Evaluation of extractability of different extractants for zinc and copper in soils under long-term fertilization

We aimed to evaluate the extractability of different extractants for zinc (Zn) and copper (Cu) in soils of long-term field experiments covering different agro-ecological zones of India. The relationships between the amounts of Zn and Cu extracted by Mehlich 3, 0.1 mol/L HCl and AB-DTPA (ammonium bicarbonate-diethylenetriaminepentaacetic acid) with those extracted by DTPA, the conventional extraction method widely used in soil testing laboratories in India, were elucidated. The treatments of the long-term experiments included control (no fertilizer), 100% NPK, 50%NPK + 50% N through FYM (farm yard manure) and a fallow soil. Some important physico-chemical properties of soil like pH, organic carbon, textural class, CaCO3 content, etc. were analyzed. The NPK + FYM treatment was found to be the most effective treatment in terms of increased content of Zn and Cu in soils. The results showed that the amount of Zn and Cu extracted by Mehlich 3 were significantly correlated with that extracted by 0.1 mol/L HCl (r = 0.970** for Zn and r = 0.914** for Cu). Accordingly, Mehlich 3 and 0.1 mol/L HCl could be used effectively for estimating Zn and Cu availability in soils of India. However, Mehlich 3 was superior to all the other extractants used for the study.