种植密度对苜蓿生长及生物量的影响

Effects of planting density on growth and biomass of Medicago sativa

种植密度作为影响作物产量和品质的重要因素,会造成植物对于光照、水分和养分的竞争。为研究种植密度对苜蓿生长与产量的影响,在日光温室环境下,以紫花苜蓿(Medicago sativa)为材料,设置25、100、400、800、1500、2000株·m^–2,共6个种植密度,对紫花苜蓿的种群密度和生长状况进行了观测。结果表明,各处理播种后15天的平均种植密度分别为25、100、373、745、1255、1938株·m^–2;随着紫花苜蓿的生长,除了低密度(25、100株·m^–2)处理没有发生植株数量的变化外,其余4个密度处理植株数量均有所减少,即发生不同程度的自疏,至第二茬收获时(播种后第187天)种群数量分别减少为297、571、759、839株·m^–2。植株个体的株高、基径和分枝数量随着现存密度的增加呈指数下降;个体生物量与现存密度的关系满足竞争密度效应的幂函数关系,即随着密度的增加而减小。紫花苜蓿单位面积地上生物量符合最终产量恒定法则,然而,随着密度的增加,地下生物量有先增加后减小的趋势。

Aims Planting density,as one of the most important factors affecting crop yield and quality,will result in plant competition for light,water and nutrients.The objective of this study is to explore the effect of planting density on growth and yield of Medicago sativa population.Methods The population density experiments of M.sativa was conducted in a greenhouse with six planting densities,i.e.25,100,400,800,1500 and 2000 plants·m^–2.At each plot,we measured plant height,basal diameter,branch number,biomass,and number of survivors.Important findings The results showed that the average planting density was 25,100,373,745,1255 and 1938 plants·m^–2 in the 15 days after sowing.With the growth of M.sativa,except for the low density treatments(25 and 100 plants·m^–2),the number of plant individuals under other density treatments decreased,and self-thinning occurred at some degrees.At the second harvest(187 days after sowing),the number of surviving plants decreased to 297,571,759 and 839 plants·m^–2,respectively.The plant height,basal diameter and branch number of individual plants decreased exponentially with the increase of existing density.The relationships between individual biomass and existing density followed the competitive density effect law,that is,individual biomass decreased with the increase of density.The results also showed that the aboveground biomass of M.sativa per unit area has no significant differences among different densities,but the underground biomass tended to increase first and then decrease with the increase of planting density.