Selecting Management Practices and Cover Crops for Reducing Tillage, Enhancing Soil Quality, and Managing Weeds in Western Washington Organic Vegetable Farms

Grower interest in reduced tillage techniques stems from concern over soil quality and energy use. Tillage decimates large-bodied soil organisms, reduces soil carbon storage and weakens the stability of aggregates. Organic vegetable growers in the Pacific Northwest currently pass over their fields 10 to 20 times annually to incorporate cover crops and amendments, prepare the soil for planting, and manage weeds. Incorporating reduced tillage into organic vegetable cropping systems requires careful integration of cover crops and specific implements. The specific objectives of this study were to identify production methods that effectively integrate cover crops and reduced tillage technologies to improve soil quality while reducing in-season weed pressure and seed bank populations. Cover crop variety trials indicated that ‘Aroostook’ rye and ‘Lana’ vetch were desirable cover crops for organic reduced tillage. Winter squash ‘Delicata’ and broccoli ‘Everest’ were grown in rotation with rye and vetch cover crops over a three-year period (2012-2014) in Puyallup, WA. Cover crops were terminated with either a roller/crimper or flail mower and ground was prepared for transplants by strip till, no-till, or full till. Among reduced-tillage treatments, squash yield was increased with flail mowing compared to rolling/crimping in 2 out of 3 years. Full tillage had greater squash yields than reduced tillage treatments in 2 out of 3 years. Cover crop termination and reduced tillage combinations did not affect broccoli yields during any of the 3 years of the trial. Mulch created from terminating cover crops did not completely suppress weeds. High-residue cultivation could improve in-season weed control and yields in reduced-tillage organic vegetable production.