Abstract: Agent for the agronomic treatment of a living plant supported by a moist substrate, for example a soil, wherein said agent is in the solid and divided state, and comprises solid particles containing at least one active entity for the agronomic treatment, characterized in that each particle comprises: —a nucleus consisting of a grain of a solid material which is inert with respect to the substrate, comprising an inner developed surface area which is greater than its apparent surface area and, as a result, suitable for adsorption and/or absorption, —the active entity for agronomic treatment, absorbed into the grain and/or adsorbed at the surface of said grain, —a membrane encapsulating the nucleus comprising the active entity, consisting of at least one hydrophilic polymer which is permeable to the outside with respect to the active entity, when it is in direct or indirect contact with the moist substrate.