## 1 Introduction  
Crop spraying is one of the most commonly used treatments in crop production. The selection of appropriate technical parameters of the spray treatment is very important and should be matched to the substance we apply to the plants [1; 2; 3]. This is vital especially during development of sustainable food production systems and is a crucial issue for protecting the environment while providing healthy food. As agricultural land shrinks due to climate change and increasing urbanisation, and as we approach the limits of the genetic potential of crops, research has been carried out to find new cultivation technologies and make existing ones more effective [4]. One way to improve the economic viability of crop production is to use plant-based biostimulants to enhance plant protection against biotic and abiotic stress. The application of biostimulants has been shown to improve--or at least stabilise, in adverse conditions--crop quality and yield [5]. Under Regulation (EU) 2019/1009, biostimulants are defined as \"products that stimulate plant nutritional processes regardless of the nutrient content of the product, whose sole purpose is to improve one or more of the following characteristics of the plant or its rhizosphere: nutrient use efficiency, abiotic stress tolerance, quality characteristics, availability of limited nutrients in the soil or rhizosphere \" [6]. According to the new definition, biostimulants are considered to be new modulators of plant life processes, adding to the effects provided by fertilizers, growth regulators, and pesticides. The underlying mechanisms of biostimulants and their bioactive compounds consist of simple, direct correlations between nutrient uptake and the effects of single plant hormones. The defining feature of these products is that they eliminate the nutritious effect in plants. It involves using a low dosage of the preparation, which is usually higher for most nutrients [7]. Extensive research has been conducted into the use of biostimulants in agriculture and horticulture. Numerous studies have found that there are differences in how individual plant species, and even varieties, respond to biostimulants [8; 9; 10; 11; 12; 13]. The use of seaweed biostimulants has been investigated extensively in recent years. Field and pot experiments have confirmed the positive effects of seaweed extract on metabolism and morphological traits, as well as plant yields [1; 14; 15; 16; 17; 18; 19; 20]. Biostimulant studies rely primarily on soil or foliar application. It is usually more advisable to employ the latter method since soil application requires substantial amounts of both the biostimulant and water. Application in the form of spraying requires the proper selection of technical parameters [21]. One of the key factors in ensuring that the liquid is sprayed correctly is the choice of suitable spray nozzles [22]. Spray nozzles--as well as their condition and working pressure--are critical for spraying quality, which, in turn, plays a fundamental role in the effectiveness of various agrochemicals, including biostimulants, and--in the case of pesticides--on the degree of environmental pollution [2; 23; 24; 25; 26]. While natural biostimulants cause no environmental pollution concerns, they pose significant problems with spray drift, which affects the amount and distribution uniformity of the liquid [27; 28; 29]. Spray nozzle type is a considerable factor in spray drift [30; 31; 32]. Spray drift reduces active substance coverage expressed as droplet count and weight per unit of plant surface area, or as plant surface coverage (%). Active substance coverage is a determining factor in the biological efficacy of spray application [33; 34]. One way to reduce spray drift is to use air-injector nozzles. Unlike standard flat-spray nozzles, they provide a significant reduction in drift. However, these nozzles also have a negative impact on plant coverage [35; 36]. Air-injector nozzles may cause runoff from plants, compromising the biological efficacy of the preparation.