Sorption And Dissipation Of The Allelochemicals Umbelliferone And Salicylic Acid In A Mediterranean Soil Environment: Effect Of Olive-Mill Waste Addition

Allelochemicals are receiving much attention as natural alternatives to synthetic pesticides. Very little is known, however, about the processes to which allelochemicals are subjected once they reach the soil environment, despite the fact that it is widely recognized that such processes can dramatically influence their bioactivity and applicability as eco-friendly pesticides. The objectives of this study were to characterize the sorption and dissipation of two phenolic allelochemicals, umbelliferone (UM) and salicylic acid (SA), after their simultaneous application to a Mediterranean agricultural soil and to assess to what extent sorption and dissipation were affected by amending the soil with an agro-industrial organic waste (olive-mill waste, OMW), as a common agronomic practice in Mediterranean agricultural systems. In experiments conducted under standard laboratory conditions, UM (pK(a) = 7.5) showed greater sorption than SA (pK(a) = 2.8) and both allelochemicals displayed very short half-lives in the tested soil (DT50 < 1 day). Furthermore, the addition of OMW increased the sorption of UM and the halflives of both SA and UM in the soil. A field experiment conducted on unamended and OMW-amended soil plots confirmed the ability of OMW to increase the persistence of SA and UM under a real Mediterranean soil environment and showed that, for all treatments, the allelochemicals displayed higher half-lives in the field than under standard laboratory conditions. This was attributed to reduced biodegradation of UM and SA under progressive soil drying, which was thus identified as a factor that can prolong the persistence of allelochemicals in semi-arid soil environments. We highlight the need to test the environmental fate of allelochemicals under specific agroclimatic scenarios and illustrate how management practices can help increase their soil persistence so that their bioactivity can be better expressed. (C) 2021 Elsevier B.V. All rights reserved.