Abstract
Field experiments were conducted in 2016 and repeated in 2017 to evaluate the effectiveness of Oil Palm Bunch Ash (OPBA) and Dried Poultry manure (DPM) as organic supplement, applied singly and in combination on growth properties and heavy metal uptake of cassava cultivars grown in crude-oil contaminated soil of the Niger Delta Region, Nigeria. There were four different organic amendments viz: DPM, OPBA, OPBA +DPM and control using TMS 30572, NR8082 and local variety as test crops. Results were elaborated statistically with the use of three-by-four factor variance analysis with ANOVA. Effect of various application of amendment on morphometric parameters of cultivars revealed in 2017 that at 36 weeks after sprouting (WAS), DPM and OPBA +DPM significantly (P≤ 0.05) enhanced plant heights of TMS 3572 and LV but had no influence on number of nodes, stem girth and leaf area. However, the interactions resulted in significant (P≤ 0.05) uptake and concentration of the heavy metals Fe, Cu, and Pb in leaves and Fe in roots ofTMS30572 and NR8082, indicating efficient metal removal by these varieties. Results of amendment also revealed remarkable increment in bacterial and fungal (from 104 to 106 and 103 to 104 ) populations respectively, correlating with reduction in soil total petroleum hydrocarbon (TPH) from 156.45 mg/kg to 146.73 mg/Kg. This is observed to diminish oil toxicity and improve soil status. The response of these cassava varieties to crude oil contamination appears to be optimistic. Consequently crop farmers are adviced against planting cassava and other arable crop at crude oil impacted soil for the risk of uptake of heavy metal in crop tissues. 
 Keywords: Remediation, Heavy metal, Oil-contaminated soil, Organic amendment, Growth properties, Cassava
Highlights
IntroductionSome of the materials that have been used locally in this direction are oil palm bunch ashes (OPBA) and poultry manure (DPM)
Site Description: Ikot Ada Udo, a Village in Ikot Abasi Local Government of Niger Delta is one of the onshore locations where hydrocarbon was discovered in commercial quantities more than 50 years ago in Nigeria, but has remained untapped
Apart from boosting growth, Oil Palm Bunch Ash (OPBA) and Dried Poultry manure (DPM) in this study offers veritable means of enhancing uptake of heavy metal in crop tissue
Summary
Some of the materials that have been used locally in this direction are oil palm bunch ashes (OPBA) and poultry manure (DPM). These materials are considered important soil supplement that can improve both biophysical and chemical properties of impacted soils. According to Mullens et al (2002), poultry droppings contain considerable amount of nitrogenous materials and the carbonates These amendments material apart from improving soil chemical and physical conditions enhances growth and multiplication of autochthonous microbial population whose activities usually aid in elimination of pollutants and increase soil fertility. This study was conducted to assess the persistence and residual effect of hydrocarbon on soil properties, plant growth and heavy metal removal efficiencies of cassava cultivarsa decade after the main pollution event
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