Effect of planting date and plant density on cotton traits as relating to mechanical harvesting in the Yellow River valley region of China

Previous studies have indicated that mechanical cotton harvesting requires a compact plant habit without fiber yield and quality reduction. The objective of this study was to determine the effects of planting date and plant density on plant habit, yield, early maturity, and fiber quality of cotton in the Yellow River valley region of China, and thus to identify the appropriate planting date and plant density suitable for its mechanical harvesting. Field experiments were conducted in 2013 and 2014 in Hejian, Hebei Province, using a split-plot design with planting date as the main plot and plant density as the subplot. The results indicated that moderately late planting in late April or early May (P2) was appropriate for mechanical harvesting of cotton as relative to P1 (local traditional planting date, 10 d earlier than P2) and P3 (10 d later than P2). P2 showed a 2.4-5.7 cm greater height to the first fruiting branch (from the bottom) and a 4.7-11.3 cm higher lowest boll (harvestable boll nearest to the ground) compared with P1, which is helpful for decreasing yield loss and reducing intake of residual plastic mulch. In addition, P2 produced slightly greater yield than P1 and P3, and the percentage of open bolls in late September for P2 was similar to that of P1 and greater than for P3, suggesting a low risk of late maturity. For plant density, 8.9 plants m−2 (D2) was appropriate for mechanical harvesting compared with 6.6 plants m−2 (D1), the local traditional density for manual harvesting, and 12.3 plants m−2 (D3). D2 showed a 2.5 cm greater height to the first fruiting branch and a 4.2 cm higher lowest boll, and exhibited 2.9-3.6 and 2.6-3.9 cm shorter lengths of lower and middle fruiting branches than D1, respectively. This type of compact plant habit is conducive to efficient mechanical harvesting. Moreover, D2 produced a similar yield to D1 for both the rainy 2013 and the dry 2014, indicating yield stability. Although D3 had a more suitable plant habit for mechanical cotton harvesting, its yield level and maturity varied across years. There were no significant interactions between planting date and plant density in the majority of tested traits. The results will contribute to the development of integrated cotton management for upcoming mechanical harvesting in the Yellow River valley region of China.