Long-term field experiment on the application of slow-release boron fertilizer Part 2 Behavior of boron in the soil

Abstract

A long-term field experiment involving repeated boron (B) applications on three kinds of soil was carried out over 15 years to investigate the fate of applied B in these soils.

After the repeated cultivation of 26–29 successive crops without the application of B, the amount of total B and the various forms of B, including hot water soluble, adsorbed and fixed forms, all decreased. This suggests that when crops absorb B from the hot water soluble fraction, adsorbed B replenishes the hot water soluble B pool, and when the adsorbed B decreases, fixed B releases B to the adsorbed B pool. While about 10% of B applied was absorbed by plants, 30–40% of the B was left in the soil and about 40–60% was leached out from the top soil. In the forms of B left in the soil, the fixed form was the greatest, followed by the adsorbed form and hot water soluble form. Hot water soluble B showed a tendency to slightly increase over time with repeated boron applications, but its concentration was far lower than the toxic level of B in soil after 15 years of application.