# Design and Construction of a Low-Cost Test Bench for Testing Agricultural Spray Nozzles
## 1 Introduction  
Spraying plant protection products (PPPs) is recognized as one of the agricultural activities most impacting on human health and the environment, also at the regulatory level [1]. Effects of PPPs on human health involve operators, farm workers and bystanders, consumers, professionals, and the general population, whereas those on the environment involve water, soil and atmosphere quality, and nontarget organisms such as vertebrates, useful arthropods, and other invertebrates. Therefore, on one hand researchers and manufacturers operate to get PPP application more sustainable according to the precision agriculture principles and on the other to promote nonchemical approaches. Precision agriculture requires treating huge amount of data coming from several sources and sensors [2; 3; 4; 5; 6; 7], from which to obtain prescription maps to be used with innovative spraying systems [8; 9; 10; 11; 12; 13; 14; 15; 16]. In addition, approaches for a more reasonable and sustainable use of PPPs include integrated pest management and organic farm [17; 18; 19; 20; 21; 22; 23], which allow for a reduction in the amount of chemical pesticides used. Worker's exposure and environmental effects of pesticides are affected by various variables, among which include active substances, adjuvants, formulation, type of equipment used and its status, task being performed, target features, canopy structure, amount of pesticide handled, packaging, environmental conditions, duration of activity, personal protective equipment used, and others. A key factor is the spray spectrum, evaluated in terms of droplet size distribution [24; 25; 26; 27; 28; 29], because an optimal droplet spectrum ensures the transfer of the required dose to the target, minimizes the off-target losses due to evaporation, drift, and run-off, and reduces dermal and inhalation worker exposure [30; 31; 32; 33; 34; 35; 36; 37]. According to [PERSON] [38], drops can be sampled for measurement purposes via spatial or flux techniques, and both methods affect the results. Spatial technique presupposes sampling instantaneously a number of drops occupying a given volume, whereas flux technique presupposes the examination of individual drops passing during an interval of time through the cross-section of a sampling region. The first method is sensitive to the number of particles in each class size and per unit volume, whereas the second to the particle flux. Drop size analyzers available on the market that implement the spatial sampling technique include the optical imaging (OI) and the laser diffraction (LD) analyzers. Both systems are nonintrusive and do not influence the spray behavior during the measurement. The flux sampling technique is implemented by optical array probes (OAPs) and phase doppler particle analyzers (PDPAs). Both systems are nonintrusive also, are single particle counters, and allow for measuring drop size and velocity contemporarily. Other methods, both intrusive and nonintrusive, are based on digital image analysis (DIA). Nonintrusive methods include the acquisition and analysis of the spray jet image [39], high-speed imaging [40], and shadowgraphy [41]. Among intrusive methods based on DIA, the use of water sensitive papers (WSPs) is probably the most diffused [42; 43; 44; 45; 46; 47; 48; 49]. WSPs are artificial targets with a yellow surface layer that turns blue when in contact with water. This property allows for registering the droplet stains in spray tests. Assuming as known the spread factor (ratio between stain diameter and drop diameter) and negligible the overlap between stains, stain image analysis allows for determining the droplet size distribution. A different approach, intrusive too, is to trap the droplets inside a layer of silicone oil of suitable density and viscosity and then analyze their image. The method is adopted by ISO 5682-1 [50], and it is exploited in this study to design and construct a low-cost test bench useful for evaluating agricultural spray nozzles.