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Dissertation/Thesis Abstract

An Evaluation of Yield and Quality Characteristics for Vegetable Crops Grown under Organic Management in Fort Collins, Colorado
by Mason, Tyler, Ph.D., Colorado State University, 2020, 195; 28153775
Abstract (Summary)

Colorado is known for having a strong natural foods industry. It also ranks ninth in the country for organic food purchases, totaling $155 million annually. Within that, the national average sales of organic fruits and vegetables accounts for 40% of total organic food sales. In Colorado, this would equate to $72 million in organic fruit and vegetable sales. Yet, the actual value of certified organic vegetable sales has only reached the level of $40 million annually. This difference represents an economic opportunity for Colorado’s organic vegetable producers to meet the demand for organic foods. It is also important to note that more than 50% of consumers between the ages of 18–29 years include organic foods in their diets, whereas only 33% of those that are 65 years and older consume organic foods, which indicates a generational difference in preference. This also suggests that the organic foods market will continue to grow with the millennial generation as they predominate the market and likely beyond.

The mission of the Specialty Crops Program (SCP) at Colorado State University (CSU) is to empower growers and producers throughout Colorado by supplying them with science based information to inspire innovation, competitiveness and success. In order to help vegetable producers address the demand for organic foods, system input studies are needed to help growers optimize the performance of their organic systems; cultivar selection (Chapter 1) is an important consideration to any production system. Over three years (2016–2018), we observed significant yield and quality characteristics differences between cultivars of tomato (Solanum lycopersicum), sweet corn (Zea mays var. saccharata), cabbage (Brassica oleracea var. capitata), bell and roasting peppers (Capsicum annuum), and winter squash (Cucurbita pepo) in an organic production system located at the Agricultural Research, Development and Education Center South (ARDEC S.) in Fort Collins, CO (lat. 40° 36’ N., long. 104° 59’ W.) elevation 5,003 feet. The top performers of the cultivar yield trial, by crop, were ‘Mountain Merit’ (tomato), ‘Nirvana’ (sweet corn), ‘Lennox’ (cabbage), ‘Aristotle’ (pepper), and ‘Bush Delicata’ (winter squash), respectively. However, there were many other top tier performers based on yield and quality characteristics that would also make for a valuable input into an organic system. Flavor was another one of the important quality characteristics assessed in this cultivar trial.

We conducted consumer sensory panels at the Larimer County Farmers Market to assess what direct-market shoppers thought of the flavor of the eight tomato and fourteen sweet pepper cultivars included in the trial. This afforded us the opportunity to characterize an important quality attribute. However, it was a time-consuming and laborious way to collect what is known to be relatively subjective data on flavor. Postharvest quality characteristics, such as taste, nutrition, and bioactive compound content can also be evaluated using mass spectrometry platforms coupled with chemometric analysis (Chapter 2). Gas chromatography-mass spectrometry (GC-MS) coupled with solid phase micro extraction (SPME) has been used to profile aroma-contributing metabolites in food crops. However, sample preparation, long acquisition times, and the need for technical lab expertise presents barriers preventing routine application of this type of technology. Ambient mass spectrometry (AMS), which detects metabolites in minimally processed samples under ambient conditions, has emerged as a promising analytical platform for assessing quality characteristics in plant products.

Here, we evaluated SPME-GC-MS and two AMS platforms, direct analysis in real time (DART) mass spectrometry and rapid evaporative ionization-mass spectrometry (REIMS) coupled with chemometric analysis, to assess quality characteristics in 40 pepper (Capsicum annuum L.) cultivars. SPME-GC-MS was able to detect metabolite differences between red and green bell peppers based on volatile aroma-contributing metabolites. DART-MS exhibited the ability to discriminate between pod colors based on metabolite fingerprints, while REIMS could distinguish pepper market class (e.g. bell, lunchbox, and popper). Furthermore, DART-MS analysis resulted in the detection of important bioactive compounds in human diet such as vitamin C, p-coumaric acid, and capsaicin. The results of this study demonstrate the potential for these approaches as accessible and reliable tools for high throughput screening of pepper quality. AMS platforms could be employed to evaluate genotypes in a cultivar trial or to evaluate the impact of a crop input on the metabolome.

In addition to the cultivar trial and metabolomics platform evaluation studies, the SCP and I evaluated the impact of crop inputs on yield and quality characteristics of three organic vegetable crops (sweet corn, onions, and peppers). Our research team quantified the impact of applying an Organic Materials Review Institute (OMRI) approved rock-powder based soil amendment (Azomite) on roasting pepper yield (Chapter 3). Azomite (0-0-0.2) supplies trace minerals from mined sources including: calcium (1.8%), magnesium (0.5%), chlorine (0.1%), sodium (0.1%). Two grades of Azomite (granulated and ultrafine) were assessed separately: granulated Azomite was banded in the field and ultrafine Azomite was applied via drip system and/or foliar application in a high tunnel. Interestingly, particle size and the application method were statistically significant predictors of pepper yield. Granulated Azomite that was banded in the field did not increase pepper yield. However, ultrafine Azomite that was applied as a foliar spray significantly increased red pepper yield compared to the water foliar control in ‘Early Perfect Italian’ peppers. In addition, the number of marketable pods significantly increased following an Azomite foliar application in ‘Stocky Red Roaster’ compared to the no foliar spray control. This study has implications for pepper growers wanting to increase their yields by applying rock powder based soil amendments that contain K and trace minerals.

The last input evaluated for organic vegetable production systems was caprylic/capric acid (CA) (Chapter 4). It is a promising next-generation herbicide for organic specialty crop production; similar to acetic acid (AA, 20% volume/volume), it functions as a post-emergent, non-selective herbicide that damages any green plant tissue it contacts. It was evaluated in a conventional onion system in a commercial onion farmer’s field in Adams County, Colorado, and it was further evaluated in an organic sweet corn system at ARDEC S. Importantly, we observed that application volumes, which are typical of herbicides applied in conventional systems (e.g. 20 gallons per acre) are insufficient carrier volumes for herbicides approved for organic systems. At 50 gallons per acre, CA and AA were equally effective at desiccating small weeds that were less than two inches in height. Each of these herbicides achieved about 50 percent weed control one day after treatment (DAT). However, CA was significantly more effective than AA at controlling weeds that were between six and nine inches in height one day after a high volume (200 gallons per acre) treatment. This is the first documentation of the superior weed control ability of CA. CA is labelled for use in and around all food crops, including organic, which could make this next generation herbicide a valuable tool for Colorado and other Intermountain West organic specialty crop producers. Taken all together, the cultivar trial results, the knowledge we gained of Azomite grades and application method, and our increased understanding of carrier volumes using next generation herbicides has positive implications for growers managing small and large acreage operations. Input system management studies, such as these, are important because they provide useful information to growers, which helps them identify the management practices and inputs that align with their production preferences and financial situation. In addition, our high throughput method for postharvest quality assessments using AMS could be useful to cultivar trial managers or research horticulturists that are interested in assessing the impact of cultivar, production system inputs, or environment on the metabolome of peppers.

Indexing (document details)
Advisor: Uchanski, Mark
Commitee: Bartolo, Michael , Johnson, Sarah, Prenni, Jessica
School: Colorado State University
Department: Horticulture & Landscape Architecture
School Location: United States -- Colorado
Source: DAI-B 82/7(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Horticulture, Agriculture
Keywords: Capsicum annuum, DART-MS, Organic, REIMS, Vegetable quality, Weed control
Publication Number: 28153775
ISBN: 9798557080651
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