Relative Toxicity of Various Nickel Species on Seed Germination and Early Seedling Growth of Vigna unguiculata L.

Cowpea (Vigna unguiculata L.) seedlings were raised in water culture and exposed to varying concentrations (1,10,100,1000μM) of nickel as Ni (NO₃)₂ NiSO₄and NiCl₂ with a view to compare the effect of the above nickel species on seed germination, ultimate percentage germination, dry matter production, chlorophyll contents and soluble protein (leaf) contents. The ultimate germination was 100% (except in 1000 μM) in all the treatments of various nickel species. The germination speed was found maximum at 1μM nickel concentration. Lower concentration of nickel resulted in an enhancement while higher levels resulted decrease in fresh mass, dry matter production and chlorophyll contents of seedlings. Soluble leaf protein contents increased linearly with increasing application rates of nickel. In general, NiCl₂ was more inhibitory than NiSO₄ and Ni (NO₃)₂. Ni (NO₃)₂ was found to be least toxic. The extent of inhibition increased with enhanced levels of Ni₂ ⁺ ions. The toxicity series was found to be NiCl₂ > NiSO₄ > Ni (NO₃)₂.