Enhancing wheat grain weight is a crucial strategy for improving yields in the Huaibei Plain (HP), China. However, the impacts and regulatory mechanisms of different irrigation regimes on wheat grain formation in the HP remained poorly understood. Therefore, a two-year field experiment was conducted to explore three treatments on wheat’s source–sink relationship and grain formation: rain-fed (RI, no irrigation, 202.5 kg ha^–1 N applied at sowing), conventional flood irrigation (CI, 60 mm irrigation at jointing stage, 112.5 kg ha^–1 N at sowing+90 kg ha^–1 N with irrigation), and micro-sprinkler irrigation (MI, irrigation based on 0–40 cm soil layer water deficit at jointing, booting and anthesis stages, 112.5 kg ha^–1 N at sowing+30 kg ha^–1 N at each irrigation). The results indicated that, compared with RI and CI, MI significantly increased chlorophyll content and enhanced sucrose phosphate synthase (SPS) activity in the flag leaf at 4 days after anthesis (DAA 4), and these parameters in CI were higher than those in RI. The sucrose and soluble sugar content in the grain of MI were the highest at DAA 4. Additionally, at DAA 4, compared with RI, both CI and MI significantly elevated the content of indole propionic acid+zeatin nucleoside (IPA+ZR) and gibberellin (GA) in grain, while reducing the content of auxin (IAA) and abscisic acid (ABA). And the highest number of endosperm cells was observed in MI. At the grain-filling stage, MI exhibited the slowest chlorophyll degradation rate and the highest activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and SPS in the flag leaf, resulting in more sugar accumulation in the leaf and grain. Moreover, MI showed the highest IAA and lowest ABA levels in grain and maintained the highest starch synthase activity during the filling stage, thereby promoting starch accumulation. Compared to CI and RI, MI significantly increased 1,000-grain weight by 4.99–5.55% and 7.33–11.51%, and grain yield by 4.99–11.60% and 15.60–39.14% over the two years, respectively. Overall, micro-sprinkler irrigation can optimize the water and nitrogen supply for wheat, effectively enhancing the source capacity in the early stage and the sink capacity in the late stage of grain development, thereby increasing grain weight and achieving high yield in the HP.

Increasing the grain yield (GY) and water use efficiency (WUE) of winter wheat in the Huaibei Plain (HP), China are essential. However, the effects of micro-sprinkler irrigation and topsoil compaction after wheat seed sowing on the GY and WUE are unclear. Therefore, a two-year field experiment was conducted during the 2021–2023 winter wheat growing seasons with a total six treatments: rain-fed (RF), conventional irrigation (CI) and micro-sprinkler irrigation (MI), as well as topsoil compaction after seed sowing under these three irrigation methods (RFC, CIC, and MIC). The results in the two years indicated that MI significantly increased GY compared to CI and RF, by averages of 17.9 and 42.1%, respectively. The increase in GY of MI was due to its significant increases in the number of spikes, kernels per spike, and grain weight. The chlorophyll concentration in flag leaves of MI after the anthesis stage maintained higher levels than with CI and RF, and was the lowest in RF. This was due to the dramatically enhanced catalase and peroxidase activities and lower malondialdehyde content under MI. Compared with RF and CI, MI significantly promoted dry matter remobilization and production after anthesis, as well as its contribution to GY. In addition, MI significantly boosted root growth, and root activity during the grain-filling stage was remarkably enhanced compared to CI and RF. In 2021–2022, there was no significant difference in WUE between MI and RF, but the WUE of RF was significantly lower than that of MI in 2022–2023. However, the WUE in MI was significantly improved compared to CI, and it increased by averages of 15.1 and 17.6% for the two years. Topsoil compaction significantly increased GY and WUE under rain-fed conditions due to improved spike numbers and dry matter production. Overall, topsoil compaction is advisable for enhancing GY and WUE in rain-fed conditions, whereas micro-sprinkler irrigation can be adopted to simultaneously achieve high GY and WUE in the HP.