| In recent years, rice production continues to increase in China, but the development of rice production is very uneven in different regions. The rice production was a classic representative in the high-altitude region of Ninglang in Yunnan Province, It’s the highest-altitude place to plant rice in China where the rice yield is much lower than in the middle-and low-altitude areas. Therefore, enhancing the production level and the production technology of the low productivity area is of great significance, which was the aim of this research, an experiment performed from2007to2008under unfavorable environmental and testing conditions. However, results were obtained that different manners of nitrogen application and temperature increasing had effect on rice plant growth and rice yield in high-altitude and cold areas. Our results may serve as referential parameters for theoretical research and practice on rice plant cultivation and defense against cold damage on rice plant in high-altitude areas.By using the local japonica rice variety Dabaigu and the new variety Lijing10as test materials, and the growth traits and the physiological-ecological characteristics of high-altitude and cold area rice plant as research background, this study mainly aimed at cultivating high-yield and high-quality rice plant in high altitude areas. The key problem to solve is:How to increase rice yield and quality under the high-altitude and low temperature conditions by proper nitrogen application and warming measures (i.e. by agronomic measures and water conservation measures). The main conclusions were arrived at as follows:(1) The population quality of Lijing10and Dabaigu was significantly improved with increased nitrogen application, but excessive nitrogen administration would have a harmful effect on the population quality and yield. When the same total amount of nitrogen was used, appropriately increasing basic and tiller fertilizer proportion might enhance the number of tillers, productive panicle, LAI, seed setting rate; and appropriately increasing panicle nitrogen proportion might raise the percentage of panicle-bearing tiller, the number of grains per panicle and reduce the attenuation of LAI at later period.When nitrogen amount was increased, the dry matter accumulation and panicle nitrogen accumulation of each treatment increased first and decreased afterwards, and the nitrogen dry matter production efficiency, nitrogen grain production efficiency, nitrogen physiological efficiency, nitrogen partial factor productivity decreased, but the nitrogen agronomy efficiency and nitrogen recovery efficiency increased first and decreased afterwards, with a maximal value under moderate nitrogen treatment. The nitrogen requirement per100kg grain have a suitable value under different varieties and nitrogen application, the suitable value for Lijing10was2.31-2.52kg, and that for Dabaigu was2.79-2.83kg. Since the air temperature in the high-altitude area was too low at later period, excessive nitrogen administration would delay rice grain grouting, postpone plant maturity and reduce filled-grain percentage.The dry matter and nitrogen transport of stem sheath was not smooth for all treatments, and massive dry matter and nitrogen remained in the stem sheath after full heading stage. Obviously, the low temperature at high altitude weakened rice plant respiration and consumption, prevented assimilates transferring, and resulted in the relatively low proportion of panicle dry weight to total dry weight.Analysis of the effect of nitrogen application on rice yield and the yield components suggested that increased production was mainly due to the increased total number of spikelets which resulted first from productive panicle increase and next from the increased grains per panicle. The best combination was60kg.hm-2of nitrogen and a7:3ratio of base-tillering fertilizer to panicle fertilizer, which improved nitrogen recovery efficiency and produced the highest of all the treatments.(2) The soil daily average temperature of ridge cultivation and warm-water irrigation was0.52-2.94℃higher than that of conventional cultivation in the period from rice transplanting to maturity. Before the critical stage of productive tillering, the root number per plant of two varieties showed a trend of warm-water irrigation>conventional cultivation> ridge cultivation, and the root dry weight and total length of the roots of each treatment presented a trend of warm-water irrigation>ridge cultivation>conventional cultivation. After the jointing stage, the property of root traits indicated a trend of ridge cultivation>warm-water irrigation> conventional cultivation.Warming measures promoted the root biomass at the lower layer of soil, and the root growth downward benefited absorption of deep soil moisture and nutrients by rice plants at the late growth stage. The relationship between upper root (0-10cm) and yield was closer than that between the lower root (10cm below) and yield under the conditions of the present investigation. The main characters of root and the ground traits and yield components indicated a significantly or very significantly positive correlation at the full heading stage and maturity stage. And of the yield component factors, the productive panicle is the most closely related to the major root characteristics.(3) The measure of warming had three functions:it was helpful in promoting rice growth, accelerating tillering, making the community form suitable stem tiller composition, increasing the productive tiller rate, and optimizing the population quality; it improved dry matter accumulation, especially crop growth rate, net assimilation rate, photosynthetic potential, and higher overall photosynthetic potential-grain ratio than the conventional cultivation, after the full heading stage; and it reduced the declining rate of leaf area after full heading stage, extending the period of leaf function which was essential in enhancing the population-photosynthesis productive forces after the heading stage. The dry matter of leaf weakened but the dry matter of stem sheath increased, the dry matter exported from the stem sheath was less than that had been accumulated, resulting negative DMER from stem and leaf and transformation rate.Compared with conventional cultivation, ridge cultivation increased the productive panicle and seed setting rate and reduced grains per panicle. Warm-water irrigation improved the productive panicle, seed setting rate and grains per panicle, and1000-grain weight difference was very small between each treatment. Path analysis showed that the highest to the lowest direct path coefficients with the yield were in the order of productive panicle, grains per panicle, seed setting rate and1000-grain weight. The highest coefficient with yield was that of the productive panicle, suggesting that the productive panicle contributed the most to rice yield. Comparing the two warming measures, ridge cultivation had a greater impact on tillering, panicle formation, nitrogen accumulation and dry matter accumulation, and higher yield.(4) Comparing the two varieties of rice plants in this investigation, warming measures and nitrogen treatment produced greater impact on head rice rate, chalky ratio, chalkiness degree, gel consistency, amylose content and protein content. This suggested that appropriate nitrogen treatment improved head rice rate and lowered chalky ratio and chalkiness degree. Increasing nitrogen application shortened gel consistency gradually, decreased amylose content but increased protein content in rice.Under warming treatment, head rice rate exhibited a varying tendency of ridge cultivation>warm-water irrigation>conventional cultivation; and chalky ratio and chalkiness degree exhibited a tendency of a ridge cultivation<warm-water irrigation and conventional cultivation. Ridge cultivation obviously improved the gel consistency, amylose content and protein content. Interaction between warming measures and nitrogen fertilizer showed a higher milling quality and appearance quality of rice under ridge cultivation and moderate nitrogen treatment (RM); and the protein content in rice was higher under ridge cultivation and high nitrogen treatment combination(RH) than under warm-water irrigation and high nitrogen treatment combination(WH).(5) Application of precise and quantitative cultivation of rice to quota design and implementation for the target yield and yield components, seeding rate, the number of basic seedling, sowing date, transplanting stage, nitrogen fertilizer amount and irrigation patterns in the high-altitude and cold areas produced the following results:precise and quantitative cultivation significantly enhanced tillering, substantially increased productive panicle, total number of spikelets and LAI, accelerated dry matter accumulation, and maintained a strong photosynthetic ability in the later period of rice growth.Analysis of the correlation between plant type indexes and yield components at the heading stage indicated that there were differences between different populations in characteristics of plant type and grain yield components such as effective panicles, total number of spikelets. The notable characteristics of high-yield group were as follows:the top three leaves were longer; the angles of top three leaves were smaller; the specific leaf weight was high at the heading stage and was closely related to the traits of leaves, stems and panicles; the internodes on stem distributed reasonably with shorter bottom internodes and longer top internodes. A significantly positive correlation was observed between first branch numbers, second branch numbers and grain yield.Both enlarging sinks (increasing the total number of spikelets) and promoting sources (increasing the leaf area index after the heading stage and the specific leaf weight) were beneficial for rice yield increase. Synchronizing nitrogen and water application in precise and quantitative cultivation and organ formation in high-yield rice raised the leaf area index and increased the total number of spikelets, and ultimately contributed to a higher rice yield in high-altitude areas.Comparatively, under the same nitrogen treatment, the rice variety of Lijing10 acquired a higher amount of dry matter accumulation, nitrogen accumulation, nitrogen recovery efficiency, crop growth rate, net assimilation rate, relative growth rate than Dabaigu. In the entire growth period, Lijing10produced greater average dry weight of single plant root, total length of the roots, root surface area, and slower weakening, than Dabaigu. All this greatly benefited Lijing10in photosynthetic efficiency and physiological activity especially after the full heading stage, which was the main reason a higher yield of Lijing10than that of Dabaigu. Lijing10enjoyed longer grain shape and gel consistency and higher protein content than Dabaigu, which was related with the hereditary characteristics of the variety. |
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