On boron turnover in plant–litter–soil system

Abstract

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<0.45μm 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.