Figure 1. Schematic depiction of the differences in the availability/recovery of a putative chemical to a competing species from a given amount of chemical produced and released from a plant in in vitro assays as compared to in situ assays that include soil and the associated microbial (bulk and rhizosphere) communities.

Sorption of chemicals onto soil particles, chemical decomposition and/or microbial degradation of chemicals are major mechanisms that influence their ability to accumulate to phytotoxic levels and influence the growth of neighboring target plants [13], [40], [41]. Sometimes physical sorption of a chemical on soil particles can actually concentrate the chemical to a level that may become physiologically active. Therefore, sorption may affect allelopathy both negatively and positively.