Evaluation Effects of Row Spacing and Irrigation Levels on Yield, and Physiological Adaptations in Cotton

Introduction
Cotton (Gossypium hirsutum L.) is a globally critical industrial crop, essential to agricultural economies and the textile industry. With climate change and increasing water scarcity posing significant challenges, optimizing cultivation practices has become imperative. Effective irrigation management under water-deficit conditions is crucial for sustaining yields and agricultural systems. Research indicates that adjusting cotton row spacing is a key strategy for influencing yield, water use efficiency, and plant physiology.
Materials & Methods
This research aimed to investigate the effects of row spacing and different irrigation levels on cotton yield, yield components, and physiological responses. The experiment was conducted as a split-plot design within a randomized complete block arrangement with three replications at the Hashemabad Cotton Research Station in Golestan Province, Iran. The experimental treatments included two row spacing levels (narrow spacing of 20×20 cm and conventional spacing of 20×80 cm) as the main factor and four irrigation levels (rainfed, 30%, 60%, and 100% of field capacity) as the sub-factor. During the flowering stage, leaf temperature was measured using a thermometer. Samples were taken from the middle third of the canopy leaves to determine cuticular wax concentration (Ebercon et al., 1977). At physiological maturity, 30 bolls were harvested, and boll weight (single boll and total boll weight) was calculated. The first harvest yield and total yield were also evaluated.
Results & Discussion
The results indicated that row spacing had a significant effect on growth indices, yield, and physiological traits. In narrow-row spacing, faster canopy closure led to increased light absorption, improving light use efficiency by 18% compared to conventional spacing. However, the higher plant density in narrow rows reduced single boll weight by 15% compared to conventional spacing. In terms of yield, the highest productivity (3200 kg/ha) was achieved with conventional row spacing and 60% field capacity irrigation, while the lowest yield (1800 kg/ha) was observed in narrow row spacing with 30% irrigation.
Physiological responses showed that under drought stress and high plant density, leaf cuticular wax concentration increased by up to 40%. This response was evaluated as a defense mechanism to reduce transpiration and maintain tissue moisture. Additionally, leaf temperature in water-stressed and high-density treatments was significantly higher (by about 3–5°C) than in other treatments, indicating reduced efficiency of leaf cooling systems under stress. Regarding yield components, the number of bolls per square meter in narrow-row spacing was 20% higher than in conventional spacing, but boll weight decreased in this treatment.
Conclusions
The findings of this study suggest that although the narrow-row spacing system can enhance yield potential through increased plant density and improved light absorption, this advantage diminishes under severe water stress. Conversely, conventional row spacing with 60% field capacity irrigation was identified as the optimal treatment in terms of yield and water use efficiency. These results can be applied in developing management strategies for cotton cultivation in water-limited regions.