Integrated application of nitrogen and mepiquat chloride improves yield of Brassica napus L. by modulating shattering, lodging and nitrogen use efficiency under rainfed conditions

Nitrogen is the major yield-limiting factor for Brassica napus but is often deficient in soils. Excessive and inefficient nitrogen application can lead to lodging, reduced nitrogen use efficiency, and increased shattering losses during mechanical harvesting. However, co-application of mepiquat chloride and nitrogen can be a viable agronomic intervention to alleviate these challenges. A two-year field study (2022-23 and 2023-24) with factorial randomized complete block design (RCBD) was conducted to unravel effects of nitrogen (0, 85, 170, 255 kg ha⁻¹) conjugated with foliar application of mepiquat chloride (0, 50, 100 mg L⁻¹) on shattering, lodging and nitrogen use efficiency (NUE) of B. napus. Increasing nitrogen from 0 to 255 kg ha⁻¹ significantly increased plant height, biological yield, lodging and shattering; however, integration of nitrogen with mepiquat chloride (MC) abridged these traits. In both years (2022-23 and 2023-24), 170 kg ha^–1 nitrogen combined with 50 mg L^–1 MC resulted in significantly higher number of pods plant^-1 (375.88, 356.13), seeds pod^-1 (24.30, 21.83), 1000-seed weight (3.84 g, 3.65 g), chlorophyll content (8.84 mg g^–1, 8.49 mg g^–1), seed yield (2362 kg ha^–1, 2260 kg ha^–1), NUE matrixes viz.; apparent recovery (53.68%, 51.57%), agronomic efficiency (6.36 kg kg^–1, 5.73 kg kg^–1), utilization efficiency (13.64 kg kg^–1, 13.45 kg kg^–1), agro-physiological efficiency (11.83 kg kg^–1, 11.14 kg kg^–1), and antioxidant activity, but lower lipid peroxidation (MAD). Lodging was positively correlated with plant height (r = 0.85, 0.71), biological yield (r = 0.94, 0.89) and nitrogen uptake efficiency (r = 0.75, 0.75), while seed yield was negatively correlated with shattering (r= – 0.74, – 0.64) and malondialdehyde (MDA) content (r= – 0.72, – 0.86). This is the first report demonstrating that combined nitrogen and MC application reduces shattering and lodging in B. napus, while improving yield. Applying 170 kg ha⁻¹ nitrogen and 50 mg L⁻¹ MC at rosette and silique formation stages is recommended for higher seed yield in water-deficient environments.