ASHS 2024 Conference

The growth of the U.S. organic vegetable industry is currently limited by the availability of viable and effective solutions for the management of soilborne pests and pathogens. Anaerobic soil disinfestation (ASD) is a pre-planting biological method proposed for the management of a range of soilborne pests and pathogens affecting horticultural crops. As an organic amendment-based approach, ASD is implemented incorporating in the soil an easily degradable carbon (C) source, tarping the soil with plastic mulch, and irrigating the soil to field capacity. The selection of organic amendments suitable as C sources is critical for the efficacy of the treatment and its sustainability. Understanding how the physicochemical properties of alternative amendments may affect the efficacy of the ASD treatment, the soil fertility during and post ASD, and consequently the crop performance is critical. Therefore, a study was conducted on organic-certified land at the Penn State High Tunnel Facility to compare wheat middlings (WM), molasses (M), and soybean meal (SM) and their combination as C sources. Treatments tested included WM, M, SM, WM SM, and M SM applied at the standard rate of 6 Mg/ha of total C, SM0.5 applied to reach the equivalent of 3 Mg/ha of total C, and the untreated controls with (UTC W) and without (UTC) initial irrigation. Three weeks after the ASD treatment, Romaine lettuce was planted as a test crop. Organic amendments tested as C source were characterized by different C:N ratio, ranging between 6.3 (SM) and 57.2 (M). All the amendments tested ensured the achievement of good soil anaerobicity levels. The C:N ratio of the amendments significantly influenced the availability of nitrate-N during and post-ASD, thereby influencing the lettuce crop yield and quality performance. Having the highest C:N ratio, M applied by itself decreased the availability of nitrate-N during and post-ASD. Instead, SM characterized by the lowest C:N ratio, increased the availability of nitrate-N. The availability of N during the growing cycle, determined by the characteristics of the organic amendment and by the ASD treatment influenced the crop yield and nutritional profile. The results of the present study provide new insight for the selection of alternative C sources and the optimization of the ASD treatment in organic protected culture systems.