Effects of substrate types and uniconazole on mechanized transplanting qualities and grain yield for late rice with different seedling ages

Abstract: The mechanized transplanting area of rice in China accounts for about 38% of the total planting area, and the area is increasing now. Preparation of nutrient soil for raising rice seedlings has become one of the obstacle factors restricting the development of rice transplanting with machine. Light soilless substrate originating from renewable resources like crop straws can solve the difficulties of getting soils and protecting environment. Few studies focus on the interaction effects between light soilless substrate, rice seedling age, and the corresponding growth regulation way. Therefore, determining the suitable substrate type, seedling age and external hormone regulation way for raising late rice will be of great importance in improving the mechanization level of transplanting late rice. In this study, 2 kinds of substrates and 2 kinds of exogenous hormone regulation ways were used in this trial to explore the effects of substrate types on physiological characteristics and mechanized transplanting qualities for different seedling-age of late rice and the regulation way. Inbred rice, Jia 58 was used in this trial as late rice cultivar. Nutrient soil and light soilless substrate were used as substrates in this trial. And 2 kinds of seed soaking concentrations for uniconazole (control and 25 mg/L uniconazole) were used in this trial as growth regulation ways. The results showed that aboveground biomass for rice seedlings was increased with the increase of rice seedling age. SPAD (soil plant analysis development) values for rice leaves and root activities for rice seedlings firstly increased and then decreased as the increase of rice seedling age. The total rice life cycle was longer and rice growth period in the field was shorter for the longer age of rice seedlings. Rice seedlings qualities were greatly improved after seeds were treated with uniconazole. After seeds were treated with uniconazole, rice stem width was increased by 0.1-0.2 mm, rice plant height was significantly decreased, and SPAD values of rice leaves and root activities of rice seedlings were significantly increased compared with the control. The rice seeds soaked with uniconazole showed a better performance on rice mechanized transplanting qualities for longer age of rice seedlings, however, the performance on rice mechanized transplanting qualities was poorer for shorter age of rice seedlings (less than 18 d). The most suitable seedlings age for Jia 58 raised by nutrient soil was 18 d, while the most suitable seedlings age for Jia 58 raised by light soilless substrate was 18-24 d. When rice seedlings age was more than 24 d, the number of effective panicles and grains per panicle treated by nutrient soil could increase after rice seeds were soaked with uniconazole, rice grain yield treated by nutrient soil was also increased after rice seeds were soaked with uniconazole, and the modifying effects for rice seeds soaked with uniconazole were more favorable for longer age of rice seedlings. The performances of rice seeds soaked with uniconazole on rice grain yield treated with light soilless substrate were poorer compared with that treated with nutrient soil. Many kinds of raw material were widely used for light soilless substrate, the management procedures raising rice seedlings by light soilless substrate were simple, and the rice grain yield treated by light soilless substrate was also higher than nutrient soil treatment. Therefore, light soilless substrate is suitable for late rice transplanting with machine.