Ameliorative effects of <i>Daniellia</i>- and <i>Vitellaria</i>-derived biochars on the chemistry of oil-contaminated soils and germination indices of cowpea

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.

Keywords

• biochar, cowpea, germination, soil improvement, waste lubricant oil