Availability and uptake of boron in a group of pedogenetically related Canterbury, New Zealand soils

Abstract

Amounts of soil boron extracted from six Canterbury, New Zealand soils by hot water (HWS), hot 0.02 M CaCl2, 0.01 M CaCl2 + 0.05 M mannitol, and a boron specific resin were significantly (P < 0.01) correlated with each other. The soils are all formed from greywacke alluvium and/or loess but cover a range of organic matter and clay contents. Hot water and hot 0.02 M CaCl2 yielded higher levels of extractable boron than did 0.01 M CaCl2 + 0.05 M mannitol and the resin. Amounts of boron extracted by all four reagents were significantly correlated with soil organic carbon contents (and to a lesser extent clay contents), but not with soil pH. Dry matter yield and boron uptake by radishes (Raphanussativus L.) over two harvests increased with increasing extractable soil boron for all four extractants showing that all were suitable for assessing the boron available to radishes. Decreased yields occurred in soils with HWS or hot 0.02 M CaCl2 extractable boron levels less than 1.1 µg g-1 and were associated with a progressively lower allocation of dry matter to roots. For analytical purposes, the hot 0.02 M CaCl2 reagent provided the most convenient measure of available soil boron.