Abstract
Coumarins represent an important family of allelochemicals with fungicidal, bactericidal, insecticidal, nematicidal, and herbicidal properties. Like for other allelochemicals, the short persistence of coumarins in soils can reduce their biological activity and hamper their application as environmentally friendly agrochemicals. We evaluated the sorption of the coumarin umbelliferone by eight soils and six sorbent materials, and then selected two nanoengineered sorbents, hexadecyltrimethylammonium-modified Arizona montmorillonite (SA-HDTMA) and olive-mill waste biochar (BC), to assess the effect of their addition to two distinct soils on umbelliferone sorption, persistence, and leaching. Umbelliferone was sorbed to a greater extent by the acid soils (A1-A2, Kd > 4.0 L kg-1) than by the alkaline soils (B1-B6, Kd < 0.5 L kg-1). The addition of BC and SA-HDTMA at a rate of 4% to alkaline soil (B2) increased the umbelliferone sorption Kd value from 0.3 to 1.6-2.0 L kg-1, whereas their addition to acid soil (A1) increased the Kd value from 4.6 to 12.2-19.0 L kg-1. Incubation experiments showed that BC had more impact than SA-HDTMA on the persistence of umbelliferone in the soils, increasing its half-life from 0.3-2.5 to 1.2-14.4 days, depending on the soil. Furthermore, the addition of BC to the top 0-5 cm of soil columns reduced leaching of umbelliferone and led to accumulation of umbelliferone residues in the top 0-5 cm soil layer. The addition of nanoengineered materials, such as organoclays and biochars, could thus be a suitable strategy to increase the persistence and reduce the mobility of coumarins in the rhizosphere with the aim of prolonging their biological activity.