Date of Graduation

12-2016

Document Type

Thesis

Degree Name

Master of Science in Horticulture (MS)

Degree Level

Graduate

Department

Horticulture

Advisor

Curt R. Rom

Committee Member

M E. Garcia

Second Committee Member

Nilda R. Burgos

Third Committee Member

Craig R. Andersen

Abstract

This two-year study investigated short-season winter cover crops to improve soil quality and growth of subsequent vegetable crops in an organic high tunnel production system. Five winter cover crop treatments including a nontreated control, Austrian winter peas (Pisum arvense), bell beans (Vicia faba), mustard (Brassica juncea cv. Kodiak), and Daikon radish (Raphanus sativus var. longipinnatus) were grown in a high tunnel in a randomized complete block design from mid-November to mid-March, mowed and incorporated into the soil, and followed by a succession of vegetable crops including tomato (Lycopersicon lycopersicum, cv. ‘Plum Dandy’) and broccoli (Brassica oleracea var. italica, cv. ‘Bay Meadows’). In 2014 winter peas yielded the greatest above-ground biomass (284 g/m2), though in 2015 mustard and radish cover crops yielded greater above-ground biomass (424 g/m2 and 395 g/m2, respectively). Across both years winter peas contained the highest foliar N concentration (3.8%) and resulted in the greatest biomass N contribution, at an average of 10.2 g N/m2. The N contribution from winter pea resulted in a significantly lower soil C:N ratio 30 days after incorporation. Cover crop treatments did not result in significant changes to soil quality variables including soil organic matter, pH, and EC, though changes were observed over time across all treatments. The winter pea cover crop resulted in greater tomato leaf chlorophyll estimates than the nontreated control across both years, greater tomato foliar N concentration than all other treatments in 2015, and greater tomato plant biomass compared to the control. Though statistical differences were not detected due to high background variation, the winter pea cover crop resulted in a 48% increase in mean tomato yield compared to the control. Broccoli plant biomass was significantly greater following winter pea and radish cover crop treatments compared to the control (808 g/plant and 726 g/plant, respectively, compared to 600 g/plant), however cover crop treatments were not found to significantly affect broccoli harvest variables. Overall findings point to a cumulative effect of cover cropping on soil quality and vegetable crop production in a high tunnel, though the two-year timeline of this project limited the ability to understand long-term effects.

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