Safe, Easy, Low-Cost Produce Handling: Irrigation Water

The primary concern of crop irrigation is to deliver “enough water in the right place at the right time.” The secondary, although more direct, concern is that irrigation equipment and management logistics must work for a farm ($, labor, water availability) and prevent harm to customers or the environment. Irrigation with contaminated water is the most common primary cause of whole-crop contamination, and recent high-profile cases of produce-born illness (e.g. 2007 Spinach, 2017 Romaine lettuce). Irrigation from a clean water source is lowest risk (e.g. drilled well), but is too expensive or not possible for many growers. Thus, more variable surface water sources are more common in the northeast, especially for larger crop fields. Although farms can’t control the upstream contamination of a surface irrigation water source, there are easy, low-cost strategies to mitigate contamination reaching customers.  

Drip line under mulch is likely the is the most efficient, precise and lowest risk method of irrigation.
Although plastic intensive, drip tape under mulch is also perhaps the most efficient way to irrigate, and it also separates potentially contaminated irrigation water from the harvested crop (strawberries shown here), thus minimizing one of the most significant produce safety risks. Photo by Vern Grubinger.

Design Goals

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  • If possible (to conserve resources and reduce contamination risk), irrigation targets root systems directly, avoiding contact with harvest portion of crops (drip irrigation under mulch layer)
  • Get to know the quality of the farm's irrigation water sources, including upstream land use and point source contamination risks of surface water sources.
  • Given constraints, use the cleanest irrigation source possible, especially for overhead applications.
  • Minimize or avoid overhead irrigation with surface water during the harvest window of raw-eaten crops (e.g. spinach, salad mix).
  • If overhead irrigation of raw-eaten crops with surface water is unavoidable, make and follow a plan to minimize the risk of whole-crop contamination.

Design Elements

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  • Drip irrigation (ideally under a mulch layer) is used for established mid- to long-season crops.
  • Backflow prevention is installed to prevent contamination of drilled well trunk lines.
  • Irrigation lines are flushed annually, or as needed to prevent clogging and contamination.
  • If surface-water is used, an upstream water-quality assessment is completed and updated seasonally, as needed.
  • Overhead irrigation of raw-eaten crops is limited to germination, seedling establishment, or if needed for maturing crop types (e.g. leafy salad mix, carrots, beets).
  • If overhead surface water is applied to raw-eaten crops during their harvest window (for irrigation or frost protection) 3-4 days minimum “die-off” waiting period is observed before harvest. This is enough time to achieve 95-99% die-off of waterborne E.coli bacteria (a proxy for human pathogens).

Benefits

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  • Use of clean irrigation water minimizes whole-crop contamination risk and improves the quality and consumer safety of market crops.
  • Effective drip irrigation systems can save water, time, and improve crop yields and quality.
  • No-cost risk reduction - observing a post-irrigation waiting period before harvest increases pathogen “die-off” on the surfaces of raw-eaten produce and is thus a no-cost strategy to reduce the risk of whole-crop contamination from overhead application of surface water.

Photos

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micro sprinklers in tunnel
Well-water through micro sprinklers saves water, reduces mud back-splash, and minimizes risk in short season leafy crops (e.g. the shoulder-season arugula shown here).  Photo by Vern Grubinger
field overhead irrigation
Overhead irrigation is generally needed for direct seeding (e.g. carrots, beets, salad greens).  Water is often efficiently pumped from surface water such as streams, rivers and ponds, and applied to crops with sprinklers or water "guns".  Although overhead irrigation of raw-eaten crops with surface water is a big food safety risk (it has been the cause of several large-scale outbreaks), this risk can be minimized by allowing 3-4 days of "drying", between irrigation and harvest (most pathogens will not survive drying). Photo by Vern Grubinger.
field drip line
Drip irrigation of starts without plastic mulch may be more practical for smaller market gardens.  This method is efficient because drip line can be seen and its position adjusted to maximize water delivery to root zones of plants;  it also reduces risk compared to overhead irrigation because irrigation water often does not come in contact with harvested crop.  Photo by Hans Estrin.

Authors: Hans Estrin and Vern Grubinger, UVM Extension

This work is supported by the Food Safety Outreach Program Name, project award no. 2023-70020-40688, from the U.S. Department of Agriculture’s National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.

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