Cover Crop, Tillage and Fertility Management for Organic Pepper and Broccoli Production.

Organic no-till and strip-till systems have gained attention because of their capacity to enhance soil health and suppress annual weeds. This study, conducted in Ames, IA, compared no tillage (NT), strip tillage (NT), and conventional tillage (CT) in organic production of broccoli and bell pepper, with data being collected on crop yield, weed suppression, nitrate leaching, and soil growing degree days. All plots were seeded to a cereal rye/hairy vetch cover crop in Sept. 2013, and were either roller-crimped (NT and ST) or tilled-in (CT) in late spring of 2014. Each tillage treatment was split into two fertility regimes—one based entirely on preplant granular fertilizer (Preplant), and the other split between the granular fertilizer and post-planting fertigation (Split)—to test the effect of fertigation on nitrate leaching and yields under the typically N-limited reduced tillage conditions.  Yields of pepper were equal among the three tillage treatments, with Preplant treatments averaging 19.0 Mg·ha^-1 and Split fertilizer treatments averaging 14.7 Mg·ha^-1. Yield of broccoli were highest in CT treatments, averaging 5.4 Mg·ha^-1, with no difference between ST and NT treatments. Weed measurements taken three weeks after planting showed that CT treatments had significantly more weed biomass ST and NT treatments, demonstrating that early season weed suppression by the cover crop mulch was effective. Averaged across the whole season, nitrate concentration in leachate was 40% higher in CT than NT and ST plots. Soil growing degree days (SGDD) was greatest under CT management for both broccoli and peppers. SGDD of ST treatments was higher than that of NT in pepper plots, but not in broccoli plots.  In summary, reduced tillage systems maintained yields of peppers, but not broccoli, while reducing nitrate leaching and providing early season weed suppression. Changing the timing of fertilizer application through use of fertigation did not increase yields.