Optimizing micro-sprinkler water-nitrogen management improves winter wheat yield and nitrogen-use efficiency in the Huang-Huai-Hai Plain

Winter wheat is a staple crop critical for food security in the Huang‑Huai‑Hai Plain, where conventional intensive irrigation and nitrogen (N) fertilization have triggered severe groundwater depletion and deep‑layer soil nitrate‑N accumulation. Despite the promising potential of micro‑sprinkler irrigation for mitigating resource‑environment conflicts, it remains insufficiently understood how plant N status and stratified root architecture jointly shape grain yield (GY) and nitrogen‑use efficiency (NUE) under jointing‑anthesis supplemental irrigation. To address this gap, we conducted a two‑year split‑plot field experiment with two irrigation regimes (W0: rainfed; W2: 75 mm supplemental irrigation at jointing and anthesis) and five N application rates (N0: 0 kg N ha −1 , N1: 180 kg N ha −1 , N2: 240 kg N ha −1 , N3: 300 kg N ha −1 , N4: 360 kg N ha −1 ). Results showed that W2N2 achieved multi‑dimensional synergistic improvements in GY, NUE, water‑use efficiency (WUE) and economic benefits. Relative to the conventional high‑input W2N4 treatment, W2N2 increased GY by 8.90% and raised three core NUE metrics, including partial‑factor‑productivity of N by 63.37%, agronomic‑efficiency of N by 72.05%, and N recovery efficiency by 57.05%, while reducing nitrate‑N residue in the 100–200 cm soil layer by 58.32%. Partial‑least‑squares path modeling revealed divergent associative patterns: plant N status was the primary correlate of GY, whereas stratified root architecture constituted the dominant correlate of NUE. Under W2N2, targeted supplemental irrigation maintained the post‑anthesis N nutrition index (NNI) within the optimal range of 0.95–1.05 to support grain formation; meanwhile, it promoted stratified root architecture, enhancing the capacity to capture deep‑soil water and N and thereby improving NUE. This study provides framework‑based interpretive insights and puts forward testable mechanistic hypotheses to guide high‑yield, nitrogen‑efficient, and eco‑friendly winter‑wheat production on fluvo‑aquic soils.