Leveraging by-products of the agri-food industry for the application of anaerobic soil disinfestation in organic high tunnel vegetable production

The expansion of the US organic vegetable industry is currently restrained by the lack of sustainable and effective solutions for managing soilborne pests and pathogens. Anaerobic soil disinfestation (ASD) constitutes an innovative microbial-driven approach to the management of a range of soilborne biotic issues. Based on the incorporation of readily labile carbon (C) sources in the soil, ASD requires the selection of effective and low-cost organic amendments, thereby offering an opportunity to recycle by-products of the local agri-food industry. However, the selection of alternative organic amendments as C sources for ASD treatments requires a prior understanding of how different amendments affects the efficacy of the treatment and the soil nutrient dynamics during and after the ASD treatment. To this purpose, we conducted a field study in an organic-certified farm at the Penn State High Tunnel Facility to compare the amendments of wheat middlings (WM), soybean meal (SM), and molasses (M) for ASD treatment. Treatments included WM, M, SM, WM+SM, and M+SM applied to reach the equivalent of 6 Mg ha^-1 of total C, SM-0.5 applied to reach the equivalent of 3 Mg ha^-1 of total C, and untreated controls with (UTC+W) and without (UTC) initial irrigation. Romaine lettuce was used as a test crop planted three weeks after the ASD treatment. Organic amendments tested were characterized by a C:N ratio that ranged between 6.3 in the case of SM to 57.2 in the case of M. The threshold of soil anaerobicity was achieved with all the amendments. The C:N ratio of the amendments significantly influenced the availability of nitrate-N during and post-ASD. Thus, also affecting lettuce crop yield and quality. The treatment with molasses (with the highest C:N) reduced the availability of nitrate-N during and post-ASD, while SM (with the lowest C:N) ensured the availability of higher nitrate-N levels. Taken together, this study provides important advances toward the optimization of ASD treatment in organic farming systems.