Effect Of Nitrogen Application On Root Growth And Yield Of Soybean Under Drought Stress

Nitrogen fixation is one of the important sources of nitrogen in soybean.The nitrogen fixation capacity of soybean affects the nitrogen absorption efficiency and thus affects the yield.Soybean is a crop that needs a lot of water for growth and development,drought has a great impact on soybean growth and development.In this experiment,drought treatment was combined with nitrogen fertilizer application,and soybean cultivars LD11 and LD14 were selected as test materials,under potted conditions,the morphological traits of root,nodule number,fresh nodule weight,the activity of nitrogenase,hemoglobin content,root dry weight,shoot dry weight,the root-shoot ratio and the nitrogen content were determined at the flowering stage,the podding stage and the grain filling stage respectively.The agronomic and yield traits were measured at maturity.The effects of nitrogen application on root morphology,physiological characteristics of nitrogen fixation in root nodule,root-shoot ratio,plant nitrogen content and yield formation of soybean under drought stress were discussed.The main research results are as follows:1.Under drought stress,the root surface area,root volume and root diameter of LD11 and LD14 were all lower than those of normal water treatment,the root system is longer than that of normal water treatment.With the increase of nitrogen application level,the root surface area,root volume,root diameter and total root length of LD11 increased first and then decreased.The root surface area and total root length of LD14 gradually increased.At the flowering and podding stages,the root diameter of LD14 first increased and then decreased and the root volume gradually increased.At the grain filling stage of soybeans,the root diameter of LD14 showed a trend of gradually increased.Under the base fertilizer treatment,the root volume gradually increased,under the R1 stage topdressing treatment,the root volume first increased and then decreased.This indicated that the root of LD14 had a stronger ability to absorb and utilize water and nutrients after applying nitrogen fertilizer,and had a better resistance to fertilizer.2.Under drought stress,the nodule fresh weight and nodule number of LD11 and LD14 decreased,and the N100 fertilization level promoted the nodule growth of LD11 and LD14.Under the N150 fertilization level,the nodule fresh weight of LD14 increased under the R1 stage topdressing treatment,while the rest were inhibited.Drought decreased the activity of nitrogenase and the content of soybean hemoglobin in root nodule,and gradually decreased with the increase of fertilization level.At the grain filling stage,the nitrogenase activities of LD11 and LD14 without fertilization were decreased by 26.67% and 24.79% respectively under drought stress.The application of base fertilizer and R1 stage topdressing treatment were lower than that of no fertilization treatment,in which R1 stage N100 topdressing treatment reduced 42.89% and 48.58%,respectively,and R1 stage N150 topdressing treatment reduced 68.35% and 69.19%,respectively.The change of soybean hemoglobin content was consistent with that of nitrogenase activity.This indicated that under drought stress,nitrogen fixation in root nodule of both LD14 and LD11 was inhibited,and the inhibition was enhanced after nitrogen application,and the inhibition of LD14 was stronger than that of LD11.3.Under drought stress,root dry weight,shoot dry weight and root-shoot ratio of LD11 and LD14 all decreased.Nitrogen application to some extent improved the root-shoot distribution ratio of the two cultivars under drought stress,and the root-shoot ratio of the two cultivars increased.Under the same nitrogen fertilizer treatment,the root-shoot ratio of LD14 was higher than that of LD11,and the root system was more capable of absorbing water and nutrients.4.Under the drought condition,the nitrogen content of plants in the maturity stage of LD11 and LD14 decreased,and the nitrogen content of plants in the nitrogen application stage increased,and the expression of LD11 was N100>N150>N0,and the expression of LD14 was N150>N100>N0.This indicated that under drought stress,nitrogen content of plants in both LD14 and LD11 would decrease.After nitrogen application,the nitrogen fixation ability of root nodule was weakened,and the energy and carbohydrate consumption of nitrogen fixation were reduced,which promoted the nutrient absorption and nitrogen content of plants under drought stress.Moreover,with the increase of nitrogen application level,the nitrogen accumulation of plants in LD14 increased.5.Under drought stress,pod height,plant height node number and branch number of LD11 and LD14 all decreased.With the increase of fertilization level,the plant height,node number and branch number of LD11 were N100>N150>N0,LD14 was N150>N100>N0,the pod height of LD11 was N150>N100>N0,and the pod height of LD14 was N100>N150>N0.Under drought stress,the seed weight per plant and the seed weight per plant of LD11 decreased to a higher degree than that of LD14.With the increase of nitrogen application level,the seed weight per plant of LD11 first increased and then decreased,while that of LD14 gradually increased.At the same nitrogen fertilizer level,the yield of LD14 was higher than that of LD11,and the fattening resistance was stronger than that of LD11 under drought stress.