Optimizing drip fertigation timing enhance nitrogen use efficiency and cotton yield and quality under nitrogen reduction

Drip irrigation practices can improve water and fertilizer use efficiency, thus, it is widely applied in agricultural production in global arid regions. However, the time for fertilizer input in drip irrigation was generally 30 min after water started to flow in, and the appropriate fertilizer application timing was not clear under different fertilizer application rates, which also restricted the improvement of nitrogen use efficiency. In 2023 and 2024, a two-factor split-plot experiment was conducted in arid Northwestern China, to precisely control the amount and timing of fertilizer application using electric irrigation valves. The main plot was divided into two nitrogen (N) application rates of 240 N kg ha −1 (N1) and 300 N kg ha −1 (N2), and the split plots were divided into three N fertigation timings, which correspond to 10%(T1), 20%(T2) and 40%(T3) of the single irrigation rate, respectively. This study examined the response of N application rate and timing interaction to cotton-soil system, using the nitrogen use efficiency(NUE bala ), cotton yield and fiber quality as the primary indicators. The results indicated that (1)As the N application rate increased, the content of available N in each soil layer increased across all growth stages, and postponing the timing of nitrogen application was conducive to the distribution of ammonium N in soil of the cotton root zone and reduced the migration of nitrate N to the 40–60 cm soil layer. (2)Both elevating nitrogen application rates and postponing nitrogen application timing significantly influenced cotton biomass and nitrogen uptake during the vegetative-reproductive stage, concurrently promoting nitrogen distribution and accumulation in roots, stems, and bolls. (3)The partial productivity of N fertilizer(PFPN) was inversely proportional to the amount of fertilizer applied. Under low nitrogen condition, postponing the timing of nitrogen application significantly enhanced the PFPN and NUE bala . (4)The N2T3 treatment (high-N with late fertilization) exhibited the highest yield index; however, there was no significant difference was observed between N2T3 and N1T3 (low-N with late fertilization). Notably, the N1T3 treatment achieved equivalent cotton yield and quality to high-N treatments while maintaining low nitrogen input, demonstrating its potential as a sustainable irrigation and fertilization strategy under precision irrigation conditions.