Date Published: March 20, 2019
Publisher: Public Library of Science
Author(s): Jiana Chen, Fangbo Cao, Xiaohong Yin, Min Huang, Yingbin Zou, Jian Liu.
In order to solve the problem of labor shortage in double-season rice production areas, machine transplanting, as opposed to manual transplanting, has become the more popular alternative method in rice cultivation. However, the most existing late rice cultivars are not suitable for machine double-season rice cultivation due to their long duration of growth. Therefore, based on the previous studies we chose early season rice cultivars to meet the needs of machine double-season rice cultivation. In this study, field experiments were conducted during the late season in 2015 and 2016 in Liuyang County, Hunan Province, China. Grain yield and yield-related traits were compared among eight early-season cultivars (Liangyou 6, Lingliangyou 211, Lingliangyou 268, Zhuliangyou 819, Xiangzaoxian 32, Xiangzaoxian 42, Zhongjiazao 17, and Zhongzao 39) in 2015 and four cultivars (Lingliangyou 268, Zhuliangyou 819, Zhongjiazao 17, and Zhongzao 39) in 2016, selected from the highest yielding cultivars grown in 2015. Lingliangyou 268 produced 8–44% higher grain yield than did the other cultivars except Zhongjiazao17 in 2015. This higher grain yield was driven by grain weight and aboveground biomass. The greater aboveground biomass in Lingliangyou 268 was mainly attributed to higher apparent radiation use efficiency (aboveground biomass/incident solar radiation). Our study suggests that improvement in grain weight and apparent radiation use efficiency were critical to the high grain yield of early-season rice cultivars grown in late season under machine transplanting conditions.
Rice is the main staple food of the majority of China’s population. Faced with the continuous reduction of cultivated land area in China and continuous increase in food demand, stabilizing and increasing the planting area of double-season rice and increasing crop yields are important approaches to increase rice production . Soil and climatic conditions in the middle and lower reaches of the Yangtze River are ideal for planting double-season rice and thus is the most important rice production areas in China . Double-season rice cropping is considered an efficient method to improve multiple-crop index and total rice yield [1, 3, 4, 5]. However, the area of double cropping rice has decreased substantially in the last decade in China due to the massive transfer of rural labor , the shortage of seasonal labor in double-season rice production areas has become increasingly prominent. Thus, rice production urgently needs the development of planting methods such as machine transplanting to meet the needs of farmers lacking workers [7, 8].
Grain yield of early-season rice cultivars grown in the late season under machine transplanting ranged from 6.11 to 9.61 t ha–1 with total growth duration of 85 to 108 d across cultivars and years. All the cultivars completed heading before September 15. All tested cultivars can be planted in the late season. However, when taking into account the grain yield, data showed that Lingliangyou 268 produced relative higher grain yield in two years. Analysis of yield components indicates that higher grain weight was responsible for the higher grain yield in Lingliangyou 268. More importantly, the high grain weight was achieved not at the expense of panicle per m2 and panicle per number. The importance of grain weight in determining grain yield has been recognized by some researchers [13, 14]. However, some reports show that grain yield is determined by spikelets per m2 and/or spikelet number per panicle [10, 15, 16, 17]. The possible reasons for the discrepancies between this study and previous studies are different planting methods and cropping systems. There was a difference in grain yield between years for Zhongjiazao 17, which was lower in 2016 than in 2015. The lower grain yield of Zhongjiazao 17 in 2016 was mainly attributed to lower yield components and biomass production than in 2015. The difference in yield was probably due to the weak compensation mechanism of Zhongjiazao 17 .
Among the tested early-season rice cultivars, Lingliangyou 268 is better to adapt to machine transplanting in the late season. Selecting early-season rice cultivars grown under machine transplanting in the late season, they should meet the following requirements: (1) have high grain weight and (2) high apparent radiation use efficiency.