Border effects of the main and ratoon crops in the rice ratooning system

Abstract

The border effect (BE) is widely observed in crop field experiments, and it has been extensively studied in many crops. However, only limited attention has been paid to the BE of ratoon rice. We conducted field experiments on ratoon rice in Qichun County, Hubei Province, Central China in 2018 and 2019 to compare the BE in the main and ratoon crops, and to quantify the contribution of BE in the main crop to that in the ratoon crop. The BE of two hybrid varieties was measured for the outermost, second outermost, and third outermost rows in each plot of both crops. To determine the contribution of BE between the two crops, portions of hills in the outermost and second outermost rows were uprooted during the harvest of the main crop so that the second and third outermost rows then became the outermost rows in the ratoon crop. Overall, the BE on grain yield was greater in the main crop than in the ratoon crop. In the main crop, the BE on grain yield was 98.3% in the outermost row, which was explained by the BE on panicles m−2, spikelets/panicle, spikelets m−2, and total dry weight. In the ratoon crop, the BE on grain yield was reduced to 60.9 and 27.6% with and without the contribution of the BE in the main crop, respectively. Consequently, 55.1% of the BE on grain yield in the ratoon crop was contributed from the main crop. High stubble dry weight and non-structural carbohydrate (NSC) accumulation at the harvest of the main crop were responsible for the contribution of BE in the main crop to that in the ratoon crop. Our results suggest that increases in stubble dry weight and NSC accumulation at the harvest of the main crop could be important strategies for developing high-yielding cropping practices in the rice ratooning system.