Minimum tillage practices affect disease and yield of lettuce

Vegetable growers have been experimenting with reduced tillage practices to increase soil organic matter, limit compaction, and reduce fuel and labor costs. We studied soil properties of different tillage practices and compared deep minimum tillage (chiseling and ripping) with shallow minimum tillage for lettuce on a farm in the Salinas Valley. We found that periodic deep minimum tillage is recommended for long-term retention of semipermanent, raised beds in lettuce production. Over a period of several years, deep minimum tillage increased lettuce yield and decreased symptoms of lettuce drop disease, as compared with shallow minimum tillage. Continuous shallow minimum tillage, despite a trend toward higher active and total organic matter in the surface layer of soil, is best used with intermittent deeper tillage to avoid disease and yield losses.