Effects Of Different Nitrogen Managements On Bud Growth And Nitrogen Utilization Characteristics In Ratoon Rice

As one of important cropping patterns of labor-saving and simplified cultivation,ratoon rice planting has being drawn more and more attentions of researchers and farmers.The growth and development of axillary buds are closely associated with grain yield of ratoon crops,the mature stage of main crops and the duration of 15 days after main season are crucial for emergence and growth of axillary buds,in which plants nitrogen status in plants has great effect on ratooning and grain yield in main and ratoon crops.In our experiment,two widely cultivated rice varieties,LY6326 and FLYX1H,were used to investigate the effects of different panicle nitrogen fertilizer application rates（low,medium and high levels,T1,T2,T3）and budding nitrogen fertilizer application rates（low,medium and high levels,N1,N2,N3）in main crop on dry matter accumulation,nitrogen uptake and distribution,and their relationships with ratooning and yield formation of main crop.The main results were as follows:（1）Sprouting of buds showed differences among panicle and budding fertilizer application rates.Panicle N fertilizer application had no effect on bud growth,however,budding N fertilizer increased elongation,numbers and bud fresh weights of buds on 3^rd,4^th,and 5^th nodes from the top.The bud length at mature stage of main crop was positively and significantly correlated with productive tiller percentage and ratoon ability in ratoon crop.The difference in bud lengths diminished gradually among various N treatments in 15days after harvesting.Compared to no budding fertilizer application,high and medium level of budding fertilizer applications increased productive tiller per area by 25.2-34.3%and ratoon crop yield by 12.4-21.6%.（2）The culm non-structural carbohydrates（NSC）content increased gradually from heading stage to maturity stage,then decreased gradually until to the 15^th day after harvest of main crop.Compared with no panicle fertilizer application,the panicle N fertilizer application had no effect on culm NSC in LY6326 and decreased the concentration in FLYX1H.Budding N fertilizer applications at high and medium levels had no effect on starch concentration,and decreased soluble sugar concentration by 23.7%and 8.0%in LY6326 and 40.2%in FLYX1H,compared with no budding fertilizer application.（3）Panicle nitrogen fertilizer influenced N concentration and accumulation to a certain extent in maturity stage of main crop.Applications of panicle N fertilizer in main crop increased nitrogen concentration,accumulation of stubble stems and panicles in both varieties.Stubble dry weight decreased gradually and axillary bud dry weight increased with the increase in budding nitrogen fertilizer.Compared with low N budding fertilizer application,high N budding fertilizer application increased N concentrations in stubble culm,stubble sheathes,buds,harvested stems and leaves by 51.5%,45.5%,97.0%,56.0%in LY6326,respectively,and increased by167.7%,89.4%,95.3%,71.9%in FLYX1H,respectively.（4）Different budding fertilizer applications influenced DW and nitrogen accumulation in maturity stage of ratoon crop.Compared to no budding fertilizer application,budding fertilizer applications at high and medium levels increased ratoon tiller DW by 38.4%and8.6%and ratoon tiller nitrogen accumulation by 38.7%and 22.5%,ratoon panicle DW by27.8%and 13.2%,leaf area index by 69.9%and 43.1%for LY6326,respectively;however,the budding fertilizer applications had no effect on N accumulation in ratoon panicles.For FLYX1H,the budding fertilizer applications increased by 27.8%and 4.5%for tiller dry matter,360.2%and 26.5%for nitrogen accumulation,57.4%and 47.3%for leaf area index,respectively;however,the two applications had no significant effect on panicle DW and N accumulation.（5）For nitrogen distribution among various parts of plants,panicle nitrogen accumulation in LY6326 and FLYX1H accounted for 42.0%-61.2%and 46.0%-68.3%of total nitrogen uptake in maturity stage of main crop under different panicle and budding fertilizer applications,stubble N accumulations for 15.7%-23.2%and 15.5%-24.9%,ratoon bud N accumulations for 4.7%-14.4%and 1.2%-11.1%.Additionally,budding fertilizer applications increased nitrogen distribution to stubbles and axillary buds,decreased nitrogen distribution to panicles in main crop.In maturity stage of ratoon crop,the proportions of stubble nitrogen in total nitrogen accumulation were 15.8%-23.2%in LY6236 and 14.3%-21.1%in FLYX1H,the proportions of ratoon tiller nitrogen accumulation in total nitrogen accumulation were21.5%-28.2%in LY6236 and 9.0%-32.2%in FLYX1H,the proportions of ratoon panicle nitrogen accumulation in total nitrogen accumulation were 50.8%-62.6%in LY6236 and53.5%-69.9%in FLYX1H.（6）Different panicle and budding nitrogen fertilizer applications influenced nitrogen uptake and nitrogen use efficiency for grain production（NUEg）in main and ratoon crops.For LY6326,high and medium panicle nitrogen fertilizer applications increased total N accumulation by 31.4%and 16.1%and decreased NUEg by 24.6%and 21.1%in main crop,and decreased total nitrogen accumulation by 12.5%and 8.6%in ratoon crop,compared to low panicle nitrogen fertilizer application.However,for FLYX1H,panicle nitrogen fertilizer applications had no effect on total nitrogen uptake and NUEg in main crop and total nitrogen uptake in ratoon crop.Budding nitrogen fertilizer application influenced total nitrogen uptake and NUEg in main crop.For LY6326,high and medium budding nitrogen fertilizer applications increased total nitrogen uptake by 31.4%and 16.1%,decreased NUEg by 23.5%and 26.5%,compared to no budding fertilizer application.Similarly,for FLYX1H,the two applications increased total nitrogen uptake by 27.2%and 3.6%,decreased NUEg 29%and 11.2%in main crop.Budding nitrogen fertilizer application influenced total nitrogen uptake and NUEg in ratoon crop.High and medium budding nitrogen fertilizer applications increased total nitrogen uptake by 38.7%and 3.5%in LY6236,27.2%and 8.3%in FLYX1H.Generally,budding nitrogen fertilizer application had no effects NUEg in ratoon crop in LY6326 and decreased NUEg in FLYX1H.（7）The bud length was positively and significantly correlated with N concentration and N accumulation,and had no correlation with NSC concentration and accumulation in stubbles in maturity stage of main crop.The grain yield of main crop was negatively and significantly correlated with DW,culm NSC accumulation,stem N accumulation in stubbles.The grain yield of ratoon crop was significantly and positively correlated with N concentration and accumulation,negatively with culm NSC concentration and accumulation in stubble at maturity stage of main crop.