Electrical conductivity followed a similar pattern as pH. EC value decreased in the contaminated soil on introduction of compost by 6% in ‘compost-only’ treated soil and 15% in ‘compost + Kenaf’ treatment. This revealed the positive impact of compost on contaminated soil EC. High EC can affect the microbial activities in soil [34]. Smith and Doran [35] demonstrated that the yield of certain crops (barley, cotton, sugar beet and wheat) decreased as EC value of soil increased beyond the threshold limit. EC of the compost is lower than the threshold limit of 4000 μS cm−1, which may be toxic to plant [36].
Organic carbon (OC) and organic matter (OM) concentrations of compost were 28.8 ± 24.0 and 49.9 ± 35.6% respectively. According to FPDD [37] rating for OM, the compost is very rich in OM and is suitable for agricultural purposes. The values of OM obtained in this study were within the range of values reported by Zmora-Nahum et al. [38] in composts derived from manures (OC = 25.5% and OM = 46.5%), spent mushroom substrate (OC = 25.6% and OM = 45.6%). The mixing of contaminated soil with compost increased OC concentration by 13 times in ‘compost-only’ treatment and 8 times in ‘compost + Kenaf’ treatment. This finding shows that mixing soils with compost may serve as a dual purpose of increasing OM and removing toxic metals. OM enhances physical, chemical and biological properties of soil for crop production.