Evaluating the Efficacy of Organic Manures and NPK Fertilizer in Enhancing Plant Growth in Oil-Contaminated Soil: A Study Using Abelmoschus esculentus (Okra)

Abstract

This study evaluates the effects of some organic manures (cow dung manure, poultry manure, fish pond wastewater) and NPK 15:15:15 fertilizer on oil-contaminated soil using Abelmoschus esculentus as a test plant. The research was conducted under controlled conditions at Nnamdi Azikiwe University, Awka, using a randomized complete block design. Soil samples were collected from an oil-contaminated mechanic workshop and treated with various organic and inorganic amendments. Growth parameters, including plant height, stem girth, leaf area, and number of leaves, were assessed over eight weeks. Results indicate that cow dung manure significantly enhanced plant height (100.33% increase), while fish pond wastewater combined with poultry droppings (FP+PD) showed the least increase (14.03%), suggesting a negative synergistic effect. The combination of cow dung and poultry manure (CD+PD) also exhibited a strong positive effect on plant growth. Soil nitrogen levels were highest in FP+PD-treated soils (5.32±1.06), while phosphorus levels were maximized with poultry droppings alone (22.90±5.80). Contaminated soil had the highest potassium levels (54.37±4.38 ppm), likely due to crude oil contamination. Despite amendments, soil pH remained largely unchanged. Leaf production was significantly enhanced by cow dung and fish pond wastewater, with a 100% increase in four weeks, while poultry droppings alone had no effect. Leaf area expansion was highest in the control group (842%), indicating that manure application may not significantly influence light-harvesting capability. Stem girth increased equally (33.33%) across all treatments except in the control (11.11%), with cow dung and fish pond wastewater showing the most rapid impact. Overall, cow dung manure proved to be the most effective treatment for improving soil fertility and enhancing A. esculentus growth in oil-contaminated soil, followed by fish pond wastewater and poultry droppings. These findings highlight the potential of organic amendments in mitigating oil pollution and promoting plant productivity.