Guodong HUA，Guanxi LI，Delong MENG，Duoming WANG

Lianyungang Academy of Agricultural Sciences，Lianyungang 222006，China

1 Introduction

Rice（Oryza sativa L.）is the most important crop in China，and its seed quality is particularly important.With the adjustment of agricultural structure，rural land transfer and seed drying area reduction as well as changes in seed drying way and planting methods，the seed production is facing new issues.Especially for the direct sowing rice，the storage time is prolonged after the farmers purchase seed，posing a higher demand on seed quality.Seed quality control is a systematic project consisting of cultivation technology，packaging and storage technology and storage technology，and the mistake in any part will make it difficult to ensure the seed quality［1－2］.The promotion of new transplanting technology and direct seeding technology brings new problems for the seed quality study［3］.In this study，from application methods of nitrogen fertilizer，weeding period control，mechanical drying and water content control，we make a preliminary study on the key technologies in rice seed production，in order to provide theoretical guidance for the seed companies to improve rice seed breeding techniques and seed quality.

2 Materials and methods

2.1 MaterialsThe rice variety for experiment is Lianjing 7，provided by Jiangsu Jinwanhe Agricultural Science and Technology Co.，Ltd.

2.2 Nitrogen fertilizer application and managementThe original seed of Lianjing 7 is used for transplanting rice seedling by hand；the best sowing period is May12；the transplanting period is June 20.The plot area is2.4×6.5 m2，and the spacing in the rows and between rows is 13 cm ×25 cm.The randomized block design is used and repeated three times，and the base fertilizers P2O5and K2O are applied before sowing（9 kg／667 m2）.The application rate of conventional pure nitrogen is 22 kg／667 m2，and the ratio of nitrogen fertilizer to tillering stage dressing and earing fertilizer is1∶1.5 treatments are set for the application proportion of tillering stage dressing and earing fertilizer：5∶5，6∶4，7∶3，8∶2 and 9：1（labeled as A1，A2，A3，A4，A5）.The tillering stage dressing is applied once；earing fertilizer is divided into spikelet promotion fertilizer and spikelet protection fertilizer，with the application ratio of 3：1.In the rice maturity period，the actual yield per unit area，thousand-grain weight，blue-and-white grain rate and germination rate under each treatment is measured.

2.3 Seed field weedingImproved variety of Lianjing 7 is used for transplanting rice seedlings，and three ways are used to weed（weeding at the jointing；weeding at the heading stage；weeding at the maturity stage）.Each weeding way sets three replicates，and each replicate is 667 m2.The randomized block design is adopted，and the hybrid strain number and types are computed during weeding.The plot yield is measured at maturity.

2.4 Drying testThe newly harvested seed（Lianjing 7）is dried by mechanical drying，and the temperature of drying machine is set at42℃，43℃，44℃，45℃，46℃，47℃ and 48℃，respectively.1000 kg of seeds are taken from the same group of newly harvested seeds（water content of22%），respectively，and dried to water content of14.5%according to the set temperature.The drying time of each sample is recorded，and the germination rate of each sample is tested.

2.5 Effect of water content on rice seed storageAfter 100 kg of newly harvested rice seeds（Lianjing 7）are weeded（October），they are dried at 44℃ to water content of 15%，16%，17%，18%，19%，20% ，21%and 22%，respectively，packaged with plastic woven bag and placed in the warehouse.In each treatment，it is covered with film，and stored at room temperature.In April of the following year，the germination rate is examined.

2.6 Data processingThe origin 8.6 software is used for statis-tical analysis of experimental results and mapping.

3 Results and analysis

3.1 Effect of different nitrogen fertilizer application methods on yield and quality of rice seedsFrom Table 1，it can be found that different nitrogen fertilizer application methods have a certain effect on the yield and quality of seeds，and the yield is highest under A3，followed by A4and A5，and the yield is low under A1and A5.Different application methods have a small effect on kernel weight.The blue-and-white grain rate is highest under A1，followed by A2，A3and A5，indicating that the higher the application rate of earing fertilizer，the higher the blue-and-white grain rate.The germination rate is high under A3，A4and A5，up to national standard；the germination rate under A1and A2is not up to national standard，but it is still more than 80%.The thousand-grain weight is highest under A4.It can be found that A1and A2have low yield，high blue-and-white grain rate and low germination rate（not up to the national standard），so they are not used for seed production；A5has high germination rate and low blue and-white grain rate，but the yield is too low，so it is not suitable for seed production；using the nitrogen fertilizer application methods of A3and A4can provide ideal seed reproduction，high yield，better commodity features，standard thousand-grain weight，low blue-and-white grain rate and high germination rate.

Table 1 Effect of different nitrogen fertilizer application methods on yield and quality of rice seeds

3.2 Effect of weeding period on rice seed purity and weed typeAs can be seen from Table 3，at the booting stage，the variants，autogeny rice and other weed types are removed most；at the tillering stage，various types of weeds are removed least；various types of weeds removed at the milk stage are more than at the tillering stage but less than at the booting stage；after removing weed，the rice seed purity at the booting stage is significantly higher than at the other two weeding stages（P＜0.05）.It suggests that the weeding effect is best at the booting stage，and the weeding effect of variants，autogeny rice and weeds is best，and the purity after weeding is highest；it is followed by the weeding effect at the milk stage，and there is a certain effect on variants and autogeny rice；the weeding effect at the tillering stage is poor，the weeding effect of autogeny rice is good，but the weeding effect of variants and is poor.

Table 2 Effect of weeding period on rice seed purity and weed type

3.3 Effect of drying on the germination rate of rice seed

As shown in Fig.1（a），when the temperature is set at42℃，the germination rate is highest after drying，but the drying time required is longest；when the temperature is set at44℃，the germination rate after drying is not significantly different from the germination rate when the temperature is set at 42℃ and 43℃ （P＜0.05），but significantly higher than the germination rate when the temperature is higher than 44℃，and the time required for drying is relatively short.Therefore，the best mechanical drying temperature is44℃.

3.4 Effect of water content on the germination rate of rice seedAs shown in Fig.1（b），when the water content is 19%，the germination rate is86%，just one percentage point higher than the national minimum standard；when the water content is 18%and 17%，the germination rate is 92%and 93%，respectively，and there is no significant difference between the two；when the water content is 16%and 15%，the germination rate is95%and 96%，respectively，and there is no significant difference between the two.Taking into account other risk factors and cost factors，the appropriate water content is18%.

4 Conclusions and discussions

The nitrogen fertilizer application and management can have a great impact on rice growth and yield，and plays an important role in controlling the blue-and-white grain rate of rice seed［3］；the weeding effect is different at different weeding stages［4］；the setting of mechanical drying temperature not only affects the drying efficiency，but also affects the seed germination rate［5］；water content is a major factor affecting the seed storage quality［6－7］.With Lianjing 7 as test material，this paper explores the effects of the key rice seed production，processing and storage technologies（such as nitrogen fertilizer application and management，weeding mode in seed breeding field，temperature control of mechanical drying and water control on seed storage）on the quality of rice seeds.The results show that the optimal application proportion of tillering stage dressing and earing fertilizer is 8∶2，followed by 7∶3；the best time of weeding is booting stage，with the highest purity；the effect of drying and germination rate is best when the temperature is controlled at 44℃ in mechanical drying process；the seed storage quality and storage costs can be guaranteed when the water content of rice seed is controlled at18%.

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