨了草本植物入侵苔原带程度与苔原土理化性质及环境之间的关系。研究表明,长白山苔原带西坡草本入侵程度区域差异明显,可分为5个不同的入侵等级;海拔、坡度、全钾含量、粘粒含量、有机质含量等10种土壤环境因子与草本植物入侵程度明显相关。RDA分析表明土壤环境因子能解释93%的植物物种多度信息,影响草本植物入侵的主要土壤因子是有机质含量,粘粒含量和坡度;第一对典型变量说明有机质含量与牛皮杜鹃多度正相关,与大白花地榆多度负相关,粘粒含量则相反;第二对典型变量说明海拔、速效氮含量与笃斯越桔、长白老鹳草多度呈负相关。长白山苔原带西坡草本植物在空间分布上是离散的,呈斑块状。可见,草本植物入侵,对生境是有所选择的。土壤有机质含量与灌木多度呈正相关,说明在草本入侵过程中,土壤有机质含量会减少;或者有机质含量减少的地方,灌木生长退化,草本由此开始侵入定植。     

Effects of area,environmental status and environmental variation on species richness per unit area in Mediterranean wetlands

Abstract. We propose a mechanistic model to relate α- and γ-diversity to area per se, moisture status and environmental variation (local and total), and explored the effects these abiotic variables have on species richness per unit area (α-diversity) for plant communities in a network of wetland habitats located in a Mediterranean mountainous region of central Spain. In this study, environmental status is measured as actual evapotranspiration (as an expression of energy), slope and soil wetness, and environmental variation refers to slope variation and soil wetness variation. Species richness per unit area was related to soil wetness, soil wetness variation, ground slope and ground slope variation. There were also positive correlations among moisture status and environmental variation variables. There is a joint effect of slope and soil wetness variation in explaining species richness per unit area of these wetland habitats, but area effects and energy are relatively unimportant. We conclude that species richness per unit area of wetland vegetation can be explained by moisture status and local environmental variation, and that habitat area may not have an important effect. Area could affect γ-diversity directly through random sampling and/or indirectly through increasing β-diversity, and energy may be important in areas with larger energy ranges. Complete surveys of environmental status, local and total environmental variation, and their associated species assemblages are needed to explain the processes that give rise to the rule that larger areas have larger species richness.     

Study on optimization of moisture retention for golf green rootzone soil mixtures

Most golf course green have been constructed with pure sand or sand-based rootzone mixes. As we know, high sand content provides rapid drainage despite sand’s inefficiency in retaining moisture. However, drainage capability and water retention are both essential elements to the golf course green, and the addition of peat could increase the soil moisture retention, therefore, the research on the drainage capability and water retention of the sandy golf green has become more and more important these years. In this study, extreme vertex design was applied which is one of the mixture experiment designs widely used in mixture experiments, the study investigated the effects of the thirteen different rootzone soil mixtures using middle-coarse, fine sand, very fine sand plus silt and clay as well as peat as the materials under three kinds of golf green profile (1-layer profile, 2-layer profile, 3-layer profile) conditions on the water retention of green rootzone. Through the qualitative, quantitative and optimization analysis of water retention capability of the sandy golf green, evidence a basis for choice of green profiles and rootzone matrix could be provided. And the significantly correlative regression model was established between the moisture retention and components of rootzone soil mixture. In addition, the order of factor contribution ratio, effect of single and double factor and optimization of the model were analyzed in detail. The results were as follows: both green profile and soil mixture, which had interaction of each other, had significant effects on soil moisture retention. Additional attributes include high porosity and greater water holding capacity than sand, and the higher content of peat, fine sand plus silt and clay, the better water retention. The mixtures had much higher water content in 1-layer profile than that in the other two profiles. There was significantly higher water content in 2-layer profile for pure sand mixtures (A–E) and low peat mixture (F) than that in 3-layer profile, while there was no higher water content for other 7 high peat mixtures (G–M) (>5%) in 2-layer than that in 3-layer profiles. The significance of key factors in rootzone soil mixture on moisture retention were: very fine sand plus silt and clay > peat > middle-coarse > fine sand. According to the moisture retention 15–25% specification of USGA (United States Golf Association), the optimal soil mixture in 1-layer profile was: middle-coarse 71.4–73.5%; fine sand 17.8–21.5%; very fine sand plus silt and clay 6.8–8.4%; peat 0–1%. The optimal soil mixture in 2-layer profile was: middle-coarse 65.0–73.4%; fine sand 17.8–20.5%; very fine sand plus silt and clay 7.5–8.9%; peat 0.2–6.3%. The optimal soil mixture in 3-layer profile was: middle-coarse 62.3– 73.9%; fine sand 17.7–21.4%; very fine sand plus silt and clay 7.3–10.7%; peat 0–6.3%. These optimal recipes took through the limitation of previous research, which were practically important to golf green soil selection and profile design. Thus, both proportion and interaction should be considered when we choose the soil mixture.     

亚热带稻田弃耕湿地土壤因子对植物群落结构的影响

采用冗余分析法对弃耕一年稻田湿地生态系统的植物群落与土壤因子进行了分析.结果表明：在亚热带湿地生态系统中,土壤水分条件、有效钾、有效磷和pH是影响物种分布的最主要土壤因子.试验区的主要植物物种可以划分为3个物种组:丁香蓼-水竹叶物种组(组1)、牛鞭草-圆叶节节菜-稻槎菜物种组(组2)和小白酒草-辣蓼-双穗雀稗物种组(组3).其中,组1主要分布于土壤有效钾含量较高的区域;组2主要分布于阶段性淹水区域;组3主要分布于排水区域,且与土壤有效磷和pH呈正相关.物种多样性与土壤pH、植被地上生物量与土壤全钾含量呈显著正相关,均匀度与土壤有效氮含量呈显著负相关,与其他指标的相关性均不显著.     

Spatial variability of soil nutrients and microbiological properties after the establishment of leguminous shrub Caragana microphylla Lam. plantation on sand dune in the Horqin Sandy Land of Northeast China

The objective of this study is to determine the spatial variability of nutrients, microbial biomass, and enzyme activities of soil due to the establishment of shrub plantation on moving sandy dunes, as part of an effort to understand the microenvironmental factors that control the soil microbiological properties. Caragana microphylla Lam., an indigenous leguminous shrub, is the dominant plant species used to control desertification in the semi-arid Horqin Sandy Land of Northeast China. In a 26-year-old C. microphylla plantation, soil samples were collected from three soil depths (0-5 cm, 5-10 cm, and 10-20 cm), three slope positions (windward slope, top slope, and leeward slope), and two microsites (under shrubs and between shrubs). The results showed significant differences in soil EC, nutrient content (except for total K), microbial biomass C and N, and the activities of dehydrogenase, urease, and protease at different slopes, soil depths, and microsites. Significant differences in pH at different microsites and slopes, soil moisture and polyphenol oxidase activity at different soil depths and slopes, and activities of phosphomonoesterase and nitrate reductase at different soil depths were also observed. The soil nutrient contents and microbiological activities were greater in the surface soil layer and decreased with the increase of soil depth. Soil organic C, total N, total P, available P and K, microbial biomass C and N, and the activities of enzymes tested (except for protease) under shrubs were higher than those in between shrubs. Furthermore, significant correlations among soil organic C, microbial biomass C and N, the activities of phosphomonoesterase, dehydrogenase, urease, protease, and nitrate reductase were observed, and correlations were also found among EC, total N, total P, available P and K, enzyme (except for polyphenol oxidase) activities, and microbial biomass C and N contents. These results suggest that microenvironmental factors (slope, soil depth and microsite) have significant influences on the spatial distribution of soil nutrients and microbiological properties when the C. microphylla sand-fixing plantation is established in the moving sand dunes in the Horqin Sandy Land.     

黔中喀斯特坡地浅层裂隙土壤机械组成对降雨的响应

运用野外取样调查结合室内吸管法,分析黔中喀斯特坡地不同土地利用类型浅层裂隙土壤机械组成随降雨的变化特征,以期为该区地下土壤漏失研究提供理论依据和技术支撑.结果表明: 黔中喀斯特坡地浅层裂隙土壤粒径含量总体以粉粒为主,约占57％.在不同降雨量的作用下,坡耕地裂隙土壤颗粒含量变化整体表现为细砂粒含量的减少和粉粒、黏粒含量的增大.草地裂隙土壤颗粒的变化主要是细砂粒含量的减少和黏粒含量的增加.乔木林地和灌木林地裂隙土壤颗粒的变化不规律.降雨量与土壤砂粒含量变化之间存在正相关关系.随着土层深度的增加,各土地利用类型的裂隙对粉粒和极粗砂粒含量的变化有一定影响,其中,粉粒含量随土层深度的增加而减少.     

Soil and forest structure in the Colombian Amazon

Forests structural differences could result of environmental variations at different scales. Because soils are an important component of plant's environment, it is possible that edaphic and structural variables are associated and that, in consequence, spatial autocorrelation occurs. This paper aims to answer two questions: (1) are structural and edaphic variables associated at local scale in a terra firme forest of Colombian Amazonia? and (2) are these variables regionalized at the scale of work? To answer these questions we analyzed the data of a 6ha plot established in a terra firme forest of the Amacayacu National Park. Structural variables included basal area and density of large trees (diameter > or = 10cm) (Gdos and Ndos), basal area and density of understory individuals (diameter < 10cm) (Gsot and Nsot) and number of species of large trees (sp). Edaphic variables included were pH, organic matter, P, Mg, Ca, K, Al, sand, silt and clay. Structural and edaphic variables were reduced through a principal component analysis (PCA); then, the association between edaphic and structural components from PCA was evaluated by multiple regressions. The existence of regionalization of these variables was studied through isotropic variograms, and autocorrelated variables were spatially mapped. PCA found two significant components for structure, corresponding to the structure of large trees (G, Gdos, Ndos and sp) and of small trees (N, Nsot and Gsot), which explained 43.9% and 36.2% of total variance, respectively. Four components were identified for edaphic variables, which globally explained 81.9% of total variance and basically represent drainage and soil fertility. Regression analyses were significant (p < 0.05) and showed that the structure of both large and small trees is associated with greater sand contents and low soil fertility, though they explained a low proportion of total variability (R2 was 4.9% and 16.5% for the structure of large trees and small tress, respectively). Variables with spatial autocorrelation were the structure of small trees, Al, silt, and sand. Among them, Nsot and sand content showed similar patterns of spatial distribution inside the plot.     

Distribution of entomopathogenic nematodes in Southern Cameroon

A first survey of entomopathogenic nematodes (EPN) was conducted in three agro-ecological zones of Southern Cameroon in 2007 and 2008. Entomopathogenic nematodes were recovered from 26 of 251 soil samples (10.4%). Three species, Heterorhabditis baujardi, Steinernema sp. A and Steinernema sp. B were found. The two steinernematids were considered unidentified species. Among the positive samples, 23 samples contained only H. baujardi (88.5%), two contained Steinernema sp. A co-occurring with H. baujardi (7.7%), and one sample contained Steinernema sp. B (3.9%). H. baujardi was frequent in forest and fruit crop (cocoa and oil palm plantations). Steinernema sp. A was found in a tree plantation of teak, Steinernema sp. B in a forest habitat. Nematodes were mostly present in acidic soils with pH ranging from 3.7 to 7.0. The highest EPN presence was recorded in sandy loam, sandy clay loam, sandy clay and clay soils. EPNs were not recovered in sand, loamy sand and clay loam soils. Using principal component analysis for elucidating the major variation patterns among sampling sites, four factors explaining for 73.64% of the overall variance were extracted. Factors were a combination of geographical (latitude, longitude, altitude), soil (pH, contents of sand, silt and clay, organic carbon, texture), and moisture (wilting point, field capacity) parameters as well as climatic parameters (mean annual rainfall, mean air temperature). Logistic regression and redundancy analyses (RDA) revealed that soil pH, longitude, available water and altitude were associated with presence and absence of EPN. Both logistic regression and RDA indicated that, increasing soil pH and longitude, associated with decreasing altitude, led to higher percentages of samples containing entomopathogenic nematodes.     

桂西北喀斯特峰丛洼地土壤物理性质的时空分异及成因

运用经典统计方法,以桂西北喀斯特峰丛洼地4个植被演替阶段(草地、灌木林、次生林、原生林)土壤表层(0～15 cm)和剖面为研究对象,采用冗余分析(RDA)方法分析土壤物理性质的时空分异成因.结果表明： 灌木林和原生林表土的粘粒(＜0.002 mm)和粉粒(0.002～0.05 mm)含量分别与其他3个演替阶段有显著差异;草地与次生林之间各粒级颗粒含量差异不显著;各演替阶段土壤砂粒(0.05～2.0 mm)含量均无显著差异;草地的容重与其他3个演替阶段差异极显著.草地粘粒含量随坡位升高而增加,其他植被类型为中坡位粘粒含量最高,且同一植被类型下不同坡位之间差异不显著.原生林0～30 cm土壤各层次间的粘粒含量变化幅度(14.55%)大于草地(7.12%)、灌木林(11.24%)和次生林(13.77%),人类干扰对表层土壤颗粒组成有很大影响.土壤物理性质主要受土壤有机碳和各演替阶段植被类型的影响,其中砂粒含量受裸岩率的影响较大.     

Acidification of sandy grasslands – consequences for plant diversity

Questions: (1) Does soil acidification in calcareous sandy grasslands lead to loss of plant diversity? (2) What is the relationship between the soil content of lime and the plant availability of mineral nitrogen (N) and phosphorus (P) in sandy grasslands? Location: Sandy glaciofluvial deposits in south‐eastern Sweden covered by xeric sand calcareous grasslands (EU habitat directive 6120). Methods: Soil and vegetation were investigated in most of the xeric sand calcareous grasslands in the Scania region (136 sample plots distributed over four or five major areas and about 25 different sites). Environmental variables were recorded at each plot, and soil samples were analysed for exchangeable P and N, as well as limestone content and pH. Data were analysed with regression analysis and canonical correspondence analysis. Results: Plant species richness was highest on weakly acid to slightly alkaline soil; a number of nationally red‐listed species showed a similar pattern. Plant species diversity and number of red‐listed species increased with slope. Where the topsoil had been acidified, limestone was rarely present above a depth of 30 cm. The presence of limestone restricts the availability of soil P, placing a major constraint on primary productivity in sandy soils. Conclusions: Acidification of sandy grasslands leads to reduced abundance of desirable species, although the overall effect is rather weak between pH 5 and pH 9. Slopes are important for high diversity in sandy grasslands. Calcareous soils cannot be restored through shallow ploughing, but deep perturbation could increase the limestone content of the topsoil and favour of target species.     

Effects of climate on soil phosphorus cycle and availability in natural terrestrial ecosystems

Climate is predicted to change over the 21st century. However, little is known about how climate change can affect soil phosphorus (P) cycle and availability in global terrestrial ecosystems, where P is a key limiting nutrient. With a global database of Hedley P fractions and key‐associated physiochemical properties of 760 (seminatural) natural soils compiled from 96 published studies, this study evaluated how climate pattern affected soil P cycle and availability in global terrestrial ecosystems. Overall, soil available P, indexed by Hedley labile inorganic P fraction, significantly decreased with increasing mean annual temperature (MAT) and precipitation (MAP). Hypothesis‐oriented path model analysis suggests that MAT negatively affected soil available P mainly by decreasing soil organic P and primary mineral P and increasing soil sand content. MAP negatively affected soil available P both directly and indirectly through decreasing soil primary mineral P; however, these negative effects were offset by the positive effects of MAP on soil organic P and fine soil particles, resulting in a relatively minor total MAP effect on soil available P. As aridity degree was mainly determined by MAP, aridity also had a relatively minor total effect on soil available P. These global patterns generally hold true irrespective of soil depth (≤10 cm or >10 cm) or site aridity index (≤1.0 or >1.0), and were also true for the low‐sand (≤50%) soils. In contrast, available P of the high‐sand (>50%) soils was positively affected by MAT and aridity and negatively affected by MAP. Our results suggest that temperature and precipitation have contrasting effects on soil P availability and can interact with soil particle size to control soil P availability.     

Pyrosequencing Reveals Contrasting Soil Bacterial Diversity and Community Structure of Two Main Winter Wheat Cropping Systems in China

Microbes are key components of the soil environment, playing an important role in maintaining soil health, sustainability, and productivity. The composition and structure of soil bacterial communities were examined in winter wheat–rice (WR) and winter wheat–maize (WM) cropping systems derived from five locations in the Low-Middle Yangtze River plain and the Huang-Huai-Hai plain by pyrosequencing of the 16S ribosomal RNA gene amplicons. A total of 102,367 high quality sequences were used for multivariate statistical analysis and to test for correlation between community structure and environmental variables such as crop rotations, soil properties, and locations. The most abundant phyla across all soil samples were Proteobacteria, Acidobacteria, and Bacteroidetes. Similar patterns of bacterial diversity and community structure were observed within the same cropping systems, and a higher relative abundance of anaerobic bacteria was found in WR compared to WM cropping systems. Variance partitioning analysis revealed complex relationships between bacterial community and environmental variables. The effect of crop rotations was low but significant, and interactions among soil properties, locations, and crop rotations accounted for most of the explained variation in the structure of bacterial communities. Soil properties such as pH, available P, and available K showed higher correlations (positive or negative) with the majority of the abundant taxa. Bacterial diversity (the Shannon index) and richness (Chao1 and ACE) were higher under WR than WM cropping systems.     

Soil Properties and their Spatial Pattern in a Degraded Sandy Grassland under Post-grazing Restoration, Inner Mongolia, Northern China

In this study, we use classical and geostatistical methods to identify characteristics of some selected soil properties including soil particle size distribution, soil organic carbon, total nitrogen, pH and electrical conductivity and their spatial variation in a 5-year recovery degraded sandy grassland after two different grazing intensity disturbance: post-heavy-grazing restoration grassland (HGR) and post-moderately grazing restoration grassland (MGR), respectively, in Horqin steppe, Inner Mongolia, northern China. The objective was to examine effect of grazing intensity on spatial heterogeneity of soil properties. One hundred soil samples were taken from the soil layer 0–15 cm in depth of a grid of 10 m×10 m under each treatment. The results showed that soil fine fractions (very fine sand, 0.1–0.05 mm and silt + clay, <0.05 mm), soil organic carbon and total nitrogen concentrations were significant lower and their coefficients of variation significant higher under the HGR than under the MGR. Geostatistical analysis of soil heterogeneity revealed that soil particle size fractions, organic carbon and total nitrogen showed different degree of spatial dependence with exponential or spherical semivariograms on the scale measured under HGR and MGR. The spatial structured variance account for a large proportion of the sample variance in HGR plot ranging from 88% to 97% for soil particle fractions, organic C and total N, however, except for organic C (88.8%), the structured variance only account for 50% of the sample variance for soil particle fractions and total N in the MGR plot. The ranges of spatial autocorrelation for coarse-fine sand, very fine sand, silt + clay, organic C and total N were 13.7 m, 15.8 m, 15.2 m, 22.2 m and 21.9 m in HGR plot, respectively, and was smaller than in MGR plot with the corresponding distance of 350 m, 144.6 m, 45.7 m, 27.3 m and 30.3 m, respectively. This suggested that overgrazing resulted in an increase in soil heterogeneity. Soil organic C and total N were associated closely with soil particle fractions, and the kriging-interpolated maps showed that the spatial distribution of soil organic C and total N corresponded to the distribution patterns of soil particle fractions, indicating that high degree of spatial heterogeneity in soil properties was linked to the distribution of vegetative and bare sand patches. The results suggested that the degree of soil heterogeneity at field scale can be used as an index for indicating the extent of grassland desertification. Also, the changes in soil heterogeneity may in turn influence vegetative succession and restoration process of degraded sandy grassland ecosystem.     

宁夏荒漠草原沙漠化过程中土壤粒径分形特征

研究宁夏荒漠草原沙漠化过程中土壤性状、土壤粒径分形维数的变化特征,以及分形维数与土壤性状的关系.结果表明: 草地沙漠化对土壤分形维数(D)影响显著,D值为1.69～2.62.除在10～20 cm土层出现较小波动外,随着沙漠化程度加剧,0～30 cm土层D值整体呈减小趋势.在荒漠草原沙漠化过程中,荒漠草地D值最大,黏粒和粉粒体积百分含量最高,极细砂粒和细砂粒体积百分含量最低;流动沙地D值最小,黏粒和粉粒体积百分含量最小,极细砂粒和细砂粒体积百分含量最高.D与<50 μm和>50 μm粒径的土壤颗粒存在显著正相关和负相关,表明50 μm粒径是决定草地沙漠化过程中土壤分形维数与土壤粒径关系的临界粒径.随着荒漠草原沙漠化加剧,土壤有机质和全氮含量逐渐降低,土壤容重逐渐升高,固定沙地至半固定沙地是荒漠草原沙漠化的质变过程,其中土壤粘粒体积百分含量、粉粒体积百分含量、土壤有机质含量、土壤全氮含量骤减,极细砂粒体积百分含量、细砂粒体积百分含量和土壤容重骤增.分形维数与土壤有机质、土壤全氮和土壤容重显著相关,固定沙地与半固定沙地分形维数的临界值为2.58,因此分形维数2.58可作为荒漠草原沙漠化的退化指标.     

黄土塬区不同地形部位和土地利用方式对土壤物理性质的影响

在黄土塬区王东沟流域采集不同地形部位和不同土地利用方式下土壤样品,测定其颗粒组成、容重和饱和导水率,借助变异系数、非参数检验等方法研究了不同地形部位和不同利用方式对土壤物理性质的影响.结果表明：土壤物理性质在水平方向和沿垂直剖面都存在变异,但在同一地形部位或同一土地利用类型内,容重和颗粒组成基本相似.水平方向,饱和导水率属强变异,粘粒和砂粒含量属中等变异,粉粒含量和容重属弱变异;沿垂直剖面,土壤的粒级分布具有连续性,但0～25 cm的土壤容重和饱和导水率与下层土壤差异显著.沿坡面从上向下,土壤趋向粘重,但饱和导水率增大;其中上坡位和中坡位的土壤性质相似,在相关研究中可以进行合并.草地与其他利用方式下的土壤性质差异显著,主要受地形部位的影响;耕地和果园的土壤性质相似且不同于其他利用类型,表明人为干扰对土壤物理性质有重要影响.     

石灰性土壤微生物量碳、氮与土壤颗粒组成和氮矿化势的关系

以黄土高原土壤类型和土壤肥力差异较大的25个农田石灰性耕层土壤为供试土样,研究了土壤微生物量碳（BC）、微生物量氮（BN）与土壤氮素矿化势（NO）、全氮（TN）、有机碳（OC）及土壤颗粒组成的关系．结果表明：BC、BN与TN、OC呈极显著正相关（P〈0．01）,表明BC、BN与土壤肥力关系密切,可作为评价土壤质量的生物学指标．BC、BN与NO均呈高度正相关,相关系数分别为0．665和0．741（P〈0．01）．BC、BN、TN、OC、NO与土壤物理性粘粒（〈0．01mm）呈显著或极显著正相关,而与物理性砂粒（〉0．01mm）呈显著或极显著负相关,与物理性粘粒和砂粒比值呈显著或极显著正相关,表明土壤有机质主要通过与土壤物理性粘粒复合而形成有机无机复合体．