Organic horticulture, compost, and season-extending tunnels: Food Safety and crop quality

Authors: Millner, Patricia; Reynolds, Sara; Nou, Xiangwu; Krizek, Donald

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2009
Publication Date: 4/15/2009
Citation: Millner, P.D., Reynolds, S.L., Nou, X., Krizek, D.T. 2009. Organic horticulture, compost, and season-extending tunnels: Food Safety and crop quality. HortScience. 44(2):242-245.

Interpretive Summary: The demand for organic produce in U.S. domestic and international markets has steadily grown over the past decade and is expected to continue. In part this demand comes from the confidence that consumers have in knowing that certified organic producers are not using pesticides, other agrichemicals, or biosolids on their crops and thus they anticipate that the produce will not contain unhealthy residues. In addition, through direct market outlets, growers often form direct connections with customers which reinforces consumer confidence in the cropping practices and the quality, flavor, and freshness of the fruits and vegetables. Another recent market factor that appeals to many direct farm market consumers is their interest in supporting local growers because of contribution they make to the community economy, landscape, and social structure. The reduced transport distances (food miles) and freshness of produce is also part of the support for locally-grown produce. Many local and small growers (organic as well as conventional) throughout the U.S. are using unheated high tunnels and other protected horticultural structures to economically extend the harvest season for local production of fresh fruits and vegetables. High tunnels and other protected structures also help growers control the plant growth environment to a greater degree than is possible in most field situations. The plant growth environment is enhanced in tunnels because of reduced weediness, insect, and plant pathogen pressure, more even soil moisture content, and reduced weather damage to crops. Compost and manure-based products are sometimes used in organic or conventional tunnels to maintain or improve soil quality and to supply plant nutrients. Growers need to be aware of the need to carefully select and time the application of soil amendments in order to minimize and/or eliminate inputs that can introduce manure pathogens that can cause illness in humans. The USDA National Organic Program standards for use of manure, composted manure, and compost tea are discussed along with the steps of Good Agricultural Practices that apply to pre-planting and production that can help reduce the risk of produce contamination by bacteria, parasites, and viruses that may survive in untreated or incompletely composted manure. High tunnels with screening and good management can also help protect crops from wildlife which have been implicated in produce contamination events with open field cropping systems. Evidence is also accumulating that certain plastic film types used for covering high tunnels can enhance beneficial dietary phytochemicals in plants. This report will be of interest to horticulturalists, organic and conventional growers interested in high tunnels and other protected horticultural structures, food safety, and quality.

Technical Abstract: Consumer demand for fresh, local, organic produce continues to increase in the U.S. and internationally. Consumers and growers often form direct market links that reinforce consumer confidence that produce contains no pesticide or agrichemical residues and is at its peak quality, flavor, and freshness because of the short time-lapse between harvest and purchase. High tunnels and protected horticultural structures provide organic and conventional growers with an economical means for extending the harvest season of fresh fruits and vegetables in a wide range of climate zones in North America and elsewhere. In addition to season-extending benefits, high tunnels provide growers with considerably more control over the plant growth environment than is available in most field situations. Some of the benefits of high tunnels can include reduced weediness, moisture fluctuations, insect, and phytopathogen pressure, and environmental damage to crops. Soil organic amendments such as compost and manure-based products in organic or conventional tunnels need to be carefully selected and managed according to Good Agricultural Practices to reduce the risk of contamination by bacteria, parasites, and viruses that can survive for extended periods in untreated manure. High tunnels that are well managed can aid growers in protecting sensitive crops from wildlife that may contaminate produce with one of several zoonotic pathogens. Careful selection and use of compost and high tunnel plastic film types can enhance beneficial dietary phytochemicals in some plants. Additional research is needed to better understand how to enhance the phytochemical content of fresh fruits and vegetables through cultural practices and cultivar selection while simultaneously protecting produce from enteric pathogens in high tunnels and other protected agricultural structures.