Effect of Partially Stabilized Organic Amendments on Volatile Acids Production and Pest Inactivation using Soil Biosolarization

Abstract. Soil biosolarization (SBS) is an enhanced soil disinfestation process, achieved by amending soil with organic matter (OM) prior to solarization. One reason for higher efficiency of SBS is the accumulation of volatile fatty acids (VFAs). The objective of this study was to assess the impact of partially stabilized organic wastes on SBS by monitoring the VFAs production kinetics and the inactivation of Fusarium oxysporum f.sp.lactucae (FOL) and Brassica nigra. The amendments were organic wastes partially composted (PC) and partially digested (solid digestate –SD- and liquid digestate -LD). Soil mesocosms, non-amended and amended, were prepared with a soil already infested with FOL. Weed seeds were placed at 12.5 cm depth. The mesocosms were solarized in an experimental plot or incubated at room temperature (RT, 25ºC) for eight days. At 5 cm, FOL levels were below the detection limit (<20.8 CFU/g) in all solarized-amended samples. In the solarized-amended samples weed seed mortality increased from ~4% at RT to ~34%. VFA production was only detected in the amended samples and it was significantly higher at the lower layer of the mesocosms. Further research is needed to understand the mechanisms involved in inactivation, specially the coupled effect of VFAs and temperature.