Crop yield is the most important factor for food security worldwide and in many cases also determines the profitability of crop production. The impact of any condition that affects yield such as fertilization and climate conditions therefore have the attention of agricultural engineer and the farmer. While for many pests and diseases agrochemical products offer the means to limit yield losses, far fewer solutions are available for mitigating abiotic stresses. Biostimulants are viewed as an easy approach to protect crops from to severe damage, despite of a history of variable impact. To allow the biostimulant market to mature and provide products of better quality, filtering the good from the bad will be important. In this review paper, we limit our discussion to the non-microbial biostimulants.
Biostimulants come in different types from organic chemicals, specific mineral formulae (silicon, phosphite, …), and micro-organisms. This large variety of materials and organisms complicates defining what biostimulants are, which has led to various attempts reported over the last decade (du Jardin, 2015; Yakhin et al., 2017; Ricci et al., 2019). The definitions that likely will have the largest impact are those given by governmental bodies. The Council of the European Union* has prepared a directive in 2018 which becomes effective 16th July 2022 and in the US the USDA, EPA, and FDA are discussing the rules in place. Fortunately, the general tendency is to define biostimulants primarily by their bioactivity, paving the way for an array of products. Evidently, new products have to be safe for humans and environment.