Evaluation of methods for determination of soil boron available to apple trees

Soil boron (B) available to plants can be determined by using several methods. This study evaluated the efficiency of hot water extraction, saturation paste, resin, mannitol, and hydrochloric acid methods for determination of soil B available to two apple tree varieties (Malus domestica, var. golden and black). Soil samples from 26 sites where the golden and black apple varieties were growing in northern Greece were collected and analyzed for B by these five procedures. Boron concentration in apple tree leaves from these sites was also determined. Hot water extractable boron (HwsB) was strongly correlated with B extracted by mannitol (Man-B) and HCI (HCl-B). Soil B extracted by all the methods was significantly correlated with B concentration in apple tree leaves of both varieties, except golden in the case of the saturation paste method. Boron extracted with use of the resin method correlated best with leaf B for both varieties followed by the mannitol and HCI methods. Resin-extractable soil B concentrations causing deficiency and toxicity were 1.20 and 5.19 mg kg(-1) soil, respectively. For the other methods, soil B concentrations corresponding to B toxicity in these apple varieties ranged from 4.0 to 6.0 mg B kg(-1) soil.