Effects of nitrogen and phosphorus reduction on grain yield, quality, and soil biological properties in strong-gluten wheat varieties

To evaluate the effects of nitrogen (N) and phosphorus (P) reduction on grain yield, quality, and soil biological properties in strong-gluten wheat varieties, a three-year field experiment (winter wheat seasons from 2021 to 2024) was conducted in Henan province using three cultivars: Kexing 3302, Yuzhou 118, and Xinmai 26. The experimental design included four treatments: (1) conventional fertilization (CF: N/P₂O₅/K₂O = 240/135/135 kg hm^-2), (2) nitrogen reduction (RN: no N application in 2021-2022, and 30% N reduction relative to CF in 2022-2024, with P and K maintained at CF levels), and (3) phosphorus reduction (RP: no P application in 2021-2022, and 30% P reduction in 2022-2024, with N and K maintained at CF levels). Results indicated that N and P reductions had no significant effects on soil total N (TN), total P (TP), or organic matter content in the first year. However, under RN treatment, TN and TP at maturity were significantly lower than those under CF during the 2022-2023 growing season. Both N and P reductions decreased soil nitrate-N and ammonium-N concentrations. Soil enzyme activities (urease, invertase, and phosphatase) showed declining trends under nutrient reduction, with RN causing significantly greater reductions than CF. P reduction had no significant effect on yield across all three varieties, while N reduction had no impact in the first year but led to significant yield losses in the second and third years. These losses were primarily due to reduced spike numbers, with RN having a more pronounced negative effect than RP, which intensified over time. Grain processing quality under RP generally met the standards for strong- or medium-strong gluten wheat, whereas RN significantly reduced protein content (by 0.85%) and sedimentation value (by 4.49 mL) compared to CF. The negative impact of RN on quality parameters was greater than that of RP. Under current agroecological and soil fertility conditions, omitting N fertilizer in the first year and applying a 30% N reduction in the second year maintained grain yield and quality while increasing N partial factor productivity by an average of 26.24%. Similarly, omitting P in the first year and applying a 30% P reduction in the second and third years stabilized yield and quality while improving P partial factor productivity by an average of 34.45%. These findings offer empirical support for optimizing fertilizer strategies in strong-gluten wheat production systems.