Background Timely sowing is an important agronomic measure to ensure the normal germination, stable seedling establishment, and yield formation for winter wheat (Triticum aestivum L.). Delayed sowing frequently occurs in the current multi-cropping system and mechanized production of this crop. However, the ways in which different sowing dates affect yield and its potential mechanism is still unknown in the middle-lower Yangtze River Basin. We sought to provide a theoretical basis for these mechanisms to improve regional wheat production. Methods We investigated the wheat’s yield differences in a two-year field study under different sowing dates and took into account related growth characteristics including meteorological conditions, growth period, tillers, dry matter accumulation (DMA), and nitrogen accumulation (NA). We used the logistic curve model to simulate DMA and NA dynamics of single stem wheat under different sowing dates. We then analyzed and compared wheat accumulation for different sowing dates. Results Our results showed that grain yield declined by 0.97 ± 0.22% with each one-day change (either early or delayed) in sowing beyond the normal sowing date. The yield loss could be explained by the inhibition of crop growth, yield components, biomass and nitrogen (N) production. The negative effects of delayed sowing were caused by environmental limitations including adverse weather factors such as low temperature during vegetative growth, shortened duration of various phases of crop development, and increased temperature during the grain-filling period. The grain yield gap decreased between the late and normal sowing periods owing to a compensatory effect between the highest average rates (Vt) and the rapid accumulation period (T) of DMA and NA for single stem wheat. The grain yield was maintained at 6,000 kg ha−1 or more when the ratio of DMA at the mature-to-jointing stage (MD/JD) and the ratio of NA at the mature-to-jointing stage (MN/JN) was 4.06 (P < 0.01) and 2.49 (P < 0.05), respectively. The compensatory effect did not prevent the impact caused by delayed sowing, which caused biomass and N production to decrease. Physiological development reached a maximal accumulation rate (Tm) of NA earlier than DMA.

Economic consumption and environmental impacts due to potassium (K) inputs in agriculture are gaining increasing attention. It is urgent to improve K use efficiency (KUE) for agricultural development. Delayed sowing has been shown to maintain grain yield in winter wheat. Still, there needs to be more information regarding the effect of sowing date on crop K status evaluated by the K nutrition index (KNI), KUE, K uptake efficiency (UPE), K utilization efficiency (UTE), and grain K concentration (GKC). Here, we assessed Shannong23 and Tainong18 winter wheat cultivars with three sowing date treatments composed of 26 September (early sowing), 8 October (normal sowing), and 22 October (late sowing) in the 2021–2022 and 2022–2023 growing seasons. The influences of sowing date on the KNI, tillering, grain yield formation, KUE, UPE, UTE, K transport, and GKC were examined. Our study indicated that late sowing in winter wheat was an almost optimal K nutritional situation, whereas early and normal sowing were under situations of excess K. As sowing was delayed, aboveground K uptake (AGK), UPE, and spike number per unit area decreased; UTE and grain number per spike increased; and grain yield and KUE were unchanged. A positive correlation between KNI and UPE and spike number per unit area and a negative correlation between KNI and UTE and grain number per spike were found, whereas no significant correlation between KNI and KUE was observed. Late sowing promoted K transport from pre-anthesis accumulation in vegetative organs to grain, resulting in a higher GKC, which could lead to high grain quality and K recovery. Therefore, late sowing winter wheat can use K more efficiently and increase GKC, implying that delayed sowing can reduce K input, favoring sustainable agriculture development.

Global warming increases the risk of pests and weeds before wintering, and decreases the grain yield of winter wheat. Therefore, the sowing date should be delayed properly. But the variety of winter wheat that can adapt to late sowing remains unclear. Here, we selected two winter wheat cultivars and evaluated four sowing date treatments on 1 October (early sowing), 8 (normal sowing), 15 (late sowing) and 22 (latest sowing) over two wheat-growing seasons at the experimental Station of Shandong Agricultural University (35°96′N, 117°06′E), Daiyue District, Taian, Shandong, China. We examined the effects of sowing date on a few traits, and found that, compared with normal sowing, though spike number decreased, grain yield was maintained above 9300 kg/ha under late and latest sowing. The main reason was that the more accumulated N from jointing to anthesis resulted in a higher grain number per spike. The higher net photosynthetic rate after anthesis, through optimizing N distribution in the canopy and increasing Rubisco content of flag leaves, improved dry matter accumulation rate and contribution ratio of vegetative organs, ultimately, ensured consistent grain weight. The grain yield of high-tillering winter wheat cultivars decreased from 9370 to 8346 kg/ha. The main reason was that spike number, accumulated N from jointing to anthesis and net photosynthetic rate decreased significantly, which reduced the dry matter accumulation rate, and only satisfied less grains to achieve consistent grain weight. Therefore, low-tillering winter wheat cultivars are more adaptable to late sowing, and can reduce the harm of global warming.

Highlight: Optimal N allocation at several integration levels accounts for improved canopy PNUE while maintaining high grain yield in winter wheat Improving canopy photosynthetic nitrogen-use efficiency ( PNUE ) may maintain or even increase yield with reduced N input. In this study, later-sown winter wheat was studied to reveal the mechanism underlying improved canopy PNUE while maintaining high yield. N allocation at several levels was optimised in late-sown wheat plants. N content per plant increased. Increased N was allocated to the flag leaf and second leaf, and to ribulose-1, 5-bisphosphate carboxylase/oxygenase ( Rubisco ) in upper leaves. Constant or reduced N was allocated to leaf 3, leaf 4, and Rubisco in lower leaves. The specific green leaf area nitrogen ( SLN ) of upper leaves increased, while that of lower leaves remained unchanged or decreased. N allocation to the cell wall decreased in all leaves. As a result, the maximum carboxylation rate of upper leaves increased, and that of lower leaves remained constant or decreased. CO ₂ diffusion capacity was enhanced in all leaves. Outperformance by light-saturated net photosynthetic rate ( P _max ) over SLN led to improved PNUE in upper leaves. Enhanced Pmax coupled with unchanged or decreased SLN resulted in improved PNUE in lower leaves. High yield was maintained because enhanced photosynthetic capacity at the leaf and whole plant levels compensated for reduced canopy leaf area.