Isotope Tracer Technique·Ecology and Environment·Physiology
In order to explore effects of sowing depth and amount on seedling growth and yield of direct-seeding rice in Ningxia， the main rice variety Fuyuan No.4 was used as the test material. The two-factor split-plot design was adopted， with four sowing depths of 1， 2， 3 and 4 cm and four sowing rates of 112.5， 187.5， 262.5 and 337.5 kg·hm-2， to study the effects of different sowing depths and sowing rates on the seedling quality and yield of direct-seeding rice. The results showed that there was a significant interaction effect between sowing depth and sowing rate on the emergence rate of rice， among which the emergence rate of four combinations with sowing depth of 1～2 cm and sowing amount of 112.5～187.5 kg·hm-2 increased significantly compared with other combinations. In seedling quality， the four indexes of seedling height， stem base width， plumpness and strong seedling index were superior to other combinations coupled with sowing depth of 2 cm and sowing amount of 262.5 kg·hm-2. The rooting ability of two combinations of sowing depth of 2～3 cm and sowing amount of 187.5 kg·hm-2 was superior to other combinations， and the uniformity of seedlings was better than others with sowing depth of 3 cm and sowing amount of 262.5 kg·hm-2. Among the indexes of seedling quality， the effects of sowing depth multipled sowing amount on plumpness and strong seedling index have extremely significant interaction effects. As for root physiological indexes， the root vigor， total absorption area and active absorption area of root system in three combinations with sowing depth of 2 cm， sowing amount of 187.5～262.5 kg·hm-2， and sowing depth of 3 cm and sowing amount of 187.5 kg·hm-2 were better than other combinations， and there was a significant interaction effect between sowing depth and sowing amount on the above three indexes. Further， the membership function combined with weight analysis method was used to comprehensively evaluate （D value） 12 seedling quality related indexes under different sowing depth and sowing rate combinations， while four better combinations with sowing depth of 2～3 cm and sowing amount of 187.5～262.5 kg·hm-2 were selected. The results of yield analysis showed that the two combinations with sowing depth of 3 cm and the sowing amount of 187.5～262.5 kg·hm-2 increased the yield obviously， and the yield increase rate reached 4.29%～17.10%. To sum up， the suitable combination of sowing depth and sowing rate （sowing depth of 3 cm， sowing amount of 187.5～262.5 kg·hm-2） can promote the growth of direct-seeding rice seedlings by improving rooting ability， seedling uniformity and root absorption area， and improve the population quality of direct-seeding rice， thus increasing the yield of direct-seeding rice. The results of this study laid a theoretical foundation for the construction of direct seeding cultivation techniques of rice covered with soil in Ningxia.