The requirement of zinc for improvement of crop yield and mineral nutrition in the maize-mungbean-rice system

A study was made over 3 years to find out an optimum rate of Zn application for the maize-mungbean-rice cropping system in a calcareous soil of Bangladesh. Zinc application was made at 0, 2 and 4 kg ha(-1) for maize (cv. Pacific 984, Thai hybrid) and at 0, 1 and 2 kg ha(-1) for rice (cv. BRRI dhan33), with no Zn application for mungbean (cv. BARI mung5). Effect of Zn was evaluated in terms of yield and mineral nutrients contents (N, P, S and Zn). All the three crops responded significantly to Zn application. The optimum rate of Zn for the maize-mungbean-rice cropping system was found to be 4-0-2 kg ha-1 for the first year and 2-0-2 kg ha-1 for subsequent years particularly when mungbean residue was removed, and such rates for mungbean residue incorporation being 4-0-1 and 2-0-1 kg ha(-1), respectively. For all crops, the Zn and N concentrations of grain were significantly increased with Zn application. For the case of grain-S, the concentration was significantly increased for maize and mungbean, but it remained unchanged for rice. The grain-P concentration on the other hand tended to decrease with Zn application. For maize, the grain-Zn concentration increased to 27.0 mu g g(-1) due to 2 kg Zn ha(-1) treatment from 16.5 mu g g(-1) for Zn control and at higher Zn rate (4 kg Zn ha(-1)) the increment was very minimum. Another field experiment was performed over 3 years on the same soil to screen out maize varieties for Zn efficiency. Of the eight varieties tested, the BARI maize 6 and BARI hybrid maize 3 were found Zn in-responsive (Zn efficient) and the others Zn responsive (Zn-inefficient).