Impact of biostimulant use in agricultural crops under different horticultural cropping systems: A systematic review.

The use of biostimulants in horticulture has gained increased attention for their potential to enhance crop growth, yield and contribute to tolerance to abiotic stresses. However, the literature on the effects of different biostimulants across diverse agricultural contexts and systems is fragmented, focusing on a single biostimulant category, crop or growing system. In this work, we reviewed the literature across all biostimulant categories in representative horticulture crops (strawberry, leafy greens and mushrooms). Our search resulted in five mushroom, 27 spinach, 94 strawberry and 140 lettuce studies reporting the effects of biostimulants in protected and unprotected production systems. Most of the studies revealed positive effects on growth or yield across crops, ‘Microbial’ biostimulants being the most studied category. The use of biostimulants in protected production systems dominated the research, especially in lettuce and strawberry, while research in spinach and mushroom production is less extensive. The potential of biostimulants to reduce reliance on chemical fertilisers was addressed in some studies and some demonstrated yield improvements under reduced fertilisation. This could offer a pathway toward more sustainable farming practices, but an increase in life-cycle assessment studies is needed to understand how biostimulants contribute to sustainable practices. This review also explored the regulatory framework governing biostimulant use, noting glaring variation between regions. The review emphasises the need to expand research to underrepresented crops and biostimulant categories, develop consistent regulatory frameworks and increase the understanding of the role of biostimulants in sustainable agriculture.