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Developing mechanically dense transplanting of single seedlings for hybrid rice production in China
Monday, 2019/01/14 | 08:00:37
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Min Huang and Yingbin Zou | Jan 3, 2019 Rice Today
Figure 1: Total and hybrid rice planting area in China from 1975 to 2015. The linear regression was performed by plotting the hybrid rice planting area (y) versus the year (x) from 1995 to 2015. The data of total rice planting area were collected from the World Rice Statistics Database (IRRI, 2018). The data of the hybrid rice planting area for 1975 to 2013 were collected from Hu et al. (2016). The data of hybrid rice planting area for 2014 and 2015 were provided by Zhongxiao Hu of the China National Hybrid Rice Research and Development Center.
Rice production plays a critical role in achieving food self-sufficiency in China where more than 65% of the population eats rice as a staple food. In order to produce enough rice, many novel rice technologies have been successfullydeveloped and implemented in China. In particular, China was the first country to commercially exploit hybrid vigor (heterosis) in rice.
Why hybrid rice?
It is crucial to maintain or even increase the productivity of intensive cropping systems in China due to limited arable land per capita. In 2015, the arable land per capita in China was 0.08 ha, which was only 43% of the world average.
Why mechanical transplanting?
Although direct seeding provides obvious benefits such as saving labor, it also has the potential to (1) increase environmental and health risks due to more frequent herbicide application 2 to 3 times higher than other establishment methods per rice-growing season; and (2) reduce the yield because of the use of short-duration cultivars in intensive rice-based cropping systems.
In hybrid rice, direct seeding and mechanical transplanting can increase seed inputs and diminish the advantages of heterosis, e.g., hybrid rice produces smaller panicles. Both can influence the cultivar choices of rice farmers who might tend to favor cheaper inbred (non-hybrid) rice cultivars. There is an urgent need to develop rice establishment methods for hybrid rice and consequently reverse the declining trend of hybrid rice use in China. Thus, our research team chose to improve mechanical transplanting for hybrid rice production.
Why dense transplanting of single seedlings?
In 2012 and 2013, we conducted field experiments in Changsha in Hunan Province and in Chengmai in Hainan Province to determine the yield performance of hybrid rice grown under twelve combinations of hill density and seedlings per hill. The results showed that high grain yield and low seed inputs were concurrently achieved in hybrid rice grown under dense transplanting of single seedlings (H4S1) (see Figure 2 above). The high grain yield in hybrid rice grown under H4S1 occurred because a compatible relationship between panicles per unit land area and spikelets per panicle was established.
Another study we conducted showed that hybrid rice transplanted as single seedlings did not necessarily require more nitrogen fertilizer to produce high grain yield. These findings suggest that dense transplanting of single seedlings is a feasible way to achieve high grain yield and low seed inputs in hybrid rice production.
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