¹⁵N Tracer Technology To Study The Effect Of Organic And Inorganic Nitrogen On The Growth And Development Of Mung Bean And Its Nutrient Absorption And Utilization

As a medical and health food,mung bean is one of the main coarse grain crops planted in China.Its nitrogen is supplied by the dual nitrogen sources of root nodule nitrogen fixation and soil nitrogen.Therefore,reasonable nitrogen application level can effectively balance the absorption of dual nitrogen sources.In this experiment,inorganic and organic nitrogen were used as nitrogen sources to study the effects of mung bean growth and development,photosynthetic physiological characteristics,nitrogen,phosphorus and potassium nutrient absorption and distribution,and soil characteristics.The ¹⁵N tracer technology was used to track the dynamic change of fertilizer nitrogen in the soil-mung bean system,and the theory of replacing inorganic nitrogen with organic nitrogen in mung bean production was explored through comprehensive analysis of mung bean’s absorption of nitrogen from nodal nitrogen fixation and fertilizer nitrogen.The pot experiment was carried out,and N0(¹⁵N=0.00g plant^-1),N1(¹⁵N=0.23g·plant^-1),N2(¹⁵N=0.29g·plant^-1),N3(¹⁵N=0.35g·plant^-1),ON1(¹⁵N=0.15g·plant^-1,N organic=0.15g·plant^-1)and ON2(N organic=0.29g·plant^-1),The dosage of phosphorus（P₂O₅）and potassium（K₂O）were 0.35g·plant^-1and 0.18g·plant^-1.The dry matter and nitrogen,phosphorus and potassium nutrient absorption of mung bean in R8 phase were measured in the field test.The results were as follows:1.The 1000-grain weight and crude protein content of mung beans were significantly increased under the low nitrogen treatment.The yield of mung beans was increased by increasing pod number and pod number under the medium nitrogen treatment.The yield of mung beans was increased by 9.6%under the high nitrogen treatment.The stem diameter,1000-grain weight,yield and crude protein of 50%organic nitrogen replacement fertilizer and100%organic nitrogen replacement fertilizer were significantly increased by 5.9%and 4.7%compared with pure nitrogen application.By controlling the height of mung bean plant,100%organic nitrogen fertilizer could make mung bean grow toward"short and strong"type.During R1～R6 stage,the fresh weight of nodule gradually decreased significantly with the increase of fertilizer nitrogen dosage,and the application of organic nitrogen could alleviate the inhibition of fertilizer nitrogen on the growth of rhizobia.2.With the increase of nitrogen application rate,the chlorophyll content,photosynthetic capacity and nitrate reductase activity of mung bean leaves were increased,and the growth of mung bean was vigorous.The SPAD value of organic nitrogen application was 2.6%～3.4%higher than that of pure nitrogen application,and the photosynthetic accumulation of mung beans during the growth period was improved.3.Dry matter accumulation and N,P and K accumulation of mung beans were positively correlated with nitrogen application rate.Medium nitrogen treatment increased grain yield and N,P and K nutrient transport accumulation,and application of organic nitrogen fertilizer increased dry weight,N accumulation and N content of mung beans and grains,and improved N fertilizer use efficiency,agronomic use efficiency and partial N productivity of mung beans.However,the mung bean treated with 100%organic nitrogen replacement significantly reduced the uptake of P,which resulted in the lowest accumulation and concentration of P in the grain.The trend of field experiment was consistent with pot experiment.4.Mung beans can assimilate nodule nitrogen fixation and fertilizer nitrogen.The early stage of R1 is the peak stage of mung beans’demand for fertilizer nitrogen.When the peak stage of nodule nitrogen fixation（R1～R3 stage）is reached,¹⁵N absorbed in the early stage of mung beans will be dynamically exchanged out of the plant through the root-rhizobium system.At R6-R8 stage,¹⁵N would be re-accumulated in mung bean plant body with the partial death of rhizobia.The proportion of ¹⁵N in grains under medium nitrogen treatment was 57.0%,which was beneficial to the transfer of fertilizer nitrogen to grains.50%organic nitrogen replacement treatment resulted in the highest soil ¹⁵N residue,and ¹⁵N accumulation in R8 stage was 39%higher than that in R1 stage.Using ¹⁵N tracer method to calculate the results found that with the increasing of application rate of nitrogen utilization rate of nitrogen fertilizer plant growth trend,utilization rate of between 14.0%～26.1%,50%nitrogen fertilizer utilization ratio of organic nitrogen replacement treatment was 23.0%,compared with that of the pure nitrogen fertilizers,there was no significant difference,difference method to calculate apparent utilization ratio of nitrogen fertilizer at the same time than the utilization rate of ¹⁵N tracer method measured were 6.6～31.3%.5.Under the influence of nodule nitrogen fixation,soil alkali-hydrolyzable nitrogen content reached the highest at R6 stage,and decreased again with the death of rhizobia at R8stage.Organic nitrogen fertilizer could increase soil alkali-hydrolyzable nitrogen content at later growth stage of mung bean.During the growth period,the content of soil available phosphorus decreased gradually under the treatment of pure nitrogen fertilizer application,and there was a significant negative correlation between the amount of phosphorus uptake by plants and the content of soil available phosphorus.Soil available phosphorus content was significantly increased by 2.7%～7.0%when organic nitrogen fertilizer was applied.At R8stage,the content of soil available potassium increased significantly in all treatments.Fertilizer nitrogen application decreased soil p H value and organic matter content,but increased soil urease activity.Organic nitrogen application decreased soil p H value and urease activity,but increased soil organic matter content and invertase activity.