The Relationship between Droplet Density and the Defoliation Effect of Cotton Harvest Aids.

Spraying harvesting aids is an important step before the mechanical harvesting of cotton. To clarify the direct relationship between the droplet density and the defoliation effect of cotton harvest aid solutions, we evaluated the relationship between the droplet density and the defoliation effect. The determination method and evaluation standard of the number of droplets required per square centimeter to achieve 50% leaves defoliation (DN50 ) of the harvest aid solution were further explored. The results revealed a linear relationship between the droplet density and the cotton defoliation rate when the spraying volume was 22.5 L/ha and the harvest aid dosage was 1/2 and 2/3 of the recommended dosage. When the harvest aid dosage was 5/6 and 1 times the recommended dosage, the relationship between the droplet density and the defoliation rate of cotton was logarithmic. The DN50 of the low-concentration harvest aid solution (450 L/ha) was significantly higher than that of the high-concentration solution (22.5 L/ha). The addition of spray adjuvant Beidatong significantly reduced the DN50 of cotton harvest aids. The field experiment showed that the droplet density increased with the increase of the spraying volume sprayed by unmanned aerial vehicles. There was a positive correlation between the spraying volume and the defoliation effect after changes in the cotton harvest aid dosage. When the dosage of Mianhai (MH) was 5/6 of the recommended dosage, the defoliation effect at the spraying volumes of 22.5, 27.0, and 30.0 L/ha reached the peak values at 71.54, 78.56, and 83.23%, respectively. This study proposed the concept of DN50 and its determination method. The fitting equations between the droplet density and defoliation effect and between the harvest aid concentration and defoliation effect were established to provide a theoretical basis for the scientific spraying of cotton harvest aid solutions.