Temporal Profiles of Soil Properties and Performance of Amaranthus Grown on Farm Yard Manure-mediated Crude Oil Polluted Soil

Abstract

An experiment was conducted in the plant house of the Department of Crop, Soil and Pest management, Federal University of Technology, Akure, Nigeria, to examine the efficacy of manuring and incubation periods on the amelioration of the toxic effects of crude oil contamination on soil properties and Amaranthus performance. The time dynamics of physical, chemical and microbial population of the manured mediated crude oil contamination were observed following 270 days (9 months) of incubation. Bonny light crude oil was applied at zero and 5% (0 and 325 ml per pot) to the containerized (pot) soil which were amended with Farm Yard Manure (FYM) at 0 and 40 g per pot. The manure-mediated crude oil polluted containerized soil were incubated for periods of 0, 2, 4, 6 and 9 months. Treatments were arranged using Completely Randomised Design (CRD) with three replications. The toxicity of the crude oil pollution and its capacity to support plant growth was assessed via germination, seedling survival and growth of Amaranthus at the various periods of incubation. Data were also collected on soil biological, physical and chemical properties at the various sampling dates (periods of incubation). Application of organic fertilizer to crude oil-contaminated soil produced significant influence on soil chemical properties, microflora populations, and on the growth characters of Amaranthus. Organic amendment of crude oil contamination at two rates of organic fertilizer produced increases in soil pH and its contents of organic matter, N, P and K, and the colony sizes of microflora populations, and improved root, shoot biomass and leaf development of Amaranthus. Soil application of of crude oil affected soil chemical properties via decreases in soil pH, organic matter, N, P and K) and the colony sizes of microflora populations (bacterium, yeast and fungi counts). Crude oil contamination inhibited seed germination and growth of Amaranthus from the commencement of experiment to 4 weeks after treatment application. The time changes in soil elemental concentrations and biological populations following contamination with crude oil was monitored. Data obtained on soil chemical constituents (pH, organic matter, CEC) biological populations were fitted to correlation and regression models. The observed trendlines in time-dependent elemental concentration and soil biological populations were described by power, logarithmic and polynomial relations with high R2values. The initial declining trends in values with time up to the forth months after crude oil application were followed by a little linear increases in soil chemical properties and microbial population with time. These trends were consistent for both soil chemical properties and microbial population. The nature of the trends (polynomial function as best fit) indicate that the responses were not sole function of a factor but suggest synergy among factors responsible for the decay of petroleum hydrocarbon compounds and hence its toxicity to soil chemical properties and biological activities. The study showed that soil microbiological population (diversity) may be useful tools for assessing the effect of petroleum hydrocarbon contamination on soil and environmental health.