Search

Fly ash (FA) is a solid waste generated from coal combustion processes every year from thermal power plant. FA was considered as a problem for the environment, but also proves to be beneficial for the agricultural crops. This review begins with the utilization of FA as a soil ameliorant, its role in enhancing the plant growth and impact of elemental uptake from FA on plant growth. FA improves the physical, chemical and biological property of the soil which thereby enhances the crop productivity. Then, it focusses on phytotoxicity of various heavy metals in plants such as chromium, arsenic, lead, zinc, etc., followed by analyzing the defense mechanism of the plants against these heavy metal stresses which is due to the presence of toxic heavy metals present in FA resulting in the generation of reactive oxygen species which further causes oxidative stress. Finally, the review analyzes the influence of heavy metals on the antioxidative system of various plant species which helps in understanding the usage of optimum concentration of FA amendment in the soil for plant cultivation and to further explore the key features regulating the heavy metal damage and utilization of FA in agriculture.

Phytoremediation of fly ash (FA) deposits using metal tolerant plant species has become an important eco-friendly technique for reclamation nowadays. The present study was carried out to determine the impact of FA application on photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids), biochemical parameters (soluble protein, reducing sugar, nitrate and nitrate reductase (NR) activity), metal accumulation (Fe, Zn, Cu, Co, Cd, Cr, and Mn) and antioxidant defense activity (SOD, CAT, POD, and APX) of Calendula officinalis. With this aim in mind, under pot culture conditions, Calendula officinalis was grown in different combinations of FA and soil which include: Control, 10%, 20%, 40%, 60%, 80%, and 100% FA. The results from the study indicated that the addition of FA (40%) in soil not only improved the physico-chemical properties of soil but also increased the photosynthetic pigment and other biochemical parameters in plants, however, these parameters declined under high FA applications. On the other hand, antioxidant enzyme activities (SOD, CAT, APX and Peroxidase) of Calendula increased with increasing FA application to combat heavy metal stress from fly ash. At high FA applications, antioxidant enzyme levels increased in leaves thereby reflecting heavy metal stress and mitigation of reactive oxygen species.

Fly ash is an important combustion residue and the most familiar industrial by-product. It is a source of various micronutrients and macronutrients which are essential for plant growth. The striking variations towards the sensitivity of fly ash are observed in the plant growth performance as fly ash comprises heavy metals which may alter the physical, biochemical, and biological properties of the plant thereby alter the plant growth. The growth and metabolism of different plant species were studied by various researchers in different soil–fly ash amendments. Certain observations were made for cotton yield and grain yield of wheat which revealed that 20% fly ash application is significant for increased growth and rice yield or wheat crops. An improved yield and growth in potato, barley and rye was reported at optimum rate of application of fly ash. Ten percent fly ash doses with soil increased the growth of tomato, petunia, and Boston fern as it increased the height of seedling and plant, increased the girth, enhanced the number of leaves, area of leaves, length of spike, and the plant dry weight. Plant growth and yield, carotenoids and chlorophyll contents of leaves were significantly increased at high fly ash rates in chilly, eggplant, and tomato. Changes in the soil characteristics and the cropping system due to the addition of fly ash were also studied and investigated by various workers that show an enhanced production of food crops. This study is an attempt to know the impact of fly ash on morphological and biochemical parameters of different plant species and also to determine the possible utilization in various agricultural practices. At high concentration of fly ash–soil doses, the experiment shows deleterious effect, the maximum being 100% fly ash with no amendment of soil. This shows that at high concentration of heavy metals generated from fly ash can cause genetic damage to plants due to their toxic concentration. At low concentration of fly ash–soil doses, heavy metals are better for the plant growth performance as well as plant productivity. Large-scale use of fly ash in agriculture holds the prospective to increase on an average 10–15% of yield and growth performance of the plants. This agro based technique can also be used with the concept of sustainable waste management by using fly ash–soil combination as a suitable growing medium for growing different plant species.

Fly ash (FA), solid waste residue, is a by-product of thermal power plant, and its disposal is considered to be the current biggest challenge faced by the entire world. Various studies have revealed that addition of FA to the soil may improve the physical, chemical, and biological properties of soil mixture. FA is also considered to provide readily available soil micro- and macronutrients. Lower doses of FA enhance the nutritional status of agricultural soil, thereby promoting plant growth, whereas higher doses of FA result in heavy metal pollution leading to deleterious effects which hinder the soil microbial communities and related enzymatic activity. Practically, FA is utilized in agriculture due to its usage as “ecofriendly and cost-effective” soil/fertilizer amendment which depends upon various factors like soil types, climatic conditions, plant selected for growth, etc. However, combined biotechnological approaches (organic and inorganic) need to be applied to soil-FA mixtures in order to reduce the amount of toxic elements present in FA and also to maintain the nutrient status as well as soil microbial activity. Overall, the lower doses of FA application could be utilized to revamp the soil structure, soil microflora, N-cycling process, and enzymatic activity which have a significant role in promoting the growth of plants.

An experiment in pot culture was conducted to analyze the ameliorative impact of different doses of fly ash (FA) in soil on the plant growth performance, total phenolics and flavonoids, and elemental uptake in Calendula officinalis. To determine the growth status of Calendula officinalis, various concentrations of FA and soil [100% garden soil (T1), 20% FA+ 80% garden soil (T2), 40% FA+ 60% garden soil (T3), 60% FA+ 40% garden soil (T4), 80% FA+ 20% garden soil (T5), and 100% FA (T6)] were selected. The physico-chemical properties of FA and soil and elemental concentrations (Ca, Mg, Al, As, Co, Zn, Fe, Mn, and Ni) in all FA treatments were determined. The results showed that under low ratio of FA amendment to the soil (40% FA treatment), the plant growth performance was increased in comparison to plants grown in control (garden soil). However, at high FA doses in soil (60%, 80% and 100% FA treatments), these parameters tend to decrease. Fly ash at 40% concentration did not contain toxic concentrations of these elements such as Co, Zn, Fe, Mn, Ca, Mg, Al, As, and Ni, therefore, beneficial effects of fly ash in terms of improved growth and yield were evident. Furthermore, the leaves showed increasing trend of total phenolic and flavonoid content with increasing FA application up to 60% FA treatment. Therefore, this study showed that 40% FA treatment to the soil is suitable for the growth and yield of Calendula officinalis. Thus, this plant has the phytoremediation potential that can promote cleanup of FA polluted sites for sustainable development.