The soil amendments are known to reduce the toxicity of heavy metals in soil. A pot experiment was conducted to evaluate the effect of four different concentrations (220:117:140, 440:117:140, 220:117:280 and 440:117:280) of Nitrogen, Phosphorous and Potassium (NPK) and their effects on Acacia auriculiformis and Casuarina equisetifolia in phytoremediation of CCA compounds. Results showed that the growth and biomass of the seedlings treated with CCA (1000 mg kg-1 soil) were significantly increased with an increase in NPK concentrations. Similarly, the amounts of Cu, Cr, and As found in the roots of A. auriculiformis at 440:117:2080 mg g-1of NPK were 3.577, 3.070, and 0.094 mg g-1 respectively. Similarly, the quantity of Cu, Cr, and As found in stem and leaves in similar concentrations of NPK were 1.683 and 2.220 mg g-1, 2.600 and 1.913 mg g-1, and 0.077 and 0.085 mg g-1 respectively. Furthermore, the amount of Cu, Cr, and As found in the roots of C. equisetifolia at similar concentrations of NPK were 1.670, 3.320 and 0.240 mg g-1 respectively. Nevertheless, the amount of Cu, Cr, and As found in stem and leaves were 0.350 and 0.398 mg g-1 and 0.110 and 1.530mg g-1, 2.540 and 0.154 mg g-1 at 440:117:2080 mg of NPK respectively. The higher concentrations of NPK significantly (p≤0.05) increased the biochemical parameters of both the test plants. The maximum amount of total carbohydrates, proteins, and chlorophyll content found in A.auriculiformis and C. equisetifolia were 4.06, 1.61 and 0.28 mg g-1, and 3.575, 1.073 and 0.369 mg g-1 at NPK ratio of 220:117:280 mg kg-1 soil respectively. The present study advocates that the higher concentrations of NPK improve soil properties and plant productivity by reducing heavy metal solubility and the NPK can greatly enhance phytoremediation in CCA-contaminated soils using A. auriculiformis and C. equisetifolia tree species.

Keywords:Acacia auriculiformis; Casuarina equisetifolia; CCA; NPK; Biochemical parameters