Optimizing water-fertilizer synergy in vegetable-type Brassica napus L.: Effects of split fertilization on crop performance and resource use efficiency

Conventional production of vegetable-type Brassica napus L . often relies on single high-dose fertilizer applications, which can promote early regrowth but tend to cause nutrient imbalance, reduced fertilizer efficiency, and poor resource use in later stages. To optimize water-fertilizer strategies, a two-year field experiment (2023–2024) was conducted in Yunnan Province, using two cultivars and three fertilization treatments under drip irrigation: single fertilization (T1), unequal split application (T2), and equal split fertigation (T3). The effects of each treatment on soil physicochemical properties, plant growth, dry matter accumulation, yield components, and resource use efficiency-including irrigation water productivity (WP I ) and partial factor productivity of nitrogen (PFP N )-were comprehensively assessed. Results showed that split fertilization, particularly T3, enhanced topsoil moisture, reduced electrical conductivity, and promoted stronger mid- to late-stage growth. Compared to T1, T3 increased yield by 36.2 %, WPI by 28.7 %, and PFPN by 25.7 %. Structural equation modeling indicated that soil nitrogen, moisture, and EC indirectly influenced yield through their effects on plant growth traits, with total inflorescence weight being the dominant yield determinant. Overall, equal-rate split fertigation (T3) was identified as the optimal regime, improving productivity, resource efficiency, and environmental sustainability. This regime is well-suited for intensive vegetable production in ecologically sensitive areas. • Split fertilization improved soil water content and reduced salt stress in root zones. • Equal-rate split fertilization enhanced growth and resource efficiency. • Structural modeling revealed yield was driven by soil traits and plant growth indicators.