Alfalfa Yield And Quality In Response To Nitrogen Fertilizer Application

Alfalfa（Medicago sativa L.）stands as a vital leguminous forage grass,playing a significant role in China’s grass industry.Alfalfa production cannot meet demands both in yield and quality due to marginal land with poor soil fertility and suboptimal climate conditions.It is necessary to apply fertilizers to achieve high yields and high-quality alfalfa in China.However,there is a lack of systematic research about fertilizer application on alfalfa production across China.In Inner Mongolia,which is one of the important regions for alfalfa production.There exists a research gap concerning the impact of nitrogen（N）fertilization on alfalfa yield and quality during growth stages,as well as the correlation between soil N supply and alfalfa N uptake.Thus,we conducted a meta-analysis to explore the contribution of fertilizer application to the yield and quality of alfalfa.Through a combined approach of alfalfa field and pot research,we systematically explored the effects of different N fertilizer levels on alfalfa yield,quality,N fixation,and soil N concentration during its growth stages.We also analyzed the effects and mechanisms of N fertilizer application on alleviating salt stress.We used field data to calibrate the APSIM model and simulate the changes in crop productivity,quality,economic returns,and soil organic carbon of long-term planting of alfalfa and alfalfa-maize crop rotations under climatic changes.1.The results of meta-analyse showed that fertilizer application not only increased alfalfa yield by 19.2%but also improved alfalfa quality by increasing crude protein（CP）by 7.7%and decreasing acid detergent fibre（ADF）by 2.9%and neutral detergent fibre（NDF）by 1.8%overall compared to the non-fertilizer control levels.The combined N and phosphorus（P）and combined N,P and potassium（K）fertilizer applications achieved the greatest yield increases of 28.7 and 27.0,respectively.The combined NP fertilizer applications achieved the highest concentration increases 13.5%.Considering both yield and quality,the optimal rate of fertilizer application ranged from 30 to 60 kg ha^-1 for N,120 to 150 kg ha^-1 for P and less than 120 kg ha^-1 for K.2.We analysed the response of alfalfa yield and quality to nitrogen fertilization:the results showed that alfalfa height,stem diameter,number of branches did not respond to N fertilizer application during the alfalfa early flowering stage.And the N application of180 kg ha^-1 could significantly increase alfalfa total yield.In addition,N application of 60kg ha^-1or 120 kg ha^-1 increased alfalfa N uptake,CP,decreased ADF and NDF in vegetative or bud stage.The N fixation of alfalfa was significant higher when N fertilizer application was 60 kg ha^-1.Considering yield,quality,and N fixation collectively,the optimal rate of N fertilizer application was 60 kg ha^-1 in Inner Mongolia.3.The results showed that salt stress significantly decreased alfalfa biomass,N content,N fixation and quality when the salt level was above 100 mmol Na₂SO₄ L^–1.However,N supply significantly improved alfalfa weight by 23.2%-45.4%,and increase shoot N content by 10.2%-28.5%for alfalfa growth in salt-affected soil.The N supply was also beneficial for the%Ndfa and N fixation for alfalfa with salt stress,and the increase reached 47.8%and 60.5%,respectively.4.We utilized field trial data to validate the adaptability of the APSIM model for alfalfa yield and quality in the Inner Mongolia region of China.The normalized root mean square errors（NRMSD）for aboveground biomass and nitrogen uptake of alfalfa were 14%and 13%,respectively.The NRMSD for nitrogen fixation and crude protein（CP）content were 44%and 3.4%,respectively,with determination coefficients（R²）of0.77 and 0.80,respectively.Based on long-term meteorological data and the model,the alfalfa-maize rotation system could ensure maize yield without reduction while reducing nitrogen fertilizer input by 90 kg ha^-1 compared with continuous maize cultivation.Through a comprehensive analysis of crop yield,economic factors,and environmental aspects,the 5-year alfalfa rotation with 1 or 2 years of maize is the optimal long-term cropping system.In summary,fertilization is an effective measure to improve the yield and quality of alfalfa in China.Fertilizer application could not only enhance yield but also improved quality and promoted nitrogen fixation.The N supply offset the negative effects on alfalfa growth and N fixation caused by salt stress.The APSIM model after parameter calibration can be used to simulate crop productivity of long-term alfalfa and alfalfa-maize rotation cultivation systems in the Inner Mongolia.