Ingrowth-core method is a useful tool to determine fine root growth of standing crops by inserting root-free soil in mesh-bags for certain period of time. However, the root density observed by the method does not directly explain the nutrient uptake potential of crop plants as it varies over soil depth and incubation time. We have inserted an access-tube up to 4.2 m of soil depth with openings directly under crop plants, through which ingrowth-cores containing labelled soil with nutrient tracers were installed, called core-labelling technique (CLT). The main advantage of CLT would be its capacity to determine both root density and root activity from the same crop plants in deep soil layers. We tested the validity of the new method using a model crop species, alfalfa (Medicago sativa) against three depth-levels (1.0, 2.5 and 4.2 m), three sampling spots with varying distance (0–0.36, 0.36–0.72 and > 5 m from core-labelled spot), two sampling times (week 4 and 8), and two plant parts (young and old leaves) under two field experiments (spring and autumn). Using CLT, we were able to observe both deep root growth and root activity up to 4.2 m of soil depth. Tracer concentrations revealed that there was no sign of tracer-leakage to adjacent areas which is considered to be advantageous over the generic tracer-injection. Root activity increased with longer incubation period and tracer concentrations were higher in younger leaves only for anionic tracers. Our results indicate that CLT can lead to a comprehensive deep root study aiming at measuring both deep root growth and root activity from the same plants. Once produced and installed, the access-tubes and ingrowth-cores can be used for a long-term period, which reduces the workload and cost for the research. Therefore, CLT has a wide range of potential applications to the research involving roots in deep soil layers, which requires further confirmation by future experiments.

中文翻译：

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核心标记技术（CLT）：向内生长核心方法和示踪技术的新组合，用于深根研究。

向内生长芯法是一种有用的工具，通过在网袋中插入无根土壤一段时间，确定立业作物的细根生长情况。然而，通过该方法观察到的根密度并不能直接解释作物植物的养分吸收潜力，因为它会随着土壤深度和孵化时间的变化而变化。我们已经插入了一个高达 4.2 m 土壤深度的接入管，其开口直接位于作物植物下方，通过该接入管安装了包含带有营养示踪剂的标记土壤的向内生长核心，称为核心标记技术 (CLT)。CLT 的主要优点是它能够确定深层土壤中相同作物植物的根密度和根活性。我们使用模式作物品种紫花苜蓿（Medicago sativa）针对三个深度水平（1.0、2.5 和 4.2 m）测试了新方法的有效性，三个不同距离的采样点（距核心标记点 0-0.36、0.36-0.72 和 > 5 m），两个采样时间（第 4 周和第 8 周），以及两个田间试验下的两个植物部分（幼叶和老叶）（春天和秋天）。使用 CLT，我们能够观察到深达 4.2 m 土壤深度的根系生长和根系活动。示踪剂浓度显示，没有示踪剂泄漏到邻近区域的迹象，这被认为比一般示踪剂注射更有利。根系活性随着潜伏期的延长而增加，并且仅对于阴离子示踪剂，年轻叶片中的示踪剂浓度更高。我们的结果表明，CLT 可以导致一项全面的深根研究，旨在测量同一植物的深根生长和根活性。一旦生产和安装，接入管和向内生长核心可以长期使用，从而减少了研究工作量和成本。因此，CLT在涉及深层土层根系的研究中具有广泛的潜在应用，这需要未来的实验进一步证实。