On boron turnover in plant–litter–soil system

• Plant litter and soil water mobile phase as factors of boron turnover were examined.
• In plant–litter–soil system, B turnover occurs as a semi-closed cycle.
• Soil water-mobile colloids are the main carrier of available B.
• Exchangeable and strong organic complexes are two main sources of soil available B.

Boron (B) is an indispensable constituent of plant lignin st\ructures inherited by soil humus compounds. However, little is known about plant litter as a factor of B turnover in the plant–soil system. Also, the sources of soil available B and the mechanism of its release and mobility are poorly understood. In a series of experiments, we considered (1) leachates from decomposing plant litter and leaves and (2) soil–water mobile phase (‘soil solution’) as the carriers and sources of potentially available B compounds. The obtained data showed that plant litter is the main source of available and water-mobile compounds of B to the soils; this is 1 to 3 orders of magnitude higher than the B income with rain and aerosol precipitation, and even more than the income from rock weathering. We can assume that the B turnover occurs in a semi-closed system ‘plant–litter–soil’ (‘plant–litter–soil organic matter–soil water mobile compounds–available B’). Mobile colloids of particular size of 0.20 < d < 0.45 μm were found to be the main carrier of the soil available B. The character of B release from the colloids indicated at least two forms of B bonding: (1) easy-exchangeable, which is pH-dependent, and (2) firmly-bound B-organic complexes.