The impact of Palm Oil Mill Effluent (POME) application on the rhizosphere heterotrophic population, nitrogen fixing bacteria and enzyme activity of an agricultural soil

Abstract

Palm Oil Mill Effluent (POME) is considered an efficient soil conditioner due to its high organic contents but the presence of phenol compounds limits their widespread use in agriculture. In the present study, POME was subjected to both aerobic and anaerobic decomposition to reduce its organic strength and degrade its toxic fractions. It was then applied to support Arachis hypogeal grown in a green house. The rhizosphere environment was monitored for changes in total bacterial counts, nitrogen fixing bacteria and enzyme activities. Results show that the bacteria counts were higher (302.0±1.41 × 105 cfu/g) in mesocosms treated with 100% aerobically digested POME but lower (280.0±1.41 × 105 cfu/g) in the batch treated with anaerobically digested POME. Nitrogen fixing bacteria was 106.0±2.83 × 102 cfu/g in mesocosms treated with aerobically fermented POME compared to 64.0±2.83 × 102 cfu/g from the counterpart treated with anaerobic digests. Dehydrogenase activity was highest (52.83±0.01 mg TPFg-124h-1) in soils treated with aerobically digested POME but not higher (48.65±0.03 mg TPFg-124h-1) than the treatments which received the anaerobically modified effluent. Acid phosphatase activity was lower (201.0±0.28 IU PNP/g/ 24h) in the soils treated with aerobically modified POME but higher (213.5±0.42 IU PNP/g/24h) in batches dosed with anaerobically treated effluent. Urease activity increased to peak level (2.437±0.004 Ppm NH +-N /g/24h) in the 4th week but dropped to its final concentration of 1.615±0.001 Ppm NH +-N /g/24h) in soils treated with anaerobically digested POME. Data from mesocosms treated with the anaerobic digests were lower (2.149±0.004 and 1.500±0.014 ppm NH +-N /g/24h respectively). 

KeyWords: Palm oil mill effluent, phenol, dehydrogenase, phosphatase, urease