## 1 Introduction  
Modern agriculture is increasingly developing soilless cultivation methods that allow for plant production under conditions of limited or entirely eliminated contact with soil. In such systems, soil is replaced by mineral substrates, primarily mineral wool and rock wool [1]. These methods, including hydroponics, aeroponics, and cultivation in organic and mineral substrates, aim to improve the efficiency of water, nutrient, and growing space utilisation [2]. However, after the substrates' period of use, disposal becomes necessary, which generates environmental concerns and affects the profitability of crop production [3].  
Among the various materials used as soilless substrates, natural materials hold a particularly important place, chief among them coconut fibre (_Cocos uncifera_), a by-productof the coconut industry. Coconut fibre is characterised by high porosity, good water retention capacity, appropriate spatial structure, and relatively stable chemical composition. It possesses natural antifungal properties, and its low pH and electrical conductivity (EC) make it suitable for a wide range of vegetable and horticultural crops [4]. Nevertheless, certain limitations such as structural instability over longer periods of use and variability in surface properties have prompted the search for ways to improve these characteristics.  
One approach to enhancing substrate durability and extending its lifespan is the use of additives or coatings on coconut fibres. Although synthetic materials can be effective in this regard, their use in coating processes may lead to additional issues due to the non-biodegradable nature of the modified materials. An alternative solution may lie in the use of various biomaterials. Biopolymers, natural polymers derived from plant, animal, or microbial sources, are highly environmentally compatible and biodegradable. Examples include chitosan, sodium alginate, carboxymethyl cellulose, modified starch, and gelatine. Their use in materials engineering, agriculture, and environmental protection is rapidly expanding due to the growing importance of sustainable development [5].  
A promising solution may involve the use of natural-origin monomer systems in which the polymerisation process can be initiated in a controlled manner. This is particularly relevant because biopolymers often exhibit properties that hinder coating processes, whereas using monomer solutions allows the coating to be effectively achieved once polymerisation has been initiated [6; 7].  
An additional component of coconut-fibre-based horticultural substrates may be biochar, obtained through biomass processing. This additive modifies the surface characteristics of the substrates in which it is used, significantly affecting their properties, particularly sorption and retention capabilities [8; 9]. To date, research on substrates has primarily focused on the use of unmodified coconut fibre as a cultivation medium [10; 11]. The application of biopolymer coatings represents a novel research direction that could significantly enhance the functionality of this material within soilless cultivation systems.  
The aim of this study was to demonstrate the applicability of coating coconut fibre--used as a plant-growing substrate--with a polymer coating obtained through the polymerisation of an isolate produced during fibreboard manufacturing, rich in biomonomers, depending on selected physical characteristics of different types of coconut fibre. For this purpose, modified horticultural substrates with varying physico-chemical properties were prepared, influencing the mobility of selected nutrients.