播期和播前刈割对羊草草甸中紫花苜蓿建植的影响

The influences of reseeding date and mowing prior to reseeding on establishment of alfalfa in Leymus chinensis meadows

为揭示播期、播前刈割及其交互作用对补播紫花苜蓿建植的影响,选取轻度退化羊草草甸,在不同日期(5月1日、6月1日、7月1日、8月1日)和补播前2个刈割(刈割、不刈割)交互处理下进行紫花苜蓿补播,研究紫花苜蓿建植表现的变化及其生态学机制。结果发现:7月1日补播后苜蓿出苗期间土壤含水量最高,刈割降低了苜蓿出苗和幼苗生长期的羊草植被高度。播期和刈割对苜蓿建植的影响存在显著交互作用。刈割通过降低羊草植被高度显著提高苜蓿出苗率,刈割后,受土壤水分季节变化影响,7月1日补播的苜蓿出苗率(20%)显著高于其他播期。通过降低植被高度和地上资源竞争,割草显著提高苜蓿幼苗存活率,割草处理下,7月1日补播的苜蓿存活幼苗数及幼苗存活率最高,分别为83株·m^(-2)和53%。随播期延后生长时间缩短,苜蓿幼苗发育受到限制,越冬率显著降低。割草通过促进幼苗生长显著提高了苜蓿幼苗越冬率。割草处理下,7月1日补播返青苜蓿植株数量达22株·m^(-2),显著高于其他播期。翌年群落调查数据表明:播前刈割显著提高了草地中紫花苜蓿生物量,且7月1日刈割后补播草地的苜蓿生物量显著高于其他处理,播前割草也显著提升了饲草粗蛋白含量。综合各处理紫花苜蓿补播效果和饲草生产实际,研究建议羊草草甸的紫花苜蓿补播应在植被刈割后进行,补播时间选择在7月1日前后对紫花苜蓿成功建植较为有利。

This research studied the effects of sowing date and cutting prior to sowing on establishment of the leguminous forage,alfalfa(Medicago sativa),in a lightly degraded Leymus chinensis meadow and investigated the sowing date×cutting interaction.The factorial experiment comprised four sowing dates(May 1,June 1,July 1,August 1)and cutting treatment(cut or uncut)prior to sowing,and evaluated the establishment performance of alfalfa and the ecological mechanisms related to establishment.It was found that soil moisture during emergence of alfalfa was the greatest when sowing occurred on July 1,and clipping prior to sowing significantly decreased the plant height of L.chinensis during emergence and seedling growth of alfalfa.There was a significant sowing date×cutting interaction effect on alfalfa establishment.Clipping prior to sowing significantly increased the emergence percentage of alfalfa through reducing the plant height of L.chinensis and associated above-and below-ground competition,and the seasonal soil moisture change resulted in a 20% higher(P<0.05)alfalfa emergence rate when sowing occurred on July 1.With cutting,the number of surviving alfalfa seedlings and seedling survival rate were greatest(83 plants·m^(-2)and 53%,respectively)when sowing occurred on July 1.For later sowing,owing to the shortened growing time,the development and overwintering survival rates of alfalfa seedlings were significantly reduced.Cutting prior to sowing significantly increased the overwintering rate of alfalfa seedlings through improving their development.In the cutting treatment,the number of overwintered alfalfa seedlings(22 plants·m^(-2))when sowing was on July 1 was significantly higher than for other reseeding dates.In the second year,a botanical composition measurement showed that clipping prior to reseeding significantly increased the alfalfa biomass within the meadow,and the alfalfa biomass was significantly greater than in other treatments when sowing occurred on July 1 after cutting.Cutting prior to sowing also significantly increased the crude protein content of forage.Based on these research results,normal production practice should include cutting when alfalfa is sown into L.chinensis meadow.Combined with cutting,a sowing date around July 1 is the most favorable for the establishment of alfalfa.