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Background: 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).Results: 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.Conclusions: 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 experimen

This study was performed to i) compare root distribution of legume/non-legume intercrops determined by qPCR and amplicon sequencing (Meta-barcoding) to root growth of the individual species determined visually, and ii) compare the qPCR and amplicon sequencing techniques as a method for quantifying root growth of individual species grown in mixtures. Red beet (Beta vulgaris L. cv Detroit) and lucerne (Medicago sativa L. cv Creno) were grown in one-meter-high transparent tubes. Root competition was studied by direct observation on the tube surface determining root intensity (RI), root wash and extraction followed by determination of root length density (RLD), and DNA-based methods. Intercropping decreased lucerne RI strongly, whereas the RI of red beet was not affected. The determination of RLD did not allow us to distinguish species in mixed samples. However, both DNA methods showed apparently a tendency to overestimate the fraction of lucerne roots compared to the direct root observations. The discrepancy between methods was explained by the fact that visual methods provide estimates of root length while the DNA methods provide estimates of root mass. In conclusion, DNA-based estimates of species fractions in mixed root samples give valuable information on root interactions in mixed crops.

Selection for deep rooting is critical for the development of genotypes that are able to explore deep soil water and nutrients, particularly as agricultural resources become more limited. However, current root phenotyping techniques demand significant investments of time, money, and effort, and measurements on very young plants or plants grown under soilless culture. This study introduced four novel and simple techniques for fast evaluation of root depth in tube rhizotrons, which enable root observation around the transparent tube walls, and allow roots growing to natural size in semi-field conditions. The first and second innovations involve the introduction of 15N tracer and herbicide to the roots, which estimated root activity by measuring the responses of the shoots aboveground. The third involves placement of a cone deep in the rhizotron, to increase chances to observe more deep roots along the tube walls. The fourth involves measurement of roots that emerge from the rhizotron bottom. The reliability of these techniques were assessed in a series of five experiments during 2014 and 2015. These tests compared two pairs of genotypes that previous studies had shown to have mutually distinctive root traits: the spring wheat pair of ‘April bearded’ vs. ‘Dacke’; and the winter wheat pair of ‘Tabasco’ vs. ‘Genius’, with the first of each pair being the genotype known for deep rooting. Results showed that the new techniques were as good as or better than existing alternatives at accurately measuring root traits. In eight of the nine comparisons, the measurements were consistent with the expectations of root characteristics for these known genotypes. Importantly, the indirect root activity measures (herbicide and 15N) showed the same trend as the direct root observation techniques in all experiments, but higher ability to distinguish the genotypes and more promise for future upscaling for plant breeding.

Root and root hairs of plants have been intensively studied in solution culture; however, correlation of such measurements in solution culture with development in soil is poorly understood. This study compared growth of roots and root hairs as well as uptake of macro- and micronutrients of six spring wheat varieties in solution culture under P stress and P abundance and in a low fertility soil. Results showed that root length and surface area under P stress was significantly positively correlated with that in the low fertility soil, while no such correlation was apparent for root hair length and density. In absolute terms the root length, surface area, root hair length and density of spring wheat varieties were substantially higher in soil than in solution culture, while the concentration and content of macro- and micronutrients in soil differed from solution culture in a complex way. The early uptake of macro- and micronutrients was intimately associated with root length and surface area as well as root hair length and density in soil but not in solution culture. Since root length under P stress was linearly correlated with early root growth vigor in soil, root measurement performed in solution culture may assist the prediction of early uptake of nutrients from low fertility soil.

Introduction: Deep roots have the potential to exploit plant resources otherwise inaccessible. The aim of this study was to develop a method, the Core-Labelling Technique (CLT), to measure root activity down to 2.5 m of soil depth under field conditions. Materials and Methods: Two stainless steel ingrowth-cores, 0.1 m in diameter and 0.55 m in length, were filled with soil labelled with nutrient tracers, i.e., LiCO3, CsCO3, Na2SeO4, RbCO3 and 15NH4Cl. The labelled cores were placed into an access-tube having openings at 1.0 m and 2.5 m of soil depth. They were kept under a lucerne (Medicago sativa) crop for 60 days, after which, the root length density (RLD) and concentration of tracers in shoot biomass (including a control) were measured. Results: RLD of lucerne measured at 1.0 m and 2.5 m of soil depth were 0.022 and 0.007 cm cm-3, respec-tively. Effects of core-labelling on shoot samples were significant for 15N, Li, Cs and Se across the soil depth but not for Rb. On average 6 times higher concentration of 15N (‰) was found at the labelled spot compared to the control. Li and Cs (mg kg-1) at the labelled area showed 2 and 3 times higher concentration than the control, respectively. Regardless of the treatment, core-labelling at 1 m of soil depth resulted in higher concentration of 15N and Cs in comparison to 2.5 m of soil depth. Discussion: To our knowledge, this report illustrates the deepest application of an ingrowth-core method as well as its first adoption of the tracer technique. Our results suggest that 15N, Li, Cs and Se can be feasible tracers for root activity detection in arable subsoil. Conclusions: The CLT can be used as an effective tool for determination of root activity in arable subsoil. We suggest that root research should progress beyond the generic depth-scale in order to discover the relevant yet hidden function of deep roots in crops in the field.

Sustaining an increasing human population with decreasing soil resources is a great challenge of the 21st century. Suboptimal availability of water and N are primary limitations to plant growth in the low-input agroecosystems in developing nations, whereas intensive fertilization at the cost of substantial environmental pollution is a problem in rich countries. The development of crops with greater rooting depth addresses these challenges. Deeper rooting improves water and nutrient uptake, which in turn reduces the need of application of external resources. In our study, we investigate the effect of intercropping on the deep root development and nutrient uptake in sugar beet – chicory mixture. The crops were chosen due to their deep roots and similar growing periods. We hypothesize that in the intercropping system one of the component crops develops roots below the root surface of the other crop, which results in deeper nutrient uptake in comparison to crops growing in pure stands. Crops will be grown in the field as monocultures and in mixture. Root growth will be monitored with minirhizotron method up to 4 m depth. Nutrient uptake will be studied using stable isotopes and ingrowth core methods. Additionally, root biomass estimation through DNA extraction from soil will be investigated. We expect that the results will help to answer the questions of whether the intercropping enhances deeper root growth and nutrient uptake in comparison to sole crops. With this knowledge, exploitation of the subsoil resources by deep roots would contribute to enhanced food production in a sustainable way. The study will start in spring 2018 and preliminary results will be presented.

Studie af en række efterafgrøder og deres egnethed til dyrkning i et system med korn i rækkedyrkning.

Fast and accurate methods for determining root growth in situ are important tools. In the present study, a rhizotron tube method was trialed as a means to more conveniently observe the dynamic development of roots under conditions similar to those encountered in the field. Crops were planted in transparent tubes covered with photomask to ensure a dark environment in the tube. This method can also be used in field studies of deep root development in crops by changing the length and diameter of the tube. Combined with root scan technology, we investigated the dynamics of root growth in oilseed rape and winter wheat at the seedling period from 16 days after germination. The results showed that winter wheat had a larger root and shoot dry weight than oilseed rape at both 7 days and 16 days. For winter wheat and oilseed rape, the root to shoot ratios at 16 days after germination were 0.513 and 0.372 respectively; the ratios of root length to total root length in the top soil layer (0-16 cm) were 62.60% and 67.76% respectively. The total surface, total volume and number of first class lateral roots of the two crops both had larger percentages in the top soil layer, indicating that most of the roots were distributed in the top 16 cm soil layer at 16 days. At 7 days after germination, the total length, total surface, total volume and number of first class lateral roots in winter wheat were higher than those in oilseed rape, while there were no differences between the two crops for the total length and total surface of roots at 16 days, suggesting that the root growth of oilseed rape was slow in the beginning but fast thereafter. The average root diameter in top soil was smaller than that in the deep soil layer, and the average root diameter of oilseed rape was smaller than that of winter wheat, which was typically between 0-0.50 mm. In terms of root growth, there were more and more thinner lateral roots, meaning that average root diameter became smaller. At 16 days after