Organic amendments from olive cake as a strategy to modify the degradation of sulfonylurea herbicides in soil

Amending soil with products rich in organic matter, such as raw olive cake or alperujo and its compost and vermicompost, could be a simple bioremediation strategy for soil pollutants such as pesticides. To investigate this hypothesis in relation to sulfonylurea herbicides, these amendments were applied to a Mediterranean agricultural soil at rates 4 times higher than agronomical dosage to stimulate biodegradation of chlorsulfuron, prosulfuron, and bensulfuron, added in a mixture to the soils. Degradation studies were conducted in microbially active and sterile soils to check the importance of biological and chemical degradation of sulfonylurea herbicides in nonamended and amended soil. The addition of alperujo stimulated soil microbial activity, as determined by dehydrogenase activity measurements, but it did not enhance the degradation of the sulfonylurea herbicides. In contrast, compost and vermicompost slightly favored the biological degradation of bensulfuron during the first week of incubation. Chlorsulfuron and prosulfuron were mainly degraded by chemical pathways in all substrates, which is probably due to a competitive or inhibitory phenomenon observed between chlorsulfuron and bensulfuron. The first-order kinetic equation satisfactorily explained the experimental data for chlorsulfuron and prosulfuron; however, a biphasic model, such as that proposed by Hoerl, better predicted the results obtained for bensulfuron.