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Organic vegetables produced in greenhouses and other controlled environments may fill a unique market niche as consumers demand local, high vegetables year round. However, limited technical information supports these production systems and more research is needed to provide recommendations for appropriate substrate mixes and nutrient management. Compost can be used as a substitute for peat-based media, and research results vary widely based on feedstock, compost method, and proportion used in mixes. Most studies consider compost in terms of peat-substitute or replacement and not as a source of fertility in soilless systems. Common challenges in using compost in soilless media are due to immaturity of the compost, poor water holding capacity, and unbalanced salinity and pH. It is possible to certify organic soilless production systems; however, the National Organic Program (NOP) of the U.S. Department of Agriculture has not yet provided clear rules and requirements supporting these systems. The objective of this article is to review the literature on soilless organic vegetable production, summarize results from the more widely studied topic of vegetable transplant production, and point to future research for organic agriculture.
High tunnels are rapidly gaining favor from growers in many regions of the United States because these structures extend the growing season and increase quality of high-value horticultural crops. Small to midsized organic growers who sell tomatoes (Solanum lycopersicum) for the fresh market can benefit from lower disease pressure and higher marketable yields that can be achieved in high tunnels. High tunnels also protect crops from environmental damage and benefit production of heirloom tomatoes as these varieties often have softer fruit and are more susceptible to diseases and cracking and splitting than hybrid varieties. The objective of this study was to determine the impacts of high tunnel production and planting date on heirloom and hybrid tomato varieties by observing differences in plant growth, yield, marketability, and early blight (Alternaria solani) development within an organic production system. This study showed no increase in total yields in high tunnels as compared with the open field, but increased marketability and size of tomatoes, and lowered incidence of defoliation resulting from early blight. Tomato planted earlier in both high tunnels and the open field yielded more marketable fruit during the production season than plants established on later planting dates. Hybrid varieties yielded more marketable fruit than heirloom varieties; however, heirloom tomatoes can have equivalent market value because of greater consumer demand and premium prices attained in the local market.
Growing North Minneapolis (GNM) is an urban agriculture and youth development summer program sited in the North Minneapolis, MN, neighborhood. The program is a university–community partnership between faculty at the University of Minnesota (UMN) and North Minneapolis community partners. We leverage resources from the city of Minneapolis Step-Up program to recruit, train, and employ youth (14–15 years old) who face barriers to employment—particularly youth from low-income families, youth of color, youth from immigrant families, and youth with disabilities. Youth interns are placed in a 10-week-long summer program and are matched with undergraduate student mentors from the UMN and North Minneapolis gardener mentors. The undergraduate students and garden mentors work together to lead teams of youth and work in multiple urban garden sites located in North Minneapolis, a designated low-resource community in the metro area. One of our goals is to develop leadership experience for UMN undergraduate students and improve food and horticultural skills among urban youth through garden-based education. Learning is experiential and contextualized in the various community garden sites through activities focused on food justice and accessibility, food production systems, and horticultural science. Youth learning and development outcomes are reported based on written postprogram qualitative survey questions prompting youth to identify what they learned throughout the program, what they enjoyed the most, and what challenged them after the summer program in 2018. Our results show that youth participants learned across multiple domains of knowledge and valued the social interaction offered by the intergenerational mentorship structure. The GNM program can serve as a model for garden-based experiential learning with early high school youth.
Consumer demand for local and organic strawberries (Fragaria ×ananassa) is increasing. Growers who can meet this demand have a competitive edge in the direct-to-consumer market. Innovations in strawberry production for northern climates offer new opportunities for growers to meet the demand for local organic strawberries. Typically adopted for season extension, the use of poly-covered tunnels for crop protection provides other benefits including protection from adverse weather. Low tunnels are easy to install, low cost, temporary protective structures that are well-adapted for annual day-neutral strawberry production, and they are more space efficient than high tunnels for these low-stature crops. A range of specialty tunnel plastics that modify and diffuse light are available, but there is little information on how these influence strawberry plant growth and performance in the field. Our objectives were to determine the effects of experimental ultraviolet blocking and transmitting plastics on light and microclimate in low tunnel environments and assess differences in fruit yield and quality in the day-neutral strawberry cultivar Albion in an organic production system. This research was conducted on U.S. Department of Agriculture-certified organic land over 2 years, in 2016 and 2017. We found that ultraviolet intensity and daily light integral (DLI) were lower in covered plots than in the open field. Maximum daily temperatures were slightly higher in covered plots. Both ultraviolet-blocking and ultraviolet-transmitting plastics improved marketable fruit yield compared with the open-field control. Strawberries grown in the open-field treatment were lower in chroma than covered plots in 2017, and there was no difference in total soluble solids between treatments in either year. Low tunnel systems allow for increased environmental control and improved fruit quality and are well-adapted for day-neutral organic strawberry production systems.
Commercially available biocontrol agents Trichoderma harzianum Rifai and the arbuscular mycorrhizal fungus Glomus intraradices Schenck and Smith were tested for their efficacy in controlling fusarium root rot in potted asparagus (Asparagus officinalis L.) seedlings. High and low concentrations of Fusarium oxysporum (Schlect.) emend. Snyd. & Hans. f. sp. asparagi Cohen & Heald (FOA) were combined with G. intraradices and/or T. harzianum treatments. In both experiments included in this study, T. harzianum and G. intraradices alone and in combination effectively reduced root rot caused by FOA when asparagus seedlings were grown in low levels of FOA-infested medium. When seedlings were grown in high levels of FOA-infested medium, the combination of T. harzianum + G. intraradices significantly increased dry shoot mass and limited root rot compared to the control.
Spotted-wing drosophila (Drosophila suzukii; SWD) is an invasive pest in the United States that is responsible for significant economic damage to soft-skinned fruit and berries worldwide. SWD uses a wide variety of cultivated and wild fruit for reproduction. Host suitability may depend on physical and chemical factors of the fruit, with a positive correlation of SWD oviposition and larval development generally associated with soluble sugar content, softer fruit, and higher pH, and a negative correlation of oviposition with fruit firmness. Variety selection is an important tool for integrated pest management, but few studies have reported host suitability across varieties within a single cultivated crop species for SWD. In this study, we investigated SWD oviposition and larval development in five half-high blueberry cultivars, Chippewa, Northblue, Northland, Patriot, and Polaris, using no-choice and two-choice laboratory bioassays. Using a host potential index, our results showed that Chippewa was the most preferred cultivar for oviposition as measured in the number of eggs laid per fruit, and Polaris was the least preferred. The inverse was true for larval development, with a higher survival rate and adult emergence in ‘Polaris’ than in ‘Chippewa’. There was a negative relationship between fruit firmness and oviposition and a positive correlation between pH and larval development. The results of this study indicate that cultivar selection for half-high blueberries may be a promising integrated pest management (IPM) tool, although further research under field conditions is needed for validation.
The brown marmorated stink bug (Halyomorpha halys) is a nonnative insect that damages vegetables and other crops in the United States. Because of the current lack of effective control options for organic growers to combat this pest, barrier screens with different mesh sizes were evaluated in their ability to exclude the brown marmorated stink bug, provide entry to beneficial species, and to produce a high percentage of marketable yield. Barrier screens with 1/6-, 1/8-, and 1/25-inch mesh sizes, along with unscreened controls, covered ‘Aristotle’ bell pepper (Capsicum annuum) plants at field sites in Kentucky and Tennessee in 2013–14. In Kentucky, where brown marmorated stink bug pressure was low, overshading decreased the marketable yield under dark, 1/25-inch mesh screens in 2013. Outbreaks of aphids (Aphididae) under light-colored, 1/25-inch mesh plots in 2014 suggest a higher risk of secondary pests proliferating under these screens. In Tennessee, where brown marmorated stink bug pressure was higher and light colored, 1/25-inch mesh screens were tested in 2013–14, the 1/25-inch mesh plots produced the highest yield, due to the general exclusion of insects and protection from sunscald. In areas with small brown marmorated stink bug populations, lighter colored, and/or wider meshes (1/8-inch or 1/6-inch) may be required to allow the entry of sunlight and beneficial species. In areas with higher brown marmorated stink bug pressure, finer meshes (1/25-inch) may be appropriate to exclude larger populations of pests and to protect the crop from sunscald.
High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.
Urban horticulture describes economically viable horticultural production activities conducted in a city or suburb. It is a growing segment of horticulture in the United States as well as in developing countries, where the enormous growth of megalopolis is not backed by a simultaneous increase of farmland or agricultural productivity. Today, urban horticulture includes food sovereignty in underprivileged neighborhoods, increased availability of vegetables and fruits in big cities, healthy and diverse diets, improved food safety, low transportation costs, efficient resource use, and the mitigation of environmental impacts of horticultural production such as the emission of greenhouse gases. The workshop “Urban horticulture: From local initiatives to global success stories,” held at the 2018 American Society for Horticultural Science (ASHS) conference in Washington, DC, featured present and historical success stories of urban horticulture from Asia, Africa, Latin America, and the United States.