Can Increased Density Compensate for Extremely Late-Sown Wheat Yield?

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.