Effects of water-soluble chitosan on Hylotelephium spectabile and soybean growth, as well as Cd uptake and phytoextraction efficiency in a co-planting cultivation system.

Intercropping a Cd-accumulator with economically valuable crops is common in slightly or moderately Cd-polluted farmland soils. A field experiment was conducted to evaluate the effects of water-soluble chitosan (WSC) on the growth and Cd uptake of the Cd-accumulator Hylotelephium spectabile and soybean (Glycine max) during a co-cultivation in Cd-contaminated agricultural soil (WSC, 0 and 10 g·m-2). The results indicated that soybean yields were highest in response to the intercropping and WSC treatment. The results from the field trials generally showed that intercropping and WSC treatments significantly decreased Cd concentrations in inedible parts of soybean by 42.9-72.1% (except for stems), in the meantime, increased 95.8%-334.6% in shoot and root tissues of H. spectabile compared with the control (p < 0.05). The data revealed that Cd uptake was highest for H. spectabile during the intercropping and WSC treatment. The application of WSC in the intercropping system significantly increased the uptake of Cd by H. spectabile, but not by soybean. The findings of this study suggest that combining an intercropping system with a WSC treatment may be better for remediating Cd-contaminated soils than other methods involving the growth of a single hyperaccumulator.

This paper clearly focused on the accumulation and uptake of Cd in the system of intercropping of Cd-accumulator (Hylotelephium spectable) and soybean (Glycine max) grown in Cd-polluted farmland soils supplied with water-soluble chitosan (WSC) under field conditions. Some studies mainly focused on active agent to promote remediation efficiency of (hyper) accumulators. This study indicated that combining the intercropping system with WSC may be better for remediating Cd-contaminated soils than the methods involving a single hyperaccumulator.

Potential evaluation of different intercropping remediation modes based on remediation efficiency and economic benefits - a case study of arsenic-contaminated soil.

Hyperaccumulator-cash crop intercropping remediation is a research hotspot for heavy metal contaminated farmland, but few studies evaluated its feasibility based on practice. Field experiments and survey statistics were conducted to obtain parameters of Pteris vittata-Citrus reticulata/Zea mays intercropping, and potential of intercropping remediation was evaluated based on remediation efficiency and economic benefits. The results showed that intercropping hyperaccumulator with cash crop (especially herbs) had a certain negative effect on remediation efficiency because of the influence on planting density and harvest times of hyperaccumulator; while trees could partly alleviate this effect. Until achieving the predetermined target, the net remediation cost of P. vittata-Z. mays was 18.2 $/g As, followed by P. vittata monoculture (13.3 $/g) and P. vittata-C. reticulata (8.6 $/g). Based on the proposed evaluation model, nealy half of the P. vittata intercropping modes had low economic benefits, insufficient to compensate the cost of sacrificing remediation efficiency. Based on the data from two soil remediation projects, when net income of cash crops intercropped with As-hyperaccumulators exceeded 5865/1607 $/hm2 (herbs/trees), the economic benefit of intercropping will be relatively obvious. Therefore, cash crops should be considered from three aspects: planting conditions, spatial allocation and economic benefits. Novelty statement: This work analyzed remediation efficiency and economic benefits of intercropping remediation. An economic benefit evaluation model was established to evaluate intercropping remediation modes. The selection principle and net income threshold of cash crops in intercropping was put forward for the first time.[Figure: see text]HighlightsThe selection principle of cash crops in intercropping remediation was put forward.An evaluation model of P. vittata intercropping remediation was established.The net cost of extracting 1.0 g of soil As in each remediation mode was proposed.Net income of herb/tree intercropped with P. vittata should exceed 5865/1607 $/hm2.

Safe utilization of cadmium- and lead-contaminated farmland by cultivating a winter rapeseed/maize rotation compared with two phytoextraction approaches.

Compared with phytoextraction, growing suitable crops may be a more profitable and practical approach for managing contaminated farmland, especially when there are multiple pollutants. In this 5-year field study, the phytoaccumulator Hylotelephium spectabile, the high-biomass species amaranth (Amaranthus hypochondriacus), and a winter rapeseed/maize rotation crop were cultivated on farmland contaminated with cadmium (Cd) and lead (Pb). Over 4 consecutive years, the annual Cd uptake and extraction efficiency of H. spectabile was 117.6 g hm-2 and 2.36%, respectively. The Cd extraction efficiency of amaranth was equivalent to that of H. spectabile because of its high biomass, and it extracted more Pb (660-2210 g hm-2) from the soil than did H. spectabile. However, neither of these species was able to remediate contaminated farmland rapidly and inexpensively, even with enhancing strategies such as variety screening and the addition of fertilizers and a chelating agent. A safe utilization approach to cultivate rapeseed instead of wheat significantly reduced the carcinogenic and noncarcinogenic risks. The concentrations of heavy metals in rapeseed oil were below the limits specified in the Chinese national food standard, and the heavy metal concentrations in the byproducts (rapeseed meal and straw) were below the limits specified in Chinese national standards for organic fertilizer and feed. The cost of safe utilization was one-quarter that of phytoextraction, and the net economic benefit was 33.5%-123.5% higher than that of wheat crops. Therefore, the rapeseed/maize rotation is a profitable and feasible approach for the safe utilization of Cd- and Pb-contaminated farmland on the northern plains of China.

Recommended risk screening values for Cd in high geological background area of Guangxi, China.

Because of unusually high cadmium concentrations in the soil, the risk screening values of soil Cd in the existing standard is not applicable to the Cd high geological background areas. The aim of our study is to explore recommended risk screening values applicable for Cd high geological background areas of Guangxi, China, to help locals with land management and guarantee the quality and safety of crops as well as providing the theoretical basis for guiding the production safety. A total of 903 pairs of rice samples and root soil samples were collected. The Cd concentration of soil-rice samples and soil pH were determined. The scatter diagram method was used to gradually increase the screening values, and the value with the most samples in the correct interval was counted as the recommended risk screening value. The soil Cd concentrations ranged from 0.06 to 7.08 mg·kg-1 and the rice Cd ranged from 0.002 to 1.488 mg·kg-1; 64.89% of soil samples exceed the RSVs and 27.8% of rice samples exceed the allowable limit of Cd. The recommended risk screening values of Cd in study area were 0.5, 0.7, 1.5, and 2.4 mg·kg-1 for soil with pH ≤ 5.5, 5.5 < pH ≤ 6.5, 6.5 < pH ≤ 7.5, and pH > 7.5, respectively. Compared with the standard screening value, the accuracy of using the recommended screening value as the reference value to judge whether the Cd concentration in rice exceeds the standard was increased by 12%, 20%, 21%, and 47%, respectively. The recommended screening value can be used as the standard value to better indicate the soil environmental quality in the study area.

Effectiveness of predicting spatial contaminant distributions at industrial sites using partitioned interpolation method.

Soil pollution at industrial sites is an important issue in China and in most other regions of the world. The accurate prediction of the spatial distribution of pollutants at contaminated industrial sites is a requirement for the development of most soil remediation strategies, and is commonly performed using spatial interpolation methods. However, significant and abrupt variations in the spatial distribution of pollutants decrease prediction accuracy. During this study, the use of partition interpolation methods was applied to benzo fluoranthene in four soil layers at a contaminated site to determine their ability to improve prediction accuracy in comparison to unpartitioned methods. The examined methods for partitioned interpolation included inverse distance weighting (IDW), radial basis function (RBF), and ordinary kriging (OK). The prediction results of the three methods for partitioned interpolation were compared, and the applicability of partition interpolation was determined. The prediction error associated with the partitioned interpolation methods decreased by 70% compared to unpartitioned interpolation. The prediction accuracy of IDW-based partition interpolation was higher than that of RBF- and OK-based partition interpolation techniques, and it was suitable for identification of highly polluted areas. Partition interpolation is also applicable to 12 other PAHs controlled by USEPA that can be detected, and the prediction effects could also verify this interpolation choice. In addition, the results also demonstrated that the more the maximum concentration deviated from the "norm", the greater the prediction error was caused by the smoothing effects of the interpolation models. These results suggest that the partition interpolation with IDW method can be effectively used to obtain relatively accurate spatial contaminant distribution information, and to identify highly polluted areas.

Effects of Soil Amendments on Soil Pb Bioavailability and Pb Absorption by a low-Pb Accumulator Kumquat Grown in Two Types of Pb-Contaminated Soils.

A pot experiment was conducted to investigate the effects of 0.5% and 1% alkaline, clay mineral and phosphorus amendments, as well as 2% and 5% organic amendments, on lead (Pb) soil bioavailability and Pb absorption by the low-Pb accumulator kumquat (Citrus japonica Thunb.) 'Cuipi' in two typical Pb-contaminated soils, Jiyuan and Yangshuo, from northern and southern China, respectively. The diethylenetriaminepentaacetic acid-extractable Pb soil concentration and Pb accumulation in kumquat significantly decreased with amendment additions. High amendment doses had greater inhibitory effects than low doses but no significant effects on the kumquat's biomass in the two typical soils. Alkaline, but not clay mineral, amendments greatly increased the soil pH level. Organic amendments effectively reduced Pb accumulation owing to their strong adsorptive capacities. Thus, using organic amendments combined with a low-Pb accumulator kumquat forms a suitable farming practice for producing safe fruit in the two common types of Pb-contaminated soils in China.

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments.

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb3(PO4)2 and Cd5(PO4)2SiO4 crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Perlite as the partial substitute for organic bulking agent during sewage sludge composting.

Composting is an efficient and cost-effective technology for sewage sludge treatment, and bulking agents are essential in sewage sludge composting. In this study, perlite was chosen as inorganic bulking agent to partially substitute for the organic bulking agent. Variations in the temperature, bulk density, moisture content, pH, electrical conductivity, organic carbon, nitrogen, phosphorus and potassium were detected during sewage sludge composting. The treatment with a mass ratio of spent mushroom substrate to perlite at 3:1 exhibited the highest pile temperature and the best effect on reducing bulk density and moisture content. In addition, Fourier transform infrared spectra showed that perlite promotes the degradation of organic matter during the composting process, and the germination index showed that the compost from all treatments was safe for agricultural application. When the mass ratios of spent mushroom substrate and perlite at 3:1 and 2:2 were chosen as bulking agents, the sewage sludge compost product could be used to produce plant cultivation substrate, and economic benefits could be obtained from sewage sludge composting according to comprehensive cost analysis.

Impact of Soil Water on the Spectral Characteristics and Accuracy of Energy-Dispersive X-ray Fluorescence Measurement.

Soil water is a major interference in the on-site analysis of soil by energy-dispersive X-ray fluorescence. Apparent consequences of this interference include lowered readings for elemental concentrations and significant changes in spectral characteristics in wet soils compared with dry soils. A rigorous interpretation on this issue remains unresolved. Thus, this study evaluated the impact of soil water on the detection of Ca, Ti, Mn, Fe, Cu, Zn, As, Rb, Sr, and Pb. Specimens were prepared from 11 certified reference soils and 3 field soils with water contents from 0 to ∼40 wt %. Results from three commercial models revealed that the readings were subjected to respective internal quantification algorithms; therefore, they could not provide a fundamental perspective of this issue. We analyzed the spectra to examine the mechanism underlying this phenomenon. The spectra of wet soils feature elevated baseline, increased Compton and Rayleigh scatter peaks, and lowered characteristic peaks of elements. Previous studies attributed the lowered characteristic peaks to the absorption of fluorescent X-rays by water and considered soil water and dry soil as separate layers in the calculation. This work argues that wet soils should be treated as mixtures. Water becomes part of the soil matrix and leads to lower attenuation capability, which could be explained by the matrix effect. Meanwhile, the mass fraction of analytes is lowered because of dilution. Results confirmed that dilution lowers the characteristic peaks, whereas the matrix effect heightens them. When estimating the elemental concentrations on a wet weight basis, the matrix effect becomes the major interference. The Compton compensation method provided satisfying results on correcting the matrix effect caused by soil water on Zn, As, Rb, Sr, and Pb.

Subcellular cadmium distribution and antioxidant enzymatic activities in the leaves of four Hylotelephium spectabile populations exhibit differences in phytoextraction potential.

Hylotelephium spectabile with high tolerance to cadmium (Cd) might be a potential candidate for phytoremediation. However, the mechanisms for Cd accumulation and tolerance in H. spectabile are poorly understood. Four H. spectabile populations, namely HB1, HB2, JS, and LN, were selected to investigate their Cd extraction potential and the underlying mechanism of Cd accumulation, focusing on subcellular distribution and antioxidant enzymes. The Cd concentration, bioconcentration factor and transfer factor of the LN was significantly higher than other populations, particularly with increasing Cd exposure, and no obvious growth inhibition observed. Segregation of excessive Cd to Cd-rich granule in LN was much higher than other populations which reveal one possible mechanism of Cd accumulation. A significant increase in superoxide dismutase (SOD) and catalase (CAT) activities with increasing Cd stress suggested SOD and CAT contribute to the Cd tolerance of H. spectabile. LN displayed significantly higher and constant peroxidase (POD) activities than other populations, which indicated that an effective mechanism existed in the LN to cope with Cd stress. Therefore, the subcellular distribution and antioxidant enzymes might play important roles in Cd accumulation and tolerance of H. spectabile. LN possessed high Cd extraction potential, and further studies under field conditions are warranted.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting.

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS2 and ZnCu(P2O7) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ±â€¯11.8%, which was the highest among all treatments.

Comparison of common spatial interpolation methods for analyzing pollutant spatial distributions at contaminated sites.

Accurate prediction of the spatial distribution of pollutants in soils based on applicable interpolation methods is often the basis for soil remediation in contaminated sites. However, the applicable interpolation method has not been determined for contaminated sites due to the complex spatial distribution characteristics and stronger local spatial variability of pollutants. In this research, the prediction accuracies of three interpolation methods (including the different values of their parameters) for the spatial distribution of benzo[b]fluoranthene (BbF) in four soil layers were compared. These included inverse distance weighting (IDW), radial basis function (RBF), ordinary kriging (OK). The results indicated: (1) IDW1 is applicable for the first layer, RBF-IMQ is applicable to the second, third, and fourth layers. (2) For IDW, the prediction error is bigger with high weight where high values and low values intersect, while the prediction error is smaller where high (or low) values aggregated distribution. (3) For RBF, if the pollutant concentration trend at the predicted location is consistent with the known points in its neighborhood, the prediction accuracy is higher. (4) IDW is suitable for fitting more drastic curved surfaces, while RBF is more effective for relatively gentle curved surfaces and OK is reasonable for curved surfaces without local outliers. (5) The interpolation uncertainty is positively associated with the contaminant concentration and local spatial variability. Therefore, we suggest the selection of the applicable interpolation model must be based on the principle of the model and the spatial distribution characteristics of the pollutants.

Comparison among soil additives for enhancing Pteris vittata L.: Phytoremediation of As-contaminated soil.

Pot experiments were conducted to assess the effects of monoammonium phosphate (NH4H2PO4) and citric acid (CA) on the arsenic uptake of Chinese brake fern (Pteris vittata L. in two typical arsenic-contaminated soils i.e. fluvo-aquic and brown) from Jiyuan (JY) City and Baoding (BD) City in Northern China. NH4H2PO4 improved the biomass of P. vittata, whereas CA exerted no significant influence. NH4H2PO4 and CA both increased the arsenic uptake of P. vittata by 6.08 and 2.72 times, respectively, in fluvo-aquic soil and 4.20 and 2.52 times, respectively, in brown soil. Moreover, CA, but not NH4H2PO4, promoted the transfer of arsenic from the root to the frond. NH4H2PO4 and CA increased Olsen's arsenic contents in the soils and promoted the transformation of residual arsenic and crystalline Fe/Al oxide-bound arsenic to nonspecifically and specifically sorbed arsenic. This study proved that P. vittata can be used in Northern China. Applying NH4H2PO4 and CA can enhance the effectiveness of P. vittata in the phytoremediation of arsenic-contaminated soils.

Oxygen Monitoring Equipment for Sewage-Sludge Composting and Its Application to Aeration Optimization.

Oxygen is an important parameter for organic-waste composting, and continuous control of the oxygen in a composting pile may be beneficial. The oxygen consumption rate can be used to measure the degree of biological oxidation and decomposition of organic matter. However, without having a real-time online device to monitor oxygen levels in the composting pile, the adjustment and optimization of the composting process cannot be directly implemented. In the present study, we researched and developed such a system, and then tested its stability, reliability, and characteristics. The test results showed that the equipment was accurate and stable, and produced good responses with good repeatability. The equilibrium time required to detect oxygen concentration in the composting pile was 50 s, and the response time for oxygen detection was less than 2 s. The equipment could monitor oxygen concentration online and in real time to optimize the aeration strategy for the compost depending on the concentration indicated by the oxygen-measuring equipment.

Comparison of chelates for enhancing Ricinus communis L. phytoremediation of Cd and Pb contaminated soil.

We studied chelate effects on castor bean (Ricinus communis L.) growth. These effects included Cd and Pb accumulation in plant tissues and the chemical behavior of Cd and Pb in the plant rhizosphere and non-rhizosphere. Tests were conducted in a glasshouse using the rhizobag method. Two castor bean cultivars (Zibo-3 and Zibo-9) were grown in soil contaminated with 3.53mg/kg Cd and 274mg/kg Pb. The soil was treated with citric acid (CA), ethylenediamine disuccinic acid (EDDS) or ethylenediamine tetraacetic acid (EDTA) (5mmol/kg). EDDS-treated soil produced 28.8% and 59.4% greater biomass for Zibo-3 and Zibo-9 respectively. In contrast, CA and EDTA inhibited the growth of the two cultivars. Zibo-9 had greater tolerance than Zibo-3 to chelate toxicity. Based on Cd and Pb plant uptake, EDDS could substitute for EDTA for phytoremediation of Cd in soil. EDTA was the most effective of the three chelates for Pb phytoremediation but it is less suitable for field use due to toxicology environmental persistence. Acid extractable Cd and Pb in the rhizosphere or reducible Cd and Pb in the non-rhizosphere of soil were the main influences on Cd and Pb accumulation in castor bean.

Subcellular cadmium distribution and antioxidant enzymatic activities in the leaves of two castor (Ricinus communis L.) cultivars exhibit differences in Cd accumulation.

The aims of this study were: (1) the study of cadmium (Cd) accumulation and toxicity in different castor cultivars (Ricinus communis L.); (2) to investigate changes in antioxidant enzymatic activities and the subcellular distribution of Cd in young and old leaves from two different castor cultivars, after exposure to two different Cd concentrations, and explore the underlying mechanism of Cd detoxification focusing on antioxidant enzymes and subcellular compartmentalization. The Cd concentration, toxicity, and subcellular distribution, as well as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were measured in Zibo-3 and Zibo-9 cultivars after exposure to two different concentrations of Cd (2mg/L and 5mg/L) for 10 days. This research revealed Cd accumulation characteristics in castor are root>stem>young leaf>old leaf. Castor tolerance was Cd dose exposure and the cultivars themselves dependent. Investigation of subcellular Cd partitioning showed that Cd accumulated mainly in the heat stable protein (HSP) and cellular debris fractions, followed by the Cd rich granule (MRG), heat denatured protein (HDP), and organelle fractions. With increasing Cd concentration in nutrient solution, the decreased detoxified fractions (BDM) and the increased Cd-sensitive fractions (MSF) in young leaves may indicate the increased Cd toxicity in castor cultivars. The BDM-Cd fractions or MSF-Cd in old leaves may be linked with Cd tolerance of different cultivars of castor. The antioxidant enzymes that govern Cd detoxification were not found to be active in leaves. Taken together, these results indicate Cd tolerance and toxicity in castor can be explained by subcellular partitioning.

Impact of composting strategies on the degradation of nonylphenol in sewage sludge.

Nonylphenol can be present in sewage sludge, and this can limit the use of the sewage sludge to amend soil. Composting is one of the most efficient and economical methods of making sewage sludge stable and harmless. The nonylphenol degradation rates during composting with added bulking agents and with aeration applied were studied. Three organic bulking agents (sawdust, corn stalk, and mushroom residue) were added to sewage sludge, and the effects of the bulking agents used and the amount added on nonylphenol degradation were determined. The highest apparent nonylphenol degradation rate (71.6%) was found for sewage sludge containing 20% mushroom residue. The lowest apparent nonylphenol degradation rate (22.5%) was found for sewage sludge containing 20% sawdust. The temperature of the composting pile of sewage sludge containing 20% sawdust became too high for nonylphenol to be efficiently degraded, and the apparent nonylphenol degradation rate was lower than was found for sewage sludge containing 10% sawdust. Increasing the ventilating time from 5 to 15 min increased the apparent nonylphenol degradation rate from 19.7 to 41.6%. Using appropriate aerobic conditions facilitates the degradation of nonylphenol in sewage sludge, decreasing the risks posed by sewage sludge applied to land. Adding too much of a bulking agent can decrease the amount of the nonylphenol degraded. Increasing the ventilating time and the amount of air supplied can increase the amount of nonylphenol degraded even if doing so causes the composting pile temperature to remain low.

[A Comparison of Arsenic Speciation in 13 Pteris vittata L. Populations].

Synchrotron radiation X-ray absorption near edge structure was employed to study the arsenic (As) speciation in 13 Pteris vittata L. populations collected from 7 provinces, cities, and autonomous regions in China. As in roots of P. vittata was mainly combined with oxygen (O), with a small amount of As combined with glutathione (GSH). Populations from Hunan and Guangxi provinces showed higher percentages of As-GSH in soots. As in roots of P. vittata was predominated with As(V), with the percentage of As(V) to the total As being 59.6±0.6%~83.8±3.8%. The As(V) percentage was in the order of HN5HN3>HN1>TW>CQ>AH>FJ>HN5>HN2>GX2>GX3>HN4>GX1, within the range of 2.4%~12.9%. Different from that in roots, As in shoots was predominated with As(III), with no As(V) detected. The disclosure of As speciation in the roots and shoots of P. vittata contributes to the future research on As accumulation mechanism.

Evaluation of Field Portable X-Ray Fluorescence Performance for the Analysis of Ni in Soil.

As a rapid, in-situ analysis method, Field portable X-ray fluorescence spectrometry (FP-XRF) can be widely applied in soil heavy metals analysis field. Whereas, some factors may affect FP-XRF performance and restrict the application. Studies have proved that FP-XRF has poorer performance when the concentration of target element is low, and soil moisture and particle size will affect FP-XRF performance. But few studies have been conducted in depth. This study took an example of Ni, demonstrated the relationship between Ni concentration and FP-XRF performance on accuracy and precision, and gave a critical value. Effects of soil moisture and particle size on accuracy and precision also had been compared. Results show that, FP-XRF performance is related to Ni concentration and the critical value is 400 mg x kg(-1). Relative standard deviation (RSD) and relative uncertainty decrease while the Ni concentration is below 400 mg x kg(-1), hence FP-XRF performance improves with increasing Ni concentration in this range; RSD and relative uncertainty change little while the Ni concentration is above 400 mg x kg(-1), hence FP-XRF performance does not have correlation with Ni concentration any more. For in-situ analysis, the relative uncertainty contributed by soil moisture is 3.77%, and the relative certainty contributed by particle size is 0.56%. Effect of soil moisture is evidently more serious than particle size both on accuracy and precision.

Improvement of salinity in sewage sludge compost prior to its utilization as nursery substrate.

UNLABELLED: Soluble salts are enriched in sewage sludge compost because of their inherent derivation. Accordingly, the content of soluble salt in sludge compost is usually much higher than most seedlings can tolerate. To determine whether sludge compost is suitable for use as a nursery substrate, some experiments were conducted. Reduction of the electrical conductivity (EC) value could improve seed germination in saturated extract from sludge compost. In addition, water elution and mixing dilution with raw soil were all shown to be able to alleviate saline inhibition on seed germination and seedling growth, including stem diameter, seedling height, and above-ground weight. Overall, salinity is a crucial problem when sewage sludge compost is reused as a nursery substrate, and some effective and convenient approaches to reduce salt should be served prior to its reuse. IMPLICATIONS: Sewage sludge after being composted is usually reused as organic fertilizer or plant substrate. However, salt is the main problem during its reclamation. What is the highest salt level the seedling can tolerate? Which types of salts are effective in salinity of sludge-amended substrate? Meanwhile, can the salinity be reduced through water elution or soil mixing dilution? This paper is the first to investigate the salinity and its reduction of sewage sludge compost prior to its use in the development of nursery substrate.