Summary
Flooding may pose a risk of contamination of soils and crops by human pathogens. Crops growing in previously flooded areas may be at risk for contamination by foodborne pathogens. In June and July of 2015 the Wabash River flooded a portion of the Southwest Purdue Agricultural Center near Vincennes, IN. When floodwaters receded, an experiment, consisting of a randomized complete block design with 4 replications of 6 treatments, was established in a previously flooded field. Soil samples were periodically collected from experimental plots. Samples were then tested for levels of coliforms, aerobic microbes, and yeast and molds. Data analysis performed at the conclusion of the experiment suggested that best practice in the case of extreme flooding is to leave soils undisturbed for a period of time following the recession of floodwaters.
Research Objectives
1. Deliver to growers a relative indication of risk, based on estimated soil indicator organism levels when BSAAO application data are entered.
2. Accept new data from researchers as they conduct additional studies using an identical protocol.
3. Automatically incorporate new data to adjust outputs such that they reflect the most current information available.
Findings & Recommendations
Our study suggests that during an extreme flooding event, waterborne microbes are deposited on soil surfaces. Leaving the soil undisturbed results in the most rapid rate of decline of indicator organisms, presumably due to sunlight and dehydration as soils dry. Tillage operations for any purpose aid in drying and aeration of soils. However, any operation that involves tillage will incorporate flood-deposited organisms, reduce their rate of decline in the soil, and increase the level of aerobic microbes. Based on our data, we offer the following recommendations –
1. Following an extreme flooding event, soils should be left undisturbed and bare in order to maximize the amount of sunlight reaching the soil surface, to encourage drying on the soil surface, and to avoid incorporation of microbes deposited by floodwaters.
2. In the period following an extreme flood, weeds should be controlled by use of herbicides to avoid disturbing soil surfaces.
3. Produce growers who wish to utilize plastic mulch following an extreme flooding event should do so with caution. Soil temperature monitoring indicated that root-zone temperatures in plastic treatments did not exceed 35C. Plastic mulch is known to trap soil moisture. Based on our observations, plastic mulch does not build a high enough temperature in the root zone to effectively decrease levels of flood-deposited organisms.