Contrasting effects of biochar, compost and farm manure on alleviation of nickel toxicity in maize (Zea mays L.) in relation to plant growth, photosynthesis and metal uptake Muhammad Zia-ur Rehman a , Muhammad Rizwan b,n , Shafaqat Ali b , Nida Fatima a , Balal Yousaf a,c , Asif Naeem d , Muhammad Sabir a , Hamaad Raza Ahmad a , Yong Sik Ok e a Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040, Pakistan b Department of Environmental Sciences and Engineering, Government College University, Allama Iqbal Road, 38000 Faisalabad, Pakistan c Chinese Academy of Science (CAS)-Key Laboratory of Crust-Mantle Materials and the Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, PR China d Soil Science Division, Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan e Korea Biochar Research Centre and Department of Biological Environment, Kangwon National University, Chuncheon 200-701, Republic of Korea article info Article history: Received 12 April 2016 Received in revised form 15 July 2016 Accepted 19 July 2016 Keywords: Organic amendments Cereals Growth Ni toxicity Phytoremediation abstract Nickel (Ni) toxicity in agricultural crops is a widespread problem while little is known about the role of biochar (BC) and other organic amendments like farm manure (FM) from cattle farm and compost (Cmp) on its alleviation. A greenhouse experiment was conducted to evaluate the effects of BC, Cmp and FM on physiological and biochemical characteristics of maize (Zea mays L.) under Ni stress. Maize was grown in Ni spiked soil without and with two rates of the amendments (equivalent to 1% and 2% organic carbon, OC) applied separately to the soil. After harvest, plant height, root length, dry weight, chlorophyll con- tents, gas exchange characteristics and trace elements in plants were determined. In addition, post- harvest soil characteristics like pH s , EC e and bioavailable Ni were also determined. Compared to the control, all of the amendments increased plant height, root length, shoot and root dry weight with the maximum increase in all parameters by FM (2% OC) treatment. Similarly, total chlorophyll contents and gas exchange characteristics significantly increased with the application of amendments being maximum with FM (2% OC) application. Amendments significantly increased copper, zinc, manganese and iron concentrations and decreased Ni concentrations in the plants. The highest reduction in shoot Ni con- centrationwas recorded with FM (2% OC) followed by BC (2% OC) being 73.2% and 61.1% lower compared to the control, respectively. The maximum increase in soil pH and decrease in AB-DTPA extractable Ni was recorded with BC (2% OC) followed by FM (2% OC). It is concluded that FM (2% OC) was the most effective in reducing Ni toxicity to plants by reducing Ni uptake while BC (2% OC) was the most effective in decreasing bioavailable Ni in the soil through increasing soil pH. However, long-term field studies are needed to evaluate the effects of these amendments in reducing Ni toxicity in plants. & 2016 Elsevier Inc. All rights reserved. 1. Introduction Heavy metals accumulate in the agricultural soils mainly through natural sources such as weathering and volcanic erup- tions and anthropogenic activities such as mining, waste disposal, and intensive use of fertilizers and pesticides (Marwa et al., 2012; Adrees et al., 2015a; Khan et al., 2016). Contamination of soils with heavy metals may reduce quality of agricultural land as well as crop yield and quality (Rehman et al., 2015; Rizwan et al., 2012, 2016a, 2016b). On the other hand, contamination of agricultural soils with heavy metals caused serious environmental and health problems (Zafar et al., 2015; Khan et al., 2016). Like most of other heavy metals, nickel (Ni) is an essential micronutrient and is required for normal growth and development of plants. However, Ni toxicity leads to a variety of physiological disorders in plants (Guo et al., 2010; Kamran et al., 2016). Nickel could enter accumulate in the human body through food crops grown onto Ni contaminated soils (Zafar et al., 2015; Khan et al., 2016). Previous studies have shown significantly higher con- centrations of Ni in different plant parts of maize (Guo et al., 2010; Marwa et al., 2012), Indian mustard (Ansari et al., 2015), rice (Nazir Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2016.07.023 0147-6513/& 2016 Elsevier Inc. All rights reserved. n Corresponding author. E-mail address: mrazi1532@yahoo.com (M. Rizwan). Ecotoxicology and Environmental Safety 133 (2016) 218–225