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1.
A long-term field experiment was carried out in the experiment farm of the Sao Paulo State University, Brazil, to evaluate the phytoavailability of Zn, Cd and Pb in a Typic Eutrorthox soil treated with sewage sludge for nine consecutive years, using the sequential extraction and organic matter fractionation methods. During 2005-2006, maize (Zea mays L.) was used as test plants and the experimental design was in randomized complete blocks with four treatments and five replicates. The treatments consisted of four sewage sludge rates (in a dry basis) : 0.0 (control, with mineral fertilization), 45.0, 90.0 and 127.5 t ha-1, annually for nine years. Before maize sowing, the sewage sludge was manually applied to the soil and incorporated at 10 cm depth. Soil samples (0-20 cm layer) for Zn, Cd and Pb analysis were collected 60 days after sowing. The successive applications of sewage sludge to the soil did not affect heavy metal (Cd and Pb) fractions in the soil, with exception of Zn fractions. The Zn, Cd and Pb distributions in the soil were strongly associated with humin and residual fractions, which are characterized by stable chemical bonds. Zinc, Cd and Pb in the soil showed low phytoavailability after nine-year successive applications of sewage sludge to the soil.  相似文献   

2.
Lai  K. M.  Ye  D. Y.  Wong  J. W. C. 《Water, air, and soil pollution》1999,113(1-4):261-272
Previous studies showed that coal fly ash could stabilize sewage sludge by reducing metal availability, but fly ash may cause an adverse effect on soil microbial activities. Therefore, an experiment was performed to evaluate the effects of amendment of soil with anaerobically digested dewatered sewage sludge, stabilised with alkaline coal fly ash, on soil enzyme activity and the implications for soil nutrient cycling. Sewage sludge was amended with 0, 5, 10, 35 and 50% w/w of fly ash, and then the ash-sludge mixtures were incubated with a sandy soil at 1:1 (v/v). Dehydrogenase activity decreased with an increase in fly ash amendment level and the time of incubation. Soil receiving 5% ash-sludge amendment had a higher dehydrogenase activity than other treatments. Soil receiving 10% ash-sludge mixture had the highest urease activity and in general, urease activity decreased with increasing incubation time. Phosphatase activity was the highest at 5% ash-sludge mixture amended soil and no general trend was observed with time. Water-soluble Zn, Mn and Cu contents were suppressed by the addition of fly ash. The present experiment indicated that addition of 10% ash-sludge mixture should have a positive benefit on the activity of soil microorganisms, N and P nutrient cycling, and reduce the availability of heavy metals.  相似文献   

3.

A long-term experiment was conducted to determine the distribution of sludge-borne metals applied to a revegetated acidic dredge spoil disposal site. The initial soil was infertile and highly acidic (pH 2.4). Sewage sludge and lime were applied in 1974 at the rates of 100 and 23 mt ha?1, respectively, and tilled into the soil to a depth of 20 cm. In 1974 an adjacent site was also revegetated with topsoil and lime but without sludge. Soil and plants were sampled 2, 4 and 16 yr following seeding. After 16 yr the total and DTPA-extractable Cu, Zn, Cr, Pb, Ni and Cd decreased in soils to nearly the levels of the control soils. Concentrations of metals in plants also decreased. Decreases in tissue concentrations ranged from 40 to 70% for Cu, Cr, Pb, Ni and Cd and up to 90% for Zn. The results showed that a single 100 mt ha?1 application of sewage sludge containing high concentrations of metals was a cost-effective method for improving plant growing conditions on highly acidic soils.

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4.
滩涂盐土农业利用的主要障碍是盐分含量过高和缺乏有机质。施用生活污泥可快速提高滩涂土壤有机质含量,加快土壤熟化,但由于担心污泥含有一定量的重金属,其施用受到一定的限制。采用盆栽苏丹草的试验方法,研究滩涂盐土施用不同量的生活污泥后对土壤性质、植物生长和对重金属累积的影响。结果表明,生活污泥施用于滩涂盐土后降低了土壤pH值,提高了EC值和总盐含量;苏丹草的出苗率、株高和鲜重增加;施用污泥提高了苏丹草植株中全氮、全磷及叶绿素的含量,且随施用量的增加而增大,但对植株中全钾的含量无显著影响;苏丹草中Zn、Cd含量随着污泥施用量增加呈增长的趋势,但Pb、Ni、Cu含量变化不大。在试验条件下,所施用污泥中重金属向苏丹草体内转移的比例介于0.13%-13.44%之间。就该种土壤而言,要更为注意含Pb量较高的污泥施用,而Cu则是最为安全的。总体考虑,一次性施用干污泥应控制在8t·667m^-2以下。  相似文献   

5.
Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about the utility of this organic amendment in the reclamation of soil polluted with heavy metals. We studied the effects of adding sewage sludge on enzymatic activities of a semi-arid soil contaminated with Cd or Ni in the laboratory. The activities of urease, phosphatase, β-glucosidase and protease-BAA were measured in soil containing concentrations of Cd or Ni in the range 0–8000 mg kg−1 soil, and their inhibition was compared with those of the enzymatic activities in the same soil amended with sewage sludge and containing similar concentrations of the heavy metals. The inhibition was tested for three different incubation times to determine changes in the effect of the heavy metals on hydrolase activity with the time elapsed after contamination. Ecological dose (ED) values of Cd and Ni were calculated from three mathematical models which described the inhibition of the enzymatic activities with increasing concentrations of heavy metal in the soil. For urease and phosphatase activities, the ED values for Cd and Ni increased after application of sewage sludge to soil, indicating a decrease in Cd and Ni toxicity. The other two enzymes (β-glucosidase and protease-BAA) were less sensitive to Cd or Ni contamination, and it was more difficult to determine whether addition of sewage sludge had affected the inhibition of these enzymes by the heavy metals.  相似文献   

6.
Effects of N-enriched sewage sludge on soil enzyme activities   总被引：5，自引：0，他引：5  
Sewage sludge is increasingly used as an organic amendment to soil, especially to soil containing little organic matter. However, little is known about utility of this organic amendment with N-enriched or adjusted C:N ratios in soil. We studied the effects of adding of different doses (0, 100, 200 and 300 t ha−1) and C:N ratios (3:1, 6:1 and 9:1) of sewage sludge on enzyme activities (β-glucosidase, alkaline phosphatase, arylsulphatase and urease) in a clay loam soil at 25 °C and 60% soil water holding capacity. Nitrogen was added in the form of (NH4)2 SO4 solution to the sludge to reduce the C:N ratio from 9:1 to 6:1 and 3:1. The addition of different doses and C:N ratios of the sludge caused a rapid and significant in the enzymatic activities in soils, this increase was specially noticeable in soil treated with high doses of the sludge. In general, enzymatic activities in sludge-amended soils tended to decrease with the incubation time. All activities reached peak values at 30 days incubation and then gradually decreased up to 90 days of incubation. Sewage sludges also the increased available metal (Cu, Ni, Pb and Zn) contents in the soils. However, the presence of available soil metals due to the addition of the sludge at all doses and C:N ratios did negatively affect all enzymatic activities in the soils. This experiment indicated that all doses and C:N ratios of sewage sludge applied to soil would have harmful effects on enzymatic activity. Some heavy metals found in sewage sludge may negatively influence soil enzyme activities during the decomposition of the sludge.  相似文献   

7.
Abstract

City sewage sludge was applied to the surface layer (0–10 cm) of two sandy soils, slightly calcareous with 8.9% CaCO3 and moderately calcareous with 26.7% CaCO3, at the rates of 0, 25, 50, 75, and 100 Mg ha‐1. The effects of sewage sludge and its rates on total soluble salts, pH of soils and concentration and movement of some heavy metals within soils were investigated. Soil samples were packed at bulk density of 1.5 g cm‐3 in PVC columns and incubated for 19 weeks. The results indicated that total soluble salts (EC) of the treated layer increased with increasing sewage sludge rates. Soluble salts also increased with an increase in soil depth for both soils. The pH values of treated layers in two soils decreased with increasing sewage sludge rates. With increasing sewage sludge rates, concentrations of heavy metals [cobalt (Co), nickel (Ni), cadmium (Cd), and leaf (Pb)] increased in the treated layers compared to the untreated layers and their mobility was restricted mostly to the upper 30‐cm depth. Movement of Co and Pb in both the soils was predominately limited up to a depth of 40 cm for Co and 5 cm for Pb below the treated soil layer. Nickel and Cd movement was mostly limited to a depth of 10 cm in slightly calcareous soil and 5 cm in moderately calcareous soil. Metal movement in the respective soils is ranked as Co>Ni=Cd>Pb and Co>Ni=Cd>Pb. The low concentrations of heavy metals and the restricted mobility with soil depth, suggest that this material may be used for agricultural crop production without any toxic effect on plants.  相似文献   

8.
The objective of this study was to evaluate the effect of sewage sludge on soil suppressiveness to the pathogens Fusarium oxysporum f. sp. lycopersici on tomato, Sclerotium rolfsii on bean, Sclerotinia sclerotiorum on tomato, Rhizoctonia solani on radish, Pythium spp. on cucumber, and Ralstonia solanacearum on tomato. Soil samples were collected from an experimental corn field in which sewage sludge had been incorporated once a year, since 1999. Sludge from two sewage treatment stations in Brazil (Franca and Barueri, SP) were applied at the rates of one (1N), two (2N), four (4N) and eight (8N) times the N recommended doses for the corn crop. Soil suppressiveness was evaluated by methods using indicator host plants, baits and mycelial growth. There was no effect of sewage sludge on soil suppressiveness to Fusarium oxysporum f. sp. lycopersici in tomato plants. For S. rolfsii, reduction of the disease in bean was inversely proportional to the dose of Franca sludge. The incidence of dead plants, caused by S. sclerotiorum, was directly proportional to sludge doses applied. For R. solani and R. solanacearum, there was a linear trend with reduction in plant death in soils treated with increasing amounts of sludge from Franca. There was an increase in the pathogen community of Pythium spp., proportional to the amounts of sewage applied. The effects of sewage sludge varied depending on the pathogen, methodology applied and on the time interval between the sewage sludge incorporation and soil sampling.  相似文献   

9.
In a small‐plot trial different doses of sewage sludge (equivalent 82‐330 tons of dry matter per hectare) were incorporated in 0—25 cm depth (1982—1985). The aim of the investigations was to study the fate of the heavy metals Zn, Cd, Cu, Ni, Pb, and Cr, to determine their concentration in different soil fractions using a sequential extraction method and to ascertain their uptake by Zea mays L. plants. Eleven years after the last application the metals supplied with the sludge had moved as far as 50 cm in depth. The concentrations of Zn, Cd, Cu, Ni, and Cr in the saturation extract of the sampled soil layers were closely correlated with the concentrations of dissolved organic carbon (DOC). This result suggests that the heavy metal displacement was partly connected with the DOC movement in the soil. Considerable amounts of Zn and Cd coming from sewage sludge were found in the mobile fractions of the soil. Cu, Ni, and Pb were located especially in organic particles, and Cr was obviously bound by Fe‐oxides. Nine years after the last application the binding species of heavy metals were still different compared with those in the untreated soil. The whole withdrawal of heavy metals by plants yielded <1 % of the applied amounts. In the case of Zn the uptake from the sludge amended soil decreased during the experimental period. No similar tendency was observed for the other elements. In any case their annual variations of uptake exceeded the effect of sludge application.  相似文献   

10.
The need for solutions to minimize the negative environmental impacts of anthropogenic activities Fhas increased. Sewage sludge is composed of predominantly organic matter and can be used to improve soil characteristics, such as fertility. Therefore, its application in agriculture is an adequate alternative for its final disposal. However, there is a lack of information on its long-term effects on soil changes in tropical areas. Thus, the objectives of this study were to determine (i) the effect of sewage sludge application on heavy metal build-up in soil and maize grains and leaves, and (ii) the effects of soil amendment with sewage sludge on the chemical properties of a Brazilian oxisol. Besides the increasing levels of Zn, Cu, Ni, and Cr, amending soil with sewage sludge also alters the distribution of these metals by increasing the mobile Phases, which correlated significantly with the increase in metal extraction with two single extractants, Mehlich 1 and DTPA (Diethylene triamine pentaacetic acid). The levels of Fe, Mn, Zn, and Cu in maize grains and leaves increased with the type and rate of sewage sludge application. Nevertheless, metal build-up in soil and plants was within the allowed limits. Significant differences were also found in soil characteristics like humic fractionation with the applied sewage doses. The data obtained does not indicate any expressive drawbacks in the use of sewage sludge as a soil amendment, as the heavy metal concentrations observed are unlikely to cause any environmental or health problems, even overestimated loadings, and are in accordance with the Brazilian regulations on farming land biosolid disposal.  相似文献   

11.
The influence of manure and composts on the leaching of heavy metals from soil was evaluated in a model lysimeter experiment under controlled conditions. Soil samples were collected from experimental fields, from 0- to 90-cm layers retaining the layout of the soil profile layers, after the second crop rotation cycle with the following plant species: potatoes, spring barley, winter rapeseed, and winter wheat. During the field experiment, 20 t DM/ha of manure, municipal sewage sludge composted with straw (SSCS), composted sewage sludge (SSC), dried granular sewage sludge (DGSS), “Dano” compost made from non-segregated municipal waste (CMMW), and compost made from municipal green waste (CUGW) was applied, i.e., 10 t DM/ha per crop rotation cycle. The concentrations (μg/dm3) of heavy metals in the leachate were as follows: Cd (3.6–11.5)?<?Mn (4.8–15.4)?<?Cu (13.4–35.5)?<?Zn (27.5–48.0)?<?Cr (36.7–96.5)?<?Ni (24.4–165.8)?<?Pb (113.8–187.7). Soil fertilization with organic waste materials did not contaminate the percolating water with manganese or zinc, whereas the concentrations of the other metals increased to the levels characteristic of unsatisfactory water quality and poor water quality classes. The copper and nickel content of percolating water depended on the concentration of those metals introduced into the soil with organic waste materials. The concentrations of Cd in the leachate increased, whereas the concentrations of Cu and Ni decreased with increasing organic C content of organic fertilizers. The widening of the C/N ratio contributed to Mn leaching. The concentrations of Pb, Cr, and Mn in the percolating water were positively correlated with the organic C content of soil.  相似文献   

12.
The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. However, there have been few attempts to compare the effects of different kinds of composts in one single study. The aim of this paper is to investigate to what extent and to which soil depth four major types of composts would affect the soil and its microbiota.In a crop-rotation field experiment, composts produced from (i) urban organic wastes, (ii) green wastes, (iii) manure and (iv) sewage sludge were applied at a rate equivalent to 175 kg N ha−1 yr−1 for 12 years. General (total organic C (Corg), total N (Nt), microbial biomass C (Cmic), and basal respiration), specific (enzyme activities related to C, N and P cycles), biochemical properties and bacterial genetic diversity (based on DGGE analysis of 16S rDNA) were analyzed at different depths (0-10, 10-20 and 20-30 cm).Compost treatment increased Corg at all depths from 11 g kg−1 for control soil to 16.7 g kg−1 for the case of sewage sludge compost. Total N increased with compost treatment at 0-10 cm and 10-20 cm depths, but not at 20-30 cm. Basal respiration and Cmic declined with depth, and the composts resulted in an increase of Cmic and basal respiration. Enzyme activities were different depend on the enzyme and among compost treatments, but in general, the enzyme activities were higher in the upper layers (0-10 and 10-20 cm) than in the 20-30 cm layer. Diversity of ammonia oxidizers and bacteria was lower in the control than in the compost soils. The type of compost had less influence on the composition of the microbial communities than did soil depth.Some of the properties were sensitive enough to distinguish between different compost, while others were not. This stresses the need of multi-parameter approaches when investigating treatment effects on the soil microbial community. In general, with respect to measures of activity, biomass and community diversity, differences down the soil profile were more pronounced than those due to the compost treatments.  相似文献   

13.
The aim of this study was to investigate factors regulating phosphatase activities in Mediterranean soils subjected to sewage sludge applications. Soils originating from calcareous and siliceous mineral parent materials were amended with aerobically digested sewage sludge, with or without physico-chemical treatment by ferric chloride. Sludge amendments, ranging from 6.2 to 10 g kg−1 soil, were carried out in order to provide soil with a P total quantity equivalent to 0.5 g P2O5 per kg of soil. Bacterial density, phosphatase activities (i.e. acid and alkaline phosphomonoesterases and phosphodiesterases) and available P (i.e. P Olsen and P water) were measured after 25 and 87 days of incubation. Results showed significant effects of sewage sludge application and incubation period. Sewage sludge effect resulted in an increase in phosphatase activities, microbial density and available P. Incubation period increased available P while decreasing phosphatase activities. This study also revealed that the origin of sludge and its chemical characteristics may show different effects on certain variables such as phosphodiesterases or bacterial density, whereas mineral parent materials of soils did not show any significant effects.  相似文献   

14.
Field experiments were conducted for four years, between 1998 and 2002, in two olive grove soils of adult olive orchards (Olea europaea L. cv. Cornicabra) in a clay loam soil in Seseña (Toledo, Spain) and in a sandy loam soil in Aranjuez (Madrid, Spain). There were four treatments, sewage sludge compost (SSC), sewage sludge compost plus urea (SSC+U), urea (U) and control (C). Each treatment was replicated four times and two depths were studied (0-15 and 15-30 cm). Once a year, before spreading sewage sludge compost, soil samples were taken at depths of 0 to 15 cm and 15 to 30 cm. Organic matter, total Kjeldhal nitrogen, phosphorus availability, pH, and electric conductivity were measured. No differences were found between treatment on organic matter and electric conductivity after four years of application of sewage sludge compost to two olive grove soils. In relation to nitrogen content, sewage sludge compost, only in Seseña, produced higher nitrogen soil content than the traditional urea treatment. Sewage sludge compost applied on olive grove soils improved the Phosphorus availability for the olive tree. In Aranjuez, the use of sewage sludge compost increased the pH of the soil with respect to Urea and Control plots. In Seseña, the reverse effect was found.  相似文献   

15.
The survival of free-living rhizobia in soil is sensitive to elevated heavy metals in soil and can explain adverse effects of metals on symbiotic nitrogen fixation in soils. A survival experiment was set-up to derive critical cadmium (Cd) and zinc (Zn) concentrations in a range of field-contaminated soils in the absence of their host plant (Trifolium repens L.). Soils applied with metal salts or sewage sludge >10 years ago were sampled and were inoculated with Rhizobium leguminosarum bv. trifolii (108 cells g−1 soil) and incubated outdoors for up to 6 months. The most probable number (MPN) decreased 1-2 orders of magnitude in uncontaminated soils during the incubation. There was no significant effect of total metal concentrations on rhizobia survival in soils contaminated with Cd salts or with high Ni/Cd sewage sludge with highest Cd concentrations between 18 and 118 mg Cd kg−1. In contrast, survival was strongly affected in soils contaminated by sewage sludge, where Zn was the principal metal contaminant. Neither total Cd nor soil solution Cd was large enough to attribute these effects to Cd when compared with the soil series, where Cd salts had been applied. The MPN decreased at least one order of magnitude above total Zn concentrations of 233 mg Zn kg−1 (soil pH 5.6) and 876 mg Zn kg−1 (soil pH 6.3). The EC50s of log MPN were 204 and 604 mg Zn kg−1, respectively, and were lower than those for the symbiotic nitrogen fixation measured in the pot trial on the same soils (respectively 602 and 737 mg Zn kg−1). This study corroborates the evidence that symbiotic nitrogen fixation is affected by Zn in the field when Zn decreases the free-living population of rhizobia to below a critical threshold.  相似文献   

16.
Accurate prediction of plant-available N release from sewage sludge is necessary to optimize crop yields and minimize NO3– leaching to groundwater. We conducted a 1.5-year study with three maize crops to determine N mineralization from an urban sewage sludge from Barueri, State of São Paulo, Brazil, and its potential to contaminate groundwater with NO3–. The soil at the experimental site was a loamy/clayey-textured Dark Red Dystroferric Oxisol. The treatments consisted of: plots without chemical fertilization or sludge, plots with complete chemical fertilization, and plots receiving four different doses of sewage sludge. Dose 1 was calculated at the agronomic N rate, while doses 2, 3 and 4 were, respectively, two, four, and eight times dose 1. The inorganic N addition increased with the rate of biosolid application. The high NO3– concentrations in relation to NH4+ were associated with intense soil nitrification. High N losses occurred for the first 27 days after soil sludge incorporation, even at the lowest dose, suggesting that land application of sewage sludge based on the N requirement of the crop may be overestimating the amount of sewage sludge to be applied.  相似文献   

17.
污泥农用对土壤和作物重金属累积及作物产量的影响   总被引：20，自引：2，他引：20  
以3 a定位试验为基础,比较3种不同处理的污泥肥料（消化污泥、污泥堆肥及污泥复混肥）农田施用下土壤养分、土壤和作物籽粒中Mn、Cu、Zn、Pb、Cd 5种重金属的积累以及作物产量的变化情况,以阐明污泥农用对土壤及作物的影响。研究表明,3种污泥肥料提高了土壤中氮素和有机质的含量;与空白和普通化肥处理相比,3种污泥肥料增加了土壤中Mn和Cu的含量,而对土壤交换态重金属含量没有显著影响;3种污泥处理均增加了小麦籽粒中Zn的含量;相对普通化肥处理,3种污泥肥料处理对小麦和玉米产量均无显著影响。合理施用污泥肥料可以有效地提高作物产量;污泥肥料施用对土壤重金属有一定累积效应,但短期施用对土壤比较安全。  相似文献   

18.
Sewage sludge application to semiarid grassland may represent a beneficial means of utilizing this waste product for restoration of degraded sites. Consequently, dried municipal sewage sludge was applied at three rates (22.5, 45, and 90 Mg ha–1) to a degraded semiarid grassland soil in order to determine the effects of sludge amendments on forage productivity, soil heavy metal content, and metal uptake by blue grama (Bouteloua gracilis).Soil and plant properties in control and amended plots were measured after 1, 2, and 5 growing seasons.Soil nutrients increased linearly with increased sludge application in the first two growing seasons. Consequently, forage quality and total production of blue grama improved significantly over the unamended control as the tissue levels of N, P, K, and crude protein increased. Cadmium and Pb in the sludge-treated plots did not increase significantly over the control after 1 and 2 growing seasons. Levels of DTPA-extractable soil micronutrients (Cu, Fe, Mn, Zn) increased linearly with increased sludge application rate to soil concentrations recommended for adequate plant growth. Soil N, P, and K concentrations remained higher in the sludge-amended soils after 5 growing seasons, while Cu and Cd increased to slightly above desireable limits as the soil pH decreased to 7.4 and 7.0 in the 45 and 90 Mg ha–1 treatments, respectively. However, with the exception of Mn which remained within desirable limits, metal concentrations (including Cu and Cd) in blue grama tissue were not significantly different from the control treatment after five growing seasons. Based on soil and plant tissue metal concentrations, it appears that sludge applied at rates between 22.5 and 45 Mg ha–1 will maintain the most favorable nutrient levels coupled with significant improvements in forage production in this semiarid grassland environment.  相似文献   

19.
The influence of sewage sludge on microbial activity in soil The effect of untreated, pasteurized and irradiated sewage sludge on soil biology was studied in model and field experiments. Sewage sludge from the sewage plant Geiselbullach in the west of Munich city was used for these experiments. The investigations were performed with 4 soil types according to the different locations. All the results demonstrate that there is an increase in biomass after application of sewage sludge while there were definite influences from the location. No significant relation could be observed according to sewage sludge treatment. Under favourable lab conditions the mineralization of the organic matter applied to the soil with higher amounts of sewage sludge induces in short time a definite decrease in pH. In accordance with these changes in pH there is a corresponding decrease in microbial biomass. Early results on the influence of microbial N-cycle demonstrated that amounts of sewage sludge applied under practical conditions brought an increase in denitrification capacity of the soil. In the experiment with soils nitrification rate was doubled after sewage sludge application.  相似文献   

20.
Three diverse field-moist soil samples were treated with five sewage sludges (applied at five loading rates) containing high concentrations of heavy metals. Urease activity was assayed after 0, 3, 7, 14 and 30 days of incubation. Results showed that when soils were treated with the sewage sludges, urease activity was often inhibited at the lower loading rates (2.2 and 8.9mg sludge g?1 soil), but was enhanced substantially with the higher application rates (22.2, 44.4 and 100 mg sludge g?1 soil). Inhibition of urease activity in the sewage sludge amended-soils ranged from 4 to 37% (Domino soil), 8–27% (Hesperia soil), and 3–49% (Ramona soil) at various times of incubation. Inhibition of the enzyme activity was attributed to the presence of heavy metals in the sludges. The increased activity of urease in the sludge-amended soils at the highest application rate (100 mg sludge g?1 soil) ranged from 1.13 to 5.00-fold (Domino soil), 1.20–4.04-fold (Hesperia soil), and 1.13–5.40-fold (Ramona soil). Enhanced urease activity was believed to be due to the additional source of organic matter and nutrients supplied by the sludge which stimulated microbial activity and subsequent urease synthesis.  相似文献   

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