Utilizing Brassicaceae Seed Meal as a Soil Amendment to Suppress Weed and Soil Borne Pathogens.

Increased demand for organic and sustainable agricultural production systems and restrictions on registration and use of toxic synthetic pesticides have generated demand for effective non-synthetic and environmentally friendly alternative weed and pathogen management strategies.  Lack of effective alternatives have hampered organic production systems and also delayed the speedy phasing out of hazardous synthetic pesticides such as methyl bromide.  Biofumigation is one technology that could be more environmentally friendly compared to the synthetic alternatives.  Biofumigation can be defined as the incorporation of plant or animal biomass into soil, resulting in the release of toxic volatiles that reduce soil pests.  Brassicaceae seed meal, a residue product of the oil extraction process, can provide a local resource for supplemental nutrients, disease control and weed suppression.  Glucosinolate hydrolysis products are thought to be directly or indirectly responsible for the weed and soil borne pathogen suppression induced by Brassicaceae residues.  The objective of this study was to evaluate the effects of amending soils with different Brassicaceae seed meals and application rates on the emergence and growth of weed seedlings and soil borne pathogens (Pythium ultimum and Rhizoctonia solani AG-8) .  In addition, the effect of delaying tomato and pepper seeding or transplanting after seed meal amendment on crop damage was evaluated.  For most effective weed management and high tomato and pepper fruit yields, S. alba seed meal soil amendments applied at 2 Mt ha^-1 and crop seedlings transplanted 4 days after seed meal amendments can be used in field production systems. Amending soils with high glucosinolate B. napus seed meal (i.e. Dwarf Essex) can achieve the same P. ultimum suppression as utilizing high glucosinolate B. juncea seed meal, but with relatively lower phytotoxicity.  S. alba based amendments effectively and consistently suppressed R. solani AG-8 in wheat production.  However, approaches to avoid or minimize crop injury such as a delay seeding time after seed meal amendment or a compromise on application rates must be further evaluated.  Brassicaceae seed meals soil amendments show good potential in suppressing weeds and soil borne pathogen; however, seeding and transplanting delays after soil amendment will likely need to be further investigated to realize the full potential on Brassicaceae seed meals as a biofumigant.