Overcoming barriers to consistent yields in reduced tillage organic vegetable production

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Ceres Trust Graduate Student Grant Annual Report

Graduate student: Dana Jokela, Department of Horticulture, Iowa State University
Faculty advisor: Ajay Nair, Department of Horticulture, Iowa State University
Amount awarded by Ceres: $9,982


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 at the Horticulture Research Station, Ames, IA, compared no tillage (NT), strip tillage (ST), and conventional tillage (CT) in organic production of broccoli and bell pepper, with data being collected on crop yield, plant health, weed suppression, soil growing degree days, nitrate leaching, and production system economics. 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, and the other split between the granular fertilizer and post-planting fertigation—to test the effect of fertigation on 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 fertility treatments averaging 14.7 Mg·ha-1. Yield of broccoli was 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 than NT and ST treatments, demonstrating that early season weed suppression by the cover crop mulch was effective. Soil growing degree days was greatest under CT management for both broccoli and pepper, and higher in ST than NT in pepper plots, but not in broccoli plots. In summary, reduced tillage systems maintained yields of peppers, but not broccoli, while providing early season weed suppression. Split application of fertilizer through use of fertigation did not increase yields.

Primary Objectives

  1. Determine effect of tillage system and fertilizer application timing on yield of broccoli and bell pepper
  2. Assess impacts of fertigation on plant N status and nitrate leaching
  3. Evaluate weed suppression by rolled cover crop mulch

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