Objectives Medium-low yield farmlands in North China are characterized by significant spatial variability in soil nutrients and untapped yield potential. We take use of intelligent machine to conduct precised stratified fertilization, in order to realize the simultaneous improvement of yield, fertilizer use efficiency, and grain quality of wheat.

Method An intelligent stratified fertilization machine was developed based on prior experimental data. Field trials were conducted in Ningjin and Quzhou, Hebei Province, comparing six fertilization strategies: farmers' conventional practice (MF1), single-layer optimized NPK application (MF2), full NPK in two layers (MF3), two-layer NP + three-layer K (MF4), two-layer NK + three-layer P (MF5), and two-layer N + three-layer PK (MF6). Flag leaf SPAD values and photosynthetic parameters were measured during grain filling. Biomass and NPK contents were analyzed at jointing, flag leaf emergence, grain filling, and maturity stages. Yield components, grain yield, and protein fractions (albumins, globulins, glutenins) were evaluated at harvest. A structural equation model (SEM) was used to dissect the mechanistic linkages between fertilization strategies, physiological traits, and yield-quality outcomes.

Results Compared with MF2, all the stratified fertilization improved the values of photosynthetic parameters, and MF6 treatment increased the most; Stratified fertilization increased N, P, and K accumulation in the above-ground parts of wheat across jointing to maturity period by 7.37%−25.54%, 9.38%−30.55%, and 0.74%−21.53%, respectively, and increased wheat yield by 5.14%−12.74%; MF5 and MF6 treatments significantly increased the albumin, globulin, and glutenin contents by 26.67%−38.01%, 21.88%−36.67%, and 9.64%−24.25%, respectively, thus enhanced glutenin-to-gliadin ratio by 1.57%−4.80%. According to the analysis results of structural equation model, stratified fertilization directly influenced wheat leaf SPAD values, dry matter accumulation, and NPK accumulation, thereby indirectly affected leaf photosynthesis, grain yield, and quality. The comprehensive evaluation scores of nutrient accumulation, yield, and quality in MF6 and MF5 treatments ranked the top two among the treatments.

Conclusion Stratified fertilization effectively promoted wheat leaf photosynthesis, increased nutrient uptake, thereby enhanced wheat yield and grain protein quality. Under the same fertilizer application amount, stratified fertilization further improved wheat yield by 5.14%−12.74%, and the grain quality.