Root Distribution And Characteristics Of Growth And Development In A Poplar Tree/alfalfa Silvopastoral System In Xinjiang Province

In order to understand the change of the root distribution,growth and development,and yield of alfalfa in a poplar(Populus L.)/alfalfa(Medicago sativa L.)silvopastoral system,temporal and spatial distribution of root length density(RLD),average root diameter(ARD)and specific root length(SRL)in 0~60 cm soil layer of 3-year-old alfalfa and 7-year-old poplar in sole and intercropping systems were determined and analyzed by WinRHIZOTM.Meanwhile,the plant height,leaf area index(LAI)and yield of alfalfa in sole and intercropping systems,and stem volume yield of sole-cropped and intercropped poplar were determined.The interaction mechanism of the root system in silvopastoral system was revealed,which was a reasonable layout of the silvopastoral system and improved the resource utilization,and provides theoretical and practical basis by studying the root distribution and characteristics of the growth and development of understory crops in the poplar/alfalfa silvopastoral system.Main conclusions were as follows:1.The RLD,ARD and SRL of alfalfa in the alfalfa and silvopastoral systems were different in different soil layers and periods,and the difference between the sole and intercropping increased after the first harvest management.Intercropping with poplar reduced the RLD and ARD of alfalfa,while the SRL of alfalfa in silvopastoral system was higher than that of sole-cropped alfalfa.Meanwhile,the harvest management caused the decrease of RLD and ARD in 20~60 cm soil layer in sole-cropped and intercropped alfalfa.The effect of harvest management on alfalfa increased as the soil depth increased,and the effect of harvest management on alfalfa in silvopastoral system was greater than that of sole-cropped alfalfa.2.The RLD and ARD of poplar trees in the 0~20 cm soil layer were significantly higher than that of the sole-crop poplar,which reflected the protective effect of understory planting on trees in a silvopastoral system.Especially in August,when the precipitation was small and the evaporation was large,the protection of poplar roots by alfalfa in silvopastoral system more significant.However,in areas without alfalfa and deeper soil layers(20~60 cm),there was no significant difference in poplar RLD and ARD between sole and silvopastoral system.The SRL values of sole-cropped and intercropped poplars was different only in the 0~20 cm soil layer on August 5,and there was no significant difference in other periods and soil layers.It indicates that the growth of poplar roots in silvopastoral system were protected and promoted in the alfalfa growing area,and the competition in the underground part of silvopastoral system had little negative effect on the growth and development of poplar roots.3.Alfalfa was weaker than poplar in the resource competition of silvopastoral system.Intercropping affected the regeneration of alfalfa after cutting managements,and the plant height and leaf area index of alfalfa in sole and silvopastoral systems were significantly different after harvest managements(P<0.05).The largest difference in plant height between sole-cropped cand intercropped alfalfa was at the third harvest,sole-cropped alfalfa was 14.38%~24.39% greater than intercropped alfalfa.The largest difference in leaf area index between sole-cropped cand intercropped alfalfa was also at the third harvest,sole-cropped alfalfa was 32.63%~25.23% greater than intercropped alfalfa.Correlation analysis showed that there was a significant positive correlation between plant height,leaf area index and yield in sole and intercropping system.The correlation coefficient between plant height,leaf area index and yield in sole cropping was 0.842 and 0.884,respectively.The correlation coefficient between plant height,leaf area index and yield in intercropping were 0.856 and 0.886,respectively.Therefore,increased the plant height and leaf area index of alfalfa in sole or silvopastoral system was conducive to increasing yield of alfalfa.4.Alfalfa can be harvested three times a year in local management practices.The highest yields of sole and intercropping systems were both at the first harvest period,and intercropping with poplars reduced the hay yield of alfalfa.At the first,second and third harvest managements the yields were reduced by 24.77%,30.97%,and 43.70%,respectively.Compared with sole-cropped alfalfa,the total yield of alfalfa in poplar/alfalfa silvopastoral system decreased by 31.29%.There was no significant difference in the stem volume yield between sole-cropped poplar and intercropped poplar(P<0.05),which again proved that poplar was dominant in the resource competition in silvopastoral system.By calculating the land equivalent ratio(1.41),it showed that the silvopastoral system had higher productivity than the sole-cropped,and the silvopastoral system increased yield by 41%.In summary,compared with sole cropping,the silvopastoral system can make more full use of resources and had a higher combined yield and land use efficiency.