Feasibility of Improving Unmanned Aerial Vehicle-Based Seeding Efficiency by Using Rice Varieties with Low Seed Weight

Wang Xinyu, Yang Guodong, Pan Xiangcheng, Xiang Hongshun, Peng Shaobing, Xu Le

Letter

Feasibility of Improving Unmanned Aerial Vehicle-Based Seeding Efficiency by Using Rice Varieties with Low Seed Weight

Wang Xinyu, Yang Guodong, Pan Xiangcheng, Xiang Hongshun, Peng Shaobing, Xu Le

()

Unmanned aerial vehicle (UAV) has offered a promising platform for rice direct seeding that can substantially reduce labor input in the crop establishment process. However, the insufficient payload capacity of UAV-based seeders is currently limiting its intensive and large-scale use for rice direct seeding. This study indicated a large variation in seed weight across varieties, ranging from 15.0 to 36.5 mg and 14.0 to 31.3 mg for inbred and hybrid varieties, respectively, with average seed weights of 25.3 mg for inbred and 24.7 mg for hybrid varieties. Seed weights of 160 out of 4 106 inbred varieties and 17 out of 311 hybrid varieties ranged from 15.0 to 20.0 mg. Reducing seed weight from 25.0 to 15.0 mg increased the seeding area per UAV flight by 67% regardless of inbred and hybrid varieties, although the absolute increase in seeding area for hybrid variety was greater than that for inbred variety because of the difference in seeding rate. The grain yield of inbred varieties was reduced when the seed weight was less than 24 mg. Moreover, 87% of inbred varieties with a seed weight ≤ 20 mg were distributed in South China where rice consumers prefer small rice grains. Therefore, the use of low-seed-weight inbred varieties for improving UAV seeding efficiency might be considered in South China. Unlike inbred rice, 64% of hybrid varieties had higher grain weights compared with their seed weights, and reducing seed weights did not necessarily cause yield loss. Therefore, the small-seed-and-large-grain strategy in hybrid rice could be used for improving UAV seeding efficiency without yield loss. This strategy can be considered for improving UAV seeding efficiency in rice production regions other than South China.

The majority of rice crop in China is established by transplanting that is labor-, water- and energy-intensive (Peng et al, 2009; Kumar and Ladha, 2011; Liu et al, 2015). Rapid urbanization and natural resource scarcity are driving a major shift in rice crop establishment method from transplanting to direct seeding in recent years (Peng, 2014; Xu et al, 2022). Until now, direct-seeded rice accounts for about 30% of the total planting area in China (Dai et al, 2020).

Rice direct seeding is primarily done by manual broadcast in China (Luo and Wang, 2014). In the United States, direct seeding is mostly done by broadcasting seeds in standing water using airplanes or mechanical drilling in dry soil (Kumar and Ladha, 2011; Zhang et al, 2018). Scientists and technicians in China have invested heavily in developing on-ground rice seeding machines and their corresponding crop managements in recent years (Zhang et al, 2018, 2021). However, the extension of the rice seeding machines is quite limited and the number of rice seeding machines in China is only 24200 currently (China Agriculture Yearbook Editorial Committee, 2019). Therefore, there is still tremendous opportunities to reduce labor input and to improve rice production efficiency through the mechanization of direct seeding (Zhang and Gong, 2014).

Recently, technology advances in UAV have provided a promising platform for rice direct seeding by the means of broadcasting or seeding in lines(Diao et al, 2020; Xiao et al, 2021). Compared with airplanes and on-ground seeding machines, UAV-based seeders largely bring the adaptability and flexibility for small fields with a variety of terrains and irregular shapes, because UAV-based seeders can conduct the autonomous operations by planning the routine of flight campaign ahead (Li et al, 2016; Wu et al, 2020). UAV-based seederscan also largely improve seeding efficiency compared to on-ground seeding machines (Li et al, 2016). Diao et al (2020) stated that the average seeding efficiency of UAV-based seeders can be increased by more than five times compared with that of the on-ground seeders. Several on-farm studies have proved the feasibility of UAV-based direct seeding for rice production (Li et al, 2016; Wu et al, 2020). However, most UAV-based seeders are powered by electric batteries,which restricts the payload capacity to less than 15 kg (Yang et al, 2018; Xiao et al, 2021). Insufficient payload capacity of UAV-based seeders is the major factor limiting its intensive and large-scale use for rice direct seeding. Despite the payload or battery capacity might be improved through the advancement in engineering technology, it is worthwhile to explore the feasibility of improving the UAV-based seeding efficiency by selecting rice varieties with low seed weights.

For inbred rice,grain weight is approximately equal to its seed weight, while the grain weight of hybrid rice is often different from its seed weight due to genetic changes (Xu E B et al, 2015; Tang et al, 2020). Decreasing grain weight might cause the reduction of rice yield to some extent (Xu Q et al, 2015). In addition, rice consumers have their preference for certain grain size (Liu et al, 2010). Therefore, when inbred rice varieties with low seed weights are used for improvingthe UAV-based seeding efficiency, grain yield and local consumers’ preference for grain size should be taken into consideration. For hybrid rice, this is not a problem because one can choose hybrid varieties with small seed weight and large grain weight (thereafter refers to small-seed-and-large-grain strategy) (Tang et al, 2020). Previous studies have found significant genotypic variations in grain weight among both traditional and improved rice varieties (Anandan et al, 2011; Xu Q et al, 2015). However, the information is limited about the seed weight distribution of commercial inbred varieties in China. Furthermore, there is a lack of comprehensive analysis on the difference between seed weight and grain weight for commercial hybrid varieties in China. Based on the data of China National Rice Database (RiceData, 2021), we assessed the feasibility of improving UAV-based seeding efficiency by using varieties with low seed weight for both inbred and hybrid varieties. This study aimed to(1) determine the seed weight distribution of commercial inbred and hybrid rice varieties in China,(2) quantify the increased magnitude in UAV-based seeding efficiency by using inbred varieties with low seed weight, (3) assess the feasibility of using small-seed-and-large-grain strategy in hybrid varieties for improving UAV-based seeding efficiency, and (4) determine whether low seed weight has a negative impact on grain yield.

Table 1. Number, minimum, median, mean, maximum and coefficient of variation (CV) for seed weight of inbred varieties, and seed and grain weights of hybrid varieties in China.

A large variation in seed weight was observed across 4 417 inbred and hybrid varieties. The seed weight of inbred and hybrid varieties ranged from 15.0 to 36.5 mg and 14.0 to 31.3 mg, respectively (Table 1).In inbred varieties, the median and mean seed weights were 25.5 and 25.3 mg, respectively. In hybrid varieties, the median and mean seed weights were 25.0 and 24.7 mg, respectively. Seed weights of 3 561 out of 4 106 inbred varietiesand 268 out of 311 hybrid varietiesranged from 22.0 to 28.0 mg (Fig. 1-A and -B), while 160 out of 4 106 inbred varieties and 17 out of 311 hybrid varietieshad a seed weight of 15.0–20.0 mg (thereafter seed weight ≤20.0 mg refers to low-seed-weight varieties). These results suggested that low-seed-weight varieties are available for improving the UAV-based seeding efficiency. The seeding area could be increased substantially with a decrease in seed weight based on our scenario assessment, especially for hybrid varieties due to lower seeding rate compared with inbred varieties (Fig. 1-C). In inbred varieties, compared to those with the seed weight of 25.0 mg, the use of the varieties with the seed weight of 15.0 mg increased the seeding area per payload from 0.400 to 0.667 hm2based on UAV seeder’s payload capacity of 15 kg and seeding rate of 150 seeds/m2. In hybrid varieties, compared to those with the seed weight of 25.0 mg, the use of the varieties with the seed weight of 15.0 mg increased the seeding area per payload from 1.000 to 1.667 hm2based on UAV seeder’s payload capacity of 15 kg and seeding rate of 60 seeds/m2. The seeding efficiency was increased by 67% regardless of inbred and hybrid varieties when seed weight was reduced from25.0 to 15.0 mg.

Fig. 1. Seed weight distribution of inbred (A) and hybrid (B) rice varieties, effect of seed weight on seeding area per payload by unmanned aerial vehicle (C), and relationship between grain weight and seed weight for hybrid rice varieties (D) in China.

Grain weight is an important yield component(Xu Q et al, 2015; Chen et al, 2020). We evaluated the relationship between seed weight and grain yield for all commercial inbred and hybrid varieties. Our results indicated that the grain yield of an inbred variety was reduced when seed weight was lower than 24.0 mg (Fig. S1). Therefore, one must be cautious when an inbred variety with low seed weight is used to improve UAV-based seeding efficiency. However, inbred varieties with low seed weight of 16.0–19.0 mg are commonly planted in South China such as Guangxi Province (Chen et al, 2017). This is also supported by the fact that 87% of China’s inbred varieties with seed weight ≤ 20.0 mg are distributed in South China (Fig. S2). In addition to the preference of local consumers for small size of rice grains (Liu et al, 2010), inbred varieties with low seed weight are often planted in South China to overcome high temperature stress (Chen et al, 2017). High temperature often occurs during the ripening phase of early-season rice and deteriorates grain quality by increasing chalkiness in South China (Shi et al, 2015; Kong et al, 2017). Reducing seed weight to less than 18.0 mg has been advocated as an important breeding strategy for mitigating the negative impact of high temperature on rice grain quality (Su, 2001).

The grain weights of hybrid varieties were positively related with their seed weights, but the seed weights only explained about 22% variation of the grain weights (Fig. 1-D). Minimum, median, mean and maximum values of seed weights were all lower than those of grain weights in hybrid varieties(Table 1). Among 311 hybrid varieties, 64% had lower seed weights compared with their grain weights (Fig. S3). Grain weights of hybrid varieties are generally higher than those of their parents due to heterosis (Yuan, 2002). Zeng et al (1979) reported that out of 34 hybrid varieties, 23 show higher grain weight than the parent with higher grain weight. In a study conducted by Jiangxi Academy of Agricultural Sciences in China, 68% of 400 hybrid varieties showed positive heterosis in grain weight (Yuan, 2002). These results suggested that seed weights are generally lower than grain weights in hybrid varieties because the seed weights of hybrid varieties are the same as the grain weights of male sterile lines (the female parents) (Xu E B et al, 2015). It was found that the seed weight of hybrid varieties was not necessarily associated with their yield performance (Fig. S1). Low-seed-weight hybrid varieties could also achieve high grain yield (Fig. S1 and Table S1). For example, three hybrid varieties with low seed weight, Zhuoliangyou 0985, Lijingyou 570 and Linyou 1005, had the grain weight of 22.4, 21.9 and 26.5 mg and produced a relatively high grain yield of 10.21, 8.99, and 8.34 t/hm2in the middle, early and late seasons, respectively. The yield levels of 8.5 and 10.0 t/hm2were similar to previous studies on hybrid varieties in the early/late and middle seasons, respectively (Zhang et al, 2009; Zhou et al, 2018). Therefore, the phenomenon of small-seed-and-large-grain in hybrid rice could be used for improving UAV-based seeding efficiency without the negative impact on grain yield.

In rice production, inbred varieties with high seeding rates are commonly practiced by farmers to mitigate undesirable seed germination under unfavorable environmental conditions (Farooq et al, 2011), and farmers generally use lower seeding rate for hybrid than inbred varieties to save seed cost (Peng, 2016). Previous study have confirmed that the seeding rate of hybrid varieties can be reduced from 150 to 60 seed/m2without yield penalty, but the grain yield of inbred varieties decreases significantly under the same conditions (Sun et al, 2015).Morphological advantages of heterosis, such as early vigor, high tillering capacity, large leaf area index and more spikelet number per panicle can compensate for the negative effects of decreased seeding rate on panicle number and grain yield in hybrid rice (Sun et al, 2015; Peng, 2016), which explained why the recommended seeding rates of hybrid varieties can be less than half that of inbred varieties under direct-seeded conditions (Huang, 2022). In fact, high seeding rates limit individual plant growth and increase lodging risk under direct-seeded conditions, which is not suitable for achieving high grain yield in hybrid varieties (Wang et al, 2014). However, the negative consequences of low seeding rate in hybrid varieties, such as high weed infestation or poor crop establishment, should be overcome to prevent yield loss (Sun et al, 2015). Moreover, Lin et al (2014) reported that seed weight is not necessarily related to rice seed vigor and seedling emergence. Therefore, the use of hybrid instead of inbred varieties offers a promising way for increasing UAV-based seeding efficiency due to low seeding rate and the phenomenon of small-seed-and-large-grain in hybrid rice.

In this study, large genotypic variability in seed weight was observed among commercial inbred and hybrid rice varieties in China, in which low-seed-weight varieties (≤ 20.0 mg) were available to increase the seeding area per UAV flight. Considering that the grain yield of inbred varieties might be reduced with lower seed weight, the use of low-seed-weight inbred varieties for improving UAV seeding efficiency is limited only in South China where rice consumers prefer small size of rice grains. In contrast, small-seed-and-large-grain strategy could be used for improving UAV seeding efficiency without the risk of yield loss in hybrid rice.

ACKNOWLEDGEMENTS

This study was supported by the National Natural Science Foundation of China (Grant Nos. 32101819 and 31971845), the China Postdoctoral Science Foundation (Grant No. 2021M691179), the earmarked fund for China Agriculture Research System (Grant No. CARS-01-20). We thank E Zhiguo (China National Rice Research Institute), Mi Jiaming (Huazhong Agricultural University) and Liu Yue (Wuhan University) for their technological assistance.

SUPPLEMENTAL DATA

The following materials are available in the online version of this article at http://www.sciencedirect.com/journal/rice-science; http://www.ricescience.org.

File S1. Methods.

Fig. S1. Grain yield of inbred and hybrid rice varieties under different seed weights in China.

Fig. S2. Number of low-seed-weight inbred rice varieties in five regions of China.

Fig. S3. Distribution of seed weight to grain weight ratio for hybrid rice varieties in China.

Table S1. Male sterile line, year of release, growing season, seed weight, grain weight and grain yield of hybrid varieties with low seed weight.

Anandan A, Rajiv G, Eswaran R, Prakash M. 2011. Genotypic variation and relationships between quality traits and trace elements in traditional and improved rice (L.) genotypes., 76(4): H122–H130.

Chen C H, Liu G L, Li H, Chen Y M, Luo Q C. 2017. The breeding strategy and practice of high-grade conventional rice with long grain in Guangxi., 36(10): 91–98. (in Chinese with English abstract)

Chen Y Y, Zhu A K, Xue P, Wen X X, Cao Y R, Wang B F, Zhang Y, Liaqat S, Cheng S H, Cao L Y, Zhang Y X. 2020. Effects ofandfor grain size editing by CRISPR/Cas9 in rice., 27(5): 405–413.

China Agriculture Yearbook Editorial Committee. 2019. 2018 China Agriculture Yearbook. Beijing: China Agriculture Press: 337. (in Chinese)

Dai Y Z, Luo X W, Zhang M H, Lan F, Zhou Y J, Wang Z M. 2020. Design and experiments of the key components for centralized pneumatic rice day direct seeding machine., 36(10): 1–8. (in Chinese with English abstract)

Diao Y, Zhu C H, Ren D H, Yu J Q, Luo X, Ouyang Y Y, Zheng J G, Li X Y. 2020. Key points and prospect of rice direct seeding technology by unmanned aerial vehicle., 26(5): 22–25. (in Chinese with English abstract)

Farooq M, Siddique K H M, Rehman H, Aziz T, Lee D J, Wahid A. 2011. Rice direct seeding: Experiences, challenges and opportunities., 111(2): 87–98.

Huang M. 2022. The decreasing area of hybrid rice production in China: Causes and potential effects on Chinese rice self- sufficiency., 14(1): 267–272.

Kong L L, Ashraf U, Cheng S R, Rao G S, Mo Z W, Tian H, Pan S G, Tang X R. 2017. Short-term water management at early filling stage improves early-season rice performance under high temperature stress in South China., 90: 117–126.

Kumar V, Ladha J K. 2011. Direct seeding of rice recent developments and future research needs., 111: 297–413.

Li J Y, Lan Y B, Zhou Z Y, Zeng S, Huang C, Yao W X, Zhang Y, Zhu Q Y. 2016. Design and test of operation parameters for rice air broadcasting by unmanned aerial vehicle., 9(5): 24–32.

Lin M Q, Xue T, Hu S D, Cao D D, Ji H, Zhao G W. 2014. The preliminary analysis on the effects of seed size and weight on seed vigor of hybrid rice., 33(9): 46–50. (in Chinese with English abstract)

Liu C G, Zhang G Q, Zhou H Q, Feng D J, Zheng H B. 2010. Genetic improvement of yield and plant-type traits of inbredrice cultivars in South China., 43(19): 3901–3911. (in Chinese with English abstract)

Liu H Y, Hussain S, Zheng M M, Peng S B, Huang J L, Cui K H, Nie L X. 2015. Dry direct-seeded rice as an alternative to transplanted-flooded rice in Central China., 35(1): 285–294.

Luo X W, Wang Z M. 2014. Research progress in rice mechanization technology., 1: 23–29. (in Chinese with English abstract)

Peng S B, Tang Q Y, Zou Y B. 2009. Current status and challenges of rice production in China., 12(1): 3–8.

Peng S B. 2014. Reflection on China’s rice production strategies during the transition period., 44(8): 845–850. (in Chinese with English abstract)

Peng S B. 2016. Dilemma and way-out of hybrid rice during the transition period in China., 42(3): 313–319. (in Chinese with English abstract)

RiceData. 2021. Online statistical database: The database for Chinese rice varieties and their genealogy. [2021-7-31]. http://www.ricedata.cn/variety/.

Shi P H, Tang L, Wang L H, Sun T, Liu L L, Cao W X, Zhu Y. 2015. Post-heading heat stress in rice of South China during 1981–2010., 10(6): e0130642.

Su X J. 2001. Quality breeding in three-line hybrid rice., 14(1): 106–110. (in Chinese with English abstract)

Sun L M, Hussain S, Liu H Y, Peng S B, Huang J L, Cui K H, Nie L X. 2015. Implications of low sowing rate for hybrid rice varieties under dry direct-seeded rice system in Central China., 175: 87–95.

Tang W B, Zhang G L, Deng H B. 2020. Technology exploration and practice of hybrid rice mechanized seed production., 34(2): 95–103. (in Chinese with English abstract)

Wang D Y, Chen S, Wang Z M, Ji C L, Xu C M, Zhang X F, Chauhan B S. 2014. Optimizing hill seeding density for high- yielding hybrid rice in a single rice cropping system in South China., 9(10): e109417.

Wu Z J, Li M L, Lei X L, Wu Z Y, Jiang C K, Zhou L, Ma R C, Chen Y. 2020. Simulation and parameter optimisation of a centrifugal rice seeding spreader for a UAV., 192: 275–293.

Xiao H X, Li Y F, Yuan L Y, Zhang Z F. 2021. Application and prospect of China agricultural unmanned aerial vehicle in rice production., 48(8): 139–147. (in Chinese with English abstract)

Xu E B, Wang Y X, Ni S, Chen H Q, Zhu X D. 2015. Application of small grain recessive gene in the mechanical sorting of hybrid rice seeds., 21(3): 8–11. (in Chinese with English abstract)

Xu L, Yuan S, Wang X Y, Chen Z F, Li X X, Cao J, Wang F, Huang J L, Peng S B. 2022. Comparison of yield performance between direct-seeded and transplanted double-season rice using ultrashort- duration varieties in central China., 10(2): 515–523.

Xu Q, Chen W F, Xu Z J. 2015. Relationship between grain yield and quality in rice germplasms grown across different growing areas., 65(3): 226–232.

Yang S L, Yang X B, Mo J Y. 2018. The application of unmanned aircraft systems to plant protection in China., 19(2): 278–292.

Yuan L P. 2002. Hybrid rice. Beijing, China: China Agriculture Press: 4. (in Chinese)

Zeng S X, Lu Z W, Yang X Q. 1979. Studies on the heterosis of F1hybrids in rice and its relation to the parents., 5(8): 23–34. (in Chinese with English abstract)

Zhang H C, Gong J L. 2014. Research status and development discussion on high-yielding agronomy of mechanized planting rice in China., 47(7): 1273–1289. (in Chinese with English abstract)

Zhang M H, Wang Z M, Luo X W, Zang Y, Yang W W, Xing H, Wang B L, Dai Y Z. 2018. Review of precision rice hill-drop drilling technology and machine for paddy., 11(3): 1–11.

Zhang M H, Mo Z W, Liao J, Pan S G, Chen X F, Zheng L, Luo X W, Wang Z M. 2021. Lodging resistance related to root traits for mechanized wet-seeding of two super rice cultivars., 28(2): 200–208.

Zhang Y B, Tang Q Y, Zou Y B, Li D Q, Qin J Q, Yang S H, Chen L J, Xia B, Peng S B. 2009. Yield potential and radiation use efficiency of ‘super’ hybrid rice grown under subtropical conditions., 114(1): 91–98.

Zhou Y J, Li X X, Cao J, Li Y, Huang J L, Peng S B. 2018. High nitrogen input reduces yield loss from low temperature during the seedling stage in early-season rice., 228: 68–75.

28 October 2021;

18 February 2022

Copyright © 2022, China National Rice Research Institute. Hosting by Elsevier B V

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Peer review under responsibility of China National Rice Research Institute

http://dx.doi.org/10.1016/j.rsci.2022.05.001

Xu Le (Le.Xu@mail.hzau.edu.cn)