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High-density planting is an effective technique to optimize yields of mulched cotton. On the other hand, deficit irrigation is an emerging water-saving strategy in cotton cultivation, especially suitable for arid and water-scarce areas. However, the relationships between deficit irrigation, high-density planting, and regulation mechanisms of canopy light radiation and light use efficiency (LUE) in cotton is not yet clear. To clarify the mechanism of light interception (LI) and the LUE of cotton canopies, three irrigation treatments [315 (50% Fc), 405 (75% Fc, farmers' irrigation practice), and 495 mm (100% Fc), where Fc was the field capacity] with three plant densities [13.5, 18.0 (farmers' planting practice), and 22.5 plants m2] were applied. The findings of this research revealed that, under deficit irrigation, the above-ground dry matter (ADM) was reduced by 5.05% compared to the farmers' irrigation practice. Over both years and across all plant densities, LI and LUE under deficit irrigation decreased by 8.36% and 4.79%, respectively, relative to the farmers' irrigation practices. In contrast, LI and LUE for the highest irrigation level increased by 10.59% and 5.23%, respectively. In the case of the interaction (plant density and irrigation level), the ADM under deficit irrigation and high-density combination increased by 7.69% compared to the control (farmers' irrigation × sowing practices interaction effects). The LI and LUE also exhibited an increase in 1.63% and 6.34%, respectively. Notably, the LI effect of the middle and upper cotton canopy under film drip irrigation reached 70%. A lower irrigation level resulted in a higher percentage of LI in the lower canopy region. The leaf area index, light interception rate, and extinction coefficient escalated with the increase in plant density. Under deficit irrigation treatment, the LI of the 0–30 cm canopy in high plant density settings increased by 8.6% compared to the control (farmers' irrigation × sowing practices interaction effects). In conclusion, deficit irrigation and increased plant density improved the interception of LI and LUE of cotton canopy. These findings may help the farmers to optimize their agricultural management strategies in water-deficient areas. [ABSTRACT FROM AUTHOR]

Nitrogen (N) loss is becoming one of the main limitations for sustainable agricultural production globally, particularly for crops such as cotton. To alleviate this issue, a promising strategy may be to exploit the N-saving potential of cotton plants by optimizing N application ratios at different growth stages under lower N rate and higher planting density with wide-row spacing. Two field experiments were carried out to investigate cotton yield, N use efficiency (NUE), N accumulation characteristics, and 15N uptake and distribution in response to N fertilization. First, a two-year experiment was conducted with N fertilization of either 0, 120, 240, 360 (control) or 480 kg ha−1. A three-year experiment was then carried out with 240 kg N ha−1 being applied with different ratios across three periods (squaring, flowering to peak boll, and late peak boll), i.e., 0:6:4 (N 064), 1:6:3 (N 163), 2:6:2 (N 262 , control), 3:6:1 (N 361) and 4:6:0 (N 460). Compared with conventional N fertilization (360 kg N ha−1), moderate fertilization at 240 kg N ha−1 resulted in steady and higher seed cotton yields of 5945 and 5603 kg ha−1 in 2017 and 2018, respectively, and improved NUE by 49.1–53.6%. Compared with conventional N 262 , a shift to later N application (N 064) increased both lint yield and partial factor fiber productivity of nitrogen (PFFPN) by 4.4–7.7%, and accumulated 6.1–14.4% more total N (K) in reproductive organs due to higher average (Vt) and maximum (Vm) accumulation rates by 25.2–49.0% and 15.0–48.7%, respectively, while the fast N accumulation period (∆t) shortened by 15.2–24.4%. N 064 partitioned 15.6% more 15N to reproductive organs. NUE was significantly positively correlated with K, t 1 (the day when ∆t started), Vt, Vm, Tm (the day on which Vm occurred) and 15N accumulation in middle and upper canopy bolls, and negatively correlated with ∆t of total N accumulation in reproductive organs. Allocating N from the squaring period to the late peak boll period led to an increase in N uptake during the reproductive growth stage and greater allocation of N to cotton bolls under reduced-N cultivation and drip fertigation. This N management strategy is a potential way to improve NUE and achieve sustainable and efficient production of cotton in arid areas. • 240 kg N ha−1 with wide-row and high-density planting was a N-reduced cultivation pattern. • Early N starvation increased cotton yield and NUE under N-reduced cultivation. • The increased in NUE was due to higher total N accumulation in reproductive organs. • Higher total N in reproductive organs was because of more fertilizer N allocated to bolls. [ABSTRACT FROM AUTHOR]

Manual removal of the main-stem growth tip is traditionally used to break the apical dominance of cotton (Gossypium hirsutum L.). Chemical topping with plant growth regulators also effectively inhibits apical dominance. However, the effect of chemical topping on yield increases and whether plant density or ecological conditions affect its efficacy are unclear. Therefore, a three-year field experiment with a split-plot design was conducted to determine the effects of plant topping, plant density, and their interactions on cotton yield and related physiological and agronomical parameters at three sites with different ecological conditions in China. In each site, the main plots were assigned low, moderate, or high plant density and the subplots were assigned no topping, manual topping, or chemical topping. Growth, yield, yield components, earliness, and late-season leaf photosynthesis as well as labor and material inputs were examined each year. Compared with no topping, both chemical and manual topping greatly reduced plant height at all sites. Manual topping increased seed cotton yield and earliness in all tested plant densities and sites. However, plant density but not ecological condition greatly mediated the effect of chemical topping on yield. At low plant density, the yields with chemical topping were 4–6% lower than those with no topping and 5.5–10.8% lower than those with manual topping at the three sites. Although yields with chemical topping were comparable with those of manual topping at moderate and high plant densities, they were 8.6–12.8% higher at moderate density and 13.8–16.4% higher at high plant density than those with no topping across years and sites. Averaged across the sites, chemical topping reduced biological yield by 12.7% at low plant density. Although biological yield decreased slightly, chemical and manual topping increased the harvest index by 12.4% and 13.3% at moderate density and by 15.6% and 17.4% at high density, respectively. In comparison with no topping, the reduction in seed cotton yield with chemical topping at low plant density was attributed to insufficient biological yield, whereas the increase in yield at moderate and high plant densities was mainly due to greater partitioning of assimilates to reproductive tissues. Compared with manual topping, chemical topping produced 23.2% lower net returns as a result of lower seed cotton yield at low plant density but produced 8.1% and 20.9% higher net returns at moderate and high plant densities, respectively, because of savings in labor inputs and comparable seed cotton yields. In addition, chemical topping increased the earliness percentage compared with that of no topping. Overall, this study demonstrates that chemical topping is a promising alternative to traditional manual topping under moderate or high cotton plant density. • Manual topping increased cotton yield regardless of plant densities and ecological conditions relative to non-topping. • Chemical topping decreased yield at low plant density relative to non-topping because of greater biomass reduction. • Chemical topping increased cotton yield at moderate and high plant densities via greater assimilates partitioning to fruits. • Chemical topping could replace manual topping at moderate and high plant densities without ecological dependence. [ABSTRACT FROM AUTHOR]

The northwest inland is currently the most dominant cotton-growing region in China. In 2015, the region measured 2.3 million hectares with a total output of 4.28 million tons of cotton. The unit yield was 1900 kg hm −2 , which was not only 21, 41 and 121% higher than the national averages of China, Brazil and the United States, respectively, but also 2.37 times as much as that of the world’s average. Enhanced cotton production, particularly the high unit yield, can largely be attributed to the adoption of a series of key cultivation techniques. These techniques, including earliness-stimulating cultivation for full utilization of accumulated heat, close planting and short plant height for adequate use of light energy, and drip irrigation under plastic mulching for water saving and yield improvement, have been recently established and applied in the northwest inland of China. At the same time, a series of labor and cost-saving technologies or practices have been adopted to increase net production returns. Mechanization and precision seeding has greatly reduced labor inputs, rational high-density planting techniques combined with chemical regulation has simplified plant pruning and harvesting, and the integrated application of water and fertilizer has reduced the inputs and costs in field management. In particular, the integration of these agronomic techniques and material equipment has not only enhanced yields, but is also convenient, cost-effective and simple. These factors have all led to the establishment of the northwest inland as the largest predominantly cotton-growing area in China. However, the region is currently facing major issues including stagnated cotton yields, serious plastic film pollution, continuous degradation in fiber quality, substantial increases in the cost of cotton production and continuously declining profits. These factors necessitate that cotton cultivation strategies in the region need to be further optimized. Yields can be enhanced by exploring heat and water potential, while quality and economic benefits can be improved by exploring light potential, fertigation and integrating agronomic techniques with mechanization. Greater attention should be paid to seed quality and seeding processes to further reduce costs and improve efficiency. Comprehensive steps for improving the cultivation system at all stages of production should also be taken to enhance the quality of the cotton fiber. [ABSTRACT FROM AUTHOR]

Plastic film mulching has been widely applied to improve crop productivity of full-season cotton (Gossypium hirsutum L.). However, in a previous study, plastic mulching did not increase seed cotton yield of short-season cotton compared with non-mulching. The aim of this study was to determine why plastic mulching fails to increase seed cotton yield of short-season cotton. A short-season cultivar Lumian 532 was planted with or without plastic mulching at an experimental station in Linqing in the Yellow River valley of China in 2020 and 2021. Yield, yield components, leaf senescence, photoassimilate accumulation and partitioning, photohormone contents, expression of senescence-related genes, and root traits were examined each year. Seed cotton yield produced with plastic mulching was not significantly different from that produced with non-mulching in short-season cotton. Although number and size of early- and mid-season bolls were significantly greater with plastic mulching than with non-mulching, plastic mulching decreased number and size of late-season bolls by 34.0% and 8.8%, respectively. At the initial boll opening stage, photosynthetic rate and chlorophyll content in main-stem functional leaves were 36.2% and 24.1% lower, respectively, with plastic mulching than with non-mulching, but malondialdehyde content was 34.2% higher, suggesting that plastic mulching accelerated late-season leaf senescence. Canopy photosynthesis and photoassimilate partitioning to reproductive organs at the initial boll-opening stage were 68.1% and 9.4% lower, respectively, with plastic mulching than with non-mulching. Compared with non-mulching, plastic mulching increased abscisic acid and methyl jasmonate contents but decreased those of cytokinins content because of differential expression of hormone metabolism-related genes in late-season main-stem leaves. Plastic mulching also increased root distribution in the shallow soil layer and lowered root vigor in the late season, compared with non-mulching. Overall, plastic mulching negatively affected root distribution and function and altered expression of senescence-related genes and hormone metabolism-related genes to affect hormone balance, which led to accelerated late-season leaf senescence. Because of late-season leaf senescence, canopy photosynthesis and photoassimilate partitioning to cotton bolls were suppressed with plastic mulching, which led to fewer and smaller late-season bolls than those with non-mulching. Thus, plastic mulching failed to improve the seed cotton yield. This study provides a clear explanation of how plastic mulching causes late-season leaf senescence and further demonstrates that plastic film mulching is not required for planting short-season cotton in the Yellow River valley of China or in other cotton growing areas with similar ecology. • Plastic mulching did not increase yield compared with non-mulching because of fewer and smaller late-season bolls in short-season cotton. • Reduced number and size of late-season cotton bolls was attributed to accelerated late-season leaf senescence in short-season cotton. • Accelerated leaf senescence was due to shallow root distribution and weak root vigor, and differential expression of senescence-related genes. [ABSTRACT FROM AUTHOR]

The plant growth regulator mepiquat chloride (1,1-dimethylpiperidinium chloride, DPC) has been successfully used worldwide in cotton production. Fortified DPC (DPC+) can slightly damage young tissues of the epidermis, which has shown potential in cotton chemical topping in China. The underlying mechanism remains unclear. We investigated whether apical meristem and leaf morpho-physiological traits contribute to delayed growth of the main stem and increased seed yield in DPC or DPC+ as a chemical inhibitor. Two different DPC-sensitive varieties (Xinluzao 60, L60; Jinken 1402, JK1402) were field-grown using three different topping treatments manual topping (MT), no topping (NT) and chemical topping (DPC+ and DPC) in irrigated arid lands of Xinjiang for two years. The plant height decreased by 1.4–13.6% for the DPC+ and DPC treatments compared with the NT treatment and increased by 3.8 –9.2% compared with the MT treatment. The thickness of the leaves, palisade tissue (Pt) and spongy tissue (St) increased by 5.1–21.5% under DPC treatment compared with other treatments. The 3-indoleacetic acid (IAA) content of the leaves significantly increased by 25.0–93.8% at 10 days under the DPC treatment compared with that under the MT and NT treatments. The zeatin riboside (ZR) content of the leaves and apical buds increased up to 7.5 times at 40 days under the DPC+ and DPC treatments compared with that under the NT treatment. The accumulation of reproductive organ biomass and proportion of reproductive organ dry matter to total dry matter under the DPC+ and DPC treatments increased by 2.0–39.7% compared with that under the MT and NT treatments. The seed cotton yield between the DPC+ and DPC treatments showed no significant difference. However, the seed cotton yield of JK1402 under the DPC+ and DPC treatments significantly increased by 9.5–11.7% compared with that under the MT and NT treatments. The main stem length was significantly correlated with the stem length of the upper part and gibberellin (GA) content in the apical buds. The leaf Pt and ZR contents were significantly correlated with the boll weight and seed cotton yield. Collectively, the data suggest that improved morpho-physiological traits of the apical part, such as an increase in the IAA and GA contents in the apical buds, leaf Pt and ZR contents, and boll weight, inhibited growth of the main stem and increased seed cotton yield for DPC, which is cheaper than DPC+ as a chemical inhibitor under chemical regulation during the whole growth period. • Chemical topping delays growth of the upper main stem. • Chemical topping enhances thickness and ZR contents of leaves. • DPC can increase boll weight and seed cotton yield in DPC-sensitive varieties. • DPC has the potential to replace manual and other chemical topping agents. [ABSTRACT FROM AUTHOR]