Plant availability of boron in acid soils as assessed by different extractants

Estimation of available-boron (B) status through conventional methods in deficient acidic inceptions and Entisols is often hampered because of their very low B content. In the present study, the extractability of available B by different extractants was tested in relation to soil prop erties. Plant availability of B was assessed with mustard (Brassica campestris L.) and wheat (Triticum aestivum L.) in pot experiments. Twelve soils with varying characteristics were extracted for available B with hot water (HW), hot CaCl2 (HCC), KH2PO4 (PDP), tartaric acid (TA), and mannitol-CaCl2 (MCC)- Mustard (cv. B-9) and wheat (cv. PBW-343) were grown with four levels of B (0, 0.25, 0.50, and 1.0 mg [kg soil](-1)). Dry-matter accumulation and B concentrations were determined at pre-flowering and full-maturity stages,for mustard and at panicle-initiation and maturity stages for wheat. The extraction of B from the soils ranked HCC > HW > PDP > TA > MCC. The higher extractability with HW and HCC was likely due to higher temperature and that of PDP because of its phosphorus content, which facilitated the desorption of B. The low B extraction with MCC resulted from the poor mannitol-B complex formation in acidic soils. The application of B increased dry-matter accumulation, plant B concentration, and uptake at all B levels and growth stages in both crops with the responses being more pronounced during the early developmental stage. Based on linear correlations, Mallow's Cp statistics, and principal-component analyses, HCC and HW were the best extractants for estimating available B in the acidic experimental soils.