Effects of darkened emergence by stacked plates in open space and seedlings mulched with non-woven fabric on seedling characteristics of indica hybrid rice

Abstract: Seedling-raising technology has been one of the most important measures to treat regional seedling raising during machine transplanting. Among them, an efficient seedling raising has been developed for darkened germination by stacked plates and seedlings mulched with non-woven fabric for the hybrid rice in Sichuan rice areas. The better performance of machine transplanting can be realized for even seedling growth and strong packing root. This study aims to clarify the effect of synergistic seedling raising of darkened emergence by stacked plates in the open area (DE) and seedlings mulched with non-woven fabric (NM) on the seedling characteristics of indica hybrid rice. Tianyouhuazhan (the indica hybrid medium rice variety) was taken as the material in 2020-2021. The mode of swing-plate emergence (SE) and seedling mulched with film (FM) were chosen as the controls. A systematic investigation was made on the microenvironment and emergence characteristics in the emergence stage, seedling quality, and the adaptability of machine transplanting under DE and NM treatments. The results show that: 1) The DE increased the average temperature and average relative humidity of the microenvironment during the emergence stage, compared with the external environment (EE). The DE decreased the coefficient of variation (CV) of temperature and relative humidity, while shortening the time of seed emergence, and greatly improving the emergence rate and emergence uniformity, compared with SE. The NM effectively improved the microenvironment of the seedling bed for the balanced growth of seedlings, compared with FM. Finally, the DE+NM effectively improved the seedling uniformity and seedling rate. The seedling uniformity under DE+NM of two years increased by 7.22-8.91, 3.67-5.55, and 8.29-10.38 percentage points, respectively (P<0.05), and the seedling rate increased by 4.08-8.09, 11.79-14.88 and 20.10-40.02 percentage points, respectively (except for DE+FM in 2021, P<0.05), compared with DE+FM, SE+NM, and SE+FM. 2) The DE significantly increased the seedling density, the total root length, the number of white roots, root superficial area, and root biomass per unit area. The NM significantly increased the root volume per unit area. Finally, the DE+NM significantly increased the root volume, root superficial area, root biomass per unit area, and root coiling force (except for DE+FM in 2020). 3) The DE+NM significantly reduced the rate of missed and hurting seedlings, whereas, there was an increase in the ratio of 3-4 plants per hole, and increased the seedlings per hole, indicating the higher quality of mechanized transplanting. The DE+NM can be expected to strengthen the seedling, particularly for the characteristic of "neat seedlings, strong root and suitable for mechanical transplanting". Therefore, the improved seedling raising performed better with the low cost, extensive resistance, high efficiency, and low carbon. The findings can provide theoretical and technical support for strong seedlings raising and higher yield cultivation of rice mechanized transplanting in Sichuan rice area.