Molecular Plant Breeding 2025, Vol.16, No.4, 250-260 http://genbreedpublisher.com/index.php/mpb 253 of mechanical transplanting of pot-shaped seedlings are vigorous, have a fast greenness recovery, high yield and good nutrient absorption. They are suitable for farms that pursue high yield and have mechanical equipment. However, the requirements for seedling management are high and the technical threshold is also high (Hu et al., 2018; Hu et al., 2020; Fu et al., 2021). The method of throwing seedlings is simple and convenient, and is very suitable for fields where machinery cannot enter. However, the seedlings do not grow very evenly and the yield is unstable (Zhou et al., 2015). 4 Influence of Transplanting Methods on Yield Components 4.1 Tiller number, panicle density, and grain filling Under the appropriate planting density (e.g. 26.88×104 holes/hectare), transplanting with mechanical pot seedlings in wide and narrow rows can significantly increase the number of effective panicles and the total number of flowers per mu, thereby enhancing the yield. Compared with equal-row spacing or carpet seedling transplanting, this transplanting method has more tillers and panicles, and higher seed setting rate and grain weight (Hu et al., 2020). Mechanical transplanting, such as pot seedling transplanting and blanket seedling transplanting, can generally bring more panicles and grains. Among them, the pot seedling method shows the most outstanding performance in terms of seed setting rate and 1000-grain weight (Hu et al., 2018; Fu et al., 2021). In addition, under these transplanting methods, more photosynthetic products accumulate in the later stage of rice, which is conducive to grain filling and plumpness. 4.2 Yield variation across methods and planting densities Different transplanting methods and densities have a significant impact on the yield. Under the mechanical pot seedling wide and narrow row transplanting, the yield was the highest when the density was 26.88×104 holes per hectare. If the density is too high or too low, the output will decrease instead, showing a trend of “high in the middle and low on both sides” (Hu et al., 2020). Overall, the yield of mechanized transplanting (pot seedlings or blanket seedlings) is generally higher than that of manual transplanting and direct seeding. This is mainly because there are more panicles and more biomass accumulation (Wu et al., 2022). At an appropriate density (195 plants per square meter), the yield of direct seeding by unmanned aerial vehicle (UAV) was slightly higher than that of dry seeding by UAV. Although it was still slightly lower than mechanical transplanting, the number of panicles and grains per panicle were also considerable (Zhu et al., 2023). 4.3 Harvest index and biomass accumulation Transplanting seedlings in mechanical POTS can also increase the total dry matter mass, especially during the period from heading to maturity when more is accumulated. The harvest index of this approach is also higher (Fu et al., 2021). Under high-yield conditions, both the biomass and harvest index of this method are higher than those of carpet seedlings or equal row spacing transplanting, indicating that photosynthetic products can be transported to the grains more effectively (Hu et al., 2020). In addition, mechanical transplanting enables the plants to absorb more nitrogen in the later stage and increases the biomass, which is an important reason for the increase in yield (Hu et al., 2024). 5 Impact on Grain Quality 5.1 Milling quality: brown rice rate, head rice rate Different transplanting methods can have a significant impact on the milling quality of japonica rice. Mechanical blanket transplanting (MC) can usually increase brown rice rate and whole polished rice rate, and is more suitable for improving processing quality than mechanical direct seeding (MD) (Bian et al., 2018; Bassuony and Zsembeli, 2019; Abou-Khalifa et al., 2021). If mechanical pot transplanting (MT) is adopted, the rates of brown rice and whole polished rice can be further increased (Fu et al., 2021). Under appropriate densities, such as wide and narrow row transplanting, it is also possible to improve processing quality while ensuring yield (Hu et al., 2020). Overall, the transplanting method performs better than the direct seeding method in processing. 5.2 Appearance and eating quality: grain shape, chalkiness, taste In terms of appearance, the rice under mechanical direct seeding (MD) has a higher aspect ratio, lower chalky grain rate, chalky rate and chalky degree, and looks better (Bian et al., 2018; Yun et al., 2023). However, the
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