Abstract
The study assessed the effectiveness of biochars derived from Daniellia oliveri and Vitellaria paradoxa in ameliorating waste lubricant oil contaminated soils and improving germination of cowpea seeds. Daniellia oliveri and Vitellaria paradoxa biochars were applied at 0.5 and 1.0 % levels to soils contaminated with 2 % v/w waste lubricant oil (WLO). The unpolluted soil and WLO-contaminated soil without biochar were also used as controls. All treatments in three replicates were arranged in a randomized block design in a screen house. Biochars and soils were analyzed for pH, organic carbon (OC), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) and total petroleum hydrocarbon (TPH exclusively analyzed for soil). Ten cowpea seeds sown in soils were observed for sprouting from 1 to 10 days after sowing (DAS). Germination percentage and indices were determined from the number of sprouted seeds at 10 DAS. Vitellaria -derived biochar (BV) had higher N, K and Mg than Daniellia -derived biochar (BD). WLO contamination significantly reduced soil P but slightly affected pH, OC and exchangeable cations. Addition of BD and BV reduced TPH and improved soil quality. Oil contamination delayed and reduced cowpea germination by 9.3 % in un-amended WLO-contaminated soil. 1 % BV addition was effective in improving germination velocity and indices of cowpea seeds in oil-contaminated soils.
Highlights
Soil pollution from petroleum derivatives, previously considered a problem of petroleum producing or processing countries, is fast becoming a global problem posing a starting challenge to non-petroleum producing countries as well (Odjegba and Sadiq, 2002)
The variation in the chemical properties of Danielliaderived and Vitellaria-derived biochars was in line with earlier report by Jindo et al (2014) that the nature or type of feedstock strongly influences the physicochemical properties of biochars. pH of Daniellia-derived and Vitellaria-derived biochars in this study exceeded the pH (8.32) reported by Gulyas et al (2014) for wood chip (WC) but fall within the range of 7 - 9 reported by Beesley et al (2011)
The percentage carbon of biochars from the two species was higher than 9.9 % reported by Gulyas et al (2014) for animal bone biochar (ABC)
Summary
Soil pollution from petroleum derivatives, previously considered a problem of petroleum producing or processing countries, is fast becoming a global problem posing a starting challenge to non-petroleum producing countries as well (Odjegba and Sadiq, 2002). Oil contamination affects the biological, physical, chemical components of the soil in various ways (Atuanya, 1987; Odjegba and Sadiq, 2002; Agbogidi and Ejemeta, 2005: Agbogidi, 2010), and its effects on the growth, development, productivity and yield of plants cannot be undermined. Oil in soil creates anaerobic condition by impeding moisture content (Shukry et al, 2013), excluding air and increasing the production of hydrogen sulphide (Udo and Oputa, 1984) which induces considerable retardation in germination and plant growth (Adam and Duncan, 2002). Apart from seed germination impairment, reductions in yield and premature death of crops have been reported in soils contaminated with waste lubricant oil (Udom et al, 2012). Since soil health is the foundation of a vigorous and sustainable food system, corrective measures are needed to alleviate the effects of contamination while improving crop production
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