Effects of planting methods on yield and quality of different types of japonica rice in northern Jiangsu plain, China

BlAN Jin-long, XU Fang-fu, HAN Chao, QlU Shi, GE Jia-lin, XU Jing, ZHANG Hong-cheng, WEl Hai-yan

Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops/Agricultural College, Yangzhou University, Yangzhou 225009, P.R.China

Abstract Mechanical transplanting with carpet seedlings (MC) and mechanical direct seeding (MD) are newly developed planting methods, which increase in popularity and planted area each year. Knowing the difference for yield and rice quality under different planting methods is of great importance for the development of high quality and yield cultivation techniques under mechanical conditions. Therefore, three kinds of japonica rice including hybrid japonica rice, inbreed japonica rice, and soft rice were adopted as materials. And the differences in the quality of processing, appearance, cooking and eating quality,nutrition, and the rapid viscosity analyzer (RVA) proflle were studied to reveal the effects of planting methods on yield and quality of different types of japonica rice. Results showed that the milled rice and head rice rates under MC was signiflcantly higher than those under MD, and the processing quality of inbreed japonica rice was the most stable. Compared with MC,length/width ratio of rice under MD was signiflcantly increased, and chalkiness rate, size, and degree were signiflcantly decreased. The protein content under MD was lower than that under MC. MC showed higher peak viscosity and breakdown value than MD. The taste value was the greatest for soft rice, followed by inbreed japonica rice, and then by japonica hybrid rice, with no signiflcant differences resulting from planting methods. Compared with MC, MD signiflcantly improved the appearance quality, though processing quality and nutritional quality were decreased. And there was no signiflcant difference in cooking and eating quality between MC and MD. Under different planting methods, the appearance quality of inbreed japonica rice changed the most and the processing quality was the most stable. The nutritional, cooking and eating quality of soft rice changed the least. Therefore, according to the different planting methods and market needs, selecting the appropriate rice varieties can reduce the risks in rice production and achieve good rice quality.

Keywords: hybrid japonica rice, inbreed japonica rice, soft rice, planting method, rice quality

1. lntroduction

In recent years, with the transfer and reduction of the agricultural labor force, rice production in China is accelerating toward simpliflcation and mechanization (Wang and Yang 2004). There are diversifled planting methods in agriculture production, such as hand transplanting,mechanical transplanting, direct seeding, and throwing seedlings (Ehsanullahet al. 2007; Rani and Jayakiran 2010). Mechanical transplanting and direct seeding are the important planting methods in the rice-wheat rotation system in the middle and lower reaches of the Yangtze River.In 2011, the total rice planting area in Jiangsu Province was 2.249 million ha, 55.9% of which used mechanical transplanting and direct seeding. The area of mechanical direct seeding and mechanical transplanting increased year by year because of saving labor force and time. The selection of rice varieties and cultivation techniques should be changed when planting methods are changed. Studying the differences of rice quality among different types ofjaponicarice under different planting methods is necessary to promote the development of a high-quality rice industry and to enhance the comprehensive strength of the rice industry in China.

Rice quality includes processing quality, appearance quality, cooking and eating quality, and nutritional quality(Webb 1991). The formation of rice quality is not only controlled by genetic characteristics of rice varieties, but is also influenced by factors such as the paddy ecological environment, soil conditions, cultivation management techniques, processing conditions, and storage technologies(Sajwanet al. 1990; Bonazziet al. 1997; Abud-Archilaet al.2000; Hanet al. 2004). Some studies have shown that the variation of the appearance quality of 44 fragrant rice varieties was larger than that for other rice qualities, and the amplitude variation of chalkiness rate and degree exceeds 50% (Chenet al. 2013). The amplitude variations of brown rice, milled rice, and head milled rice rates were less than 5%. The effects of paddy ecological environment and cultivation measures on rice quality have been extensively studied. Most studies proved that temperature during the grain-fllling stage has a signiflcant effect on rice quality(Krishnanet al. 2011). High temperature during the grainfllling stage leads to an increase of chalkiness rate and chalkiness degree, while rice transparency, brown rice rate,milled rice rate, and head milled rice rate decrease (Lanninget al. 2011; Li H Xet al. 2011). Different planting methods,which vary in timing of sowing, fertilizer application, and water management had signiflcant effects on rice growth,because these strategies result in differences in temperature and light resources during the grain-fllling stage. Other studies suggested that increasing potassium fertilizer application could signiflcantly reduce the chalkiness degree and improve rice protein content and comprehensive quality(Chaturvedi 2006; Liuet al. 2011). Dry cultivation could signiflcantly improve the appearance and nutritional quality,but cooking and eating quality worsened (Chenget al. 2003;Zhanget al. 2008).

Previous studies have concentrated on yield and the economic efflciency of mechanical transplanting and direct seeding (Gangwaret al. 2008; Farooqet al. 2011). There has been little study on the effects of planting methods on rice quality of different types ofjaponicarice (Hayashiet al.2007). In this study, three different types ofjaponicarice were used to study the differences in processing quality,appearance quality, cooking and eating quality, nutritional quality, and rapid viscosity analyzer (RVA) proflles under the mechanical transplanting and mechanical direct seeding methods.

The main objectives of this study were to reveal the changes in rice quality of different types ofjaponicarice varieties under different planting methods, and to provide the theoretical and practical basis for high-quality rice production under different planting modes.

2. Materials and methods

2.1. Plant materials and experimental design

The experiment was conducted at Huanghai Farm(38°39′6.48′′N, 104°04′35.11′′E), Jiangsu Province, China during the 2015 and 2016 rice cropping seasons, in flelds where wheat was previously cultivated, and the soil type is clay. The soil had 1.53 g kg–1total nitrogen, 34.41 mg kg–1available phosphorus, and 88.60 mg kg–1available potassium. Two hybridjaponicarice varieties (Liaoyou 9906 and Yongyou 2640) and four inbreedjaponicarice varieties(two common, Sujing 815 and Lianjing 7; and two soft,Yangjing 239 and Nanjing 2728) were used in this study.

The experiment was arranged in a split plot design, with planting method as main plot and variety as split plot. The plot area was 25 m2(5 m×5 m), with three replicates. Seeds of the mechanical transplanting treatments were sown on May 29 and the seedlings were transplanted on June 23.The mechanical transplanting density was 30.0 cm×11.7 cm.Seeds of the mechanical direct seeding treatment were sown on June 28, with a row spacing of 30 cm. The mechanical direct seeding density of conventionjaponicarice and hybridjaponicarice were 900 000 and 600 000 per hectare,respectively.

In both the experimental years, the total N application rate was 270 kg ha-1for both MC and MD. N was applied in four splits: 30% as basal fertilizer, 30% at the stage of tillering initiation, 20% at the stage of panicle initiation, and 20% when the rice has two leaves that have not appeared.Nitrogen was applied as urea, with N content of 45.6%. For each plot, calcium superphosphate (P2O5content: 12%) was applied as basal at the rate of 135 kg P2O5ha-1. Similarly,potassium chloride (K2O content: 60%) was applied at the rates of 135 and 135 kg K2O ha-1as basal and at panicle initiation stage, respectively.

For MC, plots were kept flooded with 1–2 cm water when transplanting. During tillering phase, the 2–3 cm water was kept in plots, and then water was drained to control tillering, when the number of stems and tillers was about 80% of prospective panicles. After stem elongation stage,an alternate wetting and moderate soil drying irrigation management was used until 1 week before the final harvest. For MD, a moistening irrigation management was used during seedling stage. The irrigation management during tillering stage under MD was the same with MC.After heading stage, an intermittent irrigation management was used and plots were flooded with 3 cm water for each irrigation. Other fleld practices (weeds, insects, and disease)were in conformity with the local recommendations.

2.2. Harvesting and rice quality measurements

Grain yield was determined from all plants from a 5-m2site (except border plants) in each plot and adjusted to a moisture content of 0.14 g H2O g–1fresh weight.

About 500 g of grains harvested from each plot were dried at 40°C in a forced-air oven for quality analysis. A 150-g sample of rice grains was passed twice through a dehusker, polished, then separated into broken and unbroken grains. The brown rice, milled rice, and head rice rates were expressed as percentages of total (150 g) rice grains. Chalkiness was evaluated visually on 100 milled grains per plot. Grains containing 20% or more of white belly,white center, white back, or a combination of these, were considered chalky. Gel consistency and amylose content were measured according to the Rice Quality Measurement Standards.

The Infrared 1241 Grain Analyzer from FOSS TECATOR was used to measure the protein (Fernándeziba?ezet al.2009). STA 1 A (Satake, Japan) was used to assess taste value.

2.3. RVA analysis

As starch paste parameters generated from a RVA reflect starch gelatinization, disintegration, swelling, and gelling ability, they are often used to evaluate rice quality. In this experiment, rice starch viscosity characteristics were evaluated using an RVA (Model no. RVA-3D; Newport Scientiflc, Sydney, Australia) as described by Hanet al.(2004). Viscosity values were recorded as centipoises(cP). The original components of starch viscosity characters include peak, hot, and cool (flnal) viscosities.The secondary components, such as breakdown and setback, were calculated from the original components. A breakdownvalue was calculated by subtracting hot viscosity from peak viscosity, while a setback value was calculated by subtracting peak viscosity from cool viscosity.

2.4. Statistical analysis

Analysis of variance (ANOVA) was performed using the SAS/STAT statistical analysis package (version 6.12,SAS Institute, Cary, NC, USA). The statistical model used included sources of variation due to replication,planting methods, cultivar, and interactions of planting methods×cultivar. Data from each sampling date were analyzed separately. Means were tested by least signiflcant difference atP=0.05 (LSD0.05).

3. Results

3.1. Rice yield and growth stage

The average grain yield of all rice varieties under the MC treatment was 10.58 t ha–1(2015) and 10.63 t ha–1(2016)(Table 1). The grain yield of Yongyou 2640 was the highest in both years, at 11.30 and 11.15 t ha–1, and the grain yield of Nanjing 2728 was the lowest, with 9.78 and 9.95 t ha–1.The average grain yield of all rice varieties under MD was 8.93 t ha–1(2015) and 9.00 t ha–1(2016). The highest yield in 2015 was 9.28 t ha–1(Yangjing 239) and 9.26 t ha–1(Lianjing 7) in 2016. The grain yield of Liaoyou 9906 was the lowest in both years, with 8.30 t ha–1(2015) and 8.51 t ha–1(2016). The average heading stage of MD was 13 days later than that of MC.

3.2. Effects of planting methods on rice quality

Processing quality and nutritional qualityThe milled rice and head rice rates of processing quality under MD was signiflcantly decreased when compared with that of MC (Table 2). Among all varieties, the processing quality of Yongyou 2640 under MD decreased most, especially milled rice rate, which was reduced by 11.08%. Under the different planting methods, the brown rice rate had little change (0.59–1.68%), compared to that of the milled rice rate (5.59–11.08%) and the head rice rate (4.06–9.87%),indicating that planting methods had the least effect on brown rice rate when compared with milled rice and head rice rates. The processing quality varied greatly in rice varieties, and two common rice varieties had relatively stable processing quality.

Under different planting methods, protein content was consistently lower under the MD treatment as compared to the MC treatment across six of the varieties (Table 2).However, this difference was only signiflcant in Yongyou 2640 and Lianjing 7, where MC improved the nutritional quality.The protein content was signiflcantly different for the different rice varieties. There was no signiflcant change in protein content under different planting methods.

Table 1 Effects of planting methods (PM) on yield and growth stages (2016) for japonica rice varieties

Table 2 Effects of planting methods (PM) on processing quality for japonica rice varieties (%)1)

Appearance qualityThe appearance quality was signiflcantly influenced by genetic characteristics of rice varieties, and the planting methods also have great influence on appearance quality (Table 3). In the MD treatment, the rice length is slightly longer, the rice width is slightly smaller,and the length/width ratio (2.84–13.50%) was obviously increased, compared with those values in the MC treatment(Table 3). Chalkiness rate (–39.80–(–14.04)%), chalkiness size (–35.16–(–9.08)%), and chalkiness degree (–60.23–(–29.53)%) under MD were signiflcantly less than those under MC, indicating that MD could signiflcantly improve the appearance quality. Under MD, chalkiness size and chalkiness degree of the two inbreedjaponicavarieties decreased signiflcantly, and this change was greater than that in the hybridjaponicarice and in the soft rice, indicating that MD had the most signiflcant effect on improving the appearance quality of the inbreedjaponicarice varieties.

Taste valueAmylose content together with gel consistency is an important index for assessing the taste value of rice.Low amylose content and long gel consistency results in a better taste value for rice. The result showed that gel consistency and the content of AC had signiflcant difference in planting methods, genotype, and varieties (Table 4). The amylose content under MC was less than that under MD, and the gel consistency under MC was larger than that under MD(Table 4). MD increased the amylose content and decreased the gel consistency, indicating that MD reduced the taste value of rice. Amylose content and gel consistency were signiflcantly different among cultivars (Table 4). Amylose content of soft rice was signiflcantly lower than that of hybridjaponicarice and inbreedjaponicarice. The amplitude variation of amylose content of hybridjaponicarice under different planting methods had the lowest value.

Table 3 Effects of planting methods (PM) on appearance quality for japonica rice varieties1)

Analysis of the taste value of different types ofjaponicarice (Table 4) show that the taste value under MC (0.93–4.35%) was slightly lower than that under MD, except in Yongyou 2640, but these differences were not signiflcant.Tasting value was signiflcantly different in planting methods,genotype, and varieties (Table 5). Further analysis found that hybridjaponicarice had the worst taste value, while soft rice had the best taste value. The amplitude variation for taste value of hybridjaponicarice was greater than that of other rice varieties. The results showed that MD improved the taste value of inbreedjaponicarice, and that the planting methods had little effect on taste value of soft rice. The taste value of inbreedjaponicarice under MD increased mainly because of the increasing viscosity and balance value.

3.3. RVA profile

There were great differences in RVA proflle across planting methods, varieties, and the interaction of planting method and variety, except for the values of flnal viscosity and peak time (Table 5).

Planting methods had great influence on peak viscosity,trough viscosity, breakdown, flnal viscosity, and setback of the RVA proflle (Table 5). Planting methods had the greatest impact on the setback and the least impact on peak time and pasting temperature. Compared with MC, MD signiflcantly increased the setback and reduced the peak viscosity and breakdown of the RVA proflle. There was no signiflcant difference in peak time under the different planting methods.Previous studies have shown that high peak viscosity, large breakdown value, and small setback value led to high taste value (Hanet al. 2004; Chenget al. 2005). When compared with MD, MC optimized the RVA proflle and improved the cooking and eating quality of rice. Our results also showed that the RVA proflles of soft rice were better than those of the hybridjaponicarice and inbreedjaponicarice, which was consistent with the obtained results for taste value.

Table 4 Effects of planting methods (PM) on taste value for japonica rice varieties1)

Table 5 Effects of planting methods (PM) on rapid viscosity analyzer (RVA) proflle characteristics for japonica rice varieties

3.4. Effects of climatic factors at the grain-fillingstage on rice quality and RVA profile

Temperature-sunshine factors at the grain-fllling stage were shown in Table 6. Correlation analysis (Table 7) showed that milled rice rate and protein content had a highly signiflcant positive correlation with daily mean temperature, daily highest temperature, daily lowest temperature, and daily mean temperature difference. There was also a signiflcant positive correlation between milled rice rate and daily mean temperature, daily highest temperature, and daily mean temperature difference. The appearance quality was closely related to the climate factors, while the chalkiness size was positively correlated with daily highest temperature, daily lowest temperature, and daily mean temperature difference.The chalkiness degree was positively correlated with the daily mean temperature difference. The remaining quality indicators had no signiflcant correlation with the measured temperature and light factors. Among them, brown rice rate,rice width, and chalkiness rate were positively correlated with daily mean temperature, daily highest temperature, daily lowest temperature, and daily mean temperature difference.Rice length, length/width ratio, and amylose content were negatively correlated with daily mean temperature, daily highest temperature, daily lowest temperature, and daily mean temperature.

Table 6 Differences in temperature-sunshine factors at the grain-fllling stage of japonica rice varieties (2016)

Table 7 Correlation analysis between rice quality, rapid viscosity analyzer (RVA) proflle characteristics, and temperature and light factors during the grain-fllling period of japonica rice (2016)

The peak viscosity and breakdown value had signiflcant positive correlations with the daily mean temperature, daily highest temperature, daily mean temperature difference,and daily mean light hours (Table 7). The other RVA proflle values had no signiflcant correlation with temperature and light factors. Trough viscosity was positively correlated with all temperature-sunshine factors. The flnal viscosity,setback, and peak time were negatively correlated with daily mean temperature, daily highest temperature, daily lowest temperature, daily mean temperature difference,and daily mean light hours. Pasting temperature was negatively correlated with daily mean temperature, daily highest temperature, daily mean temperature difference,and daily mean light hours, and positively correlated with daily lowest temperature.

4. Discussion

4.1. Effects of planting methods on processing quality and appearance quality

Rice processing quality, also known as grinding quality,includes the values of brown rice, milled rice, and head rice rates. Zhaoet al. (2005) hypothesized that processing quality was mainly affected by the extent of grain-fllling. A longer effective grain-fllling time and stable grain-fllling rate were conducive to improving the degree of grain-fllling, while insufflcient grain-fllling time and abnormal grain-fllling speed deteriorated processing quality (Yanget al. 2000; Yang and Zhang 2009; Huoet al. 2012). Therefore, factors that affect grain-fllling, including photosynthetic performance,population structure, soil moisture, temperature, and light resources during the heading stage can all affect processing quality. Processing quality under direct seeding was decreased from that of mechanical transplanting, and that the differences in processing quality were mediated by rice variety (Huoet al. 2012). Planting methods varied in success rate, from high processing quality and yield under machine insertion to low under hand planting or live broadcast. The results of this study conflrmed that the processing quality under MC were better than that under MD. This could be due to a stable population structure at the heading stage, with a longer functional stage of leaves and a higher accumulation of dry matter before heading under MC (Gangwaret al. 2008; Huet al. 2014). Under different planting methods, the variation in brown rice rate was not signiflcant; planting methods had little effect on brown rice rate. Milled rice and head rice rates showed signiflcant differences among cultivars. The variation of processing quality of inbreedjaponicarice was smaller than that ofjaponicahybrid rice and soft rice under different planting methods, indicating that the processing quality of inbreedjaponicarice was less affected by planting method.

Previous studies have shown that temperature at the grain-fllling stage has the most signiflcant impact on processing quality (Nagataet al. 2004; Kimet al. 2011).Head rice rate is the most important metric of processing quality, and thus is one of the main indexes to evaluate rice quality grade. Head rice rate had a negative correlation with daily mean temperature, daily highest temperature,and daily lowest temperature during the grain-fllling stage(Huoet al. 2012). When the temperature increased from 20 to 30°C during the grain-fllling stage, the head rice rate decreased signiflcantly (20–30%) (Hak 1994). The best temperature for grain-fllling ofjaponicarice was 2 124°C. It was not conducive to increase the head rice rate when the temperature was too high or too low (Kimet al. 2011). In this study, the milled rice and head rice rates were positively correlated with daily mean temperature, daily highest temperature, and daily mean temperature difference, which may result from the characteristics of rice cultivars and the low mean temperature during the grain-fllling stage. The heading stage under MD was 7–10 days later than that under MC, and the growth and development of rice was delayed; therefore, the mean temperature under MD during the grain-fllling stage was decreased. However, because the heading stage under MC was earlier than that under MD, the mean temperature during grain-fllling stage was close to the optimum temperature ofjaponicarice, which improved the temperature and light environment during the grain-fllling stage, resulting in increased grain plumpness and improvement of processing quality.

The grain shape was primarily controlled by the genetic characteristics of rice cultivars, and external environmental factors such as cultivation measures had little impact(Huanget al. 2013). When compared the value under MC,rice length under MD was slightly increased, rice width was slightly decreased, and rice length/width ratio was signiflcantly increased: the rice shape became slender,rather than stubby. Some studies showed that stubby rice was more difflcult to be break during processing (Wanget al.2002; Suiet al. 2014). Hence, the processing quality under MC was better than that under MD. Planting methods had greater impact on the rice shape of soft rice: the variation in shape for soft rice (8.33 and 13.50%) was higher than that for hybridjaponicarice (3.39 and 6.13%) and for inbreedjaponicarice (2.84 and 4.62%).

The evaluation index of appearance quality includes chalkiness degree, chalkiness rate, and chalkiness size.Chalkiness is the opaque part of rice endosperm. The formation of chalkiness is due to the presence of many globular or oval amyloids in the rice endosperm during the grain-fllling stage. The loose arrangement of these amyloids leads to the appearance of pores in endosperm starch cells, causing incident light to scatter, showing chalkiness. Previous studies showed that chalkiness was closely related to the supply and translocation of assimilates in grain (Ishimaruet al. 2009). Environmental factors affected chalkiness through grain fllling and translocation of assimilates. When the supply of assimilates was limited,then endosperm plumpness was not attained; however,an overabundance of assimilates exceeds rice storage capacity, causing rapid grain-fllling speed. Both of these conditions can produce chalkiness (Lanninget al. 2011).High temperature accelerates grain fllling and the growth process, and causes the internal material distribution of the grain to be uneven, increasing chalkiness. Low temperature prolongs the grain-filling stage, delays senescence of branches, and slows the grain-fllling speed, allowing grains to become replete, which can help to reduce the formation of chalkiness. The temperature for the grain-fllling stage under MD was lower than that under MC, which is a mechanism for the better appearance quality observed under MD (Li Jet al. 2011). After threshing, the remained grain under MD was plump, which was also an important reason for better appearance quality. Some people found that chalkiness rate, chalkiness degree, and chalkiness size under MD were signiflcantly lower than those under MC (Huoet al. 2012).In this study, appearance quality under MD was better than that under MC. The study revealed that there was signiflcant difference in the amplitude variation of chalkiness among planting methods and varieties. Appearance quality of inbreedjaponicarice under MD was signiflcantly improved,and this improvement was greater than that ofjaponicahybrid rice and soft rice under the same treatment. The results indicated that the influence of planting methods and environmental factors on appearance quality of different types ofjaponicarice was signiflcantly different, and that the adaptability of different rice varieties to environmental factors is different (Huoet al. 2012).

4.2. Effects of planting methods on nutrition, cooking,and eating quality

Protein is one of the important chemical components of rice, and is an important indicator to evaluate nutritional quality. This study showed that protein content under MC was lower than that under MD. This might be related to the higher daily mean temperature, daily highest temperature,and daily lowest temperature during the grain-fllling stage,and the increased photosynthetic production capacity and superior grain-fllling characteristics under the MC treatment conditions. Like protein content, amylose content is an important factor that affects the cooking and eating quality.In the case of similar amylose content, the higher the protein content, the harder the rice, the worse the palatability (Martin and Fitzgerald 2002).

Amylose content and gel consistency are important standards to evaluate cooking and eating quality. Rice has better cooking and eating quality with low amylose content and long gel consistency (Cagampanget al. 1973;Allahgholipouret al. 2006). Amylose content under MD was higher than that under MC, and gel consistency became shorter, making cooking and eating quality worse (Huoet al.2012). The results of this current study are consistent with these previous flndings: MC decreased amylose content,increased gel consistency, and improved cooking and eating quality. This may be due to early heading stage and high temperature during the early stage of the heading stage,shortening the effective time of amylose accumulation.Under different planting methods, the change in amylose content was different among cultivars. Amylose content of soft rice under MD changed least; thus, the taste value of soft rice decreased slightly under MD.

The RVA proflle has signiflcant correlation with cooking and eating quality (Allahgholipouret al. 2006). Rice with high peak viscosity, large breakdown value, small flnal viscosity,and small and negative setback value is considered to have good cooking and eating quality (Huoet al. 2012).Planting methods had signiflcant effects on the RVA proflle.Compared with MC, MD signiflcantly reduced peak viscosity and breakdown value, increased setback value. The RVA proflle of soft rice was signiflcantly better than that ofjaponicahybrid rice and inbreedjaponicarice under this treatment. Taste value is the comprehensive evaluation of appearance and palatability of rice. Under different planting methods, the taste value under MD was slightly higher than that under MC, except for the Yongyou 2640 variety, but these differences were not signiflcant. The unchanged taste value of Yongyou 2640 might be related to the low maturity of this grain. Late sowing date, late heading date, lower daily mean temperature, and less daily mean light hours at the grain-fllling stage, resulted in lower maturity of grain and potentially affected the cooking and eating quality. Soft rice had the best taste value, which was consistent with the values for amylose content, gel consistency, and the RVA proflle. This flnding demonstrates that amylose content,gel consistency, and RVA proflle values are signiflcantly correlated with the cooking and eating quality of rice.

5. Conclusion

Compared with MC, MD improved the appearance quality,but reduced the processing quality. Under MD, nutritional,cooking, and eating qualities deteriorated. The impact of planting methods on rice quality is closely related to the rice variety type. In terms of appearance quality and processing quality, the variation of inbreedjaponicarice under the different planting methods was less than that ofjaponicahybrid rice and soft rice. For nutritional, cooking,and eating quality, soft rice had minimal changes under the different planting methods. This experiment studied the variation of rice quality under the conditions of mechanical transplanting and mechanical direct seeding of different rice varieties in northern Jiangsu plain, which provide the basis for large-area rice production. Choosing suitable varieties for different planting methods will help to reduce the risks of rice production and achieve the desired rice quality.

Acknowledgements

We are grateful for grants from the National Key R&D Program of China (2016YFD0300503), the earmarked fund for China Agriculture Research System (CARS-01-27),the Key Research Program of Jiangsu Province, China(BE2016344), the earmarked fund for Jiangsu Agricultural Industry Technology System, China (JATS[2018]298),and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China.