# Effect of Controlled Defoliant Application on Cotton Fiber Quality
## 1 Introduction
With the recent advances in agriculture, new technologies have been adopted, such as the application of artificial intelligence [20], plant disease detection [21; 22], soil, crop, weed, and disease management [23]. Cotton growers also adopt these technologies, especially for defoliation and mechanical harvesting. Conventional boom sprayers are widely used for defoliant applications [9]. The crop cluster is another concept of agriculture spraying in which chemicals are applied in powdery form using aerial vehicles (unmanned or manned aircraft) [24; 25] and most recently the use of unmanned aerial vehicles for cotton defoliant applications has also been increasing [26; 27]. However, in all systems of chemical application, the spraying is done horizontally downward from the top, and a minimum of defoliant droplets reaches the lower canopy of the plant due to high wind turbulence (in the case of drone) and interlocking of branches and leaves on upper canopy of the plant. But for successful defoliation, each leaf must receive the defoliant as chemicals do not move within the plant [11]. Unfortunately, there are no study yet specific for cotton defoliation on the whole canopy. Therefore, to address this research gap, a new spraying system was developed using unmanned ground vehicles and pulse width modulation technology [28]. The development of autonomous spraying technology would encourage the development of new sprayer industries and the unmanned ground vehicle industries, together with the need for the global development of an agricultural system with broad market prospects and brings about huge economic, social, and ecological benefits. Fiber quality is very important for cotton production. There are two methods mainly used for cotton fiber quality measurement: high volume instrument (HVI) and Advanced Fiber Information System (AFIS). The HVI system was developed with the aim of replacing manual fiber quality measurement methods by developing the instrumental fiber quality measurement method [29]. HVI measures fiber parameters such as upper half mean length (UHML), uniformity index (UI), strength, elongation, trash, reflectance, and yellowness (color grade). HVI is faster and more cost-effective than other methods; however, HVI doesn't provide complete within-sample variation in fiber length compared to AFIS [29; 30]. In AFIS, firstly, the fibers are individualized and then presented to an electrooptical sensor aerodynamically for the measurement of different fiber quality parameters [31]. In contrast, in the case of HVI, the fiber length measurement is based on the principle of fibro gram and based on a quick assessment of a bundle of fiber [32]. The use of robotics has been widely increasing in various sectors such as medical [33], business [34; 35], and agriculture [36]. To our knowledge, no studies thus far have addressed the autonomous ground spraying platform for cotton defoliation covering the whole canopy of the plant. Thus, this study's results concerning the effect of defoliant application through the autonomous robotic platform and pulse width modulation on yield and fiber quality parameters analyzed by HVI and AFIS separately and provide new references and bases for further improving the cotton defoliant spraying technique. Therefore, the study was conducted to evaluate the effect of different duty cycles (defoliant rate) on cotton fiber quality parameters.