Use of Biostimulants to Improve Salinity Tolerance in Agronomic Crops

The world population is exceeding 7.63 billion, resulting in more than quadrupled compared to that of 1915 (1.8 billion), and according to the United Nations most recent predictions, we may reach 9.7 inhabitants by the year 2050. This exponential growth, along with the shift from rural to urban life, the increase in per capita food consumption, and the changes in diet in developing countries, due to the rise in income, are driving up the global food demand, which is expected to increase worldwide from 59% to 98% in the next 30 years. However, it will be hard to square the twin challenge of reconciling a maximization of agricultural production with environmental sustainability. Indeed, in the last 50 years, mechanization and new management techniques based on the massive use of fertilizers and irrigation have increased agricultural production also in arid and semi-arid areas, but they have also exacerbated the problems of soil salinity and pollution. In fact, one of the most serious effects of these unsustainable practices has been the salinization of at least 20% of all irrigated and productive lands. Therefore, the main objective of modern agriculture is to increase crop yield production and potential, also in marginal and salinized areas, through innovative farming systems and/or products with an eco-friendly approach. Among the new products which have favorable effects both on soil and cultivated crops, even under environmental constrains like salinity, are biostimulants. They include substances, metabolites, or mixtures of metabolites and/or microorganisms which, when applied to plants or soil, increase the nutrient availability, uptake, and assimilation while reducing the use of agrochemicals in agriculture and improving food resources, preventing leaching of nutrients, and increasing the response to stress in an eco-friendly perspective. Biostimulants do not replace fertilizers or pesticides but represent a complement to the action of both fertilizers and crop protection products, allowing enhancing crop performance even under stress. We will consider the biostimulants derived from plants or animals like seaweed extracts, humic substances, protein hydrolysates, microbial inoculations, etc. and will describe their beneficial effects on plants, especially nutrient use efficiency and plant fitness to abiotic stresses and in particular to salinity