Exploring warm-season cover crops as carbon sources for anaerobic soil disinfestation (ASD)

Anaerobic soil disinfestation (ASD) has been shown to be an effective strategy for controlling soilborne plant pathogens and plant-parasitic nematodes in vegetable and other specialty crop production systems. Anaerobic soil disinfestation is based upon supplying labile carbon (C) to stimulate microbially-driven anaerobic soil conditions in moist soils covered with polyethylene mulch. To test the effectiveness of warm-season cover crops as C sources for ASD, a greenhouse study was conducted using a sandy field soil in which several warm-season legumes and grasses were grown and incorporated and compared to molasses-amended and no C source controls. Greenhouse pots were irrigated to fill soil porosity and covered with a transparent polyethylene mulch to initiate a 3-week ASD treatment prior to planting tomatoes. Soilborne plant pathogen inoculum packets, yellow nutsedge (Cyperus esculentus L.) tubers, and Southern root-knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood; M.i.) eggs and juveniles were introduced at cover crop incorporation. In nearly all cases, ASD treatment utilizing cover crops as a C source resulted in soil anaerobicity values that were equal to the molasses-amended fallow control and greater than the no C source fallow control. In trial 1, Fusarium oxysporum Schlechtend.:Fr. (F.o.) survival was reduced by more than 97% in all C source treatments compared to the no C source control but there was no effect of C source in Trial 2. Carbon source treatments were inconsistent in their effects on survival of Sclerotium rolfsii Sacc. (S.r). In general, the number of M.i. extracted from tomato root tissue and root gall ratings were low in all treatments with cover crop C source, molasses C source, or composted poultry litter. Germination of yellow nutsedge tubers was highest in the no C source control (76%), lowest in the molasses control (31%), and intermediate from cover crop treatments (49% to 61%). Warm-season cover crops have potential to serve as a C source for ASD in vegetable and other crop production systems, but more work is needed to improve consistency and further elucidate mechanisms of control of soilborne plant pathogens and weeds during ASD treatment utilizing cover crops.