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
Growth studies on TMS 30572, NR8082 and Local cassava cultivars grown on previously crude oil polluted soil were conducted to assess effects of oil palm bunch ash (OPBA), dried poultry manure (DPM) on Leaf pigmentation and N2 status of test crops. In addition, physical and chemical properties of soils were determined. The pH was raised from 5.62±1.50 in control soil to values that ranged between 6.97±1.23 to 9.24±1.89 in soil treated with organic amendment. The result of organic amendment ensures reduction of C: N ratio from 50:1 in control to critical threshold that ranged between 8:1 – 10:1 for improved decomposition and soil quality. SPAD measurement revealed no significance (P≤ 0.05) in readings for both treatments and control experiments. However, the interactive effect of both cassava variety and type of amendments were significant. Cultivar TMS 30572 was found to be brought to high productivity under treatment with combined OPBA + DPM and recorded highest chlorophyll content per unit area of leaf surface with Chl. a/Chl.b ratio of 2.13 and thicker leaf blade. While Leaf chlorophyll is directly associated with the efficiency and capacity of the photosynthetic apparatus and hence chlorophyll content in this study was found to be directly related to good health status of the test crops. Results revealed that quality of crude oil contaminated soil was greatly enhanced by organic amendment.
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