Canopy structure and morphogenesis of Italian ryegrass intercropped with red clover under cutting intervals determined by thermal sum

ABSTRACT: The canopy structure and morphogenesis of ryegrass (Lolium multiflorum Lam.) was investigated after it was over seeded with Tifton 85 (Cynodon spp.) and intercropped with red clover (Trifolium pratense L.). Time intervals between cuts were determined by different thermal sums (125, 250, 375, and 500 degree-days [DD]). Cuts were conducted at a height equivalent to 50% of the average canopy height. Morphogenic and structural data were collected from July to October of 2016 and 2017, from a completely randomized block experimental design. Canopy height, extended tiller height, pseudostem length, and forage mass were fitted to linear equations according to the thermal sums. Interaction of ryegrass with red clover was the highest (12.1%) for longer cut intervals (375 and 500 DD). The leaf appearance rate (0.0080 leaf/DD), phyllochron value (128.8 DD), and senescence rate (0.10 cm/DD) of ryegrass were comparable between the different intervals. The slowest elongation rate (0.06 cm/DD) with the shortest interval duration between cuts (171.6 DD) was observed in the 125 DD interval. According to the findings from this 2-year experiment, the use of a 250 DD cut interval was recommended between grazing events, taking into account the efficiency of forage use, ryegrass leaf, stem ratio, and interactions with red clover in the canopy under rotational stocking.

摘要：本研究探究了多花黑麦草（ryegrass，*Lolium multiflorum Lam.*）与蒂夫顿85狗牙根（Tifton 85，*Cynodon* spp.）补播并与红三叶（red clover，*Trifolium pratense* L.）间作后的冠层结构与形态建成过程。试验采用完全随机区组试验设计（completely randomized block experimental design），以125、250、375及500 积温单位（degree-days, DD）的梯度设置刈割间隔期，刈割高度统一设置为平均冠层高度的50%。数据采集于2016年与2017年的7—10月，针对各积温梯度，对冠层高度、伸长分蘖株高、假茎长度及牧草生物量（forage mass）开展线性拟合分析。当刈割间隔期较长（375与500 DD）时，多花黑麦草与红三叶的群落交互占比最高，达12.1%。不同刈割间隔下，多花黑麦草的出叶速率（leaf appearance rate，0.0080 叶/DD）、叶序间隔值（phyllochron value，128.8 DD）及衰老速率（senescence rate，0.10 cm/DD）均无显著差异。在125 DD间隔组中，牧草伸长速率最慢（0.06 cm/DD），且实际刈割间隔时长最短（171.6 DD）。基于本两年期试验结果，综合考量牧草利用效率、多花黑麦草叶茎比及冠层内与红三叶的群落交互作用，推荐轮牧模式下采用250 DD作为刈割间隔期。