Critical limits of Mehlich 3 extractable phosphorous, potassium, sulfur, boron and zinc in soils for nutrition of rice ( Oryza sativa L.)

We evaluated the critical limits of P, K, S, B and Zn in Inceptisols and Alfisols for nutrition of rice (Oryza sativaL.) using Mehlich 3 as an extractant. Three levels, each of P (0, 14 and 23 mg kg-1 soil), K (0, 23 and 36 mg kg-1soil), S (0, 4.5 and 9.0 mg kg-1 soil), B (0, 0.5 and 1.0 mg kg1 soil) and Zn (0, 2.3 and 4.5 mg kg-1 soil) were applied separately to 20 Alfisols and Inceptisols each for growing rice in greenhouse. Biomass yield, concentration and uptake of those nutrients by rice were significantly influenced (P ≤ 0.01) by the soil and rate of each of the nutrients (P, K, S, B and Zn), but not by their interactions in both the soil orders. The amount of these five nutrients as extracted from soils by Mehlich 3, alike conventional extractants, showed significant positive correlations (P≤ 0.01) with biomass yield, nutrients concentration and their uptake by rice plant, which indicated suitability of Mehlich 3 in predicting plant available nutrients in soil. The critical levels of Mehlich 3 extractable P, K, S, B and Zn for rice in Inceptisols were 14.7, 51.2, 22.9, 0.65 and 1.27 mg kg-1; while in Alfisols those values were 8.2, 117.3, 21.9, 0.40 and 2.15 mg kg-1, respectively.