Effects of DPC on Agronomic Traits and Economic Characters of Machine-Harvested Cotton in the Yellow River Valley of China and Chemical Control Techniques

Materials and Methods Test site overview The test site was located in the dry farming agricultural water -saving test station of Hebei Academy of Agriculture and Forestry Sciences (115° 42' E, 37°44' N) with an altitude of 20 m, and the site belonged to the semi arid and semi humid monsoon climate in warm temperate zone with an annual average temperature of 12.6 %, an average annual precipitation of 510 mm, of which 70% concentrated in July-August. [...]the yields of both treatments were significantly higher than the control0 The lint yield was the highest in medium control group, but there was no significant difference among all treatments0 As shown in Table 4, DPC treatment increased the number of bolls per plant and boll weight, thereby increasing the cotton yield0 However, DPC also decreased the lint percentage, so the difference in lint yield decreased among all treatments0 There was no significant difference in upper part average length, micronaire value and elongation rate0 The uniformity index was highest in medium control, which was significantly higher than that in high control0 The ratio of specific breaking strength was the highest in high control, and both chemical control groups were significantly higher than the blank control, indicating that proper chemical control could significantly increase the specific breaking strength0 Discussion and Conclusion First, DPC shortened the internodes that were elongating, inhibited the growth of apical buds in main stem and fruit branches, thereby reducing plant height and shortening fruit branch length, and the effects increased with the increase of DPC application amount. In this study, the medium control group had the highest cotton yield, but the difference was not significant with the high control group0 The daily increase amount of plants in the medium control group was 108 cm on average, and the daily average growth amount for the high control group was 1.5 cm, so all plants had good performances in controlling the daily growth amount of plant height within 1.5-1.8 cm0 The corresponding main stem internode length was 5.5-6 cm, and the plant height was 75 -90 cm, which could meet the requirements for machine harvest0 Second, DPC improved photosynthetic efficiency to increase production by building ideal plant shape, and in this study, the medium control group had the most bolls per plant, indicating that the plants of medium control group had reasonable canopy structure, which was favorable for boll