Characteristics Of Nitrogen Utilization Under Different Nitrogen Strategies And Nitrogen Diagnosis Index In Specialty Wheats

It is important for the crop production of high quality, yield, and efficiency and unpolluted to improve nitrogen use efficiency (NUE) in wheat. Two cultivars of Huaimai 18(lower protein) and Xuzhou 26(higher protein) were evaluated to investigate the variation of NUE under different applying nitrogen rates and topdressing time, and highly efficient utilization of nitrogen physiological mechanism, and method of nitrogen diagnosis was established principally.Results showed that the indexes of NUE including nitrogen productivity of plant (NPP), nitrogen productivity of soil (NPS), nitrogen flow efficiency (NFE), nitrogen recovery efficiency (NRE) and nitrogen harvest index (NHI) increased with increasing nitrogen rates; declined with later nitrogen topdressing time. NHI varied least, which indicated NHI might be related with genetic characteristics; NFE differ most obviously, it indicated the ability of protein yield producing by using nitrogen effectively in wheat, including grain accumulation and using of soil nitrogen, was an applying appraising index.Wheat nitrogen accumulation, nitrogen translocation increased with increasing nitrogen rates and later topdressing nitrogen, but nitrogen translocation ratio reduced with increasing nitrogen rates, and increased with later topdressing nitrogen, which might be the result that NUE reduced with increasing nitrogen rates and increased with later topdressing nitrogen. Physiological indexes at different stage increased with increasing nitrogen rates and later topdressing nitrogen, including nitrogen and free AA content of different nutritional organs, NO3--N content, NRA and GSA of leaf and net photosynthesis rate of flag leaf. Correlative analysis showed wheat NUE positively correlation with AA/NCV-N of flag leaf at booting and anthesis, negatively correlation with C/N of leaf, stem and sheath. Relatively increasing AA content is good for absorption of nitrogen; increasing C assimilation and reducing nitrogen content of nutritional organs could increase wheat NUE.Wheat yields increased with increasing nitrogen rates (except high nitrogen treatment) and later topdressing nitrogen, but with 300kg.hm-2 nitrogen applied wheat yield reduced, that showed increasing wheat yield needed suitable applying nitrogen rate and topdressing time, exceeding high nitrogen rate was not good for increasing yield of wheat continue. Integrated analysis showed that medium nitrogen rate (210kg.hm-2) with later topdressing nitrogen could improve NUE, yield and protein content; it was a suitable nitrogen applying method.The leaf color varies with the leaf order and growth stage, before anthesis the SPAD of top 2nd > top lst> top 3rd > top 4th. The SPAD of top 1st catches and exceeds top 2nd 10 days after anthesis. The SPAD of different leaf order positively correlated with applying nitrogen rates and it varies with the nitrogen content of leaf at the same time. The SPAD values of top 4 leaves of the plant are higher at jointing stage, then decline little andbecome smooth, 10 days after anthesis they decline dramatically. The correlation analysis of plant nitrogen content at different growth stage and the SPAD values of different leaf order indicates that, jointing and booting stage are two critical stages, and the top 3rd leaf could be signal leaf. At jointing stage, the suitable and critical SPAD values for Huaimai 18 were 55.8 and 52.1, and for Xuzhou 26 they were 51.5 and 46.0 separately. The suitable and critical SPAD values at booting stage were 55.7 and 50.3 for Huaimai 18, and 49.3 and 46.6 for Xuzhou 26 separately. The optimal and critical nitrogen content at jointing stage were 4.26% and 3.92%, 4.55% and 3.99% for Huaimai 18 and Xuzhou 26 separately; the optimal and critical nitrogen content at booting stage were 4.25% and 3.75%, 4.33% and 4.06% separately.