Chairs: Kasia Parfitt and David Mark

Organic fertilisers are regarded as effective alternatives to chemical fertilisers in crop production and sustainable farming. However, antibiotics and antibiotic resistance genes (ARGs) are prevalent in agricultural soils due to the application of organic fertilisers such as digestates. The objective of this greenhouse trial was to evaluate the effects of two organic fertilisers and a chemical fertiliser on the antimicrobial resistance in soil and the growth of lettuce. These treatments were compared to a control with no fertiliser. Abundance of bacteria, prevalence of ARGs and intI1 were determined using qPCR. Lettuce grew best in the digestate added soils having the greatest surface area and height. This was followed by the biofertiliser and then the control soil. Seedlings grown in chemically fertilised soil died in the first two weeks of the trial. Immediately after fertilisation ARG analysis indicated that chemical fertiliser applied soil samples had the highest ARG levels followed by digestate. Lowest ARG levels were observed in the biofertiliser samples. At harvest, intl1 in the control soil was no longer detectable with bio fertilised soil displaying the smallest reductions of 27.63%. The digestate and control soils also saw ARG reductions over the course of the experiment, with some genes becoming undetectable. For all observed ARGs, the bio-fertilised soil, despite the low ARG levels at the start of the experiment, showed lower ARG reductions and an increase of tetM levels. While this is early data, digestate shows promise as a fertiliser that produces healthy growth whilst minimally impacting ARG levels.