Labor scarcity requires double-season rice to be planted by direct seeding as an alternative to transplanting. Only ultrashort-duration varieties can be used in direct-seeded, double-season rice (DSD) in central China where thermal time is limited. Whether ultrashort-duration varieties grown in DSD can be as productive and efficient in nitrogen (N) use as transplanted double-season rice (TPD) remains unclear. Field experiments were conducted in Hubei province, central China with two establishment methods (DSD, TPD) and three N rates in the early and late seasons of 2017 and 2018. Nitrogen treatments included zero-N control (N0), total N rate of 60 kg N ha⁻¹ with equal splits at basal, midtillering, and panicle initiation (N1), and weekly N application at 15 kg ha⁻¹ from seeding/transplanting to heading (N2). Both early- and late-season rice under DSD matured within 95 days, on average 9 days shorter than rice under TPD. The grain yield of DSD was comparable to or higher than that of TDP in both seasons, although the daily yield was significantly higher under DSD than under TDP. Before heading, DSD had higher leaf area, stem number, intercepted radiation, and radiation use efficiency than TPD, which compensated for the negative effect of short growth duration on biomass production. Total dry weight and harvest index under DSD were comparable to or higher than those under TDP. In general, the recovery efficiency of fertilizer-N under DSD was higher than that under TPD, but the reverse was true for physiological N use efficiency. Thus, there was no significant difference in agronomic N use efficiency between DSD and TPD. These results suggested that DSD with ultrashort-duration varieties is a promising alternative to TPD in central China for maintaining high grain yield and N fertilizer use efficiency with less labor input.

Yield loss (Y_Loss) in the ratoon crop due to crushing damage to left stubble from mechanical harvesting of the main crop is a constraint for wide adoption of mechanized rice ratooning technology. Soil drying before the harvest of the main crop has been proposed to overcome this problem. The objective of this study was to determine the effect of soil drying during the mid-to-late grain filling stage of the main crop on grain yield of the ratoon crop in a mechanized rice ratooning system. Field experiments were conducted to compare Y_Loss between light (LD) and heavy (HD) soil drying treatments in Hubei province, central China in 2017 and 2018. Y_Loss was calculated as the percentage of yield reduction in the ratoon crop with the main crop harvested mechanically, relative to the grain yield of the ratoon crop with the main crop harvested manually. In comparison with LD, soil hardness was increased by 42.8%–84.7% in HD at the 5–20 cm soil depth at maturity of the main crop. Soil hardness at 5 and 10 cm depths reached respectively 4.05 and 7.07 kg cm⁻² in HD. Soil drying treatment did not significantly affect the grain yield of the main crop. Under mechanical harvesting of the main crop, HD increased the grain yield of the ratoon crop by 9.4% relative to LD. Consequently, Y_Loss was only 3.4% in HD, in contrast to 16.3% in LD. The differences in grain yield and Y_Loss between the two soil drying treatments were explained mainly by panicles m⁻², which was increased significantly by HD in the track zone of the ratoon crop compared with LD. These results suggest that heavy soil drying practice during the mid-to-late grain filling stage of the main crop is effective for reducing Y_Loss of the ratoon crop in a mechanized rice ratooning system.