Meta-Analysis of Effects of Nitrogen Fertilizer Application Rate and Planting Years on Yield and Quality of Alfalfa
In order to explore optimal nitrogen fertilizer application rate and planting years for alfalfa(Medicago sativa L.),a meta-analysis on the Chinese region was conducted to determine how yield and quality of alfalfa change with nitrogen fertilizer application rate and planting years.The articles published were chosen from domestic journals.Each article abstracted included data on nitrogen fertilizer application,planting years,yield and quality(crude fat,crude protein,acid detergent fiber and neutral detergent fiber).Site nitrogen fertilizer application rate was classified as 0 kg/hm2(no nitrogen application),0>nitrogen application rate≥50 kg/hm2(low nitrogen application),50>nitrogen application rate≥100 kg/hm2(medium nitrogen application),>100 kg/hm2(high nitrogen application).Site alfalfa planting years were classified as 1 year,2 years,3 years and 3-5 years.The results showed that as nitrogen application rate increases,the yield and quality index of alfalfa showed first increase and then decrease,with the highest per-formance at medium nitrogen levels;nitrogen application significantly affected the quality indicators of alfalfa(except neutral detergent fiber);compared with low and high nitrogen,alfalfa under medium nitro-gen showed the highest raising effect of crude protein content and the highest reduction effect of acid deter-gent fiber(P<0.05).As planting years increase,the raising effect of yield of alfalfa increased firstly and then decreased,with the highest performance at 3 years.Based on the forage yield and quality data exam-ined in this study,peak performance occurs in 50～100 kg/hm2 nitrogen application rate and 3 year old stands.However,in actual production,the appropriate amount of nitrogen fertilizer application and plant-ing years should be selected based on production goals,combined with actual conditions such as local cli-mate,soil conditions,and alfalfa varieties.
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