Boron status of Hawaiian soils as measured by B sorption and plant uptake

Boron sorption experiments were conducted on 12 Hawaiian soils, which differed remarkably in mineralogy, pH, and organic matter content. Results indicated that soils derived from volcanic ash sorbed much more B than those from basalt or alluvium. High B sorption was attributed to great quantities of X‐ray amorphous alumino silicates and high organic matter contents that are characteristic of volcanic ash soils. Increased soil pH resulting from liming also increased B sorption. Boron status of the soils was studied further in a greenhouse experiment, using Desmodium canum (a high B resquiring tropical forage legume) as the test crop. Soil B and plant B concentrations showed that these soils were marginally B deficient. Hot water‐extractable B in these soils ranged from 0.3 to 1.6 mg B/kg, with seven soils having < 1.0 mg B/kg, the minimum B level considered essential for normal growth of the legume.