Boron extractants, shoot dry weight yield, and nutritional status of alfalfa grown in different soil types

Alfalfa (Medicago sativa L.) is a boron (B) demanding plant, and the extractants currently in use are limited in their ability to define the available B content in tropical soils accurately. This study aimed to evaluate the efficiency of seven extractants [B (Mehlich-1, Mehlich-3, Hot Water, KCl 1.0 mol L−1, Mannitol 0.05 mol L−1+CaCl2 0.01 mol L−1, Ca(H2PO4)2·H2O 0.01 mol L−1, and HCl 0.05 mol L−1] in determining soil B availability, correlating these findings with shoot dry weight and nutritional status. The experiment was conducted under greenhouse conditions, using a completely randomized design in an 8 × 2 × 2 factorial arrangement. The eight soil types were tested with two base saturations (60 and 80%), and two B rates (0 and 1.0 mg kg−1–boric acid source), and three replicates. The Mehlich-1 and Mehlich-3 extractants demonstrated a superior ability to recover the available B in the soil, while the Hot Water and Ca(H2PO4)2·H2O 0.01 mol L−1 extractants showed a higher significant correlation with each other. In terms of soil chemical attributes, significant correlations were observed between B extractants and soil organic matter (SOM) content and cation exchange capacity (CEC). Regardless of the soil type and base saturation, B fertilization had strongest influence on the shoot dry weight (SDW) yield of alfalfa and the nutrient concentrations in SDW varied according to the soil type and base saturation.