LAUSR

1229 Rice (Oryza sativa L.) is a staple food in Asia, accounting for approximately 47.8 and 38.5% of the productivity and planting areas for cereal crops in 2011, respectively (FAO, 2014). To meet the growing demand for food due to population growth over the past several decades, great efforts have been made to breed new hybrid rice cultivars with higher yield potential to improve average farm yields (Huang et al., 2017). However, the resultant yield rice cultivars have generally required more resources such as N and water (Huang et al., 2017; Wang and Peng, 2017) and wider growth space to realize the yield potential in practice (Ahmad et al., 2008; Wang et al., 2014; Wang and Peng, 2017). Sparse planting methods help to alleviate the labor intensity of rice farmers who utilize traditional manual transplanting (Peng et al., 2009). However, with the growing number of farmers migrating from rural to urban areas for jobs (Levine et al., 2008), alternative rice planting methods that require less labor than traditional manual transplanting, such as direct-seeding and/or machine-transplanting, have been rapidly developed (Chen et al., 2017). Recently, dense planting with mechanical assistance has been considered a promising choice and recommended as a practice for achieving greater grain yield with less resource inputs for rice (Huang et al., 2018; Lin et al., 2009; Zhu et al., 2016), wheat (Triticum aestivum L.) (Li et al., 2016; Liu et al., 2016), canola (Brassica napus L.) (Wang et al., 2015), and maize (Zea mays L.) (Chang et al., 2016; Shi et al., 2016). High planting density may be more practical for direct-seeded and machine-transplanted rice than for traditional manual transplanting in practice, as it can be achieved easily with less labor (Huang et al., 2018; Wang et al., 2014). However, whether hybrid rice could maintain its superior yield over inbred cultivars in dense planting conditions is still unknown. In addition, hybrid rice seed is far more expensive than inbred rice; therefore, there is also a need to evaluate the economic gain for hybrid rice before adopting dense planting. A number of reports have been published on the effect of dense planting on crop grain yield and yield attributes. Liu et al. (2016) proposed that large-spike wheat would have greater Effect of Dense Planting of Hybrid Rice on Grain Yield and Solar Radiation Use in Southeastern China