Field-scale dissipation of tebuconazole in a vineyard soil amended with spent mushroom substrate and its potential environmental impact.

The persistence, mobility and degradation of tebuconazole were assessed under field conditions in a sandy clay loam soil amended with spent mushroom substrate (SMS) at two rates. The aim was to evaluate the environmental impact of the simultaneous application of SMS and fungicide in a vineyard soil. SMS is the pasteurized and composted organic material remaining after a crop of mushroom is produced. SMS is generated in increasing amounts in La Rioja region (Spain), and could be used as soil amendment in vineyard soils, where fungicides are also applied in large amounts. The study was carried out in 18 experimental plots (6 treatments and 3 replicates per treatment) over one year. Laboratory experiments were also conducted to verify the changes over time in the adsorption of fungicide by soils and in soil dehydrogenase activity caused by the fungicide and/or SMS. Tebuconazole dissipation followed biphasic kinetics with a rapid dissipation phase, followed by a slow dissipation phase. Half-life (DT50) values ranged from 8.2 to 12.4 days, with lower DT50 for amended soils when compared to the non-amended controls. The distribution of tebuconazole through the soil profile (0-50 cm) determined at 124, 209 and 355 days after its application indicated the higher mobility of fungicide to deeper soil layers in amended soils revealing the influence of solid and dissolved organic matter from SMS in this process. Tebuconazole might be available for biodegradation although over time only chemical or photochemical degradation was evident in surface soils. The results obtained highlight the interest of field and laboratory data to design rational applications of SMS and fungicide when they are jointly applied to prevent the possible risk of water contamination.