PLANT AVAILABILITY OF NICKEL AS INFLUENCED BY FARMYARD MANURE AND ITS CRITICAL TOXIC LIMITS IN FRENCH BEAN

A greenhouse experiment was conducted to evaluate the critical toxic limits of nickel (Ni) in french bean grown on a mollisol receiving varying levels of farmyard manure (FYM). Nickel levels beyond 10 mg kg^?1 soil brought a significant reduction in the dry matter yields of french bean. Application of FYM, especially at the higher level (4.46 g kg^?1 soil), had a favorable effect on the dry matter yields of french bean. The effect of FYM application was more pronounced at the medium levels of Ni. Application of higher level of FYM could decrease Ni concentration in plants significantly. Different soil extractants employed in the present study could be arranged in the following order of their Ni extraction power: Mehlich 3 > 0.1 N hydrochloric acid (HCl) > double acid > ammonium bicarbonate (AB)-diethylenetriaminepentaacetic acid (DTPA) > DTPA. Among different extractants evaluated in the study, DTPA (pH 7.3) appeared to be most promising for predicting Ni concentration in french bean. The threshold toxic levels of Ni in french bean and also in terms of extractable soil Ni contents were influenced by FYM application.