Critical limit of zinc for response of rice to zinc application in acidic soils of Assam

Pot culture experiment was conducted with twenty five georeferenced bulk surface soil samples (0-30 cm) having variable zinc status and with four levels of zinc viz., 0, 2, 4 and 6 kg Znha-1. The dry matter yield of rice (var-Ranjit) increased significantly over control with rates of zinc application. The highest dry matter yield was recorded in 4 kg Znha-1. Bray's percent yield ranged from 57.18 to 95.7 and the highest Bray's percent yield of 95.7 was observed in the soil having DTPA-Zn of 0.4mgkg-1 and the lowest value of 57.18 was observed in the soil with DTPA-Zn of 2.49 mgkg-1.The soils were also extracted by different extractants viz., DTPA, 0.5N HCl, 0.1N HCl, NH4OAC, EDTA- (NH4)2CO3, AB-DTPA, 0.04M EDTA and 2M MgCl2 solution for available Zn, where DTPA showed the highest correlation with all the plant parameters followed by AB-DTPA, 0.05 N HCl and EDTA-(NH4)2CO3, 0.04 EDTA and NH4OAC. The critical limits of DTPA, AB-DTPA 0.5N HCl , EDTA-(NH4)2CO3 ,0.04 M EDTA and NH4OAC in soil were found to be 1.24,1.74, 1.25, 2.8, , 0.74, 0.9 mg/kg respectively. The critical limit of Zn for rice was 40 mgkg-1.