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1.
Leaching column experiments were conducted to determine the degree of mobility of heavy metals (HMs) and nutrients after the addition of municipal solid sewage sludge (MSS) in a sandy‐loam soil. Treatments were (1) soil application of low metal content MSS, (2) soil application of metal‐enriched municipal solid sewage sludge (EMSS), and (3) control. The MSS application represented a dose of 200 Mg dry weight (dw) ha–1. Soil columns were incubated at room temperature for 15 d and were irrigated daily with distilled water to make a total of 557 mm. Leachates were collected and analyzed for HMs and nutrients. The Ni and Pb added to soil via MSS and EMSS were found to be leached through the 20 cm columns of calcareous sandy soil although Ni and Pb concentrations in the percolate were small relative to the total amounts of metals applied. Losses of K+ from the EMSS, MSS, and control were 92.5, 82.0, and 52.5 kg ha–1, respectively. Losses of Mg2+ were in the range from 104.4 (control treatment) to 295.2 kg ha–1 (EMSS), while the loss of Ca2+ was in the range from 265.0 (control treatment) to 568.2 kg ha–1 (EMSS). The results showed that the amounts of P leached from EMSS (3.02 kg ha–1) and MSS (2.97 kg–1 ha–1) were significantly larger than those from the control treatment (1.54 kg ha–1). The geochemical code Visual MINTEQ was used to calculate saturation indices. Leaching of P in different treatments was controlled by rate‐limited dissolution of hydroxyapatite, β‐tri‐Ca phosphate, and octa‐Ca phosphate. The results indicate that application of MSS to a sandy soil, at the loading rate used in this study, may pose a risk in terms of groundwater contamination with Ni, Pb, and the studied nutrients.  相似文献   

2.
Effect of digested sewage sludge on the metabolism of three year old spruce and pine trees. Three year old Norway spruce and Scots pine trees were grown in mixtures of sand and sewage sludge. The mixtures used were composed of 5 litres of sand and 1.25 or 1.67 litres of digested sewage sludges from municipal waste water treatment plants. A mixture of 5 litres of sand and 1.67 litres of peat was used as a control. In all cases sewage sludge depressed growth as measured by height and the yields of fresh material. The contents of N, Ca, Mg, Zn in the needle dry matter were higher than in control. The P content was only increased in the newly formed needles in the high sewage sludge treatments. However, the corresponding Mn contents were depressed, also the K contents in spruce. The higher rate of nitrogen assimilation, in the sewage sludge treatments especially in spruce, lead to a greater accumulation of the amino acid arginine and also to a reduction in the content of organic acids and polyphenols. These effects do not explain why some plants died. For spruce a lethal factor appears to be the depression of water uptake combined with high transpiration. The ratio of K/Ca in the needles was extremly low, which indicated a possibility of both potassium deficiency and calcium toxicity. The observed enrichment of proline is also associated with water stress. Scot pine was more sensitive than spruce to treatment with sewage sludge. In all treatments with sludge some Scot pine trees died, especially when municipal wastewater sewage sludge was used.  相似文献   

3.
Soil and plant samples were collected from chlorotic plantations of Grand fir (Abies grandis) and Douglas-fir (Pseudotsuga menziesii) in Winter, 1989. The soils had been amended in 1981 with an average of 300 dry Mg ha?1 of municipal sewage sludge. The sludge amendment resulted in an N application rate of approximately 8000 kg ha?1. Foliage analysis indicated a severe Mg deficiency (0.25 g kg?1 in sludge-treated vs. 0.93 g kg?1 in untreated area) might be the cause of chlorosis. No other nutrient showed concentrations in the deficient or toxic ranges. Trace metal levels in foliage were elevated significantly for Ni, Cd and Cr in sludge-treated sites, but not toxic levels. Soil samples taken to a depth of 1.4 m indicated the potential for soil acidification (up to 0.9 pH unit) in soil surface horizons. In addition, exchangeable Ca, Mg and K may have been depleted in surface horizons. Exchangeable Al and Fe were greater in the surface of sludge-treated sites. These observations and the loss of much of the nitrogen added during the sludge amendment indicated that nitrification and cation leaching was likely the mechanism for acidification and depletion of exchangeable cations. Fertilization of the plantation with MgSO4 or dolomitic limestone was carried out in Spring 1990. New foliage collected in June, 1990 was non-chlorotic and significantly higher in Mg concentration than unfertilized foliage (1.1. vs. 0.7 g kg?1, respectively). Results of this study indicate that it is important to assess the potential for initiating a nutrient deficiency due to secondary effects of sludge application in forest systems.  相似文献   

4.
A long-term experiment set up by G. W. Dimbleby to test the effect of birch as a soil improver on a heather moor podzol is described. After 30 yr, an acid woodland type of vegetation developed under the birch trees with Deschampsia flexuosa and Vaccinium myrtillus locally dominant. The mean annual dry matter production of stems and branches was approximately 2.9 t ha?1. The raw humus layer removed as an experimental treatment had re-formed. Its pH, about 3.4, had remained unchanged for 15 yr. The mean extractable Ca content of the upper 3 cm horizon of the birch plots and of the control plots under heather had increased and on some of the birch plots the concentrations of exchangeable Ca were somewhat higher than those under heather. The N content of the Ol + Of, Oh and Ea horizons was higher under the birch than under heather but there was no evidence of movement of Fe out of the ironpan under the influence of birch. The profile under birch remained a fully differentiated podzol.  相似文献   

5.
A greenhouse experiment was conducted to evaluate the availability of metals from sewage sludge and inorganic salts, and the effect of pH and soil type on yield and metal (Zn, Cu, Cd and Ni) uptake by wheat (Triticum aestivum L. var. ‘holly’). Soils used in this study were Hartsells sandy loam (fine-loamy, siliceous Thermic Typic Hapludult) and Decatur silty clay loam (Clayey, kaolinitic, Thermic Rhodic Paleudult). Two treatments of sewage sludge containing metals were applied at the rate of 20 and 100 mt ha?1. Inorganic Salts of Zn, Cu, Cd, and Ni were applied (as sulfate salts) at concentrations equivalent to those found in the 20 and 100 mt ha?1 sludge. One treatment consisted of inorganic metals plus sewage at the 20 Mg ha?1 rate. Two soil pH levels, one at field pH (below 6.0) and another pH adjusted between 6.5 and 7.0 were used. Wheat plants were harvested four weeks after germination. Two more subsequent harvests were made at four week intervals. For each harvest, dry matter yield increased as the rate of sludge application increased for both soil types. The soil pH also influenced the dry matter yield. High yield was observed when the pH was adjusted between 6.5 to 7.0 for both soils. An increase in yield was also observed at each subsequent harvest for most of the treatments. Inorganic salt treatments produced lower dry matter yields when compared with the sludge. Both sludge application and metal salts increased plant tissue concentration of Zn, Cu, Cd, and Ni at field pH for both soils. However, increasing the pH of the soil for both sludge and inorganic salt treatments generally decreased the tissue concentration of the above metals.  相似文献   

6.
Dry weights and bioelement contents in biomass of Scots pine (aboveground) were estimated on some differently treated plots from one acidification experiment in North Sweden. Dry weight estimates of Scots pine biomass showed relatively small differences between treatments. The content of N, P, K, Ca, Mg, Mn, and S showed significant differences in a number of cases. The amount of N in different crown components increased; fertilizer-N recovered in the biomass was up to 10% of that added (in total, the NPK-plots received 1260 kg N ha?1). The concentration of other elements (P, K, Ca, Mg, Mn and S) showed some effect of the treatments, but was not as marked as that of N. Especially interesting is a decrease in the level of Mg in needles and shoots on the NPK-treated plots. The concentration of S was influenced by application of acid, but much more by NPK-fertilization throughout the period.  相似文献   

7.
Dry weights and bioelement contents in biomass of Scots pine (aboveground) were estimated on some differently treated plots from one acidification experiment in North Sweden. Dry weight estimates of Scots pine biomass showed relatively small differences between treatments. The content of N, P, K, Ca, Mg, Mn, and S showed significant differences in a number of cases. The amount of N in different crown components increased; fertilizer-N recovered in the biomass was up to 10% of that added (in total, the NPK-plots received 1260 kg N ha?1). The concentration of other elements (P, K, Ca, Mg, Mn and S) showed some effect of the treatments, but was not as marked as that of N. Especially interesting is a decrease in the level of Mg in needles and shoots on the NPK-treated plots. The concentration of S was influenced by application of acid, but much more by NPK-fertilization throughout the period.  相似文献   

8.
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   

9.
《Journal of plant nutrition》2013,36(9):1347-1365
The distribution of the nutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) in maize (Zea mays L.) was studied in a long-term sewage sludge field application in an acid coarse sandy soil at Bordeaux, France. Sewage sludge had been applied since 1974 at 100 t (dry weight) ha?1 per 2 years (SS 100) in plots cultivated annually with maize. Treatment with farmyard manure (FYM) at 10 t (dry weight) ha?1 per year and mineral fertilization served as control. Five plants per treatment were investigated at six different growth stages. The plants were separated into their different organs and the distribution of nutrients was determined in up to 12 different plant parts. Sludge application did not significantly influence the nutrient partitioning in maize, but improved slightly the plants' nutrient status compared with the FYM treatment. Grain yield was similar for both treatments. The values for N, P, K, Ca, Mg and Fe content in sludge-treated plants were in the recommended range for optimal growth. Thus, sewage sludge would be a valuable source for maize nutrition even after long-term application, if the critically high copper (Cu) and zinc (Zn) concentrations, previously reported in these sludge-amended plants, could be avoided by the use of sludge low in these elements.  相似文献   

10.
The foliar status and the factors affecting the foliar chemistry in a natural Aleppo pine forest grown on calcareous soils in Greece were examined. It was found that the Aleppo pine needles had significantly higher calcium (Ca) concentrations, but significantly lower concentrations of magnesium (Mg), potassium (K), phosphorus (P), iron (Fe) and manganese (Mn) than the respective average concentrations of natural Aleppo pine forests in Spain. It was also found that only foliar Ca and Mn had a significant correlation with the exchangeable Ca and available Mn in soils, respectively. Principal component analysis showed that the nature of the calcareous parent material, (colluvial rocks and hard limestones) were the main factors affecting both foliar and soil chemistry. This finding is important as colluvial soils always coexist with other soil types in hilly and mountainous regions containing calcareous material.  相似文献   

11.
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   

12.
Peat and needle samples were collected from an old Cu, Zn and Ni ore-prospecting experiment at Alkkia, SW Finland. The element rates applied were 100–400 kg ha-1 for Ni and 100–1000 kg ha-1 for Cu and Zn. The heavy metal toxicity of Scots pine stand was estimated primarily on the basis of stand mortality during 28 yr. The tolerance limit values were applied to pine stands growing along a Cu-Ni deposition gradient (0.9–10 km) at Harjavalta copper smelter, SW Finland. Very high heavy metal concentrations in the pine needles and strong accumulation in the surface humus and uppermost peat layers were found. A Cu concentration of 840, Ni 180 and Zn 220 mg kg-1 in peat 0–10 cm, and a Cu concentration of 50, Ni 30 and Zn 175 mg kg-1 in the current needles of the uppermost whorl are proposed as toxicity limits for peatland forests at Harjavalta. According to the heavy metal amounts in peat 0–20 cm, the toxicity area for Cu extended to a distance of 2.0 km, for Ni about 1.0 km and for Zn 0.4 km to the west of the emission point source.  相似文献   

13.
Preliminary leaching column and greenhouse plant uptake studies were conducted in two soils with contrasting characteristics amended with varying rates (0 to 148.3 Mg ha?1) of incinerated sewage sludge (ISS) and weathered sewage sludge (WISS) to estimate the leaching losses of trace elements from the soils amended with incinerated sewage sludge by products and to evaluate the uptake and accumulation of these elements in various parts of Sorghum vulgaris var. sudanense Hitche. (“Sorgrass''), a Sorghum-Sudan grass hybrid. Results of this study indicated that leaching of Cr, Cd, Zn, Cu, Ni, Fe and Mn from soils amended with ISS and WISS increased with increasing rates of amendment. Results of the leaching column study further revealed greater leaching losses from coarse-textured soil compared to medium-textured soil and also from ISS amended soils than with WISS amended soils. Results further suggested that the type of element and the interaction between the element and soil properties affected the leachability of various trace elements. The uptake study indicated uptake and accumulation of trace elements by plant parts increased with increasing rates of amendments. Greater plant uptake and accumulation of trace elements were observed in plant parts grown in soils amended with ISS compared to that of WISS. Results also indicated a greater accumulation of trace elements in below ground part of the plants (roots) compared to that was observed in above ground parts (shoots). Limited data obtained from this one season preliminary studies demonstrated that incinerated sewage sludge products from wastewater treatment plants could be used as soil amendments at low application (no more than 24.7 Mg ha?1) for optimum plant growth, and dry matter yield without resulting in substantial accumulation of metals in plant parts at concentrations above the recommended critical limits and without causing significant leaching losses of various trace elements. It is imperative that long-term field studies are necessary to evaluate the long-term impact of using these new products in leaching and accumulation of various trace elements in plants and soils.  相似文献   

14.

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.

  相似文献   

15.
In boreal forests ericaceous shrubs often dominate the forest floor vegetation. Nitrogen enrichment has been shown to decrease shrub abundance and in this study we explored whether it also affects the root associated fungal communities. Fine roots of Vaccinium myrtillus were collected in a Norway spruce dominated forest and of Vaccinium vitis-idaea in a Scots pine dominated forest. In both forests, nitrogen enrichment was experimentally induced by adding 12.5 and 50 kg N ha−1 yr−1 for 12 (spruce forest) and four (pine forest) years. Based on terminal restriction fragment length polymorphisms, subcloning and sequencing analyses, the root associated fungal communities were examined. We found 93 fungal species including Asco-, Basidio- and Zygo-mycota. In general, the Rhizoscyphus ericae aggregate was the most dominant and this was followed by Herpotrichiellaceae and Sebacina. Ordination analysis revealed that nitrogen enrichment did not change species composition of the fungal communities in neither the spruce nor the pine forest, while fungal community structures were clearly discriminated between the dominant shrub species in each forest. Similarly, no fungal species showed a significant response to nitrogen enrichment. Therefore, nitrogen enrichment appears to have no effect on root associated fungi of understorey dwarf shrubs in boreal forests, while it is clear that spruce and pine forests harbor distinctive communities of these fungi.  相似文献   

16.
A field experiment was conducted to evaluate the effect of organic amendments on grain yield, leaf chlorophyll content, and some morphological characteristics of three soybean cultivars in Mazandaran province located at north of Iran in 2006. Chemical fertilizer (75 kg ha?1 potassium sulfate and triple superphosphate), two levels of municipal solid waste, vermicompost and sewage sludge biosolid (20 and 40 Mg ha?1) enriched with%50 chemical fertilizers needed by soil were applied to soybean cultivars (‘032’ and ‘033’ promising lines and ‘JK’ cultivar). The experiment was carried out in split plot based on randomized complete block design with three replications. Some important plant characters such as grain yield, leaf chlorophyll content, number of branches, number of nodes on the main stem, length of internodes, stem diameter, first pod height and plant height were determined. Results showed that application of 40 Mg ha?1 sewage sludge enriched with chemical fertilizers increased plant grain yield and stem diameter and application of 40 Mg ha?1 vermicompost enriched with half chemical fertilizer increased the number of nodes on the main stem, significantly. The maximum length of internodes, first pod height and plant height were obtained when the 40 Mg ha?1 sewage sludge and vermicompost enriched with half chemical fertilizer in ‘032’ line was used. Biomass, number of branches, stem diameter, number of nodes on the main stem of soybean cultivars had a positive and significant correlation with grain yield.  相似文献   

17.
Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha?1 y?1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha?1 under pine and 27 Mg ha?1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha?1 y?1) than on ridges(29 Mg ha?1 y?1) and bottoms (12 Mg ha?1 y?1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.  相似文献   

18.
SW Sweden has very acidic forest soils because of deposition ofair-borne pollutants. Large-scale liming and fertilization have been proposed as countermeasures against a possible future development of forest decline. To test the effects of suggested treatments, liming (3 or 6 t ha1) and fertilization with easily soluble PK (25 or 50 kg P, 80 or 160 kg K ha1) or N(20 kg N ha1 annually in the form of NH4 NO3) were applied in different combinations in four experiments in 30–60 yr-old Picea abies forests in SW Sweden. Four yearsafter the initial application of the fertilizers, samples were taken from the O-horizon and the two uppermost 5 cm thick layersof the mineral soil. Their pH(H2O) and easily extractable Ca, Mg, K, P and inorganic N contents were analyzed. Samples werealso incubated to estimate net N mineralization and potential nitrification rates. Liming increased the pH by 0.6–1 unit in the O-horizon, and by 0.1 unit in the mineral soil. The Ca + Mg content increased by 15–25 kmolc ha1 (4–8 foldincrease) in the O-horizon of the limed plots, while an increaseof 5 kmolc ha1 (two-fold increase) was observed in theuppermost 5 cm of the mineral soil. Liming did not affect extractable P, K or inorganic N contents. Net N mineralization and potential nitrification rates in the O-horizon were enhanced 1.5- and 6-fold, respectively, by liming, but it had no apparenteffect in the mineral soil. N fertilization caused a slight increase (1.5 kg ha1) in the content of inorganic N, buthad no effects on the other variables measured. The amount ofextractable P was raised by 16 kg ha1 in plots given the high P dose (50 kg ha1), but no other effects of PK fertilization were detected.  相似文献   

19.
Summary A greenhouse study was conducted to examine the residual effects of sewage sludge on soybean Glycine max (L.) Merr., nodulation, and N fixation. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage in soils (Typic Paleudults) obtained from plots where heat-treated sludge had been applied in 1976 at rates equal to 0, 56,112, and 224 Mg ha–1 high (7.0) and low (6.2) soil pH regimes were established by CaCO3 additions. Sludge and soil pH treatments resulted in clearly defined differences in metal uptake by soybean shoots. Plant Zn, Cd, and Ni concentrations were greater on pH 6.2, sludge-amended soil than on the pH 7.0, amended soil. At low soil pH, soybean Zn and Cd concentrations, respectively, increased from 41 and 0.19 mg kg–1 (control) to 120 and 0.58 mg kg–1 at the 224 Mg hat sludge rate. At the high soil pH and 224 hg hat sludge rate, Zn and Cd concentrations were 45 and 0.15 mg kg–1, respectively.Symbiotic N fixation provided 90% of the total N accumulation. Total N accumulation, shoot N concentration, dry matter, and N fixation by nodulating soybeans exhibited a significant linear increase with sludge rate. Total N accumulation, dry matter, and N fixation were significantly greater at high soil pH. For high and low soil pH, respectively, N fixation increased from 422 and 382 mg N per plant (control) to 614 and 518 mg N per plant at the 224 Mg ha–1 sludge rate. While soybean nodulation also increased linearly on sludge-amended soil, a significant rate times pH interaction for nodule number indicated that nodulation was less strongly enhanced by sludge at low soil pH.  相似文献   

20.
Abstract

The objective of this study was to determine the effects of nitrogen fertilizer sources of ammonium sulphate and municipal sewage sludge on yield, N content and uptake of the maize (Zea mays L.). Nutrient and heavy metals were determined in soil and plant. The experiment with three sludge rates (256, 513 and 1026 kg total N ha?1 or 9.5, 18.0 and 38.1 t ha?1 sludge), two nitrogen rates (80 and 160 kg N ha?1) and zero-N control were conducted on a clay loam soils under irrigated conditions in Eastern Anatolia region in Turkey. Treatments were arranged in a randomized complete block design with four replications. Yield, N content and total N uptake of maize increased significantly with sludge application. 9.5 t and 19.0 t ha?1 sewage sludge applications did not significantly affect heavy metal content of leaf and grain. However, 38.1 t ha?1 sludge applications increased leaf Pb and Zn. DTPA-extractable Cd, Cu, Fe, Pb and Zn concentrations of the soil increased at applications of 38.1 t ha?1 sewage sludge, whereas applications of 9.5 t and 19.0 t ha?1 sludge only resulted in elevated levels of Cu and Zn, We conclude that if sewage sludge is to be used in production of maize, applications rate up to 19 t ha?1 could be accepted. However, this means also that the N requirement of maize crop is not covered by the sludge; therefore, the rest of nitrogen could be supplied as inorganic N.  相似文献   

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