Effects Of Different Nitrogen Forms On The Growth Of Malus Hupehensis Rehd. And ¹⁵N Absorption,Utilization And Loss Characteristics

Nitrogen is uptaken by plant as one of the soil main mineral element,and its content is closely related to the yield and quality of orchard.Nitrogen forms mainly include amide nitrogen,ammonium nitrogen and nitrate nitrogen three types,due to the influence of soil environment,plant characteristics and application method,the main nitrogen forms uptaken by apple,as well as its function mechanism and loss status,are significantly different.From the point of nitrogen forms,analyzing the characteristics of plant growth and soil nitrogen loss under different environmental conditions was of great significance for improving nitrogen utilization efficiency and solving the environmental pollution.Therefore,studying the state of plant growth,the absorption,utilization and loss of ¹⁵N under different treatment,such as nitrogen forms,fertilizing time,soil pH and so on,can provide theoretical basis for the scientific application of nitrogen in orchard.1.In this experiment,we used ¹⁵N labeled tracer technique,barometric process separation method（BaPS）and glycerophosphate-double sponge ventilation method as tool,to investigate the effect of each nitrogen form in different fertilizing time by the index of N utilization and loss.The results showed that in different seasons,the biomass of plant,which was treated with inorganic nitrogen（NH₄⁺-N and NO₃^--N）,was obviously higher than that of amide nitrogen treatment.And spring fertilization was beneficial to construct the plant roots.After spring fertilization treatment,the ¹⁵N utilization rate of NH₄⁺-N and NO₃^--N was as high as 13.68 % and 13.25 %,which was significantly greater than the 5.25 % of CO（NH₂）₂-N.The ¹⁵N utilization rate of plant in summer expressed as,NO₃^--N>NH₄⁺-N>CO（NH₂）₂-N,and the treatment of amide nitrogen was 6.21 %,had no obvious difference in spring fertilization treatment and summer fertilization treatment.The gross nitrification rate of each nitrogen forms in spring was significantly lower than that in summer.The loss ratio of ammonia volatilization treated with amide nitrogen in each season was 3.19 % and 3.98 %,and it had not significant difference.What’s more,the index of nitrification rate,denitrification rate and ammonia volatilization loss treated by CO（NH₂）₂-N were all lower than the treatment of NO₃^--N in summer.Therefore,the application of inorganic nitrogen fertilizer in spring is an effective measure to ensure plant growth and nitrogen use efficiency.And organic nitrogen should be used in summer,the rational distribution of it and inorganic nitrogen is an effective way to achieve the scientific management of orchard.2.In the study,the index of plant growth,¹⁵N absorption and loss were caught under the treatment of drought.And the results were as follows: under the treatment of normal irrigation and drought,the biomass of Malus hupehensis Rehd.both shown as NH₄⁺-N>NO₃^--N>CO（NH₂）₂-N.Under drought,the absorption ability of each organs treated by CO（NH₂）₂-N was significantly improved,the Ndff value of leaves,shoots and roots,was increased from 2.70,2.57 and 2.39 to 5.08,3.99 and 5.36 respectively.And its utilization rate,11.8 %,was also significantly higher than the value of normal irrigation level.But the ¹⁵N utilization rate of plant,under the treatment of NH₄⁺-N and NO₃^--N in drought,were decreased from 13.68 % and 13.25 % to 12.07 % and 10.65 %.Under the condition of drought,the nitrification and denitrification of inorganic nitrogen was obviously inhibited,and the loss rate was significantly decreased.The loss of denitrification rate and ammonium volatilization in CO（NH₂）₂-N was increased significantly,from 73.08 μg·kg^-1·h^-1 and 239.47 mg·m^-2 to 89.29 μg·kg^-1·h^-1 and 379.33 mg·m^-2,which was higher than the treatment of inorganic nitrogen.Therefore,drought treatment could reduce the loss of nitreification and denitrification of inorganic nitrogen and promote the absorption and utilization of amide nitrogen in plants.3.In this experiment,we used one-year-old apple rootstocks（Malus hupehensis Rehd.）as materials and ¹⁵N labeled tracer technique as tool,to study the effects of three different nitrogen forms on the plant growth,absorption and utilization under each soil pH gradient.The results showed that when pH<6.5,the biomass of plant under three nitrogen forms from high to low was CO（NH₂）₂-N>NH₄⁺-N>NO₃^--N,and when pH>6.5,the plant biomass was CO（NH₂）₂-N<NH₄⁺-N<NO₃^--N.Under the treatment of inorganic nitrogen,all the indexes of plant biomass reached the maximum when pH was 6.5.And the value of total nitrogen content of plant,which was treated with NH₄⁺-N and NO₃^--N,reached its maximum 0.47 g and 0.33 g.The treatment of CO（NH₂）₂-N reached the maximum value 0.40 g when pH was 5.5,and it utilization rate was 18.06 %,which was significantly higher than that of NH₄⁺-N and NO₃^--N in this pH level.And when pH increased from 6.5 to 7.5,the ¹⁵N utilization rate of NO₃^--N was still as high as 12.95 %,the change of pH had little effect on its utilization rate.But the utilization rate of CO（NH₂）₂-N and NH₄⁺-N decreased significantly,from 5.25 % and 13.68 %,to 2.86 % and 4.79 %.Therefore,we can find that,as one of the key factors that limit plant growth,soil pH significantly affect the absorption,distribution and utilization of plant under different nitrogen forms.Nitrate nitrogen is not sensitive to the change of soil pH,can be applied in a wide range of p H.And acid soil is more suitable to use organic nitrogen.