Search

The optimization of plant density plays a crucial role in cotton production, and deficit irrigation, as a water-saving measure, has been widely adopted in arid regions. However, regulatory mechanisms governing nitrogen absorption, transportation, and nitrogen use efficiency (NUE) in cotton under deficit irrigation and high plant density remain unclear. To clarify the mechanisms of N uptake and NUE of cotton, the main plots were subjected to three irrigation amounts based on field capacity (Fc): (315 [W1, 0.5 Fc], 405 [W2, 0.75 Fc, farmers' irrigation practice], and 495 mm [W3, 1.0 Fc]). Subplots were planted and applied at three densities: (13.5 [M1], 18.0 [M2, farmers' planting practice], and 22.5 [M3] plants m−2). The results revealed that under low-irrigation conditions, the cotton yield was 5.1% lower than that under the farmer's irrigation practice. In all plant densities and years, the nitrogen uptake of cotton increased significantly with the increase in irrigation. However, excessive irrigation resulted in nitrogen accumulation and migration, mainly concentrated in the vegetative organs of cotton, which reduced the NUE by 9.2% compared with that under farmers' irrigation practice. Concerning the interaction between irrigation and plant density, under low irrigation, the nitrogen uptake of high-density planting was higher, and the yield of seed cotton was only 2.9% lower than that of the control (the interaction effect of farmers' irrigation × plant density), but the NUE was increased by 10.9%. Notably, with the increase in irrigation amount, the soil nitrate nitrogen at the 0–40 cm soil layer decreased, and high irrigation amounts would lead to the transfer of soil nitrate nitrogen to deep soil. With the increase in plant density, the rate of nitrogen uptake and the amount of nitrogen uptake increased, which significantly reduced the soil nitrate nitrogen content. In conclusion, deficit irrigation and high plant density can improve cotton yield and NUE. We anticipate that these findings will facilitate optimized agricultural management in areas with limited water. [ABSTRACT FROM AUTHOR]

Xinjiang cotton is characterized by high-density planting, which easily leads to competition between the source and sink, the shading of leaves and reproductive organs, and yield reduction. Balancing the relationship between source and sink can promote high and stable cotton yield. In this study, field experiments were conducted by combining the exogenous application of brassinosteroid with a reduction in leaf source to study their effects on the physiological and yield attributes of cotton. The results indicate that brassinosteroid application increased the yield, with a maximum yield increase of 6.3%. The number of bolls per plant increased by 1.3 nos. The photosynthetic rate and dry matter accumulation were enhanced, and the proportion of reproductive organs in the dry matter increased by >4%. Under the reduced leaf source, brassinosteroid application increased the number of new leaves by 20%, delayed the shedding of reproductive organs by 5–10 days, and reduced the average shedding rate by 8.9%. Additionally, the number of bolls increased in the middle and upper parts and at the edge of the plant. The number of bolls increased by 19.4% on the 4th–8th fruiting branches and 60.7% at the edge. Under leaf reduction treatment, brassinosteroid application could generally increase yield. After brassinosteroid application and removing half the leaves of fruiting branches and all leaves of the vegetive branches, the yield was higher than that of the control. Thus, brassinosteroid application could improve the efficiency of the leaf source and promote dry matter accumulation in sinks. Moreover, it could optimize boll distribution and increase yield by reducing reproductive organ shedding. Under the high-density planting of cotton in Xinjiang, leaf source is a slight surplus, and a moderate reduction in plant density is conducive to increasing yield. [ABSTRACT FROM AUTHOR]

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]

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]

Increasing the cotton planting density can reduce irrigation while maintaining the seed cotton yield. However, the underlying physiological and ecological mechanisms remain unclear. We hypothesized that increasing the planting density and reducing irrigation would promote dynamic consistency in the distribution of the roots, soil water, and nitrogen, leading to improved cotton water productivity and ultimately achieving a stable seed cotton yield. To test this hypothesis, a 3-year field experiment (2019–2021) was conducted in Xinjiang, China. The main plots were subjected to 3 irrigation levels based on crop evapotranspiration (ETc): 0.6 (deficit), 0.8 (typical), and 1.0 ETc (adequate). Subplots were planted at 3 densities: 13.5 (low), 18.0 (typical), and 22.5 plants m−2 (high). Under typical irrigation conditions, the seed cotton yield was significantly higher at a typical planting density than at a low or high planting density. However, with adequate irrigation, a low planting density resulted in a higher yield, while a high planting density combined with adequate irrigation reduced the yield by 14.7 % compared with typical conditions (typical irrigation + typical planting density). Under deficit irrigation, the seed cotton yield at a high planting density was 9.2–23.5 % higher than that at a low or typical planting density, achieving yield stability with 20 % water saving. The dry matter accumulation and harvest index showed no significant differences between typical irrigation + typical planting density and deficit irrigation + high planting density. Deficit irrigation combined with a high planting density resulted in a higher overlap rate of the root distribution area, soil water consumption area, and nitrate nitrogen consumption area, leading to higher water productivity than that of other density and irrigation combinations. Deficit irrigation combined with a high planting density can reduce water input by 20 % without sacrificing cotton yield, likely because of increased water productivity through the enhanced dynamic consistency of root distribution and soil water-nitrogen consumption. These findings provide valuable ecological and physiological insights for achieving water savings without compromising yield in arid and water-scarce regions. • Deficit irrigation at high planting density maintains seed cotton yield. • Deficit irrigation at high planting density increases water productivity. • Deficit irrigation at high density improves consistency of root distribution and soil water-nitrogen consumption. • This consistency contributes to increased water productivity and yield stability. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization plays an important role in yield formation of field-grown cotton ( Gossypium hirsutum L.), but little is known of its interaction with mode of application or plant density under irrigated production. Our objective was to determine the effects of N application rate on cotton yield, leaf senescence and N use efficiency as mediated by mode of application and plant density. To achieve this goal, two field experiments which were conducted from 2015 to 2016 using a split-plot design in randomized complete blocks. In the first experiment, the main plots were assigned to N application modes (conventional application and drip fertigation) and the subplots to N rates (375, 319, 264 and 0 kg N/ha). In the second experiment, the main plots were assigned to plant density (12 plants/m 2 -low density and 19.5 plants/m 2 -high density) and the subplots to N rates (330, 264 and 0 kg N/ha). The N rate of 264 kg/ha under drip fertigation or high plant density did not reduce cotton yield. Agronomic nitrogen use efficiency (aNUE) and nitrogen recovery efficiency (NRE) were the highest at 264 kg N/ha under drip fertigation and high plant density. Although a reduced N rate increased boll load, fertigation or high plant density relatively reduced boll load and delayed late-season leaf senescence as indicated by the increased photosynthetic rate and chlorophyll content as well as the reduced malondialdehyde concentration compared to conventional application or low plant density. The yield stability across N rates (264–375 kg N/ha) was probably due to the delayed leaf senescence and improved N use efficiency. The results suggest that the N rate could be reduced to 264 kg/ha, or 20–30% from the traditionally recommended rate, without sacrificing yield under high plant density or drip fertigation. These results are beneficial to the formulation of a scientific and rational use of N fertilizer for sustainable cotton production and environmental health. [ABSTRACT FROM AUTHOR]