Evaluation of different soil extractants for assessing B availability to maize (Zea mays L.)

A greenhouse experiment was conducted with twenty surface (0-15 cm) soil samples using maize (cv. Pragati) as a test crop to estimate the critical limits of B in soil and plant. Five soil extractants used in the study varied in their B extraction capacity and could be arranged in the order: Mehlich 3 (pH 2.0) > 0.005 M DTPA + 1 M ammonium bicarbonate (pH 7.6) > 1 M MgCl2 (pH 6.0) > 0.01 M CaCl2 > Hot water. All B extractants employed in the present investigation showed highly significant relationships with Bray's percent yield of maize. The critical limits of B in soil for maize were 0.61 mg hot water soluble B, 2.06 mg AB-DTPA extractable B, 1.03 mg 0.01 M CaCl2 extractable B, 2.20 mg 1 M MgCl2 extractable B and 2.56 mg Mehlich 3 extractable B kg(-1) soil. The critical limit of B in maize (cv. Pragati) plants of 30 d age was found to be 11.2 mg B kg-1 dry plant tissue. The dry matter yields and total B uptake of maize plants related significantly to B extracted by AB-DTPA (pH 7.6), 0.01 M CaCl2, 1 M MgCl2 (pH 6.0) and Mehlich 3 (pH 2.0). Boron concentration of maize plants related significantly to B extracted by AB-DTPA (pH 7.6), 1 M MgCl2 (pH 6.0) and Mehlich 3 (pH 2.0). Among soil extractants examined in the present study, Mehlich 3, a multi-nutrient extractant, appeared to be more suitable for predicting B deficiency in soils as this method had easy adoptability in soil testing laboratories owing short extraction time requirement.