Fly ash application in nutrient poor agriculture soils: Impact on methanotrophs population dynamics and paddy yields Jay Shankar Singh a,n , Vimal Chandra Pandey b a Department of Environmental Microbiology, Babasaheb Bhimrao Ambedkar (Central) University, Raibarelly Road, Lucknow-226025, Uttar Pradesh, India b Department of Environmental Science, Babasaheb Bhimrao Ambedkar (Central) University, Raibarelly Road, Lucknow-226025, Uttar Pradesh, India article info Article history: Received 8 September 2012 Received in revised form 7 November 2012 Accepted 9 November 2012 Available online 20 December 2012 Keywords: Antioxidants Fly ash Heavy metals Methanotrophic bacteria Paddy crop abstract There are reports that the application of fly ash, compost and press mud or a combination thereof, improves plant growth, soil microbial communities etc. Also, fly ash in combination with farmyard manure or other organic amendments improves soil physico-chemical characteristics, rice yield and microbial processes in paddy fields. However, the knowledge about the impact of fly ash inputs alone or in combination with other organic amendments on soil methanotrophs number in paddy soils is almost lacking. We hypothesized that fly ash application at lower doses in paddy agriculture soil could be a potential amendment to elevate the paddy yields and methanotrophs number. Here we demonstrate the impact of fly ash and press mud inputs on number of methanotrophs, antioxidants, antioxidative enzymatic activities and paddy yields at agriculture farm. The impact of amendments was significant for methanotrophs number, heavy metal concentration, antioxidant contents, antioxidant enzymatic activities and paddy yields. A negative correlation was existed between higher doses of fly ash- treatments and methanotrophs number (R 2 ¼0.833). The content of antioxidants and enzymatic activities in leaves of higher doses fly ash-treated rice plants increased in response to stresses due to heavy metal toxicity, which was negatively correlated with rice grain yield (R 2 ¼0.944) and paddy straw yield (R 2 ¼0.934). A positive correlation was noted between heavy metals concentrations and different antioxidant and enzymatic activities across different fly ash treated plots.The data of this study indicate that heavy metal toxicity of fly ash may cause oxidative stress in the paddy crop and the antioxidants and related enzymes could play a defensive role against phytotoxic damages. We concluded that fly ash at lower doses with press mud seems to offer the potential amendments to improving soil methanotrophs population and paddy crop yields for the nutrient poor agriculture soils. & 2012 Elsevier Inc. All rights reserved. 1. Introduction The rise in demand for power in domestic, agricultural and industrial sectors has increased the pressure on coal combustion and thus aggravated problem of fly ash (FA) generation/disposal. According to current estimates, the FA production may increase to  170 million tons yr 1 by 2012, and 225 million tons by 2017 (Singh, 2012). Therefore, FA management remains the great concern of the current century. FA contains traces of toxic elements and heavy metals (Pandey and Singh, 2010), but also has some macro- and micro-nutrients and thus can be used as soil amendments/conditioner to boost the soil health and crop pro- ductivity (Singh et al., 2011). Toxic effect of FA is insignificant, and concentration of toxic elements within permissible limits at its low doses in some plantation work (Pandey et al., 2009). Hence, major initiatives have been taken in India and elsewhere to use such a cost effective resource in large volumes in agriculture (Lee et al., 2007; Pandey and Singh, 2010; Singh et al., 2011). The Indian subcontinent has been affected worst by humans since long. This could be the reasons climate formations being altered and/or destroyed for paddy agriculture and even other similar purposes in the region. In the dry tropical region, low soil moisture status due to scanty rainfall and higher temperature affects soil functioning and paddy crop productivity (Singh et al., 2011). The soils of most of the dry-land rice agro-ecosystem are nutrient poor (Singh et al., 2010). It is here that micro-elements in the FA and press mud could be crucial to paddy crop productivity. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety 0147-6513/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ecoenv.2012.11.011 Abbreviations: ANOVA, Analysis of variance; APX, Ascorbate peroxidase; CAT, Catalase; DAS, Day after sowing; EDTA, Ethylene di-amine tetra acetic acid; EC, Electrical conductivity; FA, Fly ash; FYM, Farm yard manure; GSSG, Glutathione disulfide; NADPH, Nicotinamide adenine dinucleotide phosphate; MB, Methano- trophic bacteria; MMO, Methane mono-oxygenase; PM, Press mud; ROS, Reactive oxygen species; SPSS, Statistical package for the social sciences; SM, Soil moisture; NTPP, National thermal power plant; MPN, Most probable number; PVP, Poly vinyl pyrrolidone; GR, Glutathione reductase n Corresponding author. E-mail addresses: jayshankar_1@yahoo.co.in (J.S. Singh), vimalcpandey@gmail.com (V.C. Pandey). Ecotoxicology and Environmental Safety 89 (2013) 43–51