Earthworm invasion alters enchytraeid community composition and individual biomass in northern hardwood forests of North America

European earthworms are invading many ecosystems worldwide and fundamentally transform habitats by acting as dominant ecosystem engineers. However, there is little knowledge of the consequences of earthworm invasion on the composition and diversity of native soil organisms. Particularly functionally similar groups, such as enchytraeids (Annelida: Enchytraeidae), may be affected through changes in the chemical and physical properties of the soil, but also due to competition for resources. In 2010–2011, we studied the impact of earthworm invasion on enchytraeids at two sites in the northern hardwood forests of North America: one site within the Chippewa National Forest in northern Minnesota and one site in the Chequamegon-Nicolet National Forest in northern Wisconsin, USA. At each site, three plots were sampled along a transect, representing (1) a non-invaded or very slightly invaded area, (2) the leading edge of earthworm invasion and (3) a heavily invaded area with an established population of the anecic earthworm Lumbricus terrestris (among other species). In total, 29 enchytraeid (morpho)species were identified (some yet to be formally described, several first or second records for the continent); of those 24 occurred at the Minnesota site and 17 at the Wisconsin site. The structure of enchytraeid assemblages differed significantly among the three invasion stages, although this was not equally pronounced at the two sites. Each stage was characterized by one or several indicator species. Mean enchytraeid densities (10,700–30,400 individuals/m²) did not differ significantly among the invasion stages, but were lowest at the leading edge of earthworm invasion at both sites. In the heavily invaded plot at the Minnesota site, the mean enchytraeid density and biomass in L. terrestris middens were significantly higher than in soil in-between the middens. This was due to a pronounced effect of L. terrestris middens in the uppermost 3 cm of soil. Differences in biomass among earthworm invasion stages were most apparent for mean individual biomass. This was significantly higher in the heavily invaded area than at the leading edge or in the non-invaded area at the Minnesota site. Compositional changes of the enchytraeid assemblage are likely to result in changes in the functioning of soil foods webs. Our results suggest that earthworm invasions can cause a loss of native species in soil, including heretofore unknown ones, that might go unnoticed.     

不同土地利用方式下的蚯蚓种群特征及其与土壤生物肥力的关系

采用样方法对华北平原(河北曲周)盐渍化改造区7种土地利用方式下的蚯蚓种群进行详细调查,并通过培养实验研究了蚯蚓种群特征对若干土壤生物学指标的影响。结果表明:(1)在7种土地利用调查样地中共存在蚯蚓有3个科,5个属,5个种,其中赤子爱胜蚓(Eisenia fetida)占调查样地总个体数的60%以上,梯形流蚓(Aporrectodea trapezoides)和赤子爱胜蚓两个种在本地区广泛分布,样点出现频率分别为74%和44%,为该地区的优势种;(2)不同土地利用方式的蚯蚓种群密度及生物量变化趋势是:庭院菜地>直立免耕>清茬免耕>商品菜地>传统玉米地>果园>原貌地。其中庭院菜地蚯蚓种群的平均密度和生物量分别达到272 Ind.m-2和68.04gm-2;(3)蚯蚓种群密度和物种数等种群特征与土壤基础呼吸强度、微生物生物量碳含量成显著正相关(p<0.01),与土壤基础呼吸商成显著负相关(p<0.01);(4)不同土地利用方式下,蚯蚓的种群密度、生物量等种群特征对土壤中微生物群落的影响作用显著。蚯蚓生物量越大、种群越丰富的土壤有机质、氮、磷、钾等有效成分越高,反之则相反。室内培养实验表明,随着蚯蚓个体数量增加土壤原生动物总丰度、微生物生物量碳、氮也存在升高的趋势,与用土壤生物学特性指标及土壤化学特性指标评价的结果基本一致。     

Earthworm density and biomass in relation to plant diversity and soil properties in a Palouse prairie remnant

Earthworms are important soil animals in grassland ecosystems and are considered to be important to soil quality. The overall impact of earthworms on soil properties and plant diversity, however, depends on earthworm species, functional group and the type of ecosystem. The primary purpose of this study was to document the relationship among earthworms, key soil properties and native and exotic plant diversity in the little studied, Palouse prairie grassland (Idaho, USA). A secondary objective was to determine the effectiveness of three methods commonly used to sample earthworms. A hillslope characterized by Palouse prairie vegetation, well-expressed, hummocky (mounded) topography and known to support both exotic and native earthworm species was selected for study. The hillslope was divided into three zones [annual-dominated (AD), mixed (MX) and perennial-dominated (PD)] based on characteristics of the inter-mound plant communities described in previous research. Total earthworm biomass in the MX zone (53.5 g m⁻²) was significantly greater than in the PD zone (14.7 g m⁻²) (P = 0.0384), but did not differ from the AD zone. Earthworm density ranged from 52 to 81.1 individuals m⁻² but was not significantly different across zones. Total C and N at 0 to 10 and 30 to 50 cm depths were significantly greater in the AD and PD zones as compared to the same depths in the MX zone. Soil textural class was silt loam within all zones and the soil silt fraction was positively correlated with total exotic earthworm density (R = 0.783, P = 0.0125) and biomass (R = 0.816, P = 0.0072). Native earthworms were only found in the zone with the greatest total and native plant diversity (PD). Total soil C and N were not correlated to earthworm density, but soil total C and N were significantly negatively correlated with exotic plant density, which indicates that invasive plants may be decreasing soil total C (R = −0.800) and N (R = −0.800). Calculated earthworm densities using data from the electroshocker were generally lower than those based on the hand-sorting method. Electroshocking, however, created lower disturbance and was the only method that resulted in the collection of the deep-burrowing, native species Driloleirus americanus.     

接种蚯蚓对加入不同植物残体土壤微生物特性的影响

通过室内试验,研究不同类型土壤和植物残体施用下接种蚯蚓对土壤微生物群落组成及活性的影响,为将蚯蚓引入农田及水土流失区提供理论依据。供试土壤为黏粒含量较低的灰潮土和黏粒含量较高的典型红壤,供试植物残体为高碳氮比的玉米秸秆和低碳氮比的三叶草,供试蚯蚓为体型较大的威廉腔环蚓(Metaphire guillelmi)。结果表明:接种蚯蚓对微生物量碳(MBC)无显著影响;不同土壤无论是否施用植物残体,接种蚯蚓均使土壤基础呼吸(BR)显著增大,尤其是不施用植物残体时;两种土壤中不施用植物残体和施用三叶草时,接种蚯蚓均使代谢熵(qCO2)增大,而施用玉米秸秆接种蚯蚓使qCO2有下降趋势。Biolog孔平均颜色变化(AWCD)在接种蚯蚓时均增大,基质利用丰富度(S)和多样性指数(H)也增大,且未施用秸秆时的变化较为明显;主成分分析(PCA)表明接种蚯蚓后土壤微生物群落组成与结构发生了明显变化。土壤微生物群落特性变化受蚯蚓、土壤及植物残体间交互作用的影响。     

地形及土壤多样性与耕地动态变化的相关分析

本文以河南豫北、豫中和豫南3个典型样区为研究对象,运用地统计学方法,从多样性、相关性角度定量分析了地形、土壤的多样性特征及其与耕地变化(2001年、2007年和2017年)面积的空间分布多样性特征的关系,以期为耕地资源动态变化的驱动力分析及合理利用提供新的研究角度。研究表明:1)豫北和豫中样区的地形构成组分多样性呈现出均匀性,豫南样区表现为相对单一性;各研究区的地形空间分布多样性为平原丘陵山地。2)豫南的土壤构成组分最为均匀且丰富,豫中的土壤构成组分相对单一;各研究区的典型土壤各异但总体上分布皆较均匀,各样区的土壤空间分布多样性的显著差异与地形条件密切相关。3)研究尺度影响地形、土壤空间分布多样性特征的表达, 3 km×3 km网格是相对适宜的研究尺度。4)地形和土壤的空间分布多样性指数与耕地变化面积空间分布都具有明显的相关性,其中地形中平原相关性较大,达0.95左右;各样区典型土壤如豫南的水稻土,豫中、豫北的褐土以及豫北的潮土的相关性更为明显,达0.9以上。综合来看,典型样区的地形、土壤因子的构成组分多样性及空间分布格局有显著差别;在不同网格尺度下,耕地的变化面积与地形、土壤因子的空间分布多样性指数密切相关。     

Soil fertility affected by land use history,relief position,and parent material under a tropical climate in NW-Vietnam

In Vietnam as much as half of the total land area is already degraded by soil erosion and nutrient depletion. In particular, degradation due to deforestation is increasingly affecting mountainous areas in north-western Vietnam. The necessity to safeguard the farmers' livelihoods requires sustainable resource management, which firstly requires a qualitative and quantitative evaluation of resources. The objectives of the present study were to (1) identify the dominant soil types and their vulnerability using elicitation of local soil knowledge, (2) characterise the physical and chemical properties of the soils and (3) link them to the relief position and land use in order to (4) initiate sustainable soil use based on recommendations deduced from objectives (1) to (3). These objectives were achieved also by the elicitation of local knowledge. The final aim of the study was to initiate sustainable soil use based on recommendations for sustainable land use scenarios. The Chieng Khoi commune in Son La province of northern Vietnam was chosen as representative for other erosion-prone Southeast Asian sloping areas. In a participatory approach, combining local and scientific knowledge, sixteen sites were selected, representative for distinct relief positions, parent material (sand stone and silt stone), land use history, and erosion hazard. Chemical (e.g. content of organic matter, nitrogen, cation exchange capacity, base saturation, and plant available phosphorous) and physical properties (e.g. air capacity, plant available water) were used to estimate soil fertility. The predominant reference soil groups in the study area are Alisols and Luvisols, with a high diversity in respect to soil fertility. These soils are locally named ‘red soil’ and ‘black soil’, respectively. Although the main physical processes are erosion and selective sedimentation, farmers tend to underestimate their impact and causes, whereas soil quality was well-evaluated. Soils with high fertility were found on less eroded upper parts of hills and at sites, where agricultural use started only recently. Once degraded by cultivation practices, soils derived from sandstone did not recover even after more than 50 years of fallow. As a result of unsustainable land use, soils on middle and lower slopes are often affected by severe soil erosion, whereas foot slope soils suffer from accumulation of eroded infertile subsoil material as well as stagnic conditions. This study showed that unsustainable land use at upslope landscape positions has a severe impact on downslope areas. The elicitation of local knowledge facilitated the identification of such hot spots, allowing the implementation of spatially targeted conservation measures.     

Earthworm activity and soil structure changes due to organic enrichments in vineyard systems

 The effect of organic enrichment on earthworm activity and soil structure was studied in two French vineyards, by comparing control and test plots. In each vineyard the organic matter quantitatively increased the abundance and biomass of the earthworm community. These increases were associated with a higher level of species diversity and a higher evenness corresponding to the development of endogeic community. These earthworm community changes were associated with an increase in granular bioturbated areas and in macroporosity in the top soil layer. The micromorphological approach incorporated an original process of image analysis which appeared to be an appropriate method for characterizing pore morphology in this study. The pores when characterized by their size and shape could be related to ecological groups and growth stages of earthworms. Received: 4 August 1997     

喀斯特坡地不同土地利用类型土壤水分差异性研究

对比分析桂西北喀斯特坡地5种土地利用类型0~20cm表层土壤含水量的差异,结果表明:喀斯特生境条件下坡地土壤含水量受降水的影响明显,雨季和旱季差异显著。各土地利用类型间,灌丛类型由于枯枝落叶层而增强了土壤的保水持水能力;生态恢复林(板栗、木豆)种植初期,土表接近于裸地,蒸发强烈,应采取一定的蓄水保墒措施;混种有匍匐类作物的复垦坡耕地,其土壤水分条件则与撂荒多年草地相似。比较土壤层间含水量的季节差异,灌丛类型土壤有明显的层间蓄水补水能力。喀斯特山地应通过建立合理的土地利用类型,改变地表覆被状况进而改善土壤水分条件,为生态重建服务。     

不同利用方式下红壤微生物生物量及代谢功能多样性的变化

研究了不同农林利用方式下红壤微生物生物量和代谢功能多样性等土壤质量指标的变化.结果表明:不同利用方式对土壤质量各指标造成了显著的影响;稻田的微生物生物量碳、氮最高,林地和草地微生物生物量次之,旱地的微生物生物量碳、氮最低(分别是稻田利用方式的4.3% 和 13.7%);稻田的微生物代谢功能多样性最高,旱地、林地和草地的细菌代谢功能多样性较低,旱地的真菌代谢功能多样性最低;微生物生物量和代谢功能多样性可以作为反映土壤质量变化的早期敏感的指标,用来衡量管理措施的改变对土壤质量造成的影响.     

A comparison of soil degradation under smallholder farming and large-scale irrigation land use in Kano State,Northern Nigeria

Changes in soil properties under two land use types: smallholder farms and large-scale irrigated agriculture were investigated over a period of 13 and 14 years respectively using the following parameters: particle size distribution, soil pH, exchangeable cations, cation exchange capacity, total organic carbon and nitrogen and total and available potassium and phosphorus. Results indicate that more adverse changes took place in soils under large-scale irrigation than in those under smallholder farms during the periods under consideration. Agricultural sustainability is more likely to be achieved for smallholder farms than for large-scale irrigation where soil degradation resulting from loss of fine soil particles through erosion can be a serious hindrance to long-term land use. In order to achieve agricultural sustainability in Kano State, it is recommended that chemical fertilizers be incorporated into the smallholder farming system, while the adoption of suitable soil conservation practices would make the large-scale irrigation systems more stable and sustainable.     

The influence of different types of urban land use on soil microbial biomass and functional diversity in Beijing,China

Soil microbes in urban ecosystems are affected by a variety of abiotic and biotic factors resulting from changes in land use. However, the influence of different types of land use on soil microbial properties and soil quality in urban areas remains largely unknown. Here, by comparing five types of land use: natural forest, park, agriculture, street green and roadside trees, we examined the effects of different land uses on soil microbial biomass and microbial functional diversity in Beijing, China. We found that soil properties varied with land uses in urban environments. Compared to natural forest, soil nutrients under the other four types of urban land use were markedly depleted, and accumulation of Cu, Zn, Pb and Cd was apparent. Importantly, under these four types of land use, there was less microbial biomass, but it had greater functional diversity, particularly in the roadside‐tree soils. Furthermore, there were significant correlations between the microbial characteristics and physicochemical properties, such as organic matter, total nitrogen and total phosphorus (P < 0.05), suggesting that lack of nutrients was the major reason for the decrease in microbial biomass. In addition, the larger C/N ratio, Ni concentration and pool of organic matter together with a higher pH contributed to the increase in microbial functional diversity in urban soils. We concluded that different land uses have indirect effects on soil microbial biomass and microbial community functional diversity through their influence on soil physicochemical properties, especially nutrient availability and heavy metal content.     

蚯蚓粪施用方式及用量对土壤入渗的影响

通过室内土柱模拟试验研究蚯蚓粪施用方式及施用量对土壤水分入渗过程的影响,试验设置了3种施用量(50 g·kg~(-1),75 g·kg~(-1),100 g·kg~(-1))和5种施用方式(0～10 cm混施、10～20 cm混施、5～8 cm层施、10～13 cm层施、15～18 cm层施),以裸土为对照,分别测定0～180 min的土壤累积入渗量、湿润锋深度以及入渗30 min后层施条件下不同土层的土壤含水率。结果表明:不同用量蚯蚓粪混施入0～10 cm土层后均可加快湿润锋迁移速率,但在10～20 cm混施方式下,75 g·kg~(-1)和100g·kg~(-1)用量会抑制湿润锋的下移;当蚯蚓粪以层施方式加入土壤时,75 g·kg~(-1)和100 g·kg~(-1)用量处理的湿润锋迁移速率明显减小,且湿润锋深度随施用量的增加而减小;10～20 cm混施蚯蚓粪处理的累积入渗量小于0～10 cm混施处理,而75 g·kg~(-1)和100 g·kg~(-1)蚯蚓粪施用于5～8 cm和10～13 cm深度时也可明显减小累积入渗量,但100 g·kg~(-1)蚯蚓粪层施时则对入渗过程无显著影响;用Kostiakov模型拟合土壤入渗过程得出,施加75 g·kg~(-1)和100 g·kg~(-1)蚯蚓粪均能够增加初始入渗率,10～13 cm和15～18 cm层施蚯蚓粪则对入渗率的减小具有延缓作用;层施50 g·kg~(-1)蚯蚓粪能够提高下层土壤含水量,但层施75 g·kg~(-1)和100 g·kg~(-1)蚯蚓粪则会使下层土壤含水量降低。     

Effects of two perennials, fallow and millet on distribution of phosphorous in soil and biomass on sloping loess land, China

Soil erosion causes sequential eco-environmental problems in the Loess Plateau of China. Therefore, vegetation restoration measures were adopted in this area by converting steep cropland into alternative land uses in order to remedy the erosion problem and alleviate land degradation. As part of the effort to understand the potential of this management practice in sequestering nutrients, the present study assessed the impact of vegetation restoration on the distribution of phosphorus (P) and aboveground biomass on a sloping land in this area. The study compared four land uses, Korshinsk Peashrub (KOP), alfalfa (ALF), natural fallow (NAF), and millet (MIL). KOP, ALF and NAF were adopted as vegetation restoration patterns, while MIL was an example of crop land. For the sampling time the average aboveground P pools of KOP, ALF, and MIL were 1.118, 0.406, and 0.091 g m^− 2, respectively. The magnitudes of the aboveground biomass and tissue P concentration of the three land uses followed the same order. Both vertical and horizontal distributions of soil Olsen P of KOP were relatively uniform. Soil Olsen P of ALF accumulated significantly at the down-slope position within the surface 60 cm soil profile. The down-slope accumulation of soil Olsen P was significant at the depth of 80 to 100 cm and 0 to 20 cm for NAF and MIL, respectively. The soil Olsen P concentrations in deeper soil layers of KOP and ALF were clearly lower than that of NAF, while MIL had apparent higher concentrations of soil Olsen P in the 0 to 20 cm layer of soil. Generally, the vegetation restoration did not present a significant effect on total soil P level, with the average values of 0.722, 0.751, 0.747, and 0.729 kg m^− 2 for KOP, ALF, NAF, and MIL, respectively. However, an apparent accumulation of total soil P at the down-slope position was observed for NAF and MIL treatments. For ALF and KOP, the soil Olsen P and the soil moisture content were correlated positively to the aboveground P pool. For MIL, however, the higher aboveground P corresponded to a higher soil Olsen P but to a lower soil moisture content. Results from the four years of data suggest that ALF is the fastest absorber of soil P, while KOP is the best vegetation to sequester soil P of the soil–plant systems in this study.     

Landscape position and soil redistribution under three soil types and land use practices in Prince Edward Island

Soil redistribution by erosive processes is a serious problem for the potato growing areas of Prince Edward Island. Studies were conducted to evaluate soil loss for three major soil types under two different cropping systems, at catenary sequences with five slope positions, using the ¹³⁷Cs tracer method. Adjacent forest catenas were sampled to provide baseline ¹³⁷Cs levels. Soil loss over time (1960–1990) on a specific mass (kg m⁻² yr⁻¹) basis was calculated by comparing the ¹³⁷Cs at the same slope positions for the cropping system and adjacent forest site. The effects of land clearing and long-term cultivation were to increase both the depth and density of the Ap horizon, and decrease the total ¹³⁷Cs on an area basis, in comparison to the forested sites. The average ¹³⁷Cs in the forested sites for all three soil types was 3133 Bq m⁻². Catena average soil loss across all soil types and slopes, for the 1960–1990 time period, was 21 and 38 Mg ha⁻¹ yr⁻¹ for the pasture and crop rotation (potato) rotations, respectively. Shoulder slope positions tended to have the highest ¹³⁷Cs loss, which was suggestive of tillage erosion.     

我国设施蔬菜产业概况与“十三五”发展重点——中国蔬菜协会副会长张真和访谈录

为了解设施蔬菜化肥减施技术领域的发展趋势,掌握该技术领域的最新研究热点。本文基于Web of Science (WOS)核心合集数据库,以“设施蔬菜化肥减施技术”为主题进行高级检索,选取2003 ~ 2022年发表的810篇文献,利用CiteSpace、VOSviewer、HistCite可视化分析软件,从年发文量、学科分布、发文期刊、发文国家、研究机构、研究学者、主要研究热点及其变化趋势等指标进行计量分析。结果表明：1）从2003 ~ 2022年,设施蔬菜化肥减施技术研究领域的文献数量整体呈上升趋势,所涉及的学科以环境科学为主,占文献总数的36.4%,发文量最多的学术期刊有Journal of Cleaner production、Science of the Total Environment等;2）中国、美国、德国在设施蔬菜化肥减施技术研究领域发表论文数量较多,并且国际合作密切,中国科学院、中国农业科学院、中国科学院大学、中国农业大学和南京农业大学是国内论文发表数量较多的研究机构,中国农业大学的陈清、林杉,卡尔斯鲁厄理工学院的Klaus Butterbach-Bahl,西南大学的陈新平是该领域较有影响力的研究学者;3）产量仍是设施蔬菜化肥减施技术研究领域一个重要关注点,未来研究趋势可能将集中于水分利用率及氮素管理等方面。综上所述,各国对设施蔬菜化肥减施技术研究已有大量基础,通过化肥减量增效技术的应用,提升水肥的利用率,提高设施蔬菜产量,推动农业可持续发展是未来的研究焦点。

     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

Fungal abundance and distribution as influenced by clearing and land use in a vertic soil of Argentina

The influence of native vegetation clearing and different further soil managements on fungal propagule population diversity was studied in the present work. In each of the 3 years (1998, 1999, and 2000), soil samples were collected at the depth of 0–7.5 cm from sites under native vegetation (V0); naturalized prairie, cleared in 1982 (P16); conventional tillage, cleared in 1972 (T26); and direct drilling, cleared in 1958 (D40). Fungal population size and relative abundance of fungal genera were studied by plate counts and further identification of isolates on potato dextrose agar. The undisturbed site and the other sites with increasing time elapsed since native vegetation clearing and different management history showed a distinctive distribution of fungal genera. There were significant differences (p<0.05) among the sites in the abundance of fungal genera analyzed in all the 3 years. Principal component analysis based on relative fungal genus abundance differentiated the sites with 75% variance explained by the first and second components. Diversity and abundance of isolated fungal genera were increased as density of Penicillium spp. decreased, suggesting a competitive effect of this fungal genus. The largest diversity was found in the site under no-till management. The different distribution and relative abundance of the fungal genera studied seemed to be influenced strongly by the management and the presence of surface residue in the no-tilled site.     

Adaptation of soil quality indices and application to three tillage systems in southern Illinois

Sustainability of agricultural management systems has become an issue of wide public concern and international debate. One result is that soil quality assessment has been suggested as a tool for evaluating sustainability of soil and crop management practices. Our objective was to adapt a soil quality index to assess the effects of three long-term tillage systems on sloping Grantsburg silt loam soil. Soil quality was evaluated using a framework that included three soil functions: (1) resist erosion (water relations), (2) provide plant nutrients (nutrient relations), and (3) provide a favorable root environment (rooting relations). A score for each of these functions was computed using measurements (indicators) that were normalized with one of the three (more is better, optimum, or worse) scoring functions. Six different indices were developed from a basic framework. Modifications included changing the weighting factors, threshold limits, or type of scoring function applied to indicators, and the addition of air-filled and water storage porosity to the nutrient and rooting relations functions. Changing threshold limits and the type of scoring function used for surface residue improved the correlation between water relations and soil loss. The addition of porosity indicators increased the sensitivity of nutrient and rooting relations functions to yield and cone index, respectively, and resulted in a better correlation between porosity indicators and plant population. Computing soil quality indices helped to combine different soil properties and processes into a simple tool that explained changes in complex soil properties in response to different tillage practices. This supports previous studies suggesting that computing soil quality indices and functions could be useful for selecting management practices to maintain or improve soil quality. Our results demonstrated that adjusting threshold limits for local conditions can make the function ratings more or less sensitive to the management practices being evaluated.     

Relationship of percolation stability of soil aggregates to land use, selected properties, structural indices and simulated rainfall erosion

Simple tests of structural stability are needed for evaluating the ease with which soils slake and erode when in contact with water. In a laboratory study, we related the percolation stability (PS) of 22 Nigerian soils to land use, soil properties, structural stability indices and simulated rainfall erosion. All measurements were carried out with the 1–2 mm diameter air-dry aggregates. Land use influenced PS more than the type of soil. Forest soils, bush fallows, mulched, minimally tilled plots and pasture lands had rapid PS (>250 ml/10 min) values, whereas mulched conventionally tilled plots, bare fallows and continuously cultivated plots from where residues were removed by burning had relatively slow to moderate PS values (34–241 ml/10 min). The single most important soil property that correlated positively with PS is organic matter (OM) (r = 0.55^*) followed by total Fe + Al (r = 0.52^*). The significant inverse relationship (r = −0.49^*) between log (PS) and log (pH/OM) indicates a decrease in PS of these acidic, low-OM soils with increasing pH levels. The percent water-stable aggregate (WSA) >0.20 mm diameter, aggregated clay index (AC) and clay dispersion ratio (CDR) correlated weakly with PS. Conversely, the sealing index (SI) (i.e. the ratio of saturated hydraulic conductivity of an uncrusted to that of a crusted soil) had a strong, inverse relationship with PS (r = −0.97^***). These relationships indicate that PS measures the slakability (and not dispersibility) of soils. The relationship between PS and erosion (E) was an exponential decay form, E = 102 e^−0.0043PS (r² = 0.98) and showed that high interrill erosion rates would be expected on soils with PS < 250 ml/10 min. The PS which is simple to measure, is, therefore, a good indicator of structural stability for assessing the potential of these soils to erode.     

Patterns of species diversity in rural herbaceous communities under different management regimes, Chiba, central Japan

The patterns of plant species diversity in herbaceous vegetation subjected to various human activities were studied in most of the landscape elements in a rural area of Chiba, central Japan. Twenty-eight transects were sampled in four types of human management-regime (cultivation, trampling, mowing, and abandonment) and were grouped into seven vegetation types using TWINSPAN and DCA analyses. The DCA axis 1 arranged all the transects into a successional order along which biomass and the degree of succession increased. Accumulated number of species increased in a stepwise pattern along the DCA axis 1, in which the dominant plant life-forms were replaced from annuals, to perennials and perennials/tree-saplings depending on different management regimes. The unique species which were confined to a certain management regime, were identified in each site. It is suggested that the coexistence of various successional communities under different human management regimes enhance regional species diversity through maintaining these unique species. Among four types of management regime, mowing sites (especially traditional verge meadows) had most abundant unique, rare species specially adapted to regular cutting. It is suggested that maintaining such traditional mown sites is important to conserve the unique biodiversity of the studied area.