矿化垃圾和绿化植物废弃物在盐碱土上利用的效果

通过矿化垃圾和绿化植物废弃物在盐碱土上的现场应用试验,研究了土壤性质的变化.结果表明,盐碱土上利用矿化垃圾和绿化植物废弃物后pH和盐分降低,土壤肥力提高;但矿化垃圾中有机质相对稳定,而绿化植物废弃物易分解,其土壤微生物量碳、土壤脲酶和土壤磷酸酶增加效果更明显;而且以矿化垃圾、绿化植物废弃物和原土混合后土地利用的效果最好,其次为矿化垃圾和绿化植物废弃物混合,以矿化垃圾和5%原土处理的利用效果最差;而不同废弃物用量中以30%的绿化植物废弃物添加量改良效果最好;不同处理间土壤微生物量碳、土壤脲酶和土壤磷酸酶的变化趋势基本一致,并与有机质存在显著或极显著相关关系,适合评价有机废弃物土地利用的效果.     

Some impacts of urban waste landfills on Mediterranean soils

Seventy soil samples around and under urban waste landfills in central Spain were studied for 28 physical and chemical properties. In the unaffected surroundings of landfills there is always a higher proportion of coarse and fine gravel. Chlorides, sulphates and nitrates increase noticeably in all the soils affected by landfills as do Na⁺, B³⁺ and Zn²⁺. Multivariate analyses show that higher or lower water retention in the surface layer plays a main role in the organization of both acid and sandier soils as well as of basic soils and those with a higher proportion of silt and clay. Depending on the acidity or basicity, however, the other main factors reveal different hierarchical levels in the soil variables with regard to the organization of these systems. Thus, in acid soils, Zn²⁺ and B³⁺ contribute most noticeably to the second hierarchical level in the edaphic organization. In basic soil without gypsum, the second important gradient of variation is the stoniness (gravel)–fine sand (<2 mm fraction) while the importance of the K⁺, B³⁺ and SO₄⁼ is relegated to the third factor. In the basic soils with gypsum, not only sulphate, but also Na⁺, Cl⁻ and Zn²⁺ plays an essential role in the first factor and the coarse surface elements are also important. The principal components analysis made it possible to establish the main factors involved in the degradation caused by leachates from landfills. Consequently, greater attention could be given to these factors with a view to rehabilitation of degraded soils. © 1998 John Wiley & Sons, Ltd.     

Physical properties of soils in Rostov agglomeration

Physical properties of natural and anthropogenically transformed soils of Rostov agglomeration were examined. The data obtained by conventional methods and new approaches to the study of soil physical properties (in particular, tomographic study of soil monoliths) were used for comparing the soils of different functional zones of the urban area. For urban territories in the steppe zone, a comparison of humus-accumulative horizons (А, Asod, Ap, and buried [A] horizons) made it possible to trace tendencies of changes in surface soils under different anthropogenic impacts and in the buried and sealed soils. The microtomographic study demonstrated differences in the bulk density and aggregation of urban soils from different functional zones. The A horizon in the forest-park zone is characterized by good aggregation and high porosity, whereas buried humus-accumulative horizons of anthropogenically transformed soils are characterized by poor aggregation and low porosity. The traditional parameters of soil structure and texture also proved to be informative for the identification of urban pedogenesis.     

Re-evaluation of the structural properties of some British swelling soils

The structural condition of swelling soils can be assessed from their shrinkage curves. We re‐evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ?. The points on the e–? curve were fitted with a constitutive shrinkage equation using an unbiased least‐squares, curve‐fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(?), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(?), from which the maximum curvature at the wet end was used to separate the structural shrinkage, S_c, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, S_c and the volumetric air content, θ_ac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential.     

Physical properties and moisture retention characteristics of some nigerian soils

Measurements were made of physical characteristics of 119 samples from 23 profiles derived from two parent materials in Nigeria. The laboratory analyses included texture, plasticity and shrinkage characteristics, and a range of soil moisture constants including saturation point and moisture retention at various suctions. Simple and multiple correlation coefficients and regression analyses were conducted to investigate the possibilities of obtaining estimates of soil moisture retention from the textural analysis. Clay and sand contents are correlated with various soil moisture constants. The textural analysis may therefore be used to estimate moisture holding capacity at different suctions for these and similar soils with a predominantly uniform clay mineralogy, dominated by kaolinite and sesquioxides. Moisture retention curves indicate that the “field capacity” for most of these soils is better estimated at 60 or 100 cm of water suction rather than at 0.3 bar. A plot of the pF curves indicated only slight differences between moisture retention at 2 or 3 bar suction and at 15 bar suction.     

Physical properties of peat soils under different land use options

Pristine peat soils are characterized by large porosity, low density and large water and organic matter contents. Drainage and management practices change peat properties by oxidation, compaction and mineral matter additions. This study examined differences in physical properties (hydraulic conductivity, water retention curve, bulk density, porosity, von Post degree of decomposition) in soil profiles of two peatland forests, a cultivated peatland, a peat extraction area and two pristine mires originally within the same peatland area. Soil hydraulic conductivity of the drained sites (median hydraulic conductivities: 3.3 × 10^?5 m/s, 2.9 × 10^?8 m/s and 8.5 × 10^?8 m/s for the forests, the cultivated site and the peat extraction area, respectively) was predicted better by land use option than by soil physical parameters. Detailed physical measurements were accompanied by monitoring of the water levels between drains. The model ‘DRAINMOD’ was used to assess the hydrology and the rapid fluctuations seen in groundwater depths. Hydraulic conductivity values needed to match the simulation of observed depth to groundwater data were an order of magnitude greater than those determined in field measurements, suggesting that macropore flow was an important pathway at the study sites. The rapid response of depth to groundwater during rainfall events indicated a small effective porosity and this was supported by the small measured values of drainable porosity. This study highlighted the potential role of land use and macropore flow in controlling water table fluctuation and related processes in peat soils.     

Physical properties of soddy-podzolic soils in a long-term field experiment

The main physical properties of soddy-podzolic soils in a long-term field experiment have been studied. It is shown that their changes under the impact of a century-long application of lime, fertilizers, and manure have been relatively small. Reliable differences in the parameters of approximation of the dependence of penetration resistance on the soil water content in the variant with regular application of organic fertilizers have been revealed. This attests to stronger interparticle bonds (within the studied moisture range) in this variant. Interparticle bonds in the control variant and in the variant with lime application tend to increase with a decrease in the soil water content more significantly than those in other experimental variants. This may be due to the coarser texture of the soil in the control variant and to the aggregation of soil particles under the impact of lime in the variant with lime application.     

Physical properties of park soils of the objects of landscape architecture

Here the comparative characteristics of the physical properties of park soils, viz., anthropogenically transformed and engineered soils of the objects of landscape architecture, are given. The mechanical strength of aggregates, density, and aggregate physical properties to characterize the soil and agro-physical and environmental condition of soil objects of landscape architecture and establish the similarities or differences of engineered soil objects with zonal soils are described. We studied the physical properties of soils of different structural and functional elements of the landscape and the regular area of the Arkhangelskoe memorial estate. The structural state of the park soils is characterized as good. The engineered soils of the regular area of the park appear to have excessively high water resistance, while the postagrigenic sod-podzolic soils of the landscape area of the park are absolutely water resistant.     

Contribution of technic materials to the mobile fraction of metals in urban soils in Marrakech (Morocco)

Background, Aim and Scope  In urban areas, soils are often dramatically altered by anthropogenic activity and these modifications distinguish these soils (Anthrosols, Technosols) from those in natural systems. In urban environments, they receive considerable pollution from industry, traffic and refuse. Since contaminated soil particles can be easily inhaled or ingested, there is a potential transfer of toxic pollutants to humans. Risk assessment is essentially based on the determination of the total or mobile contents of pollutants in soils using chemical extractions. This approach could be improved by taking into consideration the bioavailable fractions of these toxic elements as measured by biotests. The coarse soil fraction usually neglected in analyses can nevertheless have an effect on the concentration of metals in the soil solution. This coarse fraction is made up of the natural materials and of technic materials constituting anthropogenic soils (plastic, paper, fabric, wood, bones, metallic elements and building materials). These materials have variable capacities to release or adsorb trace elements. Samples representative of different technic fraction components of Marrakech urban soils permit one to quantify their contribution to the enrichment of the soluble metal concentrations. Works are carried out to achieve partial extractions of metals from the three fractions (less than 2 mm, coarse natural and coarse technic) of selected urban soils in order to determine their contribution to the metal contamination of soils. Materials and Methods  Selected soils were collected from 9 sites according to a gradient of increasing anthropogenic influence from suburban to urban zones. Soils were air-dried, homogenized, and sieved (2 mm). The coarse fraction was sorted to separate the different technic materials and natural materials. Water extractions were run, on the natural, coarse fraction, on the complete technic fraction of the 9 soils and on average samples made of technic materials sorted out of 58 topsoils sampled from different sites in the city of Marrakech. Results  Results show that the percentage of the technic fraction increases while approaching the historic city center. It represented about 14% in the most anthropogenically disturbed soils. Along this gradient, soils changed progressively from Anthrosols to Technosols according to the WRB classification of urban and industrial soils. Analyses of metal contents showed that the fine fraction (<2 mm) mainly contributed to the metallic contamination of the water soluble fraction. The natural coarse fraction had the highest contribution to the copper release and was responsible for the release of all water-extractable copper in some soils. Concerning the technic fraction, it has a significant contribution essentially in the most anthropogenically disturbed soils as characterized by an elevated percentage of anthropogenic elements. The water extractable metal contents of average samples of these anthropogenic elements shows that elevated metal concentrations were released by bones, wood, plastic and fabric/paper. Discussion  This study concerns soils in urban areas, which are strongly impacted by human activities. Part of the soils can be classified as Anthrosols, profoundly impacted through the addition of organic materials from household wastes, irrigation, or cultivation. Other soils strongly impacted by human activities are Technosols dominated or strongly influenced by man-made materials. Technosols appear mostly in urban and industrial areas and are more likely to be contaminated than Anthrosols. The composition and heterogeneity of urban soils lead to modifications of the mobility and availability of pollutants depending on successive land-uses and on the composition of technic materials. The fine fraction offers a high transferring surface capacity, leading to a high mobilization of metals. The technic fraction contributes significantly to the metal release in the Technosols. This property can be explained by a reversible adsorption of metals on the organic matter. Conclusions  Results confirm that anthropogenic activity causes a wide spatial diversity of soil quality in the urban and suburban area. It introduces large amounts of technic materials in soils that could have an impact on the metal availability. It therefore acts on the metal bioavailability in the urban Technosols. Recommendations and Perspectives  These results show that it is necessary, in addition to the characterization of the fine particles, to take into account the contribution of the coarse fraction of the Technosols in the evaluation of risks of transfer of metals to the food chain.     

Magnetic properties of the urban soils in Shanghai and their environmental implications

To study the feasibility of using magnetic techniques for monitoring soil pollution in Shanghai, magnetic properties and heavy metals in the topsoils in an urban site (Songnan Town) and a less-urbanized agricultural site (Luojing Town) in Baoshan District, Shanghai, were studied. Compared with the background, magnetic signals of the urban topsoils are extremely enhanced with magnetic susceptibility (χ_lf) from 127.3–1959 × 10^− 8 m³ kg^− 1; while those of the agricultural topsoils are only slightly increased. However, both the urban and agricultural topsoils contain few pedogenic SP grains, as indicated by their low χ_fd% (< 3.6%). Ratios of χ_arm/SIRM, χ_arm/χ_lf and SIRM/χ_lf indicate that the grain size of magnetic minerals in the urban topsoils is significantly coarser than that in the background and the agricultural topsoils. Furthermore, the urban topsoils show low coercivity and magnetic soft behaviors, as indicated by higher SOFT%, lower HARD%, higher IRM_300 mT/SIRM (close to 1) and lower IRM_− 200 mT/SIRM (close to − 1). It suggests that the urban topsoils have received some coarse ferrimagnetic particles. Heavy metals are highly enriched in the magnetic fractions of the topsoils. Geochemical properties of the magnetic fraction of the urban topsoils are significantly different from those of the agricultural topsoils, further indicating that the extra magnetic minerals accumulated in the urban topsoils are neither inherited from soil parent materials nor from pedogenic processes, but originate from anthropogenic activities. The significant correlations between heavy metals and χ_lf, χ_arm, SIRM, SOFT and HIRM of the topsoils in the district indicate that the magnetic techniques can be used for monitoring soil pollution in Shanghai. The soils with χ_lf from 39–50 × 10^− 8 m³ kg^− 1 in the district are tentatively defined as “slightly polluted soils”; those with χ_lf > 50 × 10^− 8 m³ kg^− 1 are defined as “polluted soils”.     

Andic properties in soils developed from nonvolcanic materials in Central Bhutan

A number of soils are described in the literature as having andic and spodic soil properties, but have developed in nonvolcanic and nonallophanic materials and lack typical Podzol eluvial and illuvial horizons. They cover a wide range of parent materials and different types of climate. They have always been regarded as restricted to small areas. They were assigned to Andisols/Andosols, Podzols/Spodosols, or andic Inceptisols in the WRB and Soil Taxonomy and sometimes also named Cryptopodzols or Lockerbraunerden. Recent soil surveys in Bhutan, E Himalayas, show these soils are widespread at altitudes between 2200–3500 m asl and are spanning several bioclimatic zones. The aim of this study is the detailed characterization of specific properties and processes of formation by physical and chemical analyses, NMR spectroscopy, column experiments, SEM, XRD, and ¹⁴C dating in one of these soils in E central Bhutan. The results indicate advanced soil development with high amounts of oxidic Fe and Al compounds, low bulk densities (partly <0.5 g cm^–3), P retention >85%, and a dominance of Al‐hydroxy‐interlayered phyllosilicates. Scanning electron microscopy of sand fractions indicate microaggregates highly resistant to dispersion. Column experiments show podzolization with mobilization and translocation of DOM, Fe, and Al. Nuclear‐magnetic resonance spectroscopy and ¹⁴C ages of 16,000 BP indicate stabilization of DOM. Applying classification criteria, these soils appear to have andic and spodic features, but are neither Andosols nor Podzols senso strictu. Especially the role of Fe seems to be underestimated with regard to the specific soil‐forming processes. Because of their widespread occurrence and distinct properties, we suggest either a simplification of the criteria for existing soil types or a clearly defined separation of volcanic and nonvolcanic/nonallophanic Andosols.     

不同母质发育的红壤电荷特性研究

研究了3种不同母质发育的红壤中电荷的差异,比较了不同母质对电荷的影响。结果表明:3种母质发育的红壤中,紫色土发育的红壤中全部负电荷含量明显高于花岗岩发育的红壤和第四纪红色黏土发育的红壤;第四纪红色黏土发育的红壤中正电荷的含量明显高于花岗岩发育的红壤和紫色土发育的红壤;第四纪红色黏土发育的红壤、花岗岩发育的红壤和紫色土发育的红壤中正电荷与pH呈显著性负相关;第四纪红色黏土发育的红壤正电荷与有机质呈显著负相关,花岗岩发育的红壤和紫色土发育的红壤中正电荷与有机质含量呈显著正相关;第四纪红色黏土发育的红壤和紫色土发育的红壤正电荷与黏粒含量呈一元二次线性关系,花岗岩发育的红壤正电荷与黏粒含量呈极显著负相关;紫色土发育的红壤吸附的NH4+-N含量最高,第四纪红色黏土发育的红壤吸附的NO3--N含量最高。通过对3种母质发育的土壤电荷特性的研究,可为不同母质的红壤进行合理施肥与管理提供科学依据。     

Physical properties and spatial distribution of the plowpan in different arable soils

The morphology, water-physical properties, and spatial distribution of plowpans were studied. The presence of a plowpan in the root layer is most reliably detected from the macro- and micromorphometric indices and a reliable decrease in the interaggregate porosity and in the range of active moisture. As a rule, the plowpan does not have a continuous character; its appearance in the soil profile depends on the soil texture and wetting and is usually confined to the lower and wetter mesorelief elements. Loamy and clay loamy soils are more liable to form a plowpan. The current farming system favors the propagation of overcompaction deep into the soil profile. The areas with a plowpan within plowed fields vary in a wide range. The main reasons for the unfavorable physical properties of the subplow layer in a plowland are the natural extenuation of the soil-forming processes in this layer, which is manifested in a poorer aggregation, and the residual soil deformation under the long-term pressure of heavy machines. It is suggested that the plowpan can be destroyed via deep chiseling with the use of precision agriculture technologies.     

The triad approach to ecological assessment of urban soils

The “triad” approach was suggested by Chapman [22] for assessing the risk of contamination of bottom deposits. We applied this approach for the analysis of urban soils under different loads from motor transport. On its basis, the results of chemical analysis (heavy metals, biogenic elements, and pH), bioindication parameters of the communities of microorganisms, and the results of toxicological investigations with the use of test-organisms were generalized to obtain an integral index of the soil status (IS). A comparison of IS values for test plots at different distances from a highway in the city of Kirov (58.3729–58.624722 N, 49.3743–49.628611 E) showed that the ecological status of the soils could be qualified as disturbed on the plots adjacent to the highway and as slightly disturbed at distances of 30–200 m from the highway. The IS calculated on the basis of data of three disciplines (chemistry, ecology, and toxicology) seems to be a more comprehensive characteristic for assessing the ecological status of urbanozems as compared to Zc indices of the chemical contamination of soils (suggested by Saet) or indices of the integral biological characteristics of soil quality.     

Anthropogenic effects on the physical and chemical properties of subtropical coastal urban soils

We investigated the effects of various anthropogenic factors on urban soil properties in subtropical, coastal Tampa, FL, USA. Specifically, we explored the influence of (i) urbanization as measured by land use, land cover, population density and years since urban development and (ii) socioeconomic conditions as reflected in household income and property values on bulk density (BD) and several key soil chemical properties. Results indicate that Tampa’s urban soils were affected to varying degrees by these factors with chemical properties being more variable than BD. Across land uses significant differences were found for Mehlich‐1 (M1) extractable P, Ca and Na. A similar trend was observed for land‐cover classes, although significant differences were also found for pH and M1‐Cu. Soil properties had no statistically significant relationship with population density. However, time since urbanization did with M1‐P and Na varying significantly across age categories. For our socioeconomic analyses, M1‐K and Mg levels differed significantly by household income while pH, P, Ca and Na values differed significantly by property value. Overall, our findings indicate that despite their inherent heterogeneity, there are identifiable patterns among subtropical coastal urban soil properties. We suggest that a more thorough understanding of these patterns and their drivers is an essential first step towards developing soil management strategies aimed at maintaining environmental quality and ecosystem services in subtropical cities.     

Characterizing urban soils in New York City: profile properties and bacterial communities

Purpose

The influence of human activities on the development and functioning of urban soils and their profile characteristics is still inadequately understood. Microbial communities can change due to anthropogenic disturbances and it is unclear how they exist along urban soil profiles. This study investigates the dynamic soil properties (DSPs) and the bacterial communities along the profiles of urban soils in New York City (NYC) with varying degree of human disturbances.

Materials and methods

Eleven pedons were investigated across NYC as well as one control soil in a nearby non-urban area. Six soils are formed in naturally deposited materials (ND) and five in human-altered and human-transported materials (HAHT). For each soil, the profile was described and each horizon was sampled to assess DSPs and the bacterial community composition and diversity.

Results and discussion

The development and the DSPs of NYC soils are influenced by the incorporation of HAHT materials and atmospheric deposits. The most abundant bacterial taxa observed in the NYC soils are also present in most natural and urban soils worldwide. The bacterial diversity was lower in some soils formed in ND materials, in which the contribution of low-abundance taxa was more restricted. Some differences in bacterial community composition separated the soils formed in ND materials and in dredged sediments from the soils formed in high artifact fill and serpentinite till. Changes in bacterial community composition between soil horizons were more noticeable in urban soils formed in ND materials than in those formed in HAHT materials which display less differentiated profiles and in the non-urban highly weathered soil.

Conclusions

The bacterial diversity is not linked to the degree of disturbance of the urban soils but the variations in community composition between pedons and along soil profiles could be the result of changes in soil development and properties related to human activities and should be consistently characterized in urban soils.

     

Heavy metal pollution of urban soils

The chemical properties of urban soils (southeastern administrative district, Moscow) affecting the behavior of heavy metals were studied. The current heavy metal pollution level of the soils was assessed. The use of different approaches for the pollution standardization is shown to produce different results. The fractional composition of the metal compounds in the soils and the factors affecting its formation under technogenic pollution were investigated. In the district studied, the distribution of heavy metals by the fractions primarily depended on the chemical properties of the heavy metals themselves; the pollution level; and, to a lesser degree, on the soil properties. Zinc and cadmium were the most mobile metals in the soils studied.     

Physical properties of some intensively cultivated soils of Ireland amended with spent mushroom compost

In this paper, spent mushroom compost (SMC), a by‐product of the mushroom industry, is proposed as a suitable organic amendment for soil structure restoration. A 4‐month incubation pot trial was conducted in which fresh and composted SMC was amended at three different rates (50, 100 and 200 t ha⁻¹) to a range of structurally degraded tillage soils (n = 10). Soil OC content and aggregate stability as determined by the three disrupting tests of the Le Bissonnais method (fast‐wetting, slow‐wetting and mechanical breakdown) were investigated. Applications of 50, 100 and 200 t ha⁻¹ fresh SMC increased the OC content by 2·71 per cent, 2·69 per cent and 2·49 per cent respectively, while amendments of composted SMC increased the OC content by 3·28 per cent, 2·94 per cent and 2·87 per cent for each application rate, respectively. The effect of SMC on aggregate stability was generally positive and statistically significant in most soils. However, in soils 3 and 4 an application rate of 200 t ha⁻¹ SMC decreased the aggregate stability, on average, by 15 per cent, in comparison to the control, for the fast‐wetting test. Aggregate stability was strongly controlled by the inherent OC content of the study soils; that is, the OC content prior to SMC addition. A positive correlation coefficient was also evident for the dithionite‐extractable iron, most pronounced for slow‐wetting and mechanical breakdown treatments (r = 0·844 and r = 0·817 respectively). It is clear from this research that SMC amendments have the capacity to improve soil structural stability. Copyright © 2007 John Wiley & Sons, Ltd.     

半干旱退化土壤中施入城市垃圾的长期效应研究

The addition of municipal solid wastes (MSW) is considered as a possible strategy for soil rehabilitation in southeast Spain. The objective of this study was to evaluate the long-term (17 years) effect of five doses of MSW addition on the microbiological, biochemical, and physical properties of semiarid soil. Increased values of several parameters that serve as indicators of general microbiological activity, such as, basal respiration, adenosine triphosphate (ATP) or dehydrogenase activity;microbial population size (microbial biomass C), and extracellular hydrolase activity related to macronutrient cycles, such as, urease, β-glucosidase, and N-α-benzoyl-L-argininamide protease, were observed in the amended soils. The highest MSW doses showed the highest values in these hydrolase activities. The incorporation of municipal waste resulted in a more dense development of the plant cover, 50% greater in higher doses than in the control treatment, which generated a substantial increase in several C fractions. Total organic carbon reached 12 g kg^-1 soil with the highest MSW doses, compared to 4.30 g kg^-1 soil in the control treatment. The physical properties of the soil were also improved, showing greater percentage of stable aggregates and water holding capacity. Positive correlation coefficients between C fractions and parameters related to microbial activity and aggregate stability were observed. Although these improvements were greater in the soils receiving the highest doses of organic amendment, the increases were not proportional to the amount added, demonstrating the existence of a threshold, above which an increase in the amount of organic matter added is not reflected in an increase in the soil's physical, biochemical, and microbiological properties. However, the addition of municipal solid wastes proved its suitability for improving soil quality, thereby indicating the potential of such an amendment, to prevent desertification in Mediterranean areas such as those studied.     

评价城市土壤磷素淋溶风险的化学指标

Soils from urban and suburban areas are normally enriched with phosphorus (P). Sixteen urban soils with a wide range of total P concentrations under typical urban land uses were sampled and analyzed for extractable P concentrations using water, sodium bicarbonate and citric acid. Meanwhile the soils were artificially leached in columns and P concentrations in the leachates were determined. With linear regression a two-stage linear relationship was found to exis tbetween concentrations of P in the leachates and soil P contents obtained by various chemical measurements, i.e., there was a “change-point” denoting the critical threshold value for extractable P between the regression lines, above which concentrations of P in leachates increased substantially. These threshold “change-point” values were 1.5 mg kg^-1 for water-soluble P and CaCl2-P, 25 mg kg^-1 for Olsen-P, and 250-350 mg kg^-1 for citric acid-P with the sharpest change and the best predictor [τ2 (upper) = 0.928, τ2 (lower) = 0.807] appearing for Olsen-P. These “change-points” were considered important criteria in assessing the risk of P leaching from urban soils and could be used as standards to delineate and target hazardous areas in urban and suburban areas.