摘要
本实验运用组织转化理论和分析方法，研究人工草地上不同刈割起始时间、留茬高度及刈割频率对羊草叶片和植株的再生动态、植被特征、草地生产力及羊草不同器官中可溶性碳水化合物和氮素含量变化的影响，由此解释植物对环境干扰（人工利用）的适应机制，为草地合理利用，制定合理的刈割制度提供理论依据。实验结果表明：
（1）不同刈割起始时间处理，刈割后第1周至第4周叶片伸长率和发生率差异均显著（P<0.05），但叶片萎蔫率和枯死率差异均不显著；不同刈割频率处理，除第1周叶片萎蔫率差异显著（P<0.05），第4周叶片萎蔫率差异极显著外（P<0.01），其它各参数差异均不显著；留茬高度处理，除6月刈割处理第1周、第2周叶片伸长率差异极显著（P<0.01），6月刈割处理第4周叶片伸长率、第1周叶片发生率及8月刈割处理第4周叶片伸长率差异显著（P<0.05）外，其它各参数差异均不显著。仅就叶片的组织转化速率考虑，6月初开始刈割，留茬高度8cm，叶片组织转化速率最快。
（2）不同刈割起始时间处理，刈割后第1周至第4周植株的再生速度6月刈割处理极显著高于8月刈割处理（P<0.01）；不同刈割频率处理的植株再生速度，除第3周差异显著外（P<0.05），其余几周各处理之间差异均不显著； 留茬高度处理，6月刈割处理第1周、第2周植株再生速度差异显著（P<0.05），其余两周各处理间差异不显著；8月刈割处理第1周、第2周各处理间的植株再生速度差异不显著，第3周、第4周差异显著（P<0.05）。
（3）不同刈割起始时间的产草量差异不显著；不同留茬高度间的产草量差异显著（P<0.05）；不同刈割起始时间与留茬高度间互作效应不显著。6月不同留茬高度刈割处理及CK，在6~8月期间的再生草量差异不显著。
（4）刈割处理不改变羊草须根本身可溶性碳水化合物的积累规律，只是数量上发生变化。6月刈割处理，刈割后羊草茎基部和根茎中的可溶性碳水化合物含量持续降低；6月刈割处理叶片和8月刈割处理
茎基部、叶片和根茎中可溶性碳水化合物含量刈割后先降低，然后升高；刈割后羊草茎基部和叶片中的可溶性碳水化合物含量，留茬12cm处理先降低，然后升高，其它各处理持续下降。因此，刈割时不能留茬过低，再次利用应间隔一定时间，以使牧草贮藏的可溶性碳水化合物含量恢复到较高水平。
（5）羊草叶片和茎基部中的氮素含量6月均高于8月，须根和根茎中氮素含量差异不显著。再生初期，羊草各器官中的氮素含量刈割处理均低于CK，但经过一段时间后，各刈割处理氮素含量增加并超过CK。刈割后，地上器官中的氮素含量低茬刈割处理高于高茬刈割处理，地下器官恰好相反。因此，一定程度的刈割可以刺激根对土壤中氮素的吸收，促进氮素向地上的生长部位重新分配，提高牧草的营养价值。
综上，适当刈割可以加快牧草的组织转化速率，提高牧草的营养价值。根据本实验结果，一次刈割以8月初刈割，留茬8cm为宜；就当年的生产效益，可考虑一年刈割两次，刈割时间以6月初和8月初为宜。
To explain the vegetable’s adaptive mechanism when suffered disturbance such as manpower utilization and provide the theoretical base for making the valid cutting system, one experiment was conducted to investigate dynamics of leaf and plant regrowth, characteristics of vegetation, productivity, changes of WSC (water-soluble carbohydrate) and nitrogen in Leymus chinensis at different cutting times, cutting frequency and stubble heights by applying the theory of tissue turnover. The results showed that:
(1) The leaf enlongation rate and appearance rate differed significantly, not for the other parameters between the two treatments with different initial cutting time. The leaf senescence rates of the first week and fourth week differed significantly, while other parameters were not different between the two frequency treatments. The enlongation rates of the first, second and fourth week after cutting in June differed significantly. The leaf enlongation rates of the first week when cutting happened in August differed significantly, however, other parameters were not different among different stubble heights. The leaf tissue turnover rate was the fastest if the cutting time is set in June and the stubble height is 8cm according to regrowth dynamics.
(2) The plant regrowth rate was significantly different between the two treatments with different initial cutting time. There was significantly different in the regrowth rate of the third week after cutting between the two frequency treatments, but not for other weeks. The plant regrowth rates of the first and second week after cutting in June, the third and fourth week after cutting in August differed significantly, not for other weeks among stubble height treatments.
(3) The total dry matter yield did not differ significantly between the two treatments with different initial cutting time. Nevertheless, there were significantly different among stubble height treatments. The interaction between the different initial cutting time and stubble height treatments was
not remarkably different. The grass yields of regrowth were not significantly different among stubble height treatments from June to August.
(4) Cutting treatments did not impact the change of accumulation WSC of the fibrous root. WSC in stem and rhizome decreased after cutting in June，however, WSC in leaf after cutting in June and in stem, leaf and rhizome after cutting in August decreased at first, then increased. WSC in leaf and stem when the stubble height was 8cm decreased at first, and followed increasing. Other treatments kept decreasing after cutting.
(5) The contents of nitrogen in leaf and stem in June were higher than that in August, and nitrogen content in fibrous root was as much as that in rhizome. The contents of nitrogen in different organs of Leymus chinensis were lower than CK at early days after cutting respectively, and then increased, even exceeded CK. The content of nitrogen at lower stubble height was higher than that at higher stubble with in the belowground organs, opposite to the underground. So appropriate cutting intensity will benefit the increase of nitrogen and improve the nutrition value of herbage.
Appropriate cutting could increase the tissue turnover rate and quality of forages. Based on the results of this experiment, the cutting time should be set in August and the stubble height should be 8cm if cutting once. Cutting twice annual is also feasible if the benefit in the same year is just considered, and the cutting time should be set in early June and early August.
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