Effects of antibiotics in soil on the performance of rapeseed

Background/Question/Methods

In animal farming, veterinary anti-infectives such as antibiotics are frequently used. They are incompletely metabolized by the animals and excreted with manure. Through the use of manure as fertilizer, crop species can be exposed to these antibiotics when they persist in manure and soil but little is known about the effects of antibiotics on the life cycle of crop species or whether they influence yield. We therefore aimed to test if and how different concentrations of Sulfadiazine (“SDA”), and a combination of Sulfamethoxazole and Trimethoprim (“COMBI”) affect the growth, development and yield of rapeseed (Brassica napus).

In a greenhouse experiment, the effects of six concentrations of antibiotics, ranging from 1 – 50 mg antibiotic/kg soil of SDA and COMBI, were tested on ten rapeseed individuals for every concentration. Antibiotics dissolved in water were added to the soil once before seeds were planted. A control group of ten individuals was sown without adding any antibiotics. We recorded germination time and weekly measured growth (shoot length), onset of leaves and flowers and number of flowers and fruits. Additionally, antibiotic concentrations were monitored in the soil and runoff water. Ripe fruits were harvested; seeds were weighted, counted and germinated again under control conditions.

Results/Conclusions

Time until germination was significantly prolonged with increasing antibiotics’ concentrations, regardless of the type of antibiotic. Higher concentrations of both antibiotic treatments delayed the onset of leaves but flower onset was only delayed under higher concentrations of COMBI. Germination of new seeds was affected by both antibiotic treatments, with varying germination success between different concentrations. Shoot growth decreased significantly with increasing antibiotics’ concentrations, with more pronounced effects of COMBI. These differences disappeared towards the end of the growing period. Plants in different treatments did not differ in their number of fruits or seeds. Concentrations of all antibiotics decreased over time in soil and runoff water. However, the total amount of detected antibiotics did not account for the initially added amount.

Even though yield (i.e. numbers of fruits and seeds) was not affected, we found different effects of varying concentrations of selected antibiotics on the germination, growth and the germination of the next generation in rapeseed. This might be due to the uptake and metabolism of antibiotics, which were missing in the soil and runoff water monitoring. Our results indicate that veterinary antibiotics might influence the performance of crops, depending on the type and concentration of antibiotic present in the soil.