Degree Type

Thesis

Date of Award

2016

Degree Name

Master of Science

Department

Horticulture

Major

Horticulture; Sustainable Agriculture

First Advisor

Ajay Nair

Abstract

Organic farmers rely extensively on tillage to incorporate plant residues, prepare seedbeds, and control weeds. However, tillage may have adverse effects on soil health, and conventional no-till production methods, which rely on herbicide for weed control, are not compatible with organic farming, so research was conducted on organic no-tillage (NT) and strip-tillage (ST), which rely on terminating a cover crop with a roller-crimper. Field research was carried out over two years (2013–14 and 2014–15) to compare two organic, cover crop-based reduced tillage systems (NT and ST) with conventional tillage (CT) in the production of organic bell pepper and broccoli. As nitrogen has been previously suggested as a limiting factor in organic NT systems, split fertilizer application was also included as a treatment to evaluate the impact of timing of nutrient addition on plant N status and yield. A cover crop mixture of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) was seeded in all plots in the fall and either tilled in (CT) or terminated with a roller-crimper (NT and ST) in the spring before planting. Data were collected on vegetable crop growth, yield, crop quality, cover crop biomass, weed suppression, soil temperature and moisture, leachate nitrate concentration, and soil health as indicated by soil microbial biomass and microbial diversity.

For both crops, the effect of NT and ST on yield varied from year to year. Broccoli yield was reduced under NT and ST in 2014, but was not different from CT in 2015. Pepper yield, on the other hand, was similar among treatments in 2014, but reduced by NT and ST in 2015. While soils under ST had higher soil temperatures compared to NT, there were no differences between ST and NT in yield or crop N status for either crop in either year. Preplant and split fertility treatments produced similar marketable yields of broccoli in both years and for pepper in 2015, but preplant fertility increased marketable pepper yield in 2014. Costs of production varied minimally across treatments, so the highest yielding treatments had best economic performance. Nitrate concentration in leachate was lower under NT and ST compared to CT at three sampling dates in July 2014, but few differences were observed in subsequent samples. While there was a trend toward greater soil microbial biomass and diversity in NT and ST compared to CT plots in 2015, few significant soil health benefits were observed for NT and ST. Soil microbial biomass and diversity were both consistently higher in surface soil (0–7.5 cm) than the deeper soil (7.5–15 cm), but this occurred independently of treatments. While NT and ST did not consistently perform as well as CT, we found sufficient evidence of the potential for high yield and ecological benefits to warrant further study and fine-tuning of reduced tillage organic systems.

Copyright Owner

Dana Lipinski Jokela

Language

en

File Format

application/pdf

File Size

101 pages

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