ABSTRACT
Spent mushroom substrate (SMS) can be utilized as a bioredadiant to clean up soil polluted with spent engine oil (SEO). This study was conducted in the Screen House of the Department of Crop Science, Faculty of Agriculture, University of Benin between May and August, 2023 to evaluate the effect of SEO contaminated soils remediated with SMS on post-harvest soil chemical properties after cropping with Amaranth. The study included three levels (0, 5 and 10% v/w in 10kg of soil) of spent engine oil pollution and four levels of spent mushroom substrate (0, 200, 400 and 600g), in a 3 × 4 factorial arrangement fitted into complete randomized design (CRD) with three replications. Data were collected on the properties of soil-polluted remediated with SMS before cropping with Amaranth, and the soil's chemical properties post-harvest after cropping with Amaranth. The results showed that the contaminated samples had lower pH and reduced nutrient content, high exchangeable acidity, hydrocarbon content compared to the control. Polluted soils had poor porosity and electrical conductivity but high bulky density. As the rate of spent mushroom increased, the hydrocarbon concentration in the polluted soils decreased, but the addition of spent mushroom imroved soil pH, exchangeable cations, total N, and available P, with more significant improvements at higher application rates. Spent mushroom also reduced the total hydrocarbon concentration, which decreased further with increasing application rates. After harvest, there was general reduction in all chemical properties except exchangeable acidity. However, lowest pH, highest organic carbon, exchangeable acidity, THC and heavy metals was associated with SEO polluted soil at 10%. Unpolluted soil had higher nutrient content than polluted soil. SMS improved nutrient content of the soil as soils treated with it had higher nutrient content than non-spent mushroom substrate treated soil. Soils polluted with SEO at 10% and treated with SMS at 600g had highest nutrient content and the most improved pH with 5.63, total N of 1.54gkg-1 ,13.8 available P, 1.42cmolkg-1 Ca, 0.34cmolkg-1 Mg, and 0.16cmolkg-1 Na. Soils polluted with SEO should be remediated with SMS applied at 600g per 10kg soil.
