Abstract
Biostimulants represent an important category of agricultural inputs characterized by multiple functions. They are used to assist crop growth, yield and to enhance the final quality of produces. Their classification is generally based on claims (i.e., which services they provide to the crop), even though their biological effects are often species-dependent and highly influenced by external factors (i.e., the growing conditions). This review provides a survey of the available scientific literature on the use of biostimulant substances in fruit production, with the specific aim to clarify their predominant mode and time of application. An extremely varied scenario emerged where foliar treatments are common for seaweed extracts, humic and fulvic acids, and where protein hydrolysates and silicon are applied both to the soil (drench) or sprayed to the canopy. Dosages were difficult to compare between the considered studies given the wide range of tested products and the uncertainty in their actual composition. Regarding the number of applications, biostimulants are generally applied following a calendar-approach, covering most of the growing season. When their use is intended to enhance crop tolerance toward environmental stresses, biostimulants are mainly applied before the stressful event to prime plant physiological defenses. Further studies based on multiple-year research projects and standard methodological protocols are urgently needed to verify a clear compliance with biostimulant claims and to evaluate their cost-effectiveness for the fruit production sector.
Highlights
Because of the public concern about the use and/or abuse of chemical inputs in agriculture and the urgent call guided by government, authorities for more sustainable production systems [1] have significantly boosted the interest of the food industry for innovative and bio-based technologies able to decrease the environmental impact of the current production systems
Biostimulants have been further classified into microbial and non-microbial
Seaweed extracts can be obtained from species belonging to different Phyla, such as Rhodophyta, Chlorophyta and Phaeophyta [6]
Summary
Because of the public concern about the use and/or abuse of chemical inputs (pesticides and fertilizers) in agriculture and the urgent call guided by government, authorities for more sustainable production systems [1] have significantly boosted the interest of the food industry for innovative and bio-based technologies able to decrease the environmental impact of the current production systems. After a period of fast and uncontrolled growth, at the European level, biostimulants have been recently defined based on their presumed effects on crop performances [4] According to this claim-oriented definition, biostimulants are products able to improve one or more of the following plant or plant rhizosphere characteristics: (i) nutrient use efficiency; (ii) tolerance to abiotic stresses; (iii) quality traits; (iv) availability of confined nutrients in the soil or rhizosphere. The microbial biostimulants (i.e., the arbuscular mycorrhizal fungi and the plant growth promoting bacteria), because of their specificity in terms of mode of action (i.e., possible interaction with other microorganisms and the target crop) and application (dosages referring to spores number or colony forming unit), were not considered in this review This approach allowed us to focus only on those products whose application methods are generally described following a certain standard of uniformity, allowing interesting comparative evaluations between crops and growing conditions (protected or open field). The review paper concludes by proposing some methodological criteria to follow for a claim-based evaluation of biostimulant effects and for the definition of the most efficient mode of use of these products
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