混播比例对两种苜蓿混播草地产量和种群密度稳定性的影响

Effect of planting ratio on the stability of forage yield and population density in two alfalfa-grass mixtures

混播比例是混播草地适应性和稳定性的主要调节因素,因气候和土壤条件的不同而表现区域特异性。在陇东黄土高原雨养条件下,亟需构建混播组合和比例适当的苜蓿混播草地。选用苜蓿-无芒雀麦(MB)和苜蓿-猫尾草(MP)组合,建立了3个混播比例(苜蓿∶禾草=7∶3、5∶5、3∶7)的混播草地,以3种牧草单播为对照,对牧草产量、种群密度动态进行了分析,探究不同混播组合和比例下混播草地的稳定性。结果表明,混播比例对MP和MB混播草地牧草产量和种群密度稳定性均有显著影响,群落结构稳定性随草地年龄增大逐年降低。MB的苜蓿和禾草单产量及草地总产量显著高于MP,但2和5龄时二者间差异不显著。随2种混播下苜蓿比例增大,2、4和5龄草地总产量先升高后降低,3龄草地总产量升高;草地中苜蓿相对产量相异度系数呈先降低后升高趋势(3龄MB例外),禾草相对产量相异度系数的变化趋势不一致。MP下苜蓿和禾草相对种群密度相异度系数随苜蓿比例增大而呈先降低后升高趋势,5∶5混播下群落结构稳定性最弱;MB模式下,仅5龄草地苜蓿和禾草相对种群密度相异度系数随苜蓿比例增大而呈升高趋势。综上,MB能显著提高产量,较好地维持群落稳定性。在陇东黄土高原地区,建议可优先实行7∶3苜蓿-无芒雀麦混播,并在第5年换茬或施肥。

The planting ratio is one of the main factors affecting the suitability and stability of mixed forage crop plantings,and it differs among different regions and areas because of differences in climate and soil conditions.In the rainfed area of the Longdong Loess Plateau of China,it is urgent to generate mixed alfalfa(Medicago sativa)forage crop plantings with an optimized combination and mixing ratio.In this study,to reveal the stability of mixed grasslands under different combinations and mixing ratios,we analyzed the dynamics of forage yield and population density in two different mixtures;alfalfa-smooth bromegrass(Bromus inermis)(MB)and alfalfa-timothy grass(Phleum pratense)(MP).Three alfalfa∶grass planting ratios were established:7∶3,5∶5 and 3∶7.The controls were alfalfa only and grass only.The planting ratio significantly affected the stability of forage yield and the population density of MP and MB,and the stability of community structure decreased with grassland age.The yield of alfalfa and grass and total yield were significantly higher for MB than for MP at all ages except 2 years and 5 years.As the proportion of alfalfa increased in the two mixtures,the total forage yield initially increased and then decreased at the 2-,4-and 5-year ages,but only increased at the 3-year age.With the increase in the proportion of alfalfa in the two types of mixture,the relative yield dissimilarity coefficient of alfalfa decreased and then increased(except for 3-year MB),while there were inconsistent changes for the grasses.In MP,the relative population density dissimilarity coefficient of alfalfa and grass initially decreased and then increased with increasing proportions of alfalfa,and the stability of community structure was the weakest in the 5∶5 MP treatment.In MB,the relative population density dissimilarity coefficient of alfalfa and grass increased with increasing proportions of alfalfa only in the 5-year grasslands.In conclusion,compared with MP,MB can significantly increase forage yield and better maintain community stability.In the rainfed Loess Plateau area,it is recommended to establish an alfalfa-smooth bromegrass mixture with a planting ratio of 7∶3,and to replant or supply fertilizer in the fifth year.