Suitability of Complex Extractants for Assessment of Available Soil Zinc for Nutrition of Rice (Oryza sativa L.) in Subtropical India

We evaluated the efficiency of six complex extractants such as diethylenetriaminepentaacetic acid (DTPA), Mehlich 3, ammonium bicarbonate–DTPA (AB-DTPA), modified Morgan, Morgan and diaminocyclohexanetetracetic acid-glycerol (CDTA) as to their suitability for assessing available zinc (Zn) status in soils of the Inceptisols and Alfisols soil orders for nutrition of rice (Oryza sativa L.). Twenty soils from each of the two soil orders were analyzed for extractable Zn content and used to grow rice with three levels of Zn (0, 5, and 10 kg ha−1). The relative efficiency of the Zn extractants followed the order AB-DTPA > Mehlich 3 > DTPA > CDTA > modified Morgan > Morgan in soils from the Inceptisols soil order and Mehlich 3 > AB-DTPA > modified Morgan > DTPA > Morgan > CDTA in soils classified as Alfisols. The extractable soil Zn was significantly correlated with soil organic C and clay content. All the soils showed significant response to Zn application in terms of increases in dry matter yield, Zn concentration, and plant uptake. Of the six extractants tested, AB-DTPA and Mehlich 3 were the best for assessing plant available Zn contents for nutrition of rice. The critical limits of Mehlich 3 and AB-DTPA extractants for getting higher responses of rice to Zn application were 1.2 and 1.0 μg g−1 in Inceptisols and 2.0 and 1.5 μg g−1 in Alfisols, respectively