Growth and Nodulation of Centrosema pubescens Benth (Butterfly Pea) in Soils of High Copper Levels in the Humid Zone of Nigeria

Abstract

Some farming operations contribute to heavy metal toxicity of the soil which in turn affects above ground vegetation. Soils collected from cocoa and Gmelina arborea plantations were separately used for raising Centrosema pubescens in three pots (A, B and C) in Nigeria. The cocoa plantation soil was contaminated as result of use of Cu-based fungicide. Pot A had 5kg of soil with copper-contaminated soil while Pot B was same as Pot A above but amended with poultry manure using 2:1; representing media with moderate toxicity. Similarly, Pot C or the control contained soil obtained from a nearby Gmelina plantation 200m from the cocoa plantation. C. pubescens seedlings were raised in nursery for 4 weeks and planted out into the pots. Growth parameters (leaf number and total dry weight (g)) and chemical composition of biomass (N, P, K, Fe, Cu, Pb) were determined and compared using ANOVA at @<0.05. Root nodulation was highest in Centrosema stands grown with control soil and was 260% higher than that of Cu contaminated soil (A). Both mean leaf number per plant and total dry weight (g) were highest in stands grown with Cu contaminated soil amended with poultry manure indicating possible suppression of Cu-toxicity by the manure. Cu- soil contamination affected the level of macronutrients (N, P, K) uptake especially in Pots A and B. N.P.K in Centrosema samples grown with control soils C were significantly higher than those of “A” by 48.3%, 61.4% and 66.5% respectively. Although toxicants have potential of being transmitted to man/livestock, C. pubescens showed relatively high absorption capacity for toxic elements which can enhance its choice for possible use in land clean-up and phytoremediation programme.