Search

Basal and topdressing split application of nitrogen (N) fertilizer is widely used in cotton in many cotton-growing countries, including China. Recently, in the Yellow River valley of China, one-off basal application of N fertilizer has been applied to meet the challenge of increasing labor costs. However, how one-off basal application of N fertilizer affects cotton yields and N use efficiency and by what mechanisms are not clear. Therefore, an experiment was conducted using full-season (K836) and short-season (LM532) cotton cultivars in a moderate fertility field in the Yellow River valley in 2019 and 2020. A split-plot design was established for each variety with the main plots assigned to a mulching pattern (with or without plastic film mulching) and the subplots assigned to an N rate (0 or 195 kg N ha−1, abbreviated as N0 and N195). Cotton yield and yield components, biomass accumulation and distribution, and total N and 15N absorption and utilization were determined each year. Compared with N0, one-off basal application of N fertilizer (N195) did not increase boll density, boll weight, lint percentage or seedcotton yield regardless of cultivar or mulching. Biomass and total N uptake of cotton increased significantly in N195 compared with N0, but the increases occurred primarily in vegetative organs, leading to reductions in the harvest index and N yield efficiency index. With one-off basal application of N fertilizer, more than 80 % of the N in cotton plants derived from soil. Approximately 28 % of 15N-labeled urea was absorbed by cotton plants, of which only approximately 35 % was used in forming seedcotton yield. Therefore, cotton plants with one-off basal application of N fertilizer only recovered a small amount of fertilizer N, and even less of the fertilizer N was used in yield formation. As a result, the harvest index of cotton decreased, and thus, one-off basal application of N fertilizer failed to increase seedcotton yield. Cultivar and plastic film mulching did not alter the effects of one-off basal application of N fertilizer. Therefore, although one-off basal application of N fertilizer in cotton is a labor-saving approach, it should not be encouraged in moderate fertility soil in the Yellow River valley or other areas with similar ecology. • One-off basal N application did not increase the seedcotton yield compared with no-N fertilization. • One-off N application led to a low proportion of plant N derived from 15N and even less for yield formation. • Both N uptake and N distribution to vegetative organs was improved by one-off basal N application. • Cultivar and plastic mulching did not alter the effects of one-off basal application of N fertilizer. [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]

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]