To clarify the compensatory effect of increasing density on the yield of extremely late-sown wheat and screen the best combination of the sowing date and density of extremely late-sown wheat in the wheat area of northern Xinjiang, this study set three extremely late-sown dates of October 25 (D1), November 4 (D2), and November 14 (D3) and four densities of 337.5 (M1), 450 (M2), 562.5 (M3), and 675 kg·hm⁻² (M4). Additionally, the effects of the sowing date and density combinations on the formation process of the yield element spike number, spike grain number, and 1000-grain weight were analyzed in detail using the local conventional sowing date and density (25 September, 270 kg·hm⁻²) as the control (CK). The results showed that compared to the CK, increasing the planting density of extremely late-sown wheat compensated for the reduction in the number of harvested spikes due to low emergence rates. The young spikes were stunted due to a reduction in the number of grains per spike, and the grain grouting rate caused a reduction in the defects of the 1000-grain weight in order to increase the number of harvested spikes to improve yield. Under extremely late sowing conditions, D2M2 had the highest post-spring emergence rates, the highest number of harvested spikes, better development of young spikes and grain-filling, and non-significant declines in the number of grains per spike and 1000-grain weight, which balanced the contribution of the number of harvested spikes, number of grains per spike, and 1000-grain weight to the yield and gave the highest yield. After comprehensive yield factor analysis, sowing 450 kg·hm⁻² (1.00 × 10⁶ seeds·hm⁻²) on 4 November (pre-winter cumulative temperature of 47.5 °C) was determined to be the best combination for planting extremely late-sown wheat in the northern Xinjiang wheat area, and the results of this study can provide important theoretical and technical references for guaranteeing the yield of winter wheat in extremely late-sown winter wheat areas.

Late-sown wheat, which misses the optimal photoperiod and temperature for growth, suffers irreversible losses in both grain number per spike and thousand-grain weight, resulting in severe yield reductions. To this end, a two-year field experiment was conducted to evaluate the effects of application timing (S1 at the booting stage and S2 at the flowering stage) and concentration (T0 = 0 μmol L^–1, T1 = 376 μmol L^–1, T2 = 501 μmol L^–1, T3 = 626 μmol L^–1) on the photosynthetic physiology, grain number per spike, thousand-grain weight, and quality of late-sown wheat, aiming to elucidate the mechanism by which TiO₂ enhances the yield quality–efficiency relationship in wheat. The results showed that the foliar application of TiO₂ significantly enhanced the accumulation of photosynthetic pigments (SPAD) and spectroscopic indices (CHI, PRI) in wheat flag leaves, markedly improved the net photosynthetic rate, and increased the activities of antioxidant enzymes (SOD, POD) while reducing the accumulation of membrane lipid peroxidation products (MDA), with the T2 treatment exhibiting the most pronounced effect. Foliar application of TiO₂ at the S1 stage significantly increased the number of florets and spikelets, improved grain setting rates, and consequently boosted the grain number per spike. Application of TiO₂ during the S2 stage significantly enhanced grain filling rates, thereby increasing thousand-grain weight and achieving yield improvement. T2 demonstrated optimal performance under both conditions, enhancing grain storage capacity and morphological traits. This approach not only increased late-sown wheat yields but also improved grain quality indicators such as protein content, wet gluten, and sedimentation value. Therefore, applying 501 μmol L^–1 (T2) TiO₂ during the booting stage (S1) appears to be effective for achieving high yields and superior quality in late-sown wheat.

Xinjiang, a key grain production region in arid Northwest China, faces severe water scarcity and low agricultural water use efficiency. Although subsurface drip irrigation (SDI) has been widely studied for horticultural crops, a comprehensive synthesis focusing on SDI system design, water–fertilizer management, and soil–crop responses in wheat production under arid conditions remains limited. This knowledge gap restricts the development of optimized irrigation strategies for wheat cultivation in Xinjiang, where extreme aridity, widespread oasis agriculture, soil salinization risk, and the dominance of densely planted wheat create management requirements that differ from those of humid regions and horticultural production systems. Therefore, this review summarizes the development of SDI technology, its system design parameters, and integrated water–fertilizer management strategies, while systematically integrating recent advances in soil–crop–microbial interactions and resource use efficiency under arid conditions, which have rarely been synthesized in previous SDI reviews. Synthesizing current knowledge on the impacts of SDI on soil water dynamics, soil properties, microbial communities, crop root architecture, biomass production, and resource use efficiency, this review further discusses general advances in SDI in the context of their relevance to Xinjiang, with particular emphasis on how regional soil–climate conditions and wheat production practices influence system design, fertigation management, and field applicability. Multiple studies indicate that SDI can simultaneously reduce evaporation and deep percolation, mitigate surface salt accumulation, promote deeper root development, and improve crop productivity and resource use efficiency. However, high initial investment and maintenance costs, along with risks of emitter clogging, still hinder its large-scale adoption. For Xinjiang’s wheat and other densely planted crops, future research should prioritize optimizing subsurface drip irrigation (SDI) systems, as studies have shown that SDI can increase water use efficiency (WUE) by 20–30% and enhance crop yield by 10–15%, particularly under water-scarce conditions. The study’s findings are as follows: (1) optimize SDI system parameters for local soil–climate conditions, (2) elucidate the synergistic mechanisms between water–fertilizer coupling and soil–crop systems, and (3) develop cost-effective and durable system components. Importantly, these findings are particularly relevant for Xinjiang, where extreme aridity, soil salinization, and limited water resources require region-specific optimization of SDI systems. These efforts will support efficient and sustainable wheat production in Xinjiang and other arid regions.