Modelling of Heavy Metals Concentration in Maize (Zea may L.) Grown in Artificially Contaminated Soil

Abstract

The response of maize (Zea may L.) to heavy metals (Cd, Cr, Cu, Pb and Zn) contamination was investigated in field experiments to predict the potential of the plant to extract metal toxicants. Experimental field was amended with increasing loads (2–10 kgha-1) of either metal salts and/or metal- cow manure blend (metal/cow manure ratio 1:10. Maize plants were grown and monitored for changes in growth rate.  Maize plant tissue metal concentrations were determined using standard method. Physicochemical parameters of the parent soil (control) determined were 6.20, 8.93%, 6.81 meq100-1g, 0.54% and 87.50 mgkg-1 for soil pH, soil organic matter (OM), cation exchange capacity (CEC), total nitrogen and phosphorus respectively. Soil particle size analysis showed the predominance of the sand component (74.20%), followed by clay (23.70%) and the silt (2.10%). Pseudototal metal content (mgkg-1) were 4.35, 3.00, 6.25, 0.50 and 14.25 for Cd, Cr, Cu, Pb and Zn respectively. The low levels of these metals in the parent soil suggested the need for spiking in order to assess and predict plant tissue metal concentration in the contaminated soil. The plants were generally greenish with linear growth attributes proportional to metal doses, suggesting some level of forbearance. The range of maize tissue metal concentration for Cd, Cr, Cu, Pb and Zn were 3.50 – 42.80, 3.40 – 21.80, 7.80 – 48.10, 2.50 – 30.40 and 10.20 – 44.75 respectively. Cu was most extracted from the plant while Cr was the least. Predictive models for plant tissue metal concentration were derived from soil pH, OM, plant available and pseudo-total metal with a close range of values. The models predicted the metal concentration in maize plant very well and the relationship is significant (0.01 ≤ p ≤ 0.05). However, extrapolation of the present experimental results and its broader application to other plants, still need further investigation.