Farhan Hafeez

Cadmium stress in rice: toxic effects, tolerance mechanisms, and management: a critical review

Cadmium (Cd) is one of the main pollutants in paddy fields, and its accumulation in rice (Oryza sativa L.) and subsequent transfer to food chain is a global environmental issue. This paper reviews the toxic effects, tolerance mechanisms, and management of Cd in a rice paddy. Cadmium toxicity decreases seed germination, growth, mineral nutrients, photosynthesis, and grain yield. It also causes oxidative stress and genotoxicity in rice. Plant response to Cd toxicity varies with cultivars, growth condition, and duration of Cd exposure. Under Cd stress, stimulation of antioxidant defense system, osmoregulation, ion homeostasis, and over production of signaling molecules are important tolerance mechanisms in rice. Several strategies have been proposed for the management of Cd-contaminated paddy soils. One such approach is the exogenous application of hormones, osmolytes, and signaling molecules. Moreover, Cd uptake and toxicity in rice can be decreased by proper application of essential nutrients such as nitrogen, zinc, iron, and selenium in Cd-contaminated soils. In addition, several inorganic (liming and silicon) and organic (compost and biochar) amendments have been applied in the soils to reduce Cd stress in rice. Selection of low Cd-accumulating rice cultivars, crop rotation, water management, and exogenous application of microbes could be a reasonable approach to alleviate Cd toxicity in rice. To draw a sound conclusion, long-term field trials are still required, including risks and benefit analysis for various management strategies.

Biochar soil amendment on alleviation of drought and salt stress in plants: a critical review

Drought and salt stress negatively affect soil fertility and plant growth. Application of biochar, carbon-rich material developed from combustion of biomass under no or limited oxygen supply, ameliorates the negative effects of drought and salt stress on plants. The biochar application increased the plant growth, biomass, and yield under either drought and/or salt stress and also increased photosynthesis, nutrient uptake, and modified gas exchange characteristics in drought and salt-stressed plants. Under drought stress, biochar increased the water holding capacity of soil and improved the physical and biological properties of soils. Under salt stress, biochar decreased Na+ uptake, while increased K+ uptake by plants. Biochar-mediated increase in salt tolerance of plants is primarily associated with improvement in soil properties, thus increasing plant water status, reduction of Na+ uptake, increasing uptake of minerals, and regulation of stomatal conductance and phytohormones. This review highlights both the potential of biochar in alleviating drought and salt stress in plants and future prospect of the role of biochar under drought and salt stress in plants.

Distribution of bacteria and nitrogen-cycling microbial communities along constructed Technosol depth-profiles

Technosol construction through assemblage of treated soil and recycled wastes is an innovative option for the restoration of degraded lands and re-use of industrial wastes. Recent studies have evidenced that Technosols could support soil functions such as primary production but the knowledge about other ecosystemic services, such as nutrient cycling, is limited. We investigated how the total bacterial community and key functional microbial communities involved in nitrogen cycling were influenced by the depth and type of Technosol. We found that despite being artificially constructed, Technosols exhibited a gradual change in microbial activity and abundance along the soil profile. Both nitrification and denitrification rates decreased with increasing depth as previously observed in other soil systems. Potential denitrification and nitrification were correlated with Technosol physico-chemical properties but also with abundances of nirS denitrifiers and bacterial amoA gene, respectively. The correlation between nitrification rates and bacterial ammonia-oxidizers suggests that bacteria are driving nitrification in Technosols. A-RISA fingerprints showed a distinct community structure along different Technosol layers. Technosol properties affected denitrification strongly than nitrification underlining the importance of better understanding the microbial communities in Technosols to maximize their potential for nutrient cycling, an essential ecosystem function.

Oil industry waste: a potential feedstock for biodiesel production

ABSTRACT The worldwide rising energy demands and the concerns about the sustainability of fossil fuels have led to the search for some low-cost renewable fuels. In this scenario, the production of biodiesel from various vegetable and animal sources has attracted worldwide attention. The present study was conducted to evaluate the production of biodiesel from the oil industry waste following base-catalysed transesterification. The transesterification reaction gave a yield of 83.7% by 6:1 methanol/oil molar ratio, at 60°C over 80 min of reaction time in the presence of NaOH. The gas chromatographic analysis of the product showed the presence of 16 fatty acid methyl esters with linoleic and oleic acid as principal components representing about 31% and 20.7% of the total methyl esters, respectively. The fourier transform infrared spectroscopy spectrum of oil industry waste and transesterified product further confirmed the formation of methyl esters. Furthermore, the fuel properties of oil industry waste methyl esters, such as kinematic viscosity, cetane number, cloud point, pour point, flash point, acid value, sulphur content, cold filter plugging point, copper strip corrosion, density, oxidative stability, higher heating values, ash content, water content, methanol content and total glycerol content, were determined and discussed in the light of ASTM D6751 and EN 14214 biodiesel standards. Overall, this study presents the production of biodiesel from the oil industry waste as an approach of recycling this waste into value-added products.

Assessment of the resilience and resistance of remediated soils using denitrification as model process

PurposeSoil contamination by pollutants is increasing, urging for remediation strategies but little is known about the functional sustainability of these strategies.Materials and methodsWe assessed the resistance and resistance of a microbial respiratory process, denitrification, to two different levels of heat-drought disturbances among (1) thermally treated industrial soil, (2) constructed Technosol made of thermally treated soil, compost, and paper by products, and (3) an arable soil.Results and discussionWe showed that thermal remediation lead to low resistance and resilience after disturbances. However, addition of compost and paper mill sludge improved the stability.ConclusionsThis work underlines the relevance of resistance and resilience ecological concepts for assessing remediation strategies.

Alleviation of cadmium (Cd) toxicity and minimizing its uptake in wheat ( Triticum aestivum ) by using organic carbon sources in Cd-spiked soil

Cadmium (Cd)-contamination of agricultural soils has been receiving attention worldwide due to its entry into food crops such as wheat (Triticum aestivum L.). Little is known regarding the use of organic carbon (OC) sources in alleviating Cd toxicity in cereals. The current experiment was aimed to study the effects of different OC sources on the Cd accumulation by wheat. A pot study was conducted to determine the effects of rice husk biochar (RHB), farmyard manure (FYM), and lignite (LT) either alone or in combination on crop growth, Cd bioavailability and health risk assessment. The results proved that the application of OC sources like RHB, FYM, and LT either alone or in combination were highly effective in enhancing the wheat growth and yield as well as in minimizing the phyto-available fraction of Cd and its transfer to edible tissue of wheat. The RHB was the most efficient source in enhancing the plant growth and reducing the Cd concentration in wheat tissues. RHB increased grain yield by 91% and decreased Cd concentration in shoot, roots, grains, and bioavailable fraction of Cd by 67, 69, 62.5, and 74% than control, respectively. The RHB reduced the daily Cd uptake and health risk index in adults in comparison to control. Overall, where un-amended soil resulted in diminished plant productivity, the application of other OC sources also significantly proved their potential to enhance the dry weight and grain yield, suggesting that these OC sources may be used aiming to minimize the Cd concentration in crops. However, there is still a need to explore the potential of different OC sources in combination with other frequently available amendments for their large scale implementation in metal-contaminated soils.

Efficiency of various sewage sludges and their biochars in improving selected soil properties and growth of wheat (Triticum aestivum)

Due to increasing demand of P fertilizers and gradual decrease in P resources, recyclable P is the focus of researchers in recent years. Sewage sludge (SS) is a municipal waste that contains appreciable amounts of P and probably other nutrients. In present study, the effects of various SS and their biochars (450 °C for 2 h) were investigated on soil properties and P uptake in wheat (Triticum aestivum) with and without P fertilizer. The biomass of plants and grain yield were significantly increased with application of SS and their biochars as compared to the control treatment either without or with P application. Moreover, there was significant interaction between treatments and P application for the concentration of K, and P in shoots and roots of wheat. Shoot P concentration was not significantly affected with SS than biochars whereas root P concentration was higher in SS treatments than respective biochars. Higher increase in Olsens P concentration was observed in populated area sludge applied-soil as compared to disposal sludge and their biochars. Overall, it is observed that SS application increased the wheat yield and P concentrations in plants than control depending upon SS types whereas biochar application decreased the P concentration in roots. Grain yield and P concentration in shoots were not significantly affected for the treatment with P fertilizers than without P. Sewage sludge and their biochars might be a potential source of P but further research is needed to recommend the use of modified SS-biochars as source of available P for crops.

Effect of coal and wood ash on phosphorus immobilization in different textured soils

Decreased phosphorus (P) losses and improved environmental quality are crucial to consider while recycling farm wastes and adding various soil amendments. This study investigated the impact of coal and wood ash on the extractability of P from soils (sandy loam and loamy sand) amended with organic and inorganic phosphorus fertilizers. These soils were further amended coal and wood ash, and analyses were carried out to quantify the water-, Olsen-, and Mehlich 1-extractable P. Ratio of the ashes applied to soils were 5% to sandy loam soil while 10% to loamy sand soil. Water-extractable P was observed to be mainly dependent on the ash type as well as the extraction method. Ash amendment reduced the solubilization of P across soils up to 9% and 23% and 7% to 17% upon 5% and 10% ash amendment in loamy sand and sandy loam soils, respectively. However, the water-extractable P was found to be low in wood ash-amended soil as compared to coal ash. Interestingly, this extractability was greater in soils treated with inorganic P. Phosphorus extraction from soil followed the trend as Mehlich 1 > Olsen > water. P leachability was found to be mainly dependent on ash amendment but values were high for the soil treated with inorganic P. The study inferred that using ash materials such as coal ash and wood ash can be a practical measure for moderating P losses from soils important for economic and environmental perspectives.

A field study investigating the potential use of phosphorus combined with organic amendments on cadmium accumulation by wheat and subsequent rice

A field study was performed to determine the efficiency of diammonium phosphate (DAP) applied alone or combined with biochar, lignite, and farmyard manure (FYM) on growth and cadmium (Cd) accumulation in wheat and rice. Before crop sowing, different treatments were applied in the field such as a control (T1), DAP alone (0.1%, T2), DAP + lignite (0.05% each, T3), DAP + FYM (0.05% each, T4), and DAP + biochar (0.05% each, T5). Afterwards, the wheat seeds were sown in the soil. At wheat postharvest, rice was sown without any further treatment. Raw effluent was applied as an irrigation source during the whole growth period of both crops since it is the common practice of the farmers of study area. It was revealed that the use of amendments enhanced the yield and photosynthesis but lowered the Cd contents in straw as well as grains of both crops. In both crops, the highest yield of straw and grain was found in DAP + FYM whereas the lowest Cd concentration was found in DAP alone. The ammonium bicarbonate-DTPA extractable Cd of post wheat and post rice soils were decreased while the soil pH and immobilization index were increased in all treatments as compared with the control. The present field study highlighted that the DAP + FYM can be effective in increasing yield with decreased Cd concentrations in crop grains.

Changes in Availability of Plant Nutrients during Composting of Cow Manure with Poplar Leaf Litter

ABSTRACT Safe management of animal and plant waste is one of the worlds most important environmental challenges. Composting has been proposed as a useful technique for beneficially recycling wastes. This study showed that significant temporal changes in the nutrient availability occurred during the composting of cow manure with poplar leaf litter within 120 days. In particular, total C in the final compost was directly related to the addition of tree litter and inversely related to the time of composting, whereas extractable P and NO3 increased with increasing amounts of tree litter and ammonium showed the opposite trend. During the later stages of the composting process higher concentrations of water soluble K, Ca, Mg, and Na were observed. The major benefit observed was that heavy metal concentrations initially present in the manure were significantly reduced during composting. Heavy metals in the final compost decreased in the order: Fe > Mn > Zn > Cu > Ni > Cd. The increased availability of plant nutrients following composting coupled with the lower extractability of heavy metals indicates that composting may be a sustainable option for agricultural waste recycling and increased productivity.