A study on heavy metals accumulation and its uptake by Cowpea [Vigna unguiculata (L.) Walp.] fertilized with Sugar mill effluent and DAP treatment in two cropping seasons

A study was performed under natural environment to compare heavy metal accumulation in soil and Vigna unguiculata L. (Cowpea) irrigated with five rates of SME viz. 10, 25, 50, 75 and 100% concentrations and DAP treatment (applied @100Kg/ha i.e. 0.7g / per 5 Kg) and control (Bore well water) separately in both the rainy (Kharif) and summer (Zaid) seasons for 90 days. Results revealed that among various concentration of SME and DAP treatment, irrigation with 100% SME concentration significantly (P<0.001) increased Zn (323.07-341.02 %), Cu (371.23-389.04%), Ni (3666.66-4133.33%), Cd (525.00-725.00%), Cr (1444.4-1477.77%) and Fe (224.08-244.89%) in the soil. In case of V. unguiculata irrigated with different SME concentrations, maximum range of heavy metals such as Zn (2.43-2.98 mg Kg-1), Cu (2.39-2.73 mg Kg-1), Ni (0.55-0.91 mg Kg-1), Cr (1.01-1.21 mg Kg-1), Cd (0.13- 0.17 mg Kg-1), and Fe (5.54-6.18) were observed at 100% concentration of SME than that of DAP treatment in both the cultivated seasons. However, the concentration of all the metals Zn, Cu, Ni, Cd, Cr and Fe in soil and plant were lower than toxicity threshold i.e. within the permissible limit. Enrichment factor (Ef) for soil/V. unguiculata was recorded maximum with Ni (37.66-42.33) / (24-30.33) and minimum with Fe (3.24-3.44) / (2.28-2.52) after 90 days of SME irrigation than DAP in both the cropping seasons of Kharif and Zaid. The minimum accumulation of Fe in both soil and crop showed that metals with completely filled d orbitals (d8, Fe) were least incorporated into the V. unguiculata crop