Our current understanding of the plant deep root system and its relevance for crop production is limited. A field trial was established in order to monitor the root growth of various deep-rooted crops down to 5 m of soil depth with the minirhizotron technique. Root intensity (RI: intersections m-1) and maximum rooting depth (m) of seven different crop species indicate varying degree of root penetration capacity among the tested crops. Overall, within one season over 89 % of RI was concentrated at 0-1.0 m of soil depth. Sugar beet (1.4 m) as an annual crop showed the most rapid root growth rate (10.6 mm day-1). On average the perennials resulted in 0.7 m of maximum rooting depth (5.6 mm day-1), which indicates their potential to establish deep root systems in coming seasons

Dresbøll, Dorte Bodin

Han, Eusun

Havmøller, Lisa

Thorup-Kristensen, Kristian

Organic Eprints

Rahmann et al.(2017) Proceedings of the Scientific Track   “Innovative Research for Organic Agriculture 3.0”,  Organic World Congress 2017 in New Delhi, India, November 9-11, 2017  6Identification of deep-rooting crop species in arable subsoil by the minirhizotron technique Eusun Han1,2Lisa Havmøller2,3Dorte Bodin Dresbøll3,4Kristian Thorup-Kristensen45 Key words:deep roots, maximum rooting depth, root intensity, perennials, cropping system Abstract Our current understanding of the plant deep root system and its relevance for crop production is limited. A field trial was established in order to monitor the root growth of various deep-rooted crops down to 5 m of soil depth with the minirhizotron technique. Root intensity (RI: intersections m-1) and maximum rooting depth (m) of seven different crop species indicate varying degree of root penetration capacity among the tested crops. Overall, within one season over 89 % of RI was concentrated at 0-1.0 m of soil depth. Sugar beet (1.4 m) as an annual crop showed the most rapid root growth rate (10.6 mm day-1). On average the perennials resulted in 0.7 m of maximum rooting depth (5.6 mm day-1), which indicates their potential to establish deep root systems in coming seasons.  Acknowledgments This study was part of the DeepFrontier project funded by the Villum Foundation. Introduction Arable subsoil is a hidden but important part that comprises of potentially-reachable soil resources (Lynch and Wojciechowski 2015). Therefore, promotion of plant deep roots within a cropping system is essential to enhance crop productivity without further increasing the use of external inputs (Thorup-Kristensen et al. 2012); this is one of the aims of organic agriculture (Köpke et al. 2015). Despite the previously reported capacity of numerous crop and grass species for deep-rooting (see Canadell et al. 1996), investigation on the root system in arable fields is often limited to a relatively shallow range of soil depths (e.g. 0.3-1.0 m) unlike the majority in forestry or agroforestry (e.g. 3.0 m of soil depth; da Silva et al. 2011).  Therefore, the objective of our study is to extend the range of agronomically relevant subsoil down to 5 m of depth by identifying deep-rooted crops and cropping systems.  Material and methods  A field trial was established at the experimental station of the University of Copenhagen in Taastrup, Denmark (55 o40’N; 12 o18’E). The soil was classified as an Agrudalf as sandy loam. Detailed description on the study site is available in Dresbøll et al. (2016). The experimental design was a strip-split design. Seven crop species were involved in the study (see Table 1). Prior to the crop season, 6 m long minirhizotron tubes were inserted in the plots at an angle of 30o from vertical covering approximately 0.0-5.2 m of soil depth. Multispectral images were taken along the minirhizotron tubes at each 0.05 m-length interval by a Videometer lab instrument (Videometer                                                12Department of Plant and Environmental Sciences, University of Copenhagen, Højbakkegård Allé 13,  DK-2630 Taastrup, Denmark. eusun.han@plen.ku.dk 23As above. lh@plen.ku.dk 34As above.dbdr@plen.ku.dk 45As above. ktk@plen.ku.dk Scientific Track “Innovative Research for Organic Agriculture 3.0”  19th Organic World Congress, New Delhi, India, November 9-11, 2017  Organized by ISOFAR, NCOF and TIPI   7A/S, Hørsholm, Denmark). Image-taking took place from Aug 9 to Sep 6 in 2016 to 3.0 m of soil depth at maximum. Light illumination setup for UVA, violet, amber, red and NIR was adjusted to 365, 405, 590, 660 and 970 nm, respectively. The size of each of the images was 40 mm * 50 mm (width * height) consisting of 2048 x 2448 pixels. The images were analyzed with the VideometerPreview (Videometer A/S, Hørsholm, Denmark) software as Pseudo RGB.Root intensity (intersections m-1) was calculated as the number of roots intersecting a grid overlaid the images divided by the total length of grid lines (0.89 m per image). Maximum rooting depth (m) was calculated as the soil depth where the roots were identified at the deepest depth within one minirhizotron tube. Sowing dates for the crops and root measurement dates are indicated in Table 1. Statistical analysis was done with the R version 3.3.0 (R Core Team 2016). A mixed-effects model (Pinheiro and Bates 2000) with log-transformed variables was used as univariate analysis, and if required, post hoc tests (Tukey’s HSD, P≤0.05) were carried out.    Table 1: Crops, Latin names, sowing dates/density and measurement date Crop Latin name Sowing date Sowing density Measurement date Curly dock Rumex crispus L. 29/05/2016 0.4 g m-2 9/08/2016 Intermediate wheatgrass Thinopyrum intermedium 7/04/2016 2.5 g m-2 24/08/2016 Lupine Lupinus albus L. 11/04/2016 0.5 g m-2 24/08/2016 Mugworth Artemisia vulgaris L. 28/05/2016 0.2 g m-2 6/09/2016 Silphium Silphium perfoliatum L. 30/05/2016 9 plants m-2 1/09/2016 Sugar beet Beta vulgaris L. 11/04/2016 9 plants m-2 24/08/2016 Sweet clover Melilotus officinalis L. 14/04/2016 0.6 g m-2 8/09/2016 Results Among the tested crops, sugar beet resulted in the highest maximum rooting depth (1.43 m) followed by lupine (0.93 m), intermediate wheatgrass (0.93 m), silphium (0.82 m), sweet clover (0.67 m), curly dock (0.42 m), and mugworth (0.27 m; Figure 1). In the same manner, the highest root growth rate was also observed with sugar beet (10.6 mm day-1) and mugworth revealed the lowest root growth rate (2.7 mm day-1). Below 0.5 m of soil depth sugar beet showed the highest RI (5.15 intersections m-1; Table 2). Mugworth did not deploy any roots beyond the topsoil (i.e. >0.5 m) at the time of measurement. Proportional distribution of RI showed that lupine allocated 31.5 % of roots below topsoil followed by sugar beet (30.3 %), the intermediate wheatgrass (22.3 %), silphium (9.3 %), curly dock (1.8 %) and sweet clover (0.5 %).  Discussion It is plausible to observe that establishment of deep roots beyond 1 m of soil depth was already possible in one season of cultivation. For the perennials (e.g. silphium and curly dock), a substantial increase in rooting depth in coming season is expected as duration of growth influences the root growth in deeper soil horizons  (Thorup-Kristensen et al. 2009). Ability of plants to establish deep roots mainly depend on their root diameter (Materechera et al. 1992); this corresponds with the higher root growth of the taprooted crops such as sugar beet (e.g. Thorup-Kristensen et al. 2012) and lupine (e.g. Pennisi 2008). Also our observation might be the first report showing the root growth of the intermediate wheatgrassunder European soil conditions, which showed a strong tendency to intensify its root system in the subsoil as did in its origin in the U.S. (Cox et al. 2006).  Rahmann et al.(2017) Proceedings of the Scientific Track   “Innovative Research for Organic Agriculture 3.0”,  Organic World Congress 2017 in New Delhi, India, November 9-11, 2017  8 Figure 1. Maximum rooting depth (m) and root growth rate (mm day-1) of the seven crop species. Different small letters indicate significant differences between the crop species (Tukey’s HSD; P≤0.05). Analysis was done with log-transformed variables but mean (one±SE) values are shown here (root growth rate was not analyzed).  Development of deep roots can be beneficial for the standing plants as they gain more access to the limiting nutrients and water. Deep-rooted crops also positively influence the following crops as they function as N catch crops. In addition, they provide preferential pathways for roots of the following crops by the increased biopore density.   Table2: Rootintensity (RI; intersectionm-1) measuredat 0.0-0.5 m, 0.5-1.0 m, 1.0-1.5 m, 1.5-2.0.mand 2.0-2.5 mofsoildepth Soil depth (m) Sweet clover Curly dock Intermediate wheatgrass Lupine Mugworth Silphium Sugar beet 0.0-0.5 11.06 bc 42.56 a       22.48 bc  11.33 bc 12.30 bc 8.56 c 25.17 ab 0.5-1.0 0.06 b 0.78 b         6.70 bc 5.24 b 0 0.92 b 13.69 a 1.0-1.5 1.18 b 0       0.95 b 0.05 b 0 0.42 b    6.38 a 1.5-2.0 0 0 0 0 0 0   0.02 2.0-2.5 0 0 0 0 0 0   0.50 Different small letters indicated significant differences between the crop species within the soil depth (Tukey’s HSD; P≤0.05).   Our study indicates that crop plants have potential to establish deep root systems in arable subsoil. Organic management should consider the deep soil as an alternative nutrient reservoir and formulate crop sequence/rotation to better exploit the deep soil nutrients. Future study should focus on activity of deep roots under field conditions by developing methods applying nutrient tracers in deep soil horizons.  Scientific Track “Innovative Research for Organic Agriculture 3.0”  19th Organic World Congress, New Delhi, India, November 9-11, 2017  Organized by ISOFAR, NCOF and TIPI   9References  Canadell J, Jackson RB, Ehleringer JR, et al (1996) Maximum rooting depth of vegetation types at the global scale. Oecologia 108:583–595. doi: 10.1007/Bf00329030 Cox TS, Glover JD, Van Tassel DL, et al (2006) Prospects for developing perennial-grain crops. BioScience 56:649–659. da Silva EV, Bouillet J-P, de Moraes Goncalves JL, et al (2011) Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths. 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J Exp Bot 66:2199–2210. doi: 10.1093/jxb/eru508 Materechera SA, Alston AM, Kirby JM, Dexter AR (1992) Influence of root diameter on the penetration of seminal roots into a compacted subsoil. Plant Soil 144:297–303. doi: 10.1007/BF00012888 Pennisi E (2008) Plant genetics. Getting to the root of drought responses. Science 320:173–173. Pinheiro J, Bates D (2000) Mixed-Effects Models in S and S-PLUS. Springer, New York R Core Team (2016) R: A language and environment for statistical computing.  Thorup-Kristensen K, Cortasa MS, Loges R (2009) Winter wheat roots grow twice as deep as spring wheat roots, is this important for N uptake and N leaching losses? Plant Soil 322:101–114. doi: 10.1007/s11104-009-9898-z Thorup-Kristensen K, Dresbøll DB, Kristensen HL (2012) Crop yield, root growth, and nutrient dynamics in a conventional and three organic cropping systems with different levels of external inputs and N re-cycling through fertility building crops. Eur J Agron 37:66–82. doi: 10.1016/j.eja.2011.11.004 Thorup-Kristensen K, Rasmussen CR (2015) Identifying new deep-rooted plant species suitable as undersown nitrogen catch crops. J Soil Water Conserv 70:399–409. doi: 10.2489/jswc.70.6.399     

Identification of deep-rooting crop species in arable subsoil by the minirhizotron technique

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Identification of deep-rooting crop species in arable subsoil by the minirhizotron technique

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