Assessing the impact of biofumigation and anaerobic soil disinfestation on soil biology, nitrogen cycling, crop establishment and yield in vegetable cropping systems

The need to develop alternative, environmentally benign pest management practices is one of the major challenges facing agriculture today. Novel alternatives to conventional fumigation practices in horticultural production systems can impact the chemical, biological and physical qualities of the soil in complex ways. Two such practices, biofumigation (BF) and anaerobic soil disinfestation (ASD) have demonstrated success in controlling certain soilborne pests, although results are often inconsistent. In some cases, negative impacts on crop establishment and yields have been observed following the application of these treatments. The objectives of this research were to: 1) investigate delayed seeding of crops as a method to reduce stand inhibition following BF, 2) monitor the impacts of BF and ASD on nitrogen availability, soil temperatures and microbial activity, and 3) evaluate the impact of BF and ASD on yields of warm season vegetable crops in southern Michigan. Experiments were conducted at the Southwest Michigan Research and Extension Center (Benton Harbor, MI) and the Horticulture Teaching and Research Center (Holt, MI) to address these objectives. In the first experiment, delayed seeding of a susceptible crop (Cucumis melo 'Athena') 10-15 days after BF resulted in satisfactory emergence. Yields of melon decreased significantly as planting date was delayed, however, highlighting the importance of early seeding of long-season vegetable crops during the short growing season of Michigan. In the second experiment, combinations of spring-sown brassica cover crops and plastic mulching treatments were established to evaluate the potential for BF and ASD to improve yields of fresh market tomato (Lycoperison lycopersicum 'Big Beef') and slicing cucumber (Cucumis sativus 'Cortez') while also evaluating the impact on nitrogen availability, soil temperatures and microbial biomass. As a standard ASD control, molassess was added as a carbon source for ASD in 2013 and caused dramatic reductions in N availability for the early part of the growing season while visibly stunting tomato growth. Although cover crop treatments did not significantly impact yields or N availability, black plastic mulch treatments had substantially higher NO3- and NH4+ during and immediately following ASD. Extremely high soil temperatures were also observed under plastic mulches in 2012 and are believed to have caused lower total marketable yields in tomato than bare ground treatments (under which soil temperatures were closer to the optimal root-zone temperatures for tomato growth). Results of this research highlight the importance of understanding how both alternative and commonly utilized cropping practices can influence environmental conditions in vegetable production, while identifying areas that must be addressed to effectively implement BF and ASD in the future for vegetable producers in southwest Michigan.