Conventional water and nitrogen (N) management practice in north China, comprising flood irrigation and N fertilizer broadcast (FB), limits sustainable wheat production. Drip fertigation (DF) has been widely adopted in wheat production in recent years and has effectively improved yields. However, the responses of the yield and quality to the N topdressing rate (NTR) under DF are still unclear. This study determined the responses of the wheat yield and quality to NTR under DF, as well as assessing whether DF could synergistically increase the yield and quality. A field experiment was conducted in north China for two seasons (2021–2023) using a split-plot design with three replicates. The main plot used the management practice (FB and DF) and the sub-plot had N treatment (no N applied, and NTRs of 0, 40, 80, 120, and 160 kg ha⁻¹ with 150 kg N ha⁻¹ as basal fertilizer, denoted as N0, T0, T40, T80, T120, and T160, respectively). Our results showed that high and saturated wheat yields (12.08 and 11.46 t ha⁻¹) were obtained under DF at T80, and the highest yields were produced at T160 (11.71 and 11.30 t ha⁻¹) under FB. Compared with FB, the greatest yield increase of 10.4–12.6% was achieved at T80 under DF. A higher spike number due to the increased effective stem percentage and a greater grain weight because of enhanced post-anthesis biomass production (BP_post) explained the improved yield under DF. The enhanced post-anthesis radiation use efficiency (RUE) led to the greater BP_post under DF. The enhanced specific leaf N, antioxidant capacity, and stomatal conductance under DF explained the higher light-saturated photosynthesis rate of flag leaves, which partly led to the increased post-anthesis RUE. NTR higher than 80 kg ha⁻¹ did not enhance the yield, but it significantly improved the gliadin and glutelin contents, thereby leading to a higher total protein content, better gluten characteristics, and superior processing quality. Therefore, drip fertigation is a practical strategy for increasing both yield and quality with reduced water input and appropriate N input in irrigated winter wheat in north China. Applying 80 kg ha⁻¹ of NTR under drip irrigation produces a high yield, but further gain in grain quality needs a higher NTR.

Drip fertigation (DF) can improve yield, water use efficiency (WUE), and nitrogen use efficiency (NUE, grain production per unit of the sum of soil inherent mineral N and fertilizer N), as well as reduce the risk of environmental pollution compared with flood irrigation and N fertilizer broadcast (FB). Previously, we showed that DF enhanced the response of the yield to the N topdressing rate (NTR), but the underlying mechanisms associated with the soil N supply, root architecture, and N uptake remain unclear. We conducted a field experiment by testing six N treatments (no N applied, and NTRs of 0, 40, 80, 120, and 160 kg ha⁻¹, denoted as N0, T0, T40, T80, T120, and T160, respectively) under DF and FB from 2021 to 2023. Compared with FB, the NUE and WUE were 4.8–4.9% and 10.0–10.5% higher under DF. The higher NUE was due to an improvement in N uptake efficiency (6.1–7.7%) resulting from the enhanced aboveground N uptake (AGN). The greater AGN under DF was attributed to the higher soil N availability at the soil depth of 0–40 cm. DF decreased the residual soil NO₃⁻-N at a depth of 40–200 cm but increased the NO₃⁻-N at a depth of 0–40 cm. In addition, DF combined with T80 achieved high root length density, surface density, and dry weight density and improved NUE and WUE. DF combined with T80 achieved high yield and efficient utilization of water and N, and the NTR threshold was 61.75–119.50 kg ha⁻¹, in which the production conditions were similar to those of the experimental site. Our results provide a reference for high-efficiency water and N fertilizer usage for irrigated winter wheat production in North China.

The composition and form of selenium in the soil have significant effects on the selenium content of crops. In this study, we investigated the selenium absorption pathway in plants by studying the interaction between nitrogen fertilizer and soil selenium. Our results showed that the selenium concentration enrichment factors (CEF) varied within the same region due to nitrogen fertilizer application, where they ranged from 1.33 to 5.02. The soil selenium flow coefficient (mobility factor, MF) increased with higher nitrogen application rates. The sum of the MF values for each soil layer treated with nitrogen application rates of 192 kg hm⁻² and 240 kg hm⁻² was 0.70, which was 64% higher than that for the control group with no nitrogen application. In the 0–20 cm soil layer, the highest summed water-soluble and exchangeable selenium and relative percentage of total selenium (12.45%) was observed at a nitrogen application rate of 240 kg hm⁻². In the 20–40 cm soil layer, the highest relative percentage content of water-soluble and exchangeable selenium and total selenium (12.66%) was observed at a nitrogen application rate of 192 kg hm⁻². Experimental treatment of black wheat with various concentrations of sodium selenite showed that selenium treatment at 50 μmol L⁻¹ significantly increased the reduced glutathione (GSH) levels in the leaves and roots of seedlings, where the GSH contents increased by 155.4% in the leaves and by 91.5% in the roots. Further analysis of the soil–black wheat system showed that nitrogen application in selenium-rich areas affected the soil selenium flow coefficient and morphological composition, thereby changing the enrichment coefficient for leaves (0.823), transport capacity from leaves to grains (–0.530), and enrichment coefficient for roots (0.38). These changes ultimately affected the selenium concentration in the grains of black wheat.