Effect of Controlled Defoliant Application on Cotton Fiber Quality

Cotton (Gossypium hirsutum L.) is an important industrial crop. It is a perennial crop and has indeterminate growth habit, however, in most parts of the United States, it is grown as an annual crop with the application of growth regulators. Defoliation is a major production practice influencing harvester efficiency, fiber trash content, cotton yield, and fiber quality. Currently, defoliant application is done by using a conventional boom sprayer and aerial spraying in which both systems spray chemicals horizontally downwards from the top of the canopy, which causes minimal chemical to reach at bottom canopy. However, for successful defoliation, each leaf must receive the defoliant as chemicals do not move within the plant. Thus, a new autonomous ground sprayer was developed using robotics and pulse width modulation, which can be run in between two rows covering the whole canopy of the plant. Field research was conducted to study the effect of three duty cycles (20%,40%, and 60%) on cotton fiber quality using autonomous spraying system. The result indicated that the defoliants could be applied safely at either of the three duty cycles without compromising most of the fiber quality parameters except for nep/gm, length (Ln), L (5%), SFC, trash content in field 1 and micronaire, nep size, length (Ln), L (5%), SFC, and fiber fineness in field 2 which were significant. However, application of 20% duty cycle will significantly reduce the chemical use therefore, 20% duty cycle could be a good choice for the autonomous cotton defoliation. 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.