What was it all about? 

This project was the first research study undertaken on survival of Salmonella enterica in soil contaminated with chicken manure conducted under Australian conditions. The research investigated the effect of soil type, temperature, moisture and presence/absence of chicken manure on survival of this pathogen. It also examined potential short-term remediation strategies of cover cropping and/or solarisation to reduce levels of the bacteria in soil following contamination, to allow a quick return to safe crop production.

The project research indicated that Salmonella enterica counts decline over time under natural field conditions after a contamination event. However, the rate of decline is significantly slower in clay loam soils, and is reduced by the presence of chicken manure, by soil temperatures less than 37⁰C, and by the presence of moisture. In the field trial, the bacteria was detectable up to 100 days after contaminated chicken manure was incorporated into clay loam soil. In contrast, populations quickly declined within four weeks in sandy soils, at temperatures above 37⁰C and in soil without chicken manure as a source of energy.

The research also found that solarisation (black plastic covering the soil) may have potential to promote faster die-off of Salmonella enterica, providing soil temperatures under the plastic have several hours at 37⁰C or above.

Meanwhile, the use and incorporation of the commercially-available cover crops Ethopian Mustard, Oilseed Radish and Fumig8tor Sorghum significantly enriched the soil microbiome after incorporation into the soil, but were not effective in this experiment in promoting die-off of Salmonella enterica in soil. This may have been due to short growing time (one month) and uneven cover of the cover crop which limited the amount of biomass and, consequently, biofumigant incorporated in the soil.

Further research is required to fully explore the value of cover cropping as a remediation strategy for reclaiming soil contaminated with Salmonella enterica and to determine the amount of biomass and biofumigant levels required in the soil for die-off of the bacteria and how quickly this could occur.

The Guideline for Fresh Produce Management (2015) recommends that untreated manure is not added to soils used for production of short-term crops such as leafy salad greens or herbs. This research will assist growers in assessing the risk and likelihood of food safety outbreaks with Salmonella enterica through consideration of on-farm soil characteristics and agronomic practices for remediation to reduce populations of the pathogen in soil after a contamination event using untreated chicken manure.