首页> 外文期刊>European Journal of Agronomy >How does defoliation management impact on yield, canopy forming processes and light interception of lucerne (Medicago sativa L.) crops?
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How does defoliation management impact on yield, canopy forming processes and light interception of lucerne (Medicago sativa L.) crops?

机译:去叶管理如何影响卢塞恩(Medicago sativa L.)农作物的产量,冠层形成过程和光截留能力?

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The frequency of defoliation is the major management tool that modulates shoot yield and the accumulation of C and N root reserves in lucerne crops. A fully irrigated, 2-year-old lucerne (Medicago sativa L.) crop was grown at Lincoln University (43 degrees 38'S and 172 degrees 28'E) and subjected to four defoliation treatments. These involved the combination of two grazing frequencies (28 or 42 days) applied before and/or after mid-summer. Annual shoot dry matter (DM) yield ranged from 12 to 23 t/ha. These differences were largely explained by the amount of intercepted photosynthetically active radiation (PARi) using a conservative conversion efficiency of 1.6 g DM/MJ PARi. Part of the reduced PARi in the frequently defoliated treatments was caused by the shorter regrowth period that impeded crop canopy closure to the critical leaf area index (LAIcrit) of 3.6. Canopy architecture was unaffected by treatments and a single extinction coefficient for diffuse PARi (kd) of 0.81 was found for 'Grasslands Kaituna' lucerne. The pool of endogenous nitrogen (N) in taproots was reduced by frequent defoliations. This explained differences in leaf area expansion rate (LAER), which decreased from 0.016 m2/(m2 degrees C day) at 60 kg N/ha to 0.011 m2/(m2 degrees C day) at 20 kg N/ha. The pool of soluble sugars was also positively associated with LAER but the concentrations of carbohydrates and N reserves and the pool of taproot starch were poorly related to LAER. The slower LAER in the frequently defoliated treatments was mostly caused by the smaller area of primary and axillary leaves, particularly above the 6th node position on the main-stem. Developmental processes were less affected by defoliation frequency. For example, the phyllochron was similar in all treatments at 34 degrees C day (base temperature of 5 degrees C) per primary leaf during spring/summer but increased in autumn and ranged between 44 and 60 degrees C day. Branching and senescence started after the appearance of the 4th main-stem node, and both were unaffected by defoliation frequency. These results suggest that the expansion of individual leaves, both primary and axillary, was the most plastic component of canopy formation, particularly after the appearance of the 6th primary leaf. Future mechanistic modelling of lucerne crops may incorporate the management or environmental responses of LAER that control PARi and impact on shoot DM yields..
机译:落叶的频率是主要的管理工具,可调节苜蓿作物中的枝条产量以及C和N根储备的积累。林肯大学(43度38'和172度28'E)种植了完全灌溉的2岁卢塞恩(Medicago sativa L.)作物,并进行了四种脱叶处理。这些包括在仲夏之前和/或之后应用两个放牧频率(28天或42天)的组合。年梢干物质(DM)的产量范围为12至23吨/公顷。这些差异很大程度上由使用1.6 g DM / MJ PARi的保守转换效率所截获的光合有效辐射(PARi)的量解释。在经常脱叶的处理中,PARi降低的部分原因是较短的再生期,该再生期阻碍了作物冠层关闭至临界叶面积指数(LAIcrit)为3.6。冠层结构不受处理的影响,发现“草地凯图纳”卢塞恩的单个PARi消光系数为0.81。频繁的脱叶减少了主根中的内源氮(N)库。这解释了叶面积膨胀率(LAER)的差异,从60 kg N / ha时的0.016 m2 /(m2℃天)降至20 kg N / ha时的0.011 m2 /(m2℃天)。可溶性糖池也与LAER呈正相关,但是碳水化合物和氮的含量以及主根淀粉池与LAER的关系较弱。在频繁脱叶处理中,较慢的LAER主要是由初级和腋生叶的面积较小引起的,尤其是在主茎第6节点以上的位置。发育过程受落叶频率的影响较小。例如,在所有处理中,春季/夏季在每片初叶34摄氏度日(基温5摄氏度)下,叶轮纪相似,但在秋季有所增加,在44摄氏度至60摄氏度之间。在第四个主干结点出现后开始分支和衰老,并且都不受脱叶频率的影响。这些结果表明,初生和腋生的单个叶片的扩张是冠层形成的最可塑性的组成部分,尤其是在第6个初生叶片出现之后。卢塞恩作物​​的未来机制建模可能会结合LAER的管理或环境响应,以控制PARi并影响苗DM产量。

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