DAY 1Tuesday, 2 December 2025 - America/Los_Angeles (UTC-08:00)

Assessing the efficacy of biostimulants under the FPR Regulation (EU 2019/1009): between regulatory requirements, field constraints and the importance of analytical timing.
The FPR Regulation (EU 2019/1009), which regulates biostimulants, imposes strict criteria for demonstrating efficacy linked to well-defined claims: improved nutrient use efficiency, increased tolerance to abiotic stress, and improved quality. While this regulatory approach aims to scientifically standardise proof of efficacy, it poses a major challenge in terms of experimentation under real conditions.
We present various situations aimed at documenting the effect of a product according to the desired claim. It can be difficult to identify suitable sites for each claim, to find conditions that allow the expression of an abiotic stress or a controlled deficiency in the field. This variability makes the application of FPR requirements complex in terms of real agronomic dynamics.
Another decisive parameter proved to be the timing of the analyses, particularly those measuring the effect on the availability or absorption of nutrients. Analyses carried out too early or too late can mask the benefits of the biostimulant, leading to an underestimation of the real effect.
We will discuss ways of improving the design of trial protocols, stressing the need for better coordination between regulations and agronomic realities.

The inoculation of non-legumes with diazotrophic bacteria is a much-discussed approach to improve the nitrogen supply of plants (Soumare et al. 2020). Field trials to validate this technology often show limited or no impact (Camberato et al. 2023). In contrast, experiments under controlled conditions (climate chambers, greenhouses) indicate a positive effect of microbial biostimulants in terms of crop’s yield and quality (Silveira et al. 2016). One possible cause could be a natural spread of the bacteria, as control and treated field variants are usually very close one to another in standard exact tests. This assumption is based on repeated detections of diazotrophic endophytic bacteria in untreated control fields within a few weeks after application in field trials conducted in several European countries. To identify the potential dispersal pathways in crops, we developed a detection method with three specific molecular markers for Methylobacterium symbioticum, which is used as a biostimulant. Based on this test system, the following hypotheses on the natural spread of M. symbioticum in crop stands were tested: i. Spread via guttation drops ii. Propagation via sucking insects iii. Spread via raindrops As a further influencing factor on the result of field trials with microbial biostimulants, the plot application technique was examined. We were able to show that the application rate of microorganisms (CFU) in plot sprayers can fluctuate very strongly. A significant factor in this examination was the water used for the application. This suggests that the application technique plays a significant role in the success of colonization.