Does splash from overhead sprinkler irrigation systems contaminate produce with Salmonella in the southeastern United States?

Our goal is to develop knowledge which will allow vegetable producers who rely on untreated irrigation water to address proposed FDA rules. These rules may require that all agricultural water, including irrigation water, be safe for its intended use. In a pilot study we conducted in Georgia, we found that Salmonella is present in irrigation systems using water from ponds to irrigate vegetables. These findings are intriguing but preliminary and a more comprehensive study will soon be underway to draw defensible conclusions. However, the new project will not allow us to determine whether any produce contamination we observe is caused directly by application of irrigation water or by irrigation-generated splash. To the WCFS we are proposing a project focusing on understanding whether Salmonella contamination can stem from splash associated with farm soils, directly-applied irrigation water, or both. This information will help growers and FDA with efforts to reduce contamination on produce and could lead to fairly simple management solutions to any splash problem we identify. Knowledge resulting from this project will allow vegetable producers that rely on overhead sprinkler irrigation to address new rules the FDA may implement on safe agricultural water.

The overall goal of this proposal is to develop knowledge which will allow vegetable producers who rely on untreated surface sources of irrigation water coupled with overhead sprinkler irrigation to effectively address recently proposed FDA rules. In January 2013, the FDA proposed that all agricultural water be safe for its intended use (proposed § 112.41.) FDA’s definition of agricultural water is water that comes into direct contact with produce and includes irrigation water that is applied using direct water application methods such as overhead sprinkler irrigation. Companion CPS-funded studies conducted in the southeastern United States by members of our project team have consistently found measurable concentrations of Salmonella and other pathogens in ponds used to irrigate fruits and vegetables. Members of the project team also conducted a pilot study to assess the presence of Salmonella in irrigation water in four different irrigation systems on three farms. Salmonella and generic E. coli were found in samples collected from all three irrigation systems fed by pond water. These findings are intriguing but preliminary and a more comprehensive study will soon be underway to draw defensible conclusions. However, the new project will not allow us to determine whether any produce contamination we observe is caused directly by irrigation water or by irrigation-generated splash. In the southeastern Coastal Plain, overhead sprinkler irrigation is most frequently used with leafy greens, cabbage, cantaloupe, and watermelons, some of which are highly susceptible to contamination from splash. During our pilot irrigation water study, we have observed that overhead sprinkler irrigation systems apply irrigation water at very high rates and this quickly overwhelms the infiltration capacity of the soils. As a result, irrigation water ponds on the soil surface and begins to run off. As more irrigation water is applied, the ponded water and saturated surface soils begin to splash. A recent study in Georgia showed that Salmonella can persist in the soil for several months. With that in mind, our objective is to better understand whether Salmonella contamination can stem from splash associated with farm soils, directly-applied irrigation water, or both. This information will help growers and FDA regulators with efforts to reduce contamination on produce. We have developed a research plan which will measure Salmonella and generic E. coli concentrations in overhead sprinkler irrigation water reaching the crop as well as in splash generated by the irrigation water. We will also measure Salmonella concentrations on produce and associate it with measured organic matter and soil residues deposited on the produce by splash. The expected outcome of our proposed project is information on whether splash from overhead sprinkler irrigation systems contributes to the contamination of produce by Salmonella. This information could lead to fairly simple management solutions to any splash problem we identify. For example, cover crop residues or other mulches could be used to promote infiltration and reduce splash. Knowledge resulting from this project will allow vegetable producers that rely on overhead sprinkler irrigation to effectively address new rules the FDA may implement on safe agricultural water.

1.) Quantify the levels of Salmonella, soil, and organic matter in splash resulting from solid set impact sprinkler systems and center pivot irrigations systems. 

2.) Determine if Salmonella persists on the crop until harvest in greater numbers in the presence of organic matter and soil that is deposited on the produce by irrigation water splash.

• The sampling methodology we developed successfully provided us with a vertical gradient of splash contamination. This is evidenced by the clear trend of decreasing total suspended solids concentrations with height. 

• It is not clear if our tallest sampling height (32in) was high enough to eliminate the possibility of splash contamination because the mean total suspended solids concentration at this height is slightly larger than that of pond water. If a follow-up study is conducted, an additional sampler should be installed at 64in. 

• The Salmonella data are inconclusive. However, because three of the four positive samples were from the sampling pans at 2 and 4 inches, the results may indicate that irrigation water splash may be more frequently positive than irrigation water itself. The E. coli data also support this conclusion. 

• Data from rain events more clearly indicate the effect of splash because they avoid the noise caused by irrigation water which is occasionally positive for pathogens and indicator organisms. 

• A more comprehensive study that includes the entire summer growing season is needed to answer this question conclusively. If a more comprehensive study is conducted, the sampler design should be modified to capture splash only and not irrigation water and splash. In addition, future studies should collect concurrent soil samples and analyze them for Salmonella.