Heavy soil drying during mid-to-late grain filling stage of the main crop to reduce yield loss of the ratoon crop in a mechanized rice ratooning system

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.