The effect of planting method on grain yield and quality characteristics of some rice genotypes in Guilan province

Introduction
Transplanting in puddled soil is a common method of rice cultivation in the world, which requires high labor and cost. Therefore, this method is being replaced by direct seeding system in recent years. Although direct seeding system has many advantages, this method may change various aspects of rice plant cultivation. In this experiment, the effect of changing the rice cultivation method from transplanting to direct seeding on paddy yield and some grain quality characteristics of rice varieties was investigated.
Material and methods
This experiment was carried out based on split block design with three repetitions in Rice Research Institute of Iran (RRII), Rasht, Iran, in 2019. The studied factors were cultivation methods in two levels including transplanting and direct seeding, and rice varieties in five levels including local variety, Hashemi, and improved varieties, Kian, Anam, Gilaneh and Shirodi. The measured traits were paddy yield and grain quality characteristics including head rice percentage, broken rice percentage, milled rice percentage, crude and cooked grain length and width, grain elongation rate, amylose content, gelatinization temperature and grain protein content. For data statistical analysis, analysis of variance was performed using SAS software and comparison of means by least significant difference (LSD) test at 5% probability level.
Research findings
The results showed that the effect of variety on paddy yield was significant, but the effect of cultivation method and cultivation method × variety interaction was not significant. Shirodi variety with 7820 kg/ha had the highest yield, while there was no significant difference between other vraieties. The highest milled rice percentage was related to Shirodi genotype in direct seeding system (71%), which was not significantly different from Gilaneh variety in direct seeding system (70%) and Shirodi variety in transplanting system (70%). The percentage of head rice in direct seeding system (57.06%) was lower than that of transplanting system (65.86%). Among the genotypes, Shirodi and Kian varieties had the highest and lowest head rice percentage with 84.33 and 37.5%, respectively. Amylose content of all studied varieties increased in direct seeding system compared to transplanting cultivation, but this increase was significant in Anam, Gilaneh and Kian varieties, and not-significant in Shirodi and Hashemi varieties. The highest and lowest amylose content with 27.45% and 21.27% were also observed in Shirodi variety in direct seeding and Kian variety in transplanting cultivation, respectively. Changing the cultivation method from transplanting to direct seeding system led to a significant increase in the Alkali spreading value of Gilaneh, Shirodi and Kian varieties, but had no significant effect on the Alkali spreading value of Anam and Hashemi varieties. The highest grain protein content with 11.08% was observed in Anam variety in transplanting cultivation, which was not significantly different from direct seeding system (10.76%).
Conclusion
The results of this study showed that changing the rice cultivation method from transplanting to direct seeding did not reduce the paddy yield of the studied varieties, but it had a significant effect on the quality characteristics of rice grains. One of the most important factors affecting the rice cooking quality is the grain amylose percentage. Regarding the results of the current study, changing the cultivation method from transplanting to direct seeding system did not increase the amylose content of Hashemi and Shirodi varieties, which have the largest cultivated area among the local and improved varieties in the northern rice-growing provinces of Iran. This result can be effective in the acceptance of direct seeding cultivation by paddy farmers, considering the not-significant effect of these two cultivation methods on paddy yield.