Mechanical properties of cotton shoots for topping

Cutting the shoots of cotton plants (topping) at about 10-20 cm from the top of plants is a cultural practice, which may offer advantages to improve yield and yield components in cotton production. The cutting forces of plant stalks were reported in the literature, which help understand the mechanical properties of stalks for a cultivar of field crops. However, the shearing characteristics of cotton shoots have not been addressed yet. The objective of this study was to determine some physical and mechanical properties of cotton (Gossypium hirsutum L.) shoots. The test specimens were obtained from two different plant segments, i.e. 0-15 cm (Segment A) and 16-30 cm (Segment B) from the top of cotton plants, in 21 plots in an ongoing cotton topping study. The samples were collected from each plot and were subjected to shearing test using a universal test machine in the laboratory. In Segment A, average shoot diameter, shearing force, water content, maximum shearing stress, and specific shearing energy were determined to be 4.35 mm, 73 N, 72%, 4.94 MPa, and 0.069 J mm(-2), respectively. In Segment B the same parameters were 5.79 mm, 121 N, 64.8%, 4.65 MPa, and 0.078 J mm(-2), respectively. The difference between the Segment A and B was significant at 5% level for shearing stress while all others parameters showed differences at 1% level. Although displacement at the bioyield point was similar in both sampling locations, the maximum shearing force requirement was more (121 N) in Segment B compared with Segment A (73 N) suggesting that topping should be done as high as possible from the ground to complete the topping process with low energy consumption. In terms of cutting energy requirement, it was concluded that the topping should be done as early as possible from 100 to 120 days from the planting.