DefinePK

Abstract

Cotton ( Gossypium hirsutum  L.) is a globally important cash crop cultivated primarily for fiber, yet its indeterminate growth habit often results in excessive vegetative development and yield losses. Optimizing row spacing and plant growth regulator (PGR) use is particularly critical in the context of climate change, resource-use efficiency, and narrowing yield gaps in Bt cotton production systems. Plant growth regulators (PGRs), particularly mepiquat chloride (MC; 1,1-dimethylpiperidinium chloride), are widely used to manage canopy architecture and promote reproductive growth. This field study was conducted in Agricultural field of Ghazi University, Punjab, Pakistan, during the 2020 and 2022 cotton seasons, to evaluate the combined effects of ultra-narrow row (UNR) spacing (30 cm) and MC application on the growth and productivity of two Bt cotton cultivars (BS-70 and BS-15). A factorial randomized complete block design (RCBD) with a split-plot arrangement was used, comprising two row spacings (30 cm UNR and 75 cm conventional) and three MC regimes (none, 10-day interval, and 20-day interval). Results showed that UNR and MC significantly influenced plant height, node number, branching pattern, boll weight, and seed cotton yield, while fiber quality traits ginning outturn, fiber fineness, fiber length, and strength remained unaffected. The highest yield was recorded in BS-70 under UNR without MC, closely followed by UNR with 20-day MC application. In contrast, frequent MC application (10-day interval) suppressed reproductive development and reduced yield. These findings demonstrate that UNR planting combined with judicious MC application enhances cotton productivity without compromising fiber quality, offering a sustainable intensification strategy for cotton cultivation under changing climatic and resource-limited conditions.