Effect Of Nitrogen Fertilization On The Growth Of Chamaecrista Rotundifolia And Nitrogen Utilization Efficiency

Fertilization is an important means of aritficial grassland management,sufficient nutrient are offered with proper fertilizaiton for the and growth and development of pasture,creating a favourable nutritional circumstance,modulating plant physiological metabolism,elevatingnutritional efficiency of plant,threrby,the yield of pasture is increased,the quality is improved,but nutrient lackness and excess effect the growth of pasture,especially inhibit the nitrogen-fixing ability,Exceed fertilization result in the generous waste and environmental contamination as well.Chamaecrista rotundifolia is a creepingly perennial tropical legume with,since it was introduced from Australia by Fujian Academy of Agricultural Sciences in 1989,Chamaecrista rotundifolia has been introduced successfully in Hunan, Guangdong,Fujian,Jiangxi and so on,and become an important local forage legumes resource.It has been widely applied as high-quality modified green manure and forage species in hilly and mountainous red earth regions.Forage legumes Chamaecrista rotundifolia was adopted as material in this paper to study the influence of different nitrogen supply on the nitrogenous metabolism,yield,quality and boilogical nitrogen-fixation with ¹⁵N tracer technology,the aim was to probe the rule of nitrogenous transformation in the soil-grass system,providing scientific theory for nitrogen fertilizer application. The key result are as follows:1.Proper nitrogen fertilization could promote the growth of Chamaecrista rotundifolia,it's showed that plant height,the amount of each branch and biomass have been increased significantly, and the formation of nodule has been promoted;the biomass of 30mg/kg nitrogen fertilization is 17.62%higher than the control;but when the nitrogen fertilizer is greater than or equal to 45 mg/kg, the plant height,amount of each branch and biomass of Chamaecrista rotundifolia would decrease. Proper nitrogen fertilization could promote the quality of Chamaecrista rotundifolia to some extend. In the treatment of Chamaecrista rotundifolia,with the nitrogen fertilization of 30mg/kg,the contents of crude protein,crude fat,crude ash,P and K are higher than those of the control,22.6%, 17.84%,6.32%,6.81%and 8.34%respectively,and the content of crude fiber decrease for 5.86%. From the points of production and quality of Chamaecrista rotundifolia,30mg N/kg is the proper amount under the condition of this engineered experiment.2.nitrogen element is one of the three mian fertilizers for the growth and development of plant, the inorganic nitrogens in soil are assimilated and transformed to organic matters such as protein as absorbing by plant,nitrate reductase(NR)and glutamine synthetase(GS)play an important role in the reduction of nitrate and the synthesis of amino acids,respectively,having intimate relationship with nitrogenous utilizaiton efficency.The reuslt of the research showed that,with the application of nitrogen fertilizer in the range of 0～30mg/kg soil,the activities of NR and GS of Chamaecrista rotundifolia were increased,along with the amount of applied nitrogen,as well as the soluble protein in leaves,however,the content of NO3-N in leaves was decreased.When the nitrogen fertilization was greater than 30mg/kg soil,the activity of NR and GS were decreased gradually, the content of soluble protein was reduced,while NO3-N in leaves was accumulated.3.The effect of nitrogen with different levels on the biological nitrogen-fixation in Chamaecrista rotundifolia is relatively large.At the low level,under 30mg/kg soil,the rate and amount of nitrogen-fixation in Chamaecrista rotundifolia were increased as the nitrogen concentration increased;when 30 mg/kg soil of urea was applied,the quantity of biological nitrogen-fixation in Chamaecrista rotundifolia reached the peak,occupying 29.50%.Although the high level of nitrogen applied could increase the nitrogen content of the plant,this could inhibit the formation of nodules,and decrease the nitrogen-fixation capability.4.the result in the paper display that,the content of total nitrogen in the upground and underground of plant were increased with the increase of nitrogen concentration,with the comparision with the control,increasing by 5.03%～22.01%,2.34%～10.94%,from the treatment of N₁ to N₄,differed significantly.With the increase in nitrogen concentration applied,the uptake of nitrogen element showed the tendancy of increased first and then decreased.The max N uptake was the N₂ treatment,regardless of the phase of offset,proto-blooming,or pod-knotting,increasing by 59.26%,57.72%and 23.35%,respectively,among them,the N₂ treatment was the best.5.There was three sources of plant nitrogen nutrition,including nitrogen-fixaiton by root nodule,mine nitroeng nutrient in soil and that was supplied with nitrogen fertilizer.In the whole growth period of Chamaecrista rotundifolia,the percent of nitrogen demaded from fertilizer (%Ndff)in the upground and underground of plant had a positive correlation with the amount of nitrogen feritlizer-urea.When compared to the no feritizer,the%Ndff in the up/down-ground in the treatments of N₂,N₃ and N₄ were increased by 168.74%～353.24%,61.65%～339.64%,123.45%～559.91%and 159.83%～350.65%,43.98%～331.74%,92.12%～534.31%,respectively.Among the total,the treaments of N₃ and N₄ differed markly with N₁.6.The utilizaiton rate was reduced with the increase of nitrogen appliation dose in the article, which in the treatment of N₂,N₃ and N₄ were decreased by 1.91%,17.10%and 18.89%, respectively,while compared to N₁.the result of variance analysis showed,the difference in the treatments between N₁ and N₂,N₃ and N₄ came to extreme markly.Howerver,the residual of nitrogen applying with fertilizer was oppsite to utilization rate,N₂,N₃ and N₄ were increased by 1.53%,18.98%and 30.21%,respectively,as compared to N₁,among them,the difference between N₃,N₄ and N₁ reached extreme strikingly.As far as lose rate of nitrogen fertilizer,N₁ and N₂ were comparatively large,holding 38.654%and 38.693%,respectively,but no significant difference was found among N₂,N₃,N₄.Among them,N4 lose rate was the minumun of all,it might be have some relation with the redimental rate of nitrogen element.