Influence of Organic Amendment on Microbial Activities and Growth of Pepper Cultured on Crude Oil Contaminated Niger Delta Soil

Abstract

Land contamination with crude oil is one of the challenges of effective crop production in the Niger Delta Region of Nigeria. This condition is inherent thus creates the need for developing effective remedial methods of managing contaminated lands as well as improve crop production. This study was designed to assess the effect of Brewers Spent Grains (BSG) on microbial activities and growth of Capsicum annum L cultured in crude oil contaminated soil. The results have shown that depending on the level of contamination, crude affected both the physical and chemical attributes of soil. It increased the acidity from pH 5.67 to a range of 5.58 - 5.64 and the total organic carbon content from 0.05% to 0.14% - 0.21 while the total nitrogen and available phosphorus levels of soil were remarkably reduced from 0.39% to 0.21% - 0.28%, and from 0.036% to 0.028% - 0.032% respectively. Amendment of contaminated soil with BSG had variable influence on the microbial properties of test soil. It increases the heterotrophic activity of bacteria in soil while retarding the activities of nitrogen fixing bacteria (Nitrosomonas sp and Nitrobacter sp). However at a stimulating amendment level of 150g of BSG in a 0.208% level of contamination, the activities of hydrocarbon degrading bacteria was enhanced from the hitherto low number of 3.6 log CFU/g found in test soil to 6.2 log CFU/g obtained on the 6th week of the remediation period. This resulted in 62.09% hydrocarbon degradation in soil at the end of the 8-week remediation course. BSG amendment of the oil contaminated had clear but variable influence on some agronomic traits of the cultured pepper. Growth was generally promoted by the amendment and the most significant (P<0.05) growth attributes affected were the plant height, number of branches, leaves, flowers and fruits as well as the leaf area. Pepper seedlings exposed to 0.624% of oil and remedied with 300g (1.5%) had the highest number of flowers but the flower did develop into fruits. However plant exposed to 0.416% of oil contamination and remedied with 0.75% of BSG produced flowers that formed fruits. Although the cultured pepper plants exhibited necrotic spots, this study has shown that plants grow in crude oil contaminated soil if alternative source of nutrients is provided. This tend to grow more in lightly contaminated soil and remediation using BSG has proven to enhance the activities of microorganisms and subsequent degradation of hydrocarbons in contaminated soil. It is highly recommended for use as soil conditioner to "unmask" nutrients in contaminated soils.