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Tomato (Lycopersicon esculentumL.) is a sensitive crop to B deficiency, but information on critical concentrations of the element in plant tissues and soils for the crop is scarce. An experiment was, therefore, undertaken to assess available B content in the Gangetic alluvial soils (Entisolsand Inceptisols) for tomato and to determine critical limits of B in soils and leaves of tomato involving second order polynomial curve fitting. Soils and tomato leaves were collected from 94 tomato growing fields. Soils were analysed for hot-calcium chloride (HCC), potassium dihydrogen phosphate (PDP), tartaric acid (TA) and hydrochloric acid (HCl) extractable B and tomato leaves for B concentration. Among the four extractants, HCl extracted the highest amount of B followed by HCC > TA > PDP. Extractability of the extractants for B was explained mechanistically with soil properties. Hot-CaCl2showed stronger relationships with soil properties, tomato fruit weight and leaf B concentration, and thus proved to be the superior over other extractants for assessing available B status in soil for tomato. Critical limits of HCC extractable B were 0.51 and 0.52 mg kg−1and of mature tomato leaf B concentration were 40.5 and 37.5 mg kg−1in Entisolsand Inceptisols, respectively. The method of determining critical concentrations of B in soils and plants involving polynomial equations with non-destructive on-field samples was efficient for delineation of B deficiency in both Entisolsand Inceptisols. Multi-criteria based novel approach established HCC as the best extractant for assessment of available B in soils.