Greenhouse gas emissions in reduced tillage organic vegetables

Bethany Rose Wolters

High residue vegetative mulches created by spring terminated cover crops have been shown to suppress weeds in organic systems as well as increase soil moisture when compared to conventional tillage systems. However, many details of cover crop based strip tillage have not been explored, including the impacts of rye cover crop termination timing on between row weed suppression, conservation of soil moisture, and influence of high biomass residue on root zone soil temperature. Two field experiments were conducted to assess the influence of organic strip tillage and cover crop management on biomass production, weed suppression, rye regrowth, and water use efficiency in western Washington. The goal of the first experiment was to determine the influence of flail mown rye cover crop termination timing on residue production, residue C:N ratio, rye regrowth, between row weed suppression, and resulting kale yield. Cover crop biomass ranged between 2.5 Mg/ha-1 to 11 Mg/ha-1 and was influence by termination time, with later termination timing producing the highest values. When terminated at mid and late anthesis, rye regrowth and broadleaf weed emergence was greatly minimized. Termination timing did not result in a consistent effect on kale yield. The goal of the second experiment was to determine the influence of flail mown rye residue on water use efficiency of winter squash production and root zone soil temperature. Strip till root zone temperature was decreased compared to a bare ground treatment prior to canopy closure. Strip till resulted in a 66% compaction increase over full width tillage within the 0-10cm soil depth. Reduced ST yield and irrigation requirement resulted in no difference in water use efficiency one year. ST crop loss resulted in unreliable data water use efficiency data the second trial year. The results of these studies indicate that termination timing is an important factor influencing rye biomass production as well as rye regrowth and may contribute to between row weed suppression in organic strip tillage systems. Additionally, this research demonstrates between-row rye residue has the potential to reduced intra row root zone soil temperature in comparison to bare soil tillage systems.

Greenhouse gas emissions in reduced tillage organic vegetables

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