Removal of Cd from aqueous solution by chitosan coated MgO-biochar and its in-situ remediation of Cd-contaminated soil.

In this study, magnesium oxide biochar-chitosan composite (MgO-BCR-W) prepared through modification with MgCl2 and chitosan was investigated as an adsorbent for the removal of Cd from the aquatic and soil environment. Kinetic and thermodynamics revealed that the Cd(II) adsorption onto MgO-BCR-W was well fitted by pseudo-second-order and the Langmuir adsorption isotherm. The adsorption capacities of rice husk biochar (BCR) and MgO-BCR-W for Cd(II) reached 11.09 mg/g and 59.66 mg/g, respectively. Attractively, the computed values of RL ranged between 0 and 1, suggesting that the adsorption of Cd(II) onto MgO-BCR-W is favourable. Characterisations of the adsorbents revealed that the synergistic effect of surface complexation and precipitation mechanisms played a major role in the removal of Cd. In soil incubation experiment, the addition of MgO-BCR-W at the level of 2% was most effective in Cd stabilization compared to the control, which reduced the content of bioavailable Cd by 22.32%. Furthermore, it reduced the acid extractable Cd by 24.77%, while increased the residual Cd content by 22.24%. The results demonstrated that MgO-BCR-W could be used as an effective and eco-friendly adsorbent for Cd remediation in both water and soil environment.

Determination of phthalate esters in soil using a quick, easy, cheap, effective, rugged, and safe method followed by GC-MS.

A quick, easy, cheap, effective, rugged, and safe procedure was designed to extract pesticide residues from fruits and vegetables with a high percentage of water. It has not been used extensively for the extraction of phthalate esters from sediments, soils, and sludges. In this work, this procedure was combined with gas chromatography with mass spectrometry to determine 16 selected phthalate esters in soil. The extraction efficiency of the samples was improved by ultrasonic extraction and dissolution of the soil samples in ultra-pure water, which promoted the dispersion of the samples. Furthermore, we have simplified the extraction step and reduced the risk of organic solvent contamination by minimizing the use of organic solvents. Different extraction solvents and clean-up adsorbents were compared to optimize the procedure. Dichloromethane/n-hexane (1:1, v/v) and n-hexane/acetone (1:1, v/v) were selected as the extractants from the six extraction solvents tested. C18/primary secondary amine (1:1, m/m) was selected as the sorbent from the five clean-up adsorbents tested. The recoveries from the spiked soils ranged from 70.00 to 117.90% with relative standard deviation values of 0.67-4.62%. The proposed approach was satisfactorily applied for the determination of phthalate esters in 12 contaminated soil samples.

Design and Optimization of a Hybrid-Driven Waist Rehabilitation Robot.

In this paper a waist rehabilitation robot driven by cables and pneumatic artificial muscles (PAMs) has been conceptualized and designed. In the process of mechanism design, the human body structure, the waist movement characteristics, and the actuators' driving characteristics are the main considerable factors to make the hybrid-driven waist rehabilitation robot (HWRR) cost-effective, safe, flexible, and well-adapted. A variety of sensors are chosen to measure the position and orientation of the recovery patient to ensure patient safety at the same time as the structure design. According to the structure specialty and function, the HWRR is divided into two independent parallel robots: the waist twist device and the lower limb traction device. Then these two devices are analyzed and evaluated, respectively. Considering the characters of the human body in the HWRR, the inverse kinematics and statics are studied when the waist and the lower limb are considered as a spring and link, respectively. Based on the inverse kinematics and statics, the effect of the contraction parameter of the PAM is considered in the optimization of the waist twist device, and the lower limb traction device is optimized using particle swarm optimization (PSO) to minimize the global conditioning number over the feasible workspace. As a result of the optimization, an optimal rehabilitation robot design is obtained and the condition number of the Jacobian matrix over the feasible workspace is also calculated.

Formation, breakage and re-formation of flocs formed by cationic starch.

The efficiency of flocculation can be significantly improved through floc breakage and re-formation under appropriate conditions. To obtain a better understanding of the mechanisms involved and to relate floc properties to separation efficiency, the effects of mixing conditions on the formation, breakage and re-formation of flocs formed by kaolin and cationic starch were investigated through conventional jar test procedure and continuous optical monitoring. It has been found that the breakage of flocs was fully reversible and the polymer flocculant could resist strong shear; even having been sheared for four times, the flocculation index (FI) value would be higher than that of the original flocs. The results indicated flocs formed at neutral and alkaline conditions had better shear resistance than those at acidification conditions, and the mode of floc rupture was large-scale fragmentation.

Sources and health risks of heavy metals in soils and vegetables from intensive human intervention areas in South China.

Heavy metal pollution greatly harms the soil environment and poses threats to food safety and human health. This study aimed to quantify and analyze the sources of heavy metals and assess the health risks associated with the human intake of contaminated vegetables in South China. Heavy metals (Cd, As, Hg, Cu, Ni, Pb, Zn, and Cr) in soil and vegetables (leaf vegetables, legume vegetables, and cucurbits) were investigated and evaluated for contamination. By combining the correlation analysis (CA), positive matrix factorization (PMF), and GeoDetector model, source apportionments were comprehensively identified. Results showed that Cd was the predominant element in soils throughout the study area. Industrial (28.36 %, 20.24 %, 31.50 %), agricultural (27.19 %, 46.50 %, 27.30 %), besides traffic, atmospheric deposition and natural sources were identified as the dominant sources of heavy metals in GD01, GD02, and GD03, respectively. The human health risk assessment showed that the total non-cancer risk of heavy metals (i.e., Cr, Ni, As, Cd, and Pb) ingested through vegetables was 2.3E+00 for children and 9.67E-01 for adults, and the total cancer risk for children was 2.54E-02 and 1.07E-02 for adults, both of which exceeded acceptable levels. It is worth noting that children are more susceptible to health risks due to the consumption of contaminated vegetables than adults.

Flocculation mechanism by a novel combined aluminum-ferrous-starch flocculant (CAFS).

A combined flocculant (CAFS) was prepared with Al(2)(SO(4))(3)·18H(2)O, FeSO(4)·7H(2)O and starch. The flocculation mechanism of reactive brilliant red X-3B was studied. The results showed that CAFS was a cationic polymeric flocculant with high charge density, and its mesh starch chains grafted polyaluminum and polyferrous. At the preliminary stage, the main flocculation mechanism was adsorption and charge neutralization. At a later stage, the high molecular weight and flexible linear chains of CAFS initiated bridge-aggregation and sweep-flocculation. Moreover, the zeta potential and dynamic changes of flocs were closely related to flocculant dosages and the pH. The optimum dosage of CAFS and pH value were 0.990 mg/L and 5.0. Taken together, these results suggested CAFS as a novel flocculant in water treatment, with good results for the studied conditions.

A novel interpolation method to predict soil heavy metals based on a genetic algorithm and neural network model.

To improve the prediction accuracy of soil heavy metals (HMs) by spatial interpolation, a novel interpolation method based on genetic algorithm and neural network model (GANN model), which integrates soil properties and environmental factors, was proposed to predict the soil HM content. Eleven soil HMs (Cu, Pb, Zn, Cd, Ni, Cr, Hg, As, Co, V and Mn) were predicted using the GANN model. The results showed that the model had a good prediction performance with correlation coefficients (R2) varying from 0.7901 to 0.9776. Compared with other traditional interpolation methods, including inverse distance weighting (IDW), ordinary kriging (OK), universal kriging (UK), and spline with barriers interpolation (SBI) methods, the GANN model had a relatively lower root mean square error value, ranging from 0.0497 to 77.43, suggesting that the GANN model might be a more accurate spatial interpolation method and the soil properties together with the environmental geographical factors played key roles in prediction of soil HMs.

Quantitative analysis on the mechanism of Cd2+ removal by MgCl2-modified biochar in aqueous solutions.

In this study, a pristine biochar (BC) and MgCl2-modified biochar (MBC) were prepared using Pennisetum sp. straw for removing Cd2+ from aqueous solutions. Scanning electron microscope (SEM) imaging combined with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), as well as the surface area and porosity analyses were used to reveal the physico-chemical characteristics of the pristine and modified adsorbents. Results suggested that MgCl2 impregnation during the synthesis had enhanced the specific surface area and pore volume of the biochar. Batch adsorption experiments indicated that the Cd2+ adsorption data of MBC fitted the Langmuir isothermal and pseudo-second order kinetic models, indicating a chemical adsorption was undergoing in the system. The maximum adsorption capacity of Cd2+ on MBC was 763.12 mg/g, which was 11.15 times higher than that of the pristine BC. The Cd2+ removal by MBC was mainly attributed to the mechanisms in an order: Cd(OH)2 precipitation (73.43%) > ion exchange (22.67%) > Cd2+-π interaction (3.88%), with negligible contributions from functional group complexation, electrostatic attraction and physical adsorption. The MBC could thus be used as a promising adsorbent for Cd2+ removal from aqueous solutions.

Effect of lignosulfonate on the adsorption performance of hematite for Cd(II).

Lignin is a precursor of humus in soil and sediment. Lignin can be separated from vascular plants in the form of lignosulfonate via pulping processes. On the other hand, composites of iron oxide and organic matter can adsorb heavy metals, and thus influence the migration of these heavy metals in the environment. In this paper, a hematite/lignosulfonate composite (HLS) was prepared via coprecipitation to compare the adsorption performance of hematite (α-Fe2O3) toward Cd(II) before and after the incorporation of lignosulfonate (LS). The HLS is found to exhibit a weakly crystalline structure and possess a large number of nanoscale particles. Specific surface area of HLS (291.97 m2/g) is about 11 times that of α-Fe2O3, and the pore volume of HLS (0.22 cm3/g) is twice that of α-Fe2O3. The adsorption of Cd(II) is well illustrated by the pseudo-second-order adsorption kinetics and the initial adsorption rate (h) of HLS is 13.83 times that of α-Fe2O3. The maximum adsorption capacities are significantly improved from 4.89-6.35 mg/g (α-Fe2O3) to 39.03-53.65 mg/g (HLS). A greater affinity and more favorable association between Cd(II) and HLS is observed via fitting models. The incorporation of LS provides HLS with significantly better adsorption properties toward Cd(II) than α-Fe2O3, as is further confirmed by FT-IR and XPS characterization. Fe-O-O-H and Fe-O-H structures as well as more hydroxyl groups are observed, which promote the adsorption performance since the process are mainly influenced by complexation via coordination bonds.

Di-(2-Ethylhexyl) Phthalate as a Chemical Indicator for Phthalic Acid Esters: An Investigation into Phthalic Acid Esters in Cultivated Fields and E-Waste Dismantling Sites.

Phthalic acid esters (PAEs) represent an ongoing pollution problem and have attracted extensive attention due to their ubiquitous presence in the environment. We investigated the distribution of 6 PAEs (benzyl butyl phthalate [BBP], dibutyl phthalate [DBP], di-(2-ethylhexyl) phthalate [DEHP], diethyl phthalate [DEP], dimethyl phthalate [DMP], and di-n-octyl phthalate [DnOP]) in cultivated soils, including vegetable fields and paddy fields, as well as the soils of E-waste dismantling sites. We also explored the relationship between the particle size of soils and the distribution of PAEs, put forward a novel method to forecast the occurrence and fate of PAEs in soils with DEHP used as a chemical indicator, and made a preliminary assessment of the potential ecological risks of the 6 target compounds in soils. The results showed that the detection rate of target PAEs was 100%, and that the concentrations of ∑6 PAEs ranged from 1.2 to 7.3 mg/kg in vegetable fields, 1.2 to 1.5 mg/kg in paddy fields, and 11.8 to 17.9 mg/kg in E-waste dismantling sites. In addition, DEHP exhibited the maximum concentrations (0.480-15.34 mg/kg) in all soil samples. The results also showed that in the wake of decreasing particle size, increasing soil organic carbon would enhance the sorption of PAEs in soils. Moreover, the correlation formula of DEHP successfully predicted the concentrations of other PAEs and ∑ 6 PAEs in soils, suggesting that DEHP could be a dependable chemical indicator for forecasting the environmental occurrence of PAEs in soils. Based on the residual levels in the trial sites and limited toxicity data, high risks to soil organisms are expected for DBP, DEP, and DEHP, and low-medium risks for BBP, DnOP, and DMP. Environ Toxicol Chem 2019;00:1-11. © 2019 SETAC.

Adsorption of Cd(II) from aqueous solution by Pennisetum sp. straw biochars derived from different modification methods.

The adsorption mechanism of Cd (II) was investigated by Pennisetum sp. straw biochars (JBC) that were modified by two different methods: KMnO4 impregnation (JMB1) and H2O2 impregnation (JMB2). A scanning electron microscope and energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), a Fourier transform infrared spectrometer (FTIR), and a Brunauer-Emmett-Teller (BET) specific surface area analysis were employed to examine the physicochemical characteristics of biochars. The Cd(II) adsorption kinetic fit, the Langmuir model well, and the maximum adsorption capacity occurred in the following order: JMB1 (90.32 mg/g) > JMB2 (45.18 mg/g) > JBC (41.79 mg/g), suggesting that JMB1 had an excellent adsorption performance. Finally, X-ray photoelectron spectroscopy (XPS) was used to explore the main adsorption mechanism. Our results showed that JMB1 was an excellent adsorbent in removing Cd(II) from aqueous solution.

Potassium lignosulfonate as a washing agent for remediating lead and copper co-contaminated soils.

Lignin is a renewable aromatic polymer which is present in large quantities in the cell walls of terrestrial plants and is the main binding agent for fibrous plant components. Potassium lignosulfonate (KLS), as a by-product of pulping processes, can be applied to agricultural fields as a soil conditioner and chelate fertilizer. In this study, based on its solubility and complexing ability, batch washing and column leaching was explored to evaluate the potential application of KLS in the washing remediation of soil contaminated with lead and copper. Under optimum conditions KLS concentration of 8%, pH of 5.24 and 6 h duration, the removal ratios for the simulated and mining area soils in the batch experiment were 67.40% and 52.87% respectively, for Pb and 73.42% and 55.20% respectively, for Cu. In the column leaching experiment, the removal efficiencies of Pb and Cu increased with solution volume and that the removal ratios of the simulated and mining area soils were 36.46% and 20.31%, respectively, for Pb and 39.74% and 22.76%, respectively, for Cu. KLS can reduce the ratio of acid-soluble and reducible fractions, which may have the most potential hazardous and poisonous for plants. Cation exchange capacity (CEC) and pH of soil were all stable after washing. However, the organic matter and available K, N, and P in the treated soil, which are important factors for plant growth increased significantly. This study showed that KLS can remove Pb and Cu from soil, while improve nutrient (ammonium nitrogen, available phosphorus and available potassium) levels of soil.

Enhanced adsorption of Cd(II) from aqueous solution by a magnesium oxide-rice husk biochar composite.

In this study, a magnesium oxide-rice husk biochar composite (MgO-BCR) was successfully prepared by a MgO impregnation method, and its adsorption performance was investigated in Cd(II) aqueous solution. A pseudo-second-order kinetic model described the Cd(II) adsorption behaviour on BCR and MgO-BCR well, while a Langmuir adsorption isotherm was more suitable for Cd(II) adsorption on the adsorbent. The fitting results of the monolayer model indicated that the number of ions captured by per site varied between 0.97 and 1.09. The calculated thermodynamic parameters indicated that Cd(II) adsorption onto MgO-BCR was spontaneous and endothermic. Characterisation of the adsorbent revealed that in situ precipitation, surface complexation, and electrostatic attraction contributed to the Cd(II) adsorption. The adsorption capacities of rice husk biochar (BCR) and MgO-BCR for Cd(II) reached 6.36 and 18.1 mg/g, respectively. The results demonstrated that MgO-BCR composite could be used as an effective and eco-friendly adsorbent to enhance the removal of Cd(II) from aqueous solution.

[Effect of Calcium Silicate-biological Humus Fertilizer Composite on Uptake of Cd by Shallots from Contaminated Agricultural Soil].

The safety of vegetable production is a key link in reducing cadmium consumption through the food chains. Field experiments were conducted to investigate the effects of composite materials (calcium silicate-biological humus fertilizer) on the growth of shallots and the uptake of Cd by shallots from contaminated agricultural soil. Four treatments (T1: 0.5% calcium silicate+0.5% biological humus fertilizer; T2: 0.5% calcium silicate+1.0% biological humus fertilizer; T3: 1.0% calcium silicate+0.5% biological humus fertilizer; and T4: 1.0% calcium silicate+1.0% biological humus fertilizer) and a control group (CK) were adopted. The changes in soil pH, DTPA-extractable Cd, biomass of shallots, and cadmium concentrations in shallots over time under different treatments were analyzed. The results show that the application of composite amendments decreased the concentrations of DTPA-extractable Cd in the soil. In particular, after T3 treatment, the concentrations of soil DTPA-extractable Cd decreased by 60.71%, 49.54%, 44.63%, and 58.94% after 14, 28, 42, and 56 d, respectively. The biomass of the shallots aboveground increased significantly by 107.99% and 107.19% after T3 and T4 treatment, respectively. The composite amendments exhibited different effects on the uptake of Cd by the shallots from the soil, and the T4 treatment was the most effective in immobilizing Cd and inhibiting translocation of Cd into the shallots. The cadmium concentration in the shallots decreased by 43.80% after 56 d with the T4 treatment. In conclusion, T4 is the optimum treatment for soil cadmium immobilization.

Recalcitrant carbon components in glomalin-related soil protein facilitate soil organic carbon preservation in tropical forests.

Glomalin-related soil protein (GRSP) is known as an important microbial by-product which is crucial for preserving or accumulating soil organic carbon (SOC). However, the underlying mechanisms are not well understood. In this study, we investigated the chemical structures of GRSP and its relationship with SOC using 13C nuclear magnetic resonance (NMR) in three tropical forests. The three forests, including a planted forest (PF), a secondary forest (MF) and a primary forest (BF), were selected to represent the natural successional process after disturbance in southern China. Results showed that the average concentrations of GRSP were (3.94 ± 1.09) mg cm-3 and accounting for (3.38 ± 1.15)% of the SOC in the top 10 cm soil. NMR analysis indicated rich aromatic C (~30%) and carboxyl C (~40%) in GRSP, and abundant alkyl C (~30%) and O-alkyl C (~50%) in SOC. The recalcitrance indexes (RI), as defined as the ratio of sum of alkyl C and aromatic C over sum of O-alkyl C and carboxyl C, was (98.6 ± 18.9)%, (145.5 ± 10.9)% and (20.7 ± 0.3)% in GRSP higher than that in SOC in the PF, MF and BF, respectively. This study demonstrated that the stubborn structure of GRSP probably regulate the resistance of SOC sequestration in tropical forests, especially in the planted and secondary forests.

Phosphorus uptake in four tree species under nitrogen addition in subtropical China.

Atmospheric N deposition is a serious problem in subtropical China where N is present in large amounts but P is deficient. Several studies hypothesized that N2 fixers can overcome phosphorus limitation by trading fixed N2 for soil phosphorus. In order to know whether N2 fixers could invest fixed N2 in extracellular phosphatase production and could stimulate arbuscular mycorrhizal fungi (AMF) to acquire soil P in N-rich subtropical China, an open-air greenhouse experiment was carried out. Two N2 fixers (Acacia mangium and Ormosia pinnata) and two non-N2 fixers (Schima superba and Pinus massoniana) were exposed to three levels of N addition: 5.6 kg ha-1 a-1 (ambient N), 15.6 kg ha-1 a-1 (middle N), and 20.6 kg ha-1 a-1 (high N). We found that the capacity of plants to acquire soil P in N-rich subtropical China is species specific. The higher P uptake rates were found for N2 fixers than non-N2 fixers under N addition, which were related to the greater soil APA and higher AMF (p < 0.01) in the soil of N2 fixers. However, with time, high N addition decreased more significant quantities of soil microbial phospholipid fatty acids (PLFAs) in the soil of N2 fixers than that of non-N2 fixers (p < 0.05). We conclude that N2 fixers have higher P uptake capacity than non-N2 fixers under ambient N deposition in subtropical China. However, continuing N deposition in the future might affect P uptake ability of N2 fixers as high N addition would decrease soil microbial PLFAs of N2 fixers.

[Influencing Mechanism of Eh, pH and Iron on the Release of Arsenic in Paddy Soil].

The massive release of soil arsenic and its enrichment in rice are significantly associated with the flooded and anaerobic management in paddy soil. Soil redox potential (Eh), pH and iron oxides exert remarkable impacts on arsenic release, which remain to be explored. In this study, long-term aerobic and anaerobic as well as intermittent aerobic incubation treatments were applied to investigate the influences of Eh, pH and iron content on arsenic release. It was found that anaerobic and flooded treatment contributed to the highest arsenic release. With decreasing Eh, significant enhancement in As(Ⅲ) and As(Ⅴ) contents in soil solution was observed. Particularly, As(Ⅲ) and As(Ⅴ) contents during the second phase increased by 1.37 and 0.99 µg·L-1compared with those in the first phase. Conversely, significant reduction in soil arsenic release (P<0.05) occurred when intermittent aerobic treatment was adopted, and the lowest level of arsenic release was observed along with the longest treatment time (6 d). The exponent relationships between arsenic and soil Eh, pH and Fe2+ content were also established, which indicated that arsenic release could be accelerated by lower pH and elevated Eh. In addition, a significant positive correlation was also found between iron(Ⅱ) content and arsenic content in soil solution. Since low Eh and elevated pH served as critical factors driving arsenic release, intermittent and aerobic water management was proved to be an effective method for the inhibition of arsenic release and uptake and accumulation of arsenic by rice.

[Effect of Different Iron Minerals on Bioaccessibility of Soil Arsenic Using in vitro Methods].

To explore the effects of different iron minerals on soil arsenic bioaccessibility, ferrihydrite, goethite and hematite were used in PBET, SBRC and IVG in-vitro experiments in this study. The relationship between arsenic bioavailability in gastric, small intestinal phases and arsenic speciation was also studied. The results showed that when 1% ferrihydrite was added, arsenic bioavailability in gastric phase was 2.22%, 5.11% and 7.43% by PBET, SBRC and IVG methods, respectively, while in the small intestinal phase it was 3.39%, 2.33% and 6.18%. At an elevated ferrihydrite dosage of 2%, significant difference in arsenic bioavailability was observed in both phases (P<0.05). According to in vitro experiments, the addition of the same amount of different iron minerals had contributed to the decrease in arsenic bioavailability to varying extents in contrast with the blank group, in the descending order of ferrihydrite(F1) > goethite(G1) > hematite(H1) (F2 > G2 > H2). Total arsenic in exchangeable (F1) and specifically sorbed (F2) state was found positively correlated with arsenic bioavailability in gastric phase by PBET, SBRC and IVG methods, the correlation coefficient of which being r=0.93, P=0.002, r=0.90, P=0.004 and r=0.89,P=0.006, respectively. It was also found that arsenic bioavailability in gastric phase was positively correlated with total arsenic in F1 and F2 states by PBET(r=0.94,P=0.001) and IVG (r=0.87,P=0.009) methods, but no significant correlation was observed by SBRC method. Additionally, three in vitro experiments showed that amorphous iron bound arsenic had significant negative correlation with arsenic bioavailability in gastric phase and small intestinal phase, except that no correlation was found in small intestinal phase by SBRC method.

Removal of both cationic and anionic contaminants by amphoteric starch.

A novel amphoteric starch incorporating quaternary ammonium and phosphate groups was applied to investigate the efficiency and mechanism of cationic and anionic contaminant treatment. Its flocculation abilities for kaolin suspension and copper-containing wastewater were evaluated by turbidity reduction and copper removal efficiency, respectively. And the kinetics of formation, breakage and subsequent re-formation of aggregates were monitored using a Photometric Dispersion Analyzer (PDA) and characterized by flocculation index (FI). The results showed that amphoteric starch possessed the advantages of being lower-dosages-consuming and being stronger in shear resistance than cationic starch, and exhibited a good flocculation efficiency over a wide pH range from 3.0 to 11.0.

Sap flow response of Eucaylyptus (Eucalyptus urophylla) to environmental stress in South China.

Sap flow and environmental conditions were monitored at two Eucalyptus (Eucalyptus urophylla S.T.Blake) plantations at Hetou and Jijia, located in Leizhou, Zhanjiang, Guangdong Province. It was found that daily sap flux density (SFD) of Eucalyptus was closely related to daily atmospheric vapor pressure deficit (VPD) (R2 = 0.76, P = 0.01 at Hetou and R2 = 0.7021, P = 0.01 at Jijia) at both sites. No significant relationship existed between daily SFD and mean daily air temperature at both sites. Daily SFD varied with wind speed Y = -17585X3 + 15147X2 - 1250.7X + 2278.4 (R2 = 0.68; P = 0.01) at Hetou and Y = -101.67X3 - 1.65X2 - 376.4X + 1914.8 (R2 = 0.40, P = 0.05) at Jijia, where Y was daily SFD, X was daily wind speed. Experimental observations yielded the following data: (1) the critical lower and upper daily VPD threshold were 0 and 2 kPa, within which daily SFD varied from 540+/-70 L/(m2.d) to 4739+/-115 L/(m2.d) at Hetou site, from 397+/-26 L/(m2.d) to 3414+/-191 L/(m2.d) at Jijia site; (2) Diurnal SFDs at Hetou site were much higher under low relative humidity (< 30%) and slightly lower under high relative humidity (> 80%) compared with those at the Jijia site; (3) The upper and lower threshold of daily and diurnal RAD for the optimal water use of E. urophylla plantations were 18+/-2.7 and 2+/-1 MJ/(m2.d), 669 and 0 J/(cm2.h) during the observation period.