|Di Gioia, Francesco - University Of Florida|
|Ozores-hampton, Monica - University Of Florida|
Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2016
Publication Date: N/A
Interpretive Summary: Anaerobic soil disinfestation (ASD) is a non-chemical method of disinfesting soil using a simple three-step process that involves the incorporation of organic amendments, a labile carbon source, and irrigation to saturate soil. Raised beds are formed, amendments applied, and beds covered with gas-impermeable film to prevent the re-entry of oxygen. The quantity of labile carbon can be adjusted to compensate for low soil temperatures, but the specific rates of added carbon have not been evaluated for the production of tomatoes for the Florida market. In the reported study, several rates of molasses used as the labile carbon source were tested for their effect on tomato biomass, redox potential of the treated soil, and the production or organic acids known to be one mechanism associated with disease suppression using ASD. Soil was extracted from treated pots throughout the three-week ASD treatment period and characterized for organic acids using high pressure liquid chromatography. Tomato biomass data was collected by cutting the plants at the soil line and weighing. Anaerobicity (redox potential) was measured using oxidation-reduction probes mounted in pots for the duration of the treatment. The lowest rate of molasses resulted in the greatest biomass accumulation and higher rates resulted in phytotoxicity. There was no increase in anaerobicity with increased molasses application and the greatest amount of most measured organic acids resulted from the two highest rates, which may have lead to the observed phytotoxicity. Of the rates tested, 13.9 m3/ha was the most beneficial rate.
Technical Abstract: Anaerobic soil disinfestation (ASD) is a non-chemical soil disinfestation technique proposed for the control of soil-borne pathogens, plant parasitic-nematodes, and weeds in different crops. ASD is applied in three steps: 1) Soil amendment with a labile carbon (C) source; 2) Cover the soil with totally impermeable film (TIF) or solarization film; 3) Irrigate to saturation. These three steps allow the creation of anaerobic conditions and stimulate anaerobic decomposition of incorporated organic material through facultative anaerobic microorganisms, producing organic compounds that are toxic or suppressive to soil-borne pathogens, nematodes, and weeds (Rosskopf et al, 2015). The quantity of labile carbon to apply is an important area of research. The objective of the reported experiment was to determine the effect of increasing Agricultural Carbon Source (ACS, molasses, Terra Feed, LLC., Plant City, FL) on cumulative redox potential (Eh), tomato plant growth, and generation of organic acids. The experiment was conducted in greenhouse at the UF/SWFREC (Immokalee, FL), during the fall-winter season of 2015. Black 10-L plastic pots were filled with Immokalee fine sand, amended with composted poultry litter (22 Mg ha-1), and molasses was applied at the rate of 0 (control), 13.9, 27.7, 41.6 and 55.5 m3 ha-1. Pots were saturated with 5-cm of water and tarped with Vaporsafe® Totally Impermeable Film (TIF™, Raven Industries, Sioux Falls, SD). Treatments were arranged according to a randomized complete block design with four replications and five pots per experimental unit. After three-weeks, a tomato seedling ‘Ridge Runner’ (Syngenta) was transplanted into each pot to evaluate plant growth response. During the three-week treatment period, three soil cores were taken from one pot per experimental unit at 1, 3, 7, 14, and 21 days after treatment application. A 30-g subsample was transferred to a centrifuge tube and 1M KCl was added to each tube. Tubes were shaken and centrifuged and the supernatant was collected, filtered through a 0.45 µm membrane filter and analyzed using High pressure liquid chromatography (HPLC). Cumulative anaerobicity (Eh) was not affected by increasing C rates above the 13.9 m3 ha-1. The two highest rates resulted in significant levels of tomato plant mortality and biomass declined with increasing rate. Of the acids identified, lactic, propionic, isobutyric, and valeric acids increased over time and with increasing carbon rate. While it is was anticipated that increasing molasses amendment rate would increase the level of anaerobicity, it was not expected that higher rates would result in phytotoxicity. Increased rates of molasses application would be beneficial when ASD is conducted with high nitrogen organic amendments in order to mitigate the generation of nitrous oxide. Higher application rates resulted in excessive production of organic acids, reducing plant growth.