JIA-2019-11

2494 NIE Jun-jun et al. Journal of Integrative Agriculture 2019, 18(11): 2492–2504 different yield formation that were widely planted in the Yellow River region at different periods were selected in this experiment: 99B, a mid-season conventional variety with an insect-resistant gene, introduced from the United States with a growth period of approximately 130 days, boll weight of 4.9–5.5 g, and lint percentage of 36.0–38.8%; L21, China’s first-era of a mid-season conventional variety that is self-breeding and has a transgenic insect-resistant gene, with a growth period of approximately 133 days, boll weight of 5.8 g, and lint percentage of 41.6%; and J169, China’s second-era transgenic mid-season conventional variety with an insect-resistant gene, a growth period of 123 days, boll weight of 6.3 g, and lint percentage of 39.4%. 2.2. Experimental design and field management Cotton seeds were planted with manual hill-drop planting methods in late-April in a randomized complete block design with three biological replications. Each plot consisted of eight rows with wide-narrow row planting; the wide row was 100 cm, the narrow row was 60 cm, plant-to-plant distances were 25 cm, and the area of every plot was 51.2 m 2 (8 m×6.4 m). Compound fertilizer (N:P:K=15:15:10) was used as the basal fertilizer, which was applied at 750 kg ha –1 , with flowering stage topdressed urea (46%) at 210 kg ha –1 . Other management practices, e.g., insect and weed control and chemical control with plant growth regulators, were conducted according to local agronomic practices. 2.3. Data collection Twenty plants in the center rows of each plot were used to investigate the agronomic traits (i.e., plant height, first fruiting branch node and height, the number of fruiting branches and nodes, and the ratio of fruit nodes and branches) and boll spatial distribution in the boll opening stage. The fruits were vertically divided into the lower bolls (first to fourth sympodial branches), middle bolls (fifth to eighth sympodial branches), and upper bolls (ninth and beyond sympodial branches), and they were horizontally divided into inner bolls (first to second sections) and distal bolls (3rd section and beyond) according to the position of the bolls on the cotton plant (Hofs et al . 2006; Lv et al . 2013; Mao et al . 2015; Wang et al . 2016; Zhang et al . 2017). The opening bolls were manually harvested according to different spatial positions, and the number of harvested bolls in each position was recorded. Seed cotton was weighed after sun-drying, and then the individual boll weight was calculated. Cotton seed and ber were separated using a roller ginning machine. Lint percentage was gin turnout, which was calculated as the weight of the ber divided by the weight of the seed cotton. Lint yield was calculated by multiplying three yield components: the number of bolls, average boll weight, and lint percentage. Fiber quality (fiber length, fiber strength, micronaire, fiber uniformity, and fiber 2017 Rainfall (mm) 0 20 40 60 80 100 2013 Mean air temperature (°C) Mean air temperature (°C) 0 10 20 30 40 Mean air temperature Rainfall 2014 2015 Rainfall (mm) 0 20 40 60 80 100 2016 0 10 20 30 40 5 6 7 8 9 10 11 5 6 7 8 9 10 11 5 6 7 8 Month Month Month Month Month 9 10 11 5 6 7 8 9 10 11 5 6 7 8 9 10 11 Fig. 1 Daily mean air temperature (°C) and rainfall (mm) recorded during cotton growing seasons in 2013–2017.