Oxygen diffusion in biochar-based mixtures as plant growth media: Experimental and modelling.

A large amount of agricultural waste is produced annually. Producing biochar is an excellent solution for waste management, resource recovery, emission reduction, energy production, reduction in transportation and enhancing carbon sequestration. This study was done to investigate the aeration status of biochar-based growth media as compared with the commercial soilless medium of cocopeat-perlite. Biochars from oven-dried residues were produced by slow pyrolysis at 300 (B300) and 500°C (B500) with a rate of 2°C min-1 and using a continuous inflow of nitrogen. Sawdust (Sd), wheat straw (WS), rice hull (Rh), palm bunches (Plm) and sugarcane bagasse (SC), their biochars, vermiculite (V) and zeolite (Z) were used to prepare 13 mixed growth media. Oxygen diffusion coefficient (Dp) of media was measured at six matric potentials (h) of -5, -10, -15, -20, -40 and -60 hPa. Troeh et al. (1982) model was fitted to Dp/D0 versus air-filled porosity (AFP) data. Although AFP was more than 0.1 m3 m-3 for some media, the Dp/D0 was very low. Considering optimum Dp/D0 (i.e. 0.010-0.015) for growth substrates at h = -8 hPa, aeration status of four media (cocopeat-perlite, Rh-SCB300-Z, Sd-SCB300-Z and WSB500-Rh-V) was optimum. Highest Dp/D0 at h = -8 hPa was observed for Rh-SCB300-Z. The AFP at h = -10 hPa was highest for Rh-SCB300-Z, cocopeat-perlite and WSB500-Rh-V. Biochar-based media with good aeration status and water retention can be a suitable substitute for commercial soilless culture in greenhouse production. Overall, WSB500-Rh-V is a suitable substitute for cocopeat-perlite.

Performance of new biodegradable chelants in enhancing phytoextraction of heavy metals from a contaminated calcareous soil.

Chelant-assisted phytoextraction has widely been exploited as a feasible option for removing heavy metals from the contaminated soils. Some synthetic chelants have shown promising performances for this option, but they have also revealed several negative environmental consequences. This study has sought to investigate the feasibility of two biodegradable eco-friendly chelants, namely methylglycinediacetic acid (MGDA) and N,N-Bis(carboxymethyl)-L-glutamic acid (GLDA), as compared to the resistant ethylenediaminetetraacetic acid (EDTA), in enhancing phytoextraction of Zn and Pb from a contaminated calcareous soil. For this purpose, a greenhouse experiment was carried out comparing the growth and metal absorption of maize (Zea mays L.) grown on soils treated with EDTA, MGDA, and GLDA chelants at 2, 4 and 8 mmol kg- 1 levels. Results showed that the heavy metal uptakes by the plant shoots generally increased with increasing the chelant application level. Pb uptake by maize shoots increased from 10.6 mg plant- 1 in control to 416, 398, and 416 mg plant- 1 in the soils treated with 8 mmol kg- 1 MGDA, GLDA, and EDTA, respectively. The corresponding increases in Zn uptake were from 100.9 mg plant- 1 to 798.9, 718.9, and 530.4 mg plant- 1 in the MGDA-, GLDA-, and EDTA-amended soils, respectively. Moreover, the amounts of water-extractable, and thereby potentially leachable, Pb and Zn in the post-harvest soil were considerably greater in the soil treated with EDTA than those treated with MGDA and GLDA. Therefore, MGDA and GLDA would be potential alternatives to environmentally-persistent EDTA for enhanced metal phytoextraction from contaminated soils.

The role of plant growth-promoting rhizobacteria (PGPR) in improving iron acquisition by altering physiological and molecular responses in quince seedlings.

Due to insoluble iron (Fe) sources in soil, limited Fe availability leads to the disruption of the photosynthetic apparatus; this affects the growth and productivity of plants such as quince (Cydonia oblonga) that are very sensitive to low Fe content. Plant growth-promoting rhizobacteria (PGPR) play an important role in the regulation of Fe uptake under its limited availability. Therefore, in this research, two PGPR (Pseudomonas fluorescens and Microccucuce yunnanensis), at two Fe levels [50 µM (Fe-sufficiency) or 5 µM (Fe-deficiency)], were used to investigate the impact of the given bacteria on improving the acquisition of Fe in quince seedlings. Upon Fe-deficiency, the highest shoot and root biomass (7.14 and 6.04 g plant-1 respectively), the greatest chlorophyll concentration (0.89 mg g-1FW), and the largest Fe concentrations in roots and shoots (30% and 48.7%, respectively) were shown in the quince treated with M. yunnanensis. Both PGPR increased the root citric acid and the phenolic compound concentration. Two days after Fe-deficiency and PGPR treatments, a 1.5- fold increase, was observed in the expression of HA7. The highest PAL1 gene expression and the greatest PAL activity (95.76 µmol cinnamic acid g-1FW) were obtained from the M. yunnanensis treatment. The expression of the FRO2 gene was also affected by Fe-deficiency and PGPR treatments, resulting in an increase in the FCR activity and a surge in the Fe concentrations of leaves and roots. It could, therefore, be concluded that the PGPR modulated Fe acquisition in the quince seedlings upon Fe-deficiency by influencing the physico-chemical and molecular responses.

Bentonite addition to a PCB-contaminated sandy soil improved the growth and phytoremediation efficiency of Zea mays L. and Alternanthera sessilis L.

In this study, the removal of 17 selected PCBi congeners was assessed in a transformer oil-contaminated soil amended with bentonite clay powder applied at the three levels of 0, 2, and 4% and cultivated by Zea mays L. or Alternanthera sessilis L. in a pot experiment. Results showed that Z. mays and A. sessilis were able to reduce the residual concentrations of the PCBi congeners in the contaminated soil significantly (p < 0.05). The average reductions in the Æ©PCBi due to Z. mays or A. sessilis cultivations were 34.3 and 21.4%, respectively, depending on initial soil Æ©PCBi loading and plant growth period. Moreover, addition of bentonite led to significant (p < 0.05) enhancements in plant growth and dissipation of residual soil PCBi congeners under Z. mays and A. sessilis cultivations. Addition of 4% bentonite to the soil was found to have the greatest positive impact on PCBi removal so that average PCBi dissipations in the soil were 56.1 and 51.8% after growing Z. mays and A. sessilis, respectively. It might be concluded that the combined phytoremediation and bentonite addition is an effective technique for removing PCBi and remediating transformer oil-contaminated coarse-textured soils.

Feasibility of agricultural residues and their biochars for plant growing media: Physical and hydraulic properties.

This study was conducted to examine feasibility of using some agricultural residues and their biochars as substitutes for commercial horticultural growing media as cocopeat, sand, perlite, zeolite, pumice, vermiculite and rockwool. Biochars of wheat straw, sawdust, rice hull, sugarcane bagasse and date palm bunches were produced at 300 and 500 °C. Following substrate properties were determined: easily available water (EAW) defined by the difference between water contents (θ) at absolute matric potentials (h) of 10 and 50 hPa (EAW = θ10 - θ50), air after irrigation (AIR = θ0 - θ10), water holding capacity (WHC = θ10), water buffering capacity (WBC = θ50 - θ100), saturated water content (θs), bulk density (BD), total porosity (TP), water drop penetration time (WDPT), pH and electrical conductivity (EC). A classification system was developed to evaluate the substrates as horticultural growing media. Higher pyrolysis temperature produced biochars with higher pH, EC, TP, θs, WHC, EAW, and WBC and lower biochar yield, AIR, BD and WDPT. Sugarcane bagasse biochars had higher θs, TP and WBC and lower BD than other biochars. Comparison among organic residues and inorganic substrates showed that highest TP, θs and EAW were observed in rockwool, whereas, among organic residues, maximum values of these properties were achieved for sugarcane bagasse, wheat straw and sawdust, respectively. Considering pH, EC, BD, TP, EAW, AIR, WBC and WDPT, wheat straw and sawdust were classified as very good substrates similar to cocopeat and rockwool. Other organic residues were placed in good class. Wheat straw and date palm bunches biochars produced at 500 °C and sugarcane bagasse and rice hull biochars were good growing media and can be suitable candidates for amendments or replacements of commercial growing media.

Coupling of bioaugmentation and phytoremediation to improve PCBs removal from a transformer oil-contaminated soil.

This study was carried out to assess the dissipation of 17 selected polychlorinated biphenyl (PCBi) congeners in a transformer oil-contaminated soil using bioaugmentation with 2 PCB-degrading bacterial strains, i.e., Pseudomonas spp. S5 and Alcaligenes faecalis, assisted or not by the maize (Zea mays L.) plantation. After 5 and 10 weeks of treatment, the remaining concentrations of the target PCBi congeners in the soil were extracted and measured using GC-MS. Results showed that the bacterial augmentation treatments with Pseudomonas spp. S5 and A. faecalis led to 21.4% and 20.4% reduction in the total concentration of the target PCBs (ΣPCBi), respectively, compared to non-bioaugmented unplanted control soil. The ΣPCBi decreased by 35.8% in the non-bioaugmented planted soil compared with the control. The greatest degradation of the PCB congeners was observed over a 10-week period in the soil inoculated with Pseudomonas spp. S5 and cultivated with maize. Under this treatment, the ΣPCBi decreased from 357 to 119 ng g-1 (66.7% lower) and from 1091 to 520 ng g-1 (52.3% lower). Overall, the results suggested that the combined application of phytoremediation and bioaugmentation was an effective technique to remove PCBs and remediate transformer oil-contaminated soils.

Physiological characteristics of Plantago major under SO2 exposure as affected by foliar iron spray.

Sulfur dioxide (SO2) is considered as a main air pollutant in industrialized areas that can damage vegetation. In the present study, we investigated how exposure to SO2 and foliar application of iron (Fe) would affect certain physiological characteristics of Plantago major. The plant seedlings exposed or unexposed to SO2 (3900 µg m-3) were non-supplemented or supplemented with Fe (3 g L-1) as foliar spray. Plants were exposed to SO2 for 6 weeks in 100 × 70 × 70 cm chambers. Fumigation of plants with SO2 was performed for 3 h daily for 3 days per week (alternate day). Lower leaf Fe concentration in the plants exposed to SO2 at no added Fe treatment was accompanied with incidence of chlorosis symptoms and reduced chlorophyll concentration. No visible chlorotic symptoms were observed on the SO2-exposed plants supplied with Fe that accumulated higher Fe in their leaves. Both at with and without added Fe treatments, catalase (CAT) and peroxidase (POD) activity was higher in the plants fumigated with SO2 in comparison with those non-fumigated with SO2. Foliar application of Fe was also effective in increasing activity of antioxidant enzymes CAT and POD. Exposure to SO2 led to reduced cellulose but enhanced lignin content of plant leaf cell wall. The results obtained showed that foliar application of Fe was effective in reducing the effects of exposure to SO2 on cell wall composition. In contrast to SO2, application of Fe increased cellulose while decreased lignin content of the leaf cell wall. This might be due to reduced oxidative stress induced by SO2 in plants supplied with Fe compared with those unsupplied with Fe.

Phytosiderophore release by wheat genotypes differing in zinc deficiency tolerance grown with Zn-free nutrient solution as affected by salinity.

There is limited information concerning the effect of salinity on phytosiderophores exudation from wheat roots. The aim of this hydroponic experiment was to investigate the effect of salinity on phytosiderophore release by roots of three bread wheat genotypes differing in Zn efficiency (Triticum aestivum L. cvs. Rushan, Kavir, and Cross) under Zn deficiency conditions. Wheat seedlings were transferred to Zn-free nutrient solutions and exposed to three salinity levels (0, 60, and 120 mM NaCl). The results indicated that Cross and Rushan genotypes exuded more phytosiderophore than did the Kavir genotype. Our findings suggest that the adaptive capacity of Zn-efficient 'Cross' and 'Rushan' wheat genotypes to Zn deficiency is due partly to the higher amounts of phytosiderophore release. Only 15 days of Zn deficiency stress was sufficient to distinguish between Zn-efficient (Rushan and Cross) and Zn-inefficient (Kavir) genotypes, with the former genotypes exuding more phytosiderophore than the latter. Higher phytosiderophore exudation under Zn deficiency conditions was accompanied by greater Fe transport from root to shoot. The maximum amount of phytosiderophore was exuded at the third week in 'Cross' and at the fourth week in 'Kavir' and 'Rushan'. For all three wheat genotypes, salinity stress resulted in higher amounts of phytosiderophore exuded by the roots. In general, for 'Kavir', the largest amount of phytosiderophore was exuded from the roots at the highest salinity level (120mM NaCl), while for 'Cross' and 'Rushan', no significant difference was found in phytosiderophore exudation between the 60 and 120 mM NaCl treatments. More investigation is needed to fully understand the physiology of elevated phytosiderophore release by Zn-deficient wheat plants under salinity conditions.

Adsorption-desorption behavior of 2,4-D on NCP-modified bentonite and zeolite: implications for slow-release herbicide formulations.

Clay minerals have obtained considerable attention for slow-release formulation of herbicides to increase weed control efficacy and reduce leaching potential and environmental pollution. This study deals with preparing, characterizing and examining the potentials of modified bentonite and zeoilite in adsorption and release of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide. 2,4-D sorption of the N-cetylpyridinium (NCP)-modified bentonites and zeolites were much higher than those of unmodified substrates. The 2,4-D adsorption capacity of the organo-minerals increased with increasing surfactant loading. Desorption isotherms of 2,4-D did not coincide their corresponding sorption isotherms showing hysteresis. The proportion of 2,4-D released from the organo-minerals after seven desorption cycles varied between 29% and 50% of the total retained herbicide. The sorbed 2,4-D on the adsorbents showed gradual release pattern with time. The release pattern of 2,4-D from NCP-modified bentonite and zeolite, make these synthetic organo-minerals suitable candidate for slow release formulation of 2,4-D.

Sorption hysteresis of Cd(II) and Pb(II) on natural zeolite and bentonite.

Sorption hysteresis in natural sorbents has important environmental implications for pollutant transport and bioavailability. We examined sorption reversibility of Cd(II) and Pb(II) on zeolite and bentonite. Sorption isotherms were derived by sorption of Cd(II) and Pb(II) from solutions containing a range of the metal concentrations corresponding to 10-100% maximum sorption capacity (SCmax) of the sorbents. The desorption experiments were performed immediately following the completion of sorption experiments. Sorption and desorption isotherms of Cd(II) and Pb(II) were well described by the Freundlich model. The results revealed that the desorption isotherms of Cd(II) and Pb(II) from zeolite significantly deviated from the sorption isotherms indicating irreversible or very slowly reversible sorption. For bentonite sorption/desorption isotherms were similar indicating reversible sorption. The extent of hysteresis was evaluated from sorption and desorption Freundlich parameters (K(f) and n) through the apparent hysteresis index (HI = n(desorb)/n(sorb); n is the exponent in the Freundlich equation) and differences in Freundlich K(f) parameters. Higher sorption irreversibility was obtained for Pb(II) as compared to Cd(II). The amounts of Cd(II) and Pb(II) desorbed from bentonite were more than from zeolite, indicating that zeolite was a more effective sorbent for water and wastewater treatment.