Cotton fiber quality response to nitrogen depends on source-sink process, boll growth habit, and weather condition

Abstract

Nitrogen can be critical in determining fiber yield and quality in cotton. Major purpose of this 3-years (2017, 2018, and 2019) study in Faizabad-Iran was to investigate the effect of nitrogen rates, excess on the need for maximum yield and its interaction with environment on fiber quality of bolls with different spatial and temporal distribution in cotton canopy. Field experiment was a split-plot design with four replications. Main plots included two nitrogen rates (LN: 100 and HN: 200 kg ha −1 ). Sub plots included four boll growth habits: U P E R –Upper bolls Early in the season; L O E R –Lower bolls Early in the season; U P L A –Upper bolls Late in the season; L O L A –Lower bolls Late in the season. Results showed that fiber yield and fiber quality in terms of fiber uniformity and fiber strength were not affected by experimental factors and their interactions. In all years, LN led to an optimum micronaire (3.5–4.9 µg inch −1 ) and medium length (25.4–28.6 mm) fibers in all growth habits. However, in 2017, HN combined with lower temperature (25.2 °C) during the boll development decreased LAI to boll number ratio (source restriction), delayed maturity, and shifted fiber yield to U P L A boll growth habit with fine (micronaire < 3.5 µg inch −1 ) and short length (< 25.4 mm) fibers. In 2018 and 2019 with 1.7 °C and 2.3 °C higher temperatures than 2017, HN increased LAI to boll number ratio (sink restriction), led accelerated maturity, and shifted fiber yield to U P E R and L O E R boll growth habits, while with the increase of nitrogen, the difference between growth habits in terms of fiber quality was observed only in 2018 that led to production of coarse (micronaire > 4.9 µg inch −1 ) and long length (> 28.6 mm) fibers in U P E R and L O E R growth habits. In 2019, the lowest lint yield distribution was observed in U P L A treatment, but the fiber quality parameters were similar in all growth habits. These results may conclude that nitrogen consumption, in excess of what required for maximum yield, affects the source-sink relationship and leads to the formation of bolls with different fiber quality within a canopy, and the response of these processes to nitrogen is affected by the environment. • High N did not improve fiber yield but decreased fiber quality. • Low N led to an optimum micronaire and medium-length fibers in all seasons. • In cold weather, high N led to fine and short fibers. • In warm weather, high N led to coarse and long length fibers. • High N changed lint yield contribution and its quality within canopy.