Effects Of Nitrogen Application And Cutting Frequency On Yield And Quality Of Alfalfa In Seasonal Cultivation

In order to find out the appropriate nitrogen application and cutting frequency for alfalfa(Medicago sativa L)in Nanjing area,a field experiment was conducted at Liuhe experimental station of Jiangsu Academy of Agricultural Sciences from September 2012 to June 2013 and September 2013 to May 2014.The trail was designed in split-plot.Cultivar Sanditi was used to research the effect of nitrogen application and cutting frequency on alfalfa growth,yield and its components and forage quality.Nitrogen rate was the main treatment applying 60,120,180,240 kg N/hm2 respectively.Cutting frequency was auxiliary treatment with 3,4,5 cutting times respectively.Each treatment had three replicates.The results showed as follows:1.The effect of nitrogen application and cutting frequency on yield components showed that under different cutting frequency alfalfa plant height,shoots per plant,leaf area per plant and weight per shoot were increased significantly(P<0.05)with N rate.Each component was higher than other treatments with applying 180 kg N/hm2 nitrogen fertilizer,but it was not continue to increase with applying 240 kg N/hm2 nitrogen fertilizer.Increasing cutting frequency decreased plant height,leaf area per plant and mass per shoot.High cutting frequency accelerated shoot growth of alfalfa.Nitrogen application increased alfalfa photosynthetic capacity,net photosynthetic rate had a rising trend,but there had no significant difference between each treatment.Compared the impact of cutting frequency on alfalfa photosynthetic capacity under different nitrogen application,net photosynthetic rate at cutting 4 times in spring was higher than other treatment.2.The variation of alfalfa above ground dry matter accumulation was in accordance with yield components and increased significantly(P<0.05)with N rate.Applying 180 kg N/hm2 nitrogen fertilizer had the highest hay yield in two years.In 2013,alfalfa dry matter yield was 11.44 t/hm2,11.09 t/hm2 and 9.59 t/hm2 respectively with 180 kg N/hm2 nitrogen application at each cutting frequency and these yield were higher than those of 120 kg N/hm2 and 240 kg N/hm2 treatment from 2.23%to 12.93%.In 2014,alfalfa dry matter yield was 11.79 t/hm2,12.03 t/hm2 and 10.79 t/hm2 respectively with 180 kg N/hm2 nitrogen application at each cutting frequency and these yield were higher than those of 120 kg N/hm2 and 240 kg N/hm2 treatment from 1.98%to 9.86%.Under different nitrogen application,alfalfa dry matter yield was decreased with cutting frequency increasing.Cutting 3 times in spring had the supreme forage yield.3.Mass per shoot,plant height and leaf area per plant were made great contribution to DMY and had important influence on alfalfa yield.4.By measuring alfalfa forage quality we found that at same cutting frequency,quality was improved with N rate.Moderate nitrogen application enhanced alfalfa CP,DDM and decreased the S/L,NDF and ADF.But when applied 240 kg N/hm2,it might cause an inhibiting effect to forage quality.High cutting frequency made alfalfa plant more fresh and tender,low fiber content and good digestibility.The minimum value of NDF and ADF was 42.64%,21.69%(2013)and 39.75%,21.10%(2014)respectively at 5 cutting frequency.Moderate cutting 4 times treatment had a higher DDM with highest DMY in spring.5.The nitrogen application × cutting frequency interaction was not significant in alfalfa yield and forage quality.In conclusion,180 kg N/hm2 nitrogen application and cutting 3-4 times in spring could be the best standard for high yield and quality forage production.