Studies Of Mixed Forms Of Nitrogen On Regulating The Formation Of Grain Yield And Quality Of Wheat (Triticum Aestivum L.) Cultivars With Specialized End-uses

Improving grain yield and quality of wheat cultivars with specialized end-uses is now one of key subjects.The nitrogen nutrition absorbed by crop is mainly NH₄⁺-N and NO₃^--N which could also be metabolized meanwhile.Applying different or mixed forms of nitrogen is one of important methods to regulate the growth and development of crop.Thus, pot experiments,field experiments and sand culture experiments were completed on a sandy loam at Henan Agricultural University Experimental Station during 2004-2006,respectively. Three winter wheat(Triticum aestivum L.)cultivars differing in gluten strength were used in experiments including Yumai 34(a strong gluten cultivar),Yumai 49(medium gluten) andYumai 50(weak gluten).Equal amounts of nitrogen in different forms were NH₂-N(urea), NH₄⁺-N(NH₄HCO₃),NO₃^-N(NaNO₃)or in mixed forms were the ratio of NH₄⁺-N to NO₃^--N was 75:25,50:50,25:75,and nitrification inhibitors dicyandiamide(DCD)was applied in each treatments.Effects were studied of different(or mixed)forms of nitrogen on rhizospheric microbial populations and activity of soil enzymes in the middle-later growing period,on content of endogenous hormones in different organs of wheat after anthesis,on activity of key enzyme involved in nitrogen metabolism and GS isozymes,on the photosynthetic characteristic of leaves,and on grain yield and quality.Details are as follows:1.Three cultivars and nitrogen of three forms(NH₂-N,NH₄⁺-N and NO₃^-N)were used in pot experiments to investigate the effects of nitrogen forms on rhizospheric microbial populations and activity of soil enzyme for wheat cultivars with specialized end-uses in the middle-late growing period.The results showed that the populations of microorganisms, activity of enzymes and pH in rhizospheric soil of wheat cultivars with specialized end-uses responded differently to nitrogen forms.The quantity of fungi,bacteria and actinomyces in rhizospheric soil was the highest when NO₃^--N was applied to wheat cultivar Yumai 34.The quantity of bacteria and actinomyces in rhizospheric soil of wheat cultivar Yumai 49 were promoted greatly by NH₄⁺-N,and fungi were stimulated by NH₂-N at booting and anthesis stage and by NO₃^--N in ripening stage.When NO₃^--N was applied to wheat cultivar 'Yumai 50',the quantity of fungi,bacteria and actinomyces in rhizospheric soil was increased greatly. The activity of urease,protease and nitrate reductase in rhizosphereic soil of all three wheat cultivars was stimulated by NH₂-N,NH₄⁺-N and NO₃^--N,respectively,and pH was the highest in NO₃^--N treatments.2.In the same pot experiments stated above,studies were carried out to evaluate the effects of nitrogen forms on content of endogenous hormones in roots,flag leaves and grains of wheat cultivars with specialized end-uses after anthesis.The results showed that content of endogenous hormones in wheat organs after anthesis responded differently to nitrogen forms, and hence grain filling process and grain weight was regulated.Zeatin riboside(ZR)content in roots and grains was the highest in grains formation stage,content of gibberellins(GA₃) in flag leaves was the lowest and content of indoleacetic acid(IAA),GA₃,and abscisic acid (ABA)in grains were higher 5～20 days after anthesis when NH₂-N was applied to wheat cultivar Yumai 34.ZR content in grains was higher 5 days after anthesis.Content of IAA,ABA in grains was lower about 15 days after anthesis.Content of ZR,GA₃ in roots, Content of IAA and GA₃ in flag leaves,and content of ABA,GA₃ in grains was lower, content of ABA in flag leaves,and content of IAA in grains were higher 15～25 days after anthesis when NH₄-N was applied to wheat cultivar Yumai 49.ZR content in roots,flag leaves and grains were higher 5 days after anthesis,content of IAA and GA₃ in grains 5～20 days after anthesis and content of IAA in grains 20～25days after anthesis were higher When NH₄⁺-N was applied to wheat cultivar 'Yumai 50'.3.Three forms of nitrogen(NH₂-N,NH₄⁺-N and NO₃^-N)or three mixed forms of nitrogen(the ratio of NH₄⁺-N to NO₃^--N was 75:25,50:50,25:75)were used in pot experiments to elucidate the effects of nitrogen forms on activity of key enzyme involved in nitrogen metabolism,on activity of glutamine synthetase(GS)isozymes,on content of free amino acid in different organs of wheat cultivars with specialized end-uses.The results indicated that nitrate reductase(NR)activity in roots and flag leaves was higher in all NO₃^-N treatments,NR activity in grains was higher in either all NH₂-N or NH₄⁺-N treatments.GS activity and activity of GS isozymes in flag leaves responded differently to three forms of nitrogen.Three GS isozymes was found in flag leaves after jointing stage of wheat,ie.GS1, GSx and GS2.GSx isozyme stripe was between GS1 and GS2.Among those GS2 activity was the highest,GSx activity was the lowest,GS1 was in the middle.Activity of GS2 and GSx showed the same trend and their activities were changeable with different forms of nitrogen. But GS1 activity was steady after jointing stage.GS activity was the highest within 14 days after anthesis when NH₄⁺-N was applied to wheat cultivar Yumai 34.Among those GS1 activity was the highest in NH₂-N treatments,and activity of GSx and GS2 was the highest in NH₄⁺-N treatments.GS activity was the highest at jointing and anthesis stage when NH₂-N was applied to wheat cultivar Yumai 49 and it was the highest in NH₄⁺-N treatments 7～28 days after anthesis.Among those GS1 activity was the highest in NO₃-N treatments,and activity of GSx and GS2 was the highest in NH₂-N treatments.GS activity was the highest at jointing,anthesis stage and 21,28 days after anthesis when NH₄⁺-N was applied to wheat cultivar Yumai 50,Among those GS1 activity was the highest in NO₃^-N treatments,activity of GS2 and GSx was higher in NH₄⁺-N or NH₂-N treatments.The free amino acid content in roots,flag leaves and grains was higher when NH₂-N or NH₄⁺-N was applied to wheat cultivars with specialized end-uses.Activity of NR,GS and GS2 was higher when applying NH₂-N or NH₄⁺-N to wheat cultivars with specialized end-uses,therefore,different organs had sufficient free amino acid which were favorable to increase protein content in grains.4.Three forms of nitrogen and three mixed forms of nitrogen were used in pot and field experiments to clearify the effects of nitrogen forms on photosynthetic characteristic in flag leaves and soluble sugar contents in different organs of wheat cultivars with specialized end-uses.This study indicated LAI,and SPAD reading,net photosynthetic rate(Pn),stomatal conductance(Gs),and transpiration rate(E)in leaves were higher either mixed forms of nitrogen or NO₃^--N was applied to wheat cultivars with specialized end-uses,and intercellular CO₂ concentration(Ci)in leaves was the contrary.Soluble sugar contents (SSC)in flag leaves was higher when NO₃^--N or the ratio of NH₄⁺-N to NO₃^--N was 25:75 was applied to wheat cultivar Yumai 34 and SSC in grains was higher when NH₂-N or the ratio of NH₄⁺-N to NO₃^--N was 50:50 was applied.SSC in flag leaves was higher when the ratio of NH₄⁺-N to NO₃^--N was 75:25 or 50:50 was applied to wheat cultivar Yumai 49 and SSC in grains was higher when NH₂-N was applied.SSC in flag leaves and grains was higher when NH₄⁺-N or the ratio of NH₄⁺-N to NO₃^--N was 50:50 was applied to wheat cultivar Yumai 50, respectively.LAI,and SPAD reading,Pn,Gs,E in leaves and SSC content in flag leaves and grains are higher when mixed forms of nitrogen or NO₃^--N were applied to wheat cultivars with specialized end-uses mean 'source' is abundant which is favorable to increase grain yield.5.Three forms of nitrogen and three mixed forms of nitrogen were used in pot and field experiments to investigate its effects on grain yield and quality of wheat cultivars with specialized end-uses.The results showed that grain yield was higher when the ratio of NH₄⁺-N to NO₃^--N was 75:25 were applied to wheat cultivar Yumai 34.Compared with NH₄⁺-N treatments,when the ratio of NH₄⁺-N to NO₃^--N was 75:25,grain yield increased by 13.84%and 11.04%in pot and field experiments,respectively.And protein content in grains was higher either applying NH₄⁺-N or NH₂-N.Compared with NO₃^--N treatments,protein content in grain in all NH₂-N treatments increased by 14.12%%and 11.17%%in pot and field experiments,respectively.Grain yield was higher when the ratio of NH₄⁺-N to NO₃^--N was 75:25 or 50:50 to wheat cultivar Yumai 49.Compared with NO₃^--N treatments,when the ratio of NH₄⁺-N to NO₃^--N was 75:25 or 50:50,grain yield increased by19.71%and 9.60%in pot experiments,respectively,and by 5.30%and 7.93%in field experiments.Protein content in grains was higher when NH₄⁺-N or NH₂-N were applied,but it was eligible in all forms of nitrogen treatments.Grain yield was higher when the ratio of NH₄⁺-N to NO₃^--N was 50:50 was applied to wheat cultivar Yumai 50.Compared with NH₂-N treatments,when the ratio of NH₄⁺-N to NO₃^--N was 50:50,grain yield increased by 19.75%and 6.11%in pot and field experiments,respectively.Meanwhile,protein content was lower when applying the ratio of NH₄⁺-N to NO₃^--N was 50:50 to wheat cultivar 'Yumai 50'.Therefore,it is recommended that NH₂-N be applied to wheat cultivar Yumai 34 to ensure its grain quality,that the ratio of NH₄⁺-N to NO₃^--N was 75:25 or 50:50 be applied to wheat cultivar 'Yumai 49' to take account of grain yield and quality,and that the ratio of NH₄⁺-N to NO₃^--N was 50:50 be applied to wheat cultivar 'Yumai 50' to achieve higher grain yield and quality.