| The contradiction between the low temperature climate and the thermophily of rice is one of the major problems of rice production in the rice planting region of Northeast. Dry-nursery seedling at early spring in the protected area, alleviated the problem of lack of accumulated temperature during the rice growth period and of delayed chilling injury, secured the rice grain yield stably and highly, promoted the leapfrog development of rice area in Northeast, and made the huge contribution to the national food security. However, dry-nursery rice seedlings needed a large amount of upland soil and biochar. Long-term digging excessively the upland soil resulted in no desirable soil to use, and resources and environments were destroyed heavily in many areas. Moreover, using the paddy soil as substrate to cultivate the rice seedlings always led to the poor quality seedlings and blight disease occurrence because of clay, heavy and cold plasma of paddy soil. On the other hand the problems that excess crop straws were burned out and soil fertility decreased in Northeast China have been becoming more and more serious. If the straw is returned to the field, the straw will not decay in time because of the low temperature, and influence the growth and development of crops next year. Biochar has been studied widely and approved by many experts and scholars with good structure and the physical and chemical properties. The deserted materials such as crops straws might be processed into biochar and added to the dry-nursery seedlings substrate and the paddy soil, and the physical and chemical properties of the seedlings substrate and the paddy soil would be improved, and helped cultivate the strong and healthy rice seedlings and promoted the growth of rice. Thus, it would not only solve the problems for dry-nursery seedling in the rice planting region of northeast, but also the crops straw resources could be fully utilized and realized the improvement of soil and enhancement of fertility, and would be conducive to promoting the sustainable development of rice production in Northeast.In view of this, different amounts of biochar were added to the rice seedling substrate basing on the paddy soil in the research in order to ascertain the effects of biochar on soil water and temperature properties, nutrients changes of seedling substrate soil along with the quality of seedlings etc. Further, effects of biochar on the growth and development, nutrient absorption and distribution, yield and grain quality of rice were also investigated. The main conclusions are as follows:1. Adding biochar in paddy soil as rice seedling substrate had significant effects on soil moisture and temperature under the condition of dry-nursery rice seedlings in the greenhouse at early spring in Northeast. The water-holding capacity of biochar was higher than that of the paddy soil. When 30% biochar was added in the paddy soil, the water-holding capacity of seedling substrate was strongest and the average daily evaporation amount reduced by 6.4% compared with the control. When 5%?10% biochar was added to the paddy soil, the temperature of rice seedling substrate was the highest and there was 1.6? difference for daily maximum temperature of rice seedling substrate between treatments and control,1.05? difference for daily average temperature of rice seedling substrate between treatments and control. So, adding 5%?10% biochar in the paddy soil substrate, was helpful to overcome the low temperature obstacle factor at early spring northeast cold, created the soil condition of cultivating the strong and healthy rice seedlings.2. Adding biochar in paddy soil as rice seedling substrate had apparent regulating roles on soil nutrients under the condition of dry-nursery rice seedlings at early spring in Northeast. Therein, the contents of N, P, Mg, S, Zn and Cu increased, while the contents of K, Ca, Mn, Fe and Na decreased. The N?P?Ca?Mg?S?Mn?Zn?Cu and Na content with biochar treatment increased even by 0.41%,5.1%,2.9%,36.3%,97.5%,2.6%,85.0%,4.9% and 3.4% compared with control, respectively?3. Adding biochar in paddy soil as rice seedlings had obviously positive regulating roles on the quality of rice seedlings under the condition of dry-nursery rice seedlings at early spring in Northeast. Adding 5.0%?10.0%b iochar in the seedling substrate, can promote the roots growth and development of rice seedlings through the increase of root length, root surface area, root volume of rice seedlings, particular in the substantial increase of fine roots. There were apparent variations in root physiology and structure for the biochar treatments. The epidermal cells, thick-walled cells of roots developed well and arranged loosely, and the cortex tissue developed well and the vessel numbers increased. The indexes such as the radius of root, the epidermis thickness root, the cortex thickness of root, the cortex chamber areas of root, and the cross-sectional area of root vessel of rice increased significantly. Meanwhile, the plant height, dry matter accumulation, C/N, leaf age index and absorption ability of rice seedlings for mineral elements(N?P?K?Ca?Mg?S?Mn?Z?Cu?Fe?Na) enhanced and the quality of rice seedlings enhanced.4. The dry matter accumulation of rice root, leaf sheaths, leaf and panicles for the biochar treatments were significantly higher than those of control in the rice field after transplanting, showing the dry matter accumulation of these organs increased with the increase of biochar application amount. During the main growth periods of rice, biochar had obvious regulating roles on dry matter accumulation and distribution of different organs of rice. At in the tillering stage, the root-shoot ratio for the biochar treatments were obviously higher than that of control. But at the booting stage, the root-shoot ratio for the biochar treatments were all lower than that of control, taking on the descended trend with increases of biochar application amount. And at full panicle stage and mature period, root-shoot ratio for all the treatments did not change significantly. The dry stem and sheath of rice also increased, with the apparent transportation, exportation rate and transportation rate increased, that beneficial to the yield formation.5. Biochar promoted the nutrients absorption of rice plants in the rice field after for the biochar treatments were higher than those of control and the absorption and accumulation amount of Mn?Zn?Cu and Fe of rice plants were obviously higher than those of control when 20?80 t·hm-1 biochar were applied in the rice field. Biochar had more effects on the allocation of nutrient elements in different organs of rice at tillering stage and booting stage, while biochar had little effects on the allocation rates of most of mineral elements in different organs of rice at heading stage and maturity stage. It was clear that biochar could promote the allocation of nutrient elements in different organs of rice more reasonable.6. Biochar had important promotion roles on the yield formation of rice. The yield of rice for the biochar treatments were averagely 13.8% higher than that of control. When the biochar application amount arrived at 40 t·hm-1, the yield of rice was the highest and increased 27.8% compared with that of control, indicating the obvious yield increase roles of biochar. The main reasons that biochar promoted the yield increase of rice were increasing of the panicles per unit area and the factual kernels of each panicle. When moderate biochar (20 t?60 t·ha-1) was applied in the rice soil, the panicles numbers per unit area, factual kernels of each panicle, harvest index and biomass yield increased singificanltly. The reason of rice yield increased main due to the panicles numbers per unit area, factual kernels of each panicle, and the factual kernels of each panicle improved. At the same time, the application of biochar had no obvious effects on the quality of rice. |
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