Characteristics Of Alfalfa And Poa Pratensis Rotation Sequences On Aboveground Dry Biomass,Forage Quality And Soil Nitrogen

The study was carried out in Lanzhou forage experimental station of Gansu Agricultural University,5-year-old Alfalfa grassland and 5-year-old Poa pratensis grassland were selected as the samples,The treatment of Poa pratensis-alfalfa and Alfalfa-Poa pratensis was carried out,and the continuous cropping of Poa pratensis and Alfalfa was used as a control.Rotation for 1² years?2017²018?,The aboveground samples of the different cuts and 0²0 cm,20⁴0 cm soil samples from April to October were collection.Study on the aboveground dry biomass,forage quality and spatial and temporal characteristics of soil nitrogen in different rotation sequences of Alfalfa and Poa pratensis.the following research results were obtained.?1?The aboveground dry biomass?Alfalfa,Poa pratensis?under rotation was significantly higher than that under continuous cropping.In the first year after rotation,Poa pratensis-alfalfa and Alfalfa-Poa pratensis were 7.37%and 8.38%higher than that continuous cropping of Alfalfa and Poa pratensis,respectively;In the second year after rotation,the aboveground dry biomass of Poa pratensis-alfalfa and Alfalfa-Poa pratensis was23.44%and 41.13%higher than that of the control,respectively.The aboveground dry biomass of Alfalfa and Poa pratensis increased by 6.09%and 13.57%respectively in the second year after rotation compared with the first year,respectively.?2?The content of CP and RFV of Alfalfa and Poa pratensis were higher than that of continuous cropping,and the contents of NDF and ADF were lower than continuous cropping.In the first year,the CP content and RFV of Alfalfa under rotation were 7.62%and19.38%higher than that of continuous cropping,respectively,and the NDF and ADF contents were 10.91%and 11.46%lower,respectively.The CP content and RFV of Poa pratensis under rotation were 8.17%and 20.39%higher than that of continuous cropping,and the NDF and ADF contents were 11.41%and 8.58%lower,respectively.In the second year,the CP content and RFV of Alfalfa under rotation were 12.80%and 21.59%higher than that of continuous cropping,respectively,but ADF content was 9.05%and 17.33%lower,respectively.The CP content and RFV of Poa pratensis were compared.The continuous cropping rate was 25.36%higher than that of 15.73%,but the NDF and ADF contents were 8.44%and 11.22%lower,respectively.In the second year of rotation,the CP content and RFV of Alfalfa and Poa pratensis were higher than that of the first year,and the NDF and ADF contents were lower than the first year.The Alfalfa feed quality of second and third cuts are better than the first and fourth Alfalfa.The Poa pratensis feed quality of first and second cuts have better forage quality than the third one.?3?The contents of total nitrogen,available nitrogen and NH₄⁺-N in the soil of Poa pratensis-Alfalfa sequence were significantly higher than those of Poa pratensis continuous cropping?P<0.05?,but the content of NO₃^--N was not significantly different.The contents of total N,available nitrogen and NH₄⁺-N in the soil of Poa pratensis-Alfalfa sequence were significantly lower than those of Alfalfa continuous cropping,but the content of NO₃^--N was not significantly different.In October of the second year after rotation,the total nitrogen,available nitrogen and NH₄⁺-N contents in the Poa pratensis-Alfalfa sequence were 15.55%,18.32%and 39.70%higher than those in continuous cropping?P<0.05?,while the soil total nitrogen,available nitrogen and NH₄⁺-N contents in Alfalfa-Poa pratensis were 23.60%,11.17%and 26.86%lower than those in Alfalfa continuous cropping?P<0.05?.The Poa pratensis-Alfalfa can significantly increase the soil total nitrogen,available nitrogen and NH₄⁺-N content.The Alfalfa-Poa pratensis rotation reduced the accumulation of soil total nitrogen,available nitrogen and NH₄⁺-N content.?4?There were no significant differences in available nitrogen/total nitrogen value?in April^October?,NO₃^--N/available nitrogen values,NH₄⁺-N/available nitrogen values between Poa pratensis-Alfalfa sequence and Poa pratensis continuous cropping?P>0.05?in the 0²0 cm and 20⁴0 cm soil layers of the first to second years.In the Alfalfa-Poa pratensis sequence,the available nitrogen/total nitrogen value of 0²0 cm soil rotation for1² years was significantly higher than that of Alfalfa continuous cropping,the available nitrogen/total nitrogen value of 20⁴0 cm soil rotation for 1² years was significantly lower than that of Alfalfa continuous cropping.The NO₃^--N/available nitrogen value of 0²0 cm and 20⁴0 cm soil rotation in the first to second years is not significantly different from the Alfalfa continuous cropping,but NH₄⁺-N/available nitrogen values was significantly lower than that of Alfalfa continuous cropping.The Alfalfa-Poa pratensis sequence is beneficial to increase the available nitrogen content of soil surface nitrogen.