Pot culture studies were conducted taking ten different soils collected from red and laterite soils from Mayurbhanj district of Odisha with groundnut, rice and potato as test crops to determine the critical limit of zinc (Zn) in soil and plants. The soils were acidic in reaction (pH 4.72-5.84), low to medium in organic carbon content and texture varied from loamy sand to silt loamy. About 50% soils were deficient in Zn. Rice, groundnut and potato received recommended dose of NPK. Each crop received seven levels of Zn varying from 0, 1.25, 2.5, 5.0, 7.5, 10 and 12.5 kg ha^-1. The critical level of Zn in soils and plants as determined by simple graphical method in red and laterite soils was 0.8, 0.7 and 0.7 mg kg^-1. The critical concentration of Zn in rice, groundnut and potato leaves was 24.5, 23 and 27 mg kg-1, respectively. Maximum biomass yield (g pot^-1) attained its highest value (114.17, 117.68) at 7.5 kg Zn ha^-1 in Zn deficient soils and at 5 kg Zn ha^-1 in medium Zn content soils (115.3, 127.59) in rice and ground nut, respectively; whereas in potato, the maximum yield (457.9) was recorded when the crop received 5 kg Zn ha^-1 level, indicating knowledge of critical concentration will help in maximizing the yield and performance of crop.