Semester

Summer

Date of Graduation

2020

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Horticulture

Committee Chair

Sven Verlinden

Committee Co-Chair

Nicole Waterland

Committee Member

James Kotcon

Abstract

Reducing or eliminating waste from organic vegetable production can conserve money as well as resources. Conventional greenhouse production of vegetable transplants often relies on abundant fertigation which produces large amounts of polluted runoff, and the field production of organic vegetables frequently relies on the use of polyethylene mulch. A greenhouse study was conducted to determine if organic transplants can be successfully produced in a greenhouse under reduced soil moisture in order to reduce leaching of nutrients and potential water pollution. To test this, we compared the effect of reduced irrigation volumes to the standard practice of irrigating with 120% of container capacity on plant growth. A second and more detailed aspect of our study investigated the influence of irrigation levels on nutrient changes in the media throughout transplant production. We compared unfertilized organic media to a conventional medium which was fertilized with every irrigation, which is the standard conventional industry practice. Three concurrent experiments were carried out on lettuce, tomato and pepper transplants over the course of six weeks. EC and pH of soil leachate as well as plant height, leaf number, shoot fresh weight and shoot dry weight were compared. We found that the choice of potting medium influences transplant production, with some organic media performing comparably to the conventional control. Additionally, it was discovered that organic transplants can be produced under 80% volumetric water content (VWC) deficit irrigation. These findings will allow organic producers to implement production protocols that conserve water and reduce the financial impact of fertilizer use. In a field experiment we compared soil moisture retention, soil temperature regulation, and sweet pepper yield using the organic mulches hay, wool, leaf litter, two sizes of conventional polyethylene mulch with hand weeding and no weeding (control). Four blocks containing the seven treatments were laid out with treatments placed randomly within each block. Soil moisture and temperature probes were placed in the center of each plot and connected to centrally located data loggers. Data were recorded hourly over the course of the experiment (90 days). Pepper fruits were evaluated in terms of harvestable weight per plot. We found that plots with plastic-mulch were hotter and drier and had greater yield than plots with organic mulch. Among organic mulches, wool had the greatest yield, and all mulches were superior to the control. These findings will hopefully allow producers to make informed choices regarding mulch use in organic vegetable production.

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