Effects of skip-row planting on grain yield and quality of mechanized ratoon rice

Decreases in grain yield and milling quality in the ratoon crop due to crushing damage to stubbles from mechanical harvesting of the main crop constrain the further extension of mechanized rice ratooning technology. Skip-row planting (SP), where the track zone is left untransplanted in the main crop to provide traffic paths for harvest machines, might be effective to alleviate these constraints by avoiding the crushing damage. However, it is remains unclear if border effects could compensate for the yield loss due to decreased planting density from SP in both the main and ratoon crops, and if SP could improve the milling quality of the ratoon crop. To address these questions, a SP pattern with 33.3% decrease in planting density was compared to conventional planting (CP) pattern in field experiments on mechanized ratoon rice in 2018 and 2019. Compared with CP, the grain yield of the main and ratoon crops in SP was reduced by 4.8% and increased by 4.6%, respectively. The large decrease in planting density from SP did not affect grain yield substantially because of the border effects on grain yield in the rows next to traffic paths in both crops. Panicle number, spikelet number panicle−1, and total dry weight were responsible for the border effects on grain yield in the main crop, whereas panicle number and total dry weight were responsible for the border effects on grain yield in the ratoon crop. Milling quality of the ratoon crop was improved by SP, and the improvement in head rice rate was 2.5–7.0% compared with CP. Our results suggest that SP is effective for improving milling quality of the ratoon crop in mechanized rice ratooning system by avoiding the crushing damage, while maintaining high grain yield of the two crops due to the border effects.