Biostimulatory effect of organic and inorganic nutrients on soil biological indicators in diesel contaminated soil

Abstract

Conventional soil remediation has been known to be expensive treatment. Thus, various strategies have been opted to investigate cost-effective solution to contaminated sites and an example is bio-stimulation. The study investigated effect of organic and inorganic nutrients on soil biological indicators of dieselcontaminated soil. The parameters investigated include determination of pH, conductivity, nitrate, phosphate, total organic carbon, moisture content, temperature, baseline, soil respiration, dehydrogenase activity, urease activity, soil microbial biomass carbon, protease activity, germination index (GI), total viable count technique (THBC and TCHUB), microscopic and biochemical characteristics in 56th days experimental period. The result revealed that the soil is neutral to slightly alkaline in pH, moderate in conductivity, low in nitrate, phosphate and total organic carbon contents, high in moisture content with moderate (mesophilic) temperature. The result of baseline study also revealed that soil respiration is 99.30 s days, dehydrogenase activity is 02.69 µg TPFg -1 dm (24 hr) -1 ), microbial biomass carbon is 02.69 mg/kg, urease activity is 24.52 µmol N-NH4 / g 2 hrs, protease activity is 36.66 µg / ml, GI is 09.24 %, THBC is 06.53 logCFU /g and TCHUB 06.73 logCFU /g. There were significant effect (P < 0.05) on dehydrogenase activities, urease activities, total heterotrophic bacteria counts (THBC) and total culturable hydrocarbon utilizing bacteria counts (TCHUBC) respectively but no significant effect (P > 0.05) on soil respiration, soil microbial biomass carbon, protease activity and germination index respectively by the organic and inorganic nutrients. There was negative and positive correlations between germination index, microbial count and other biological indicators measured. More so, the result revealed that the hydrocarbon utilizing bacterial isolates were Aeromonas sp., Serratia fonticola, Citrobacter freundii, Citrobacter diversus and Corynebacterium sp. Thus, application of organic and inorganic nutrients sources is suggested as a good strategy for bioremediation of diesel impacted soil.