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Dilma Daniela Silva and Richard C. Beeson Jr.

( McDougall, 1916 ). However, most methods used to study root development are extremely time-consuming and tedious ( Calfee, 2003 ). A rhizotron is a device for non-destructively observing plant roots over time ( Garrigues et al., 2006 ). Root observation

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Maxim J. Schlossberg, Keith J. Karnok, and Gil Landry Jr.

1 Doctoral candidate. 2 Professor. Research conducted at the University of Georgia Rhizotron, Athens, from the MS thesis of Maxim J. Schlossberg. The authors wish to acknowledge the thorough internal reviews by Hugh Earl and Tim Murphy, the

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Wesley T. Watson*, David N. Appel, Michael A. Arnold, Charles M. Kenerley, and James L. Starr

Several techniques have been used to study root growth and pathogen movement along roots between trees, including profile walls, micro-rhizotrons, and soil cores. These assessments can be very time consuming, cost prohibitive, and ineffective when studying soilborne pathogen movement across overlapping roots between adjacent trees in an orchard. Three aboveground rhizotrons were designed and constructed to study the movement of Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) along overlapping apple roots [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] in simulated orchard conditions. Two experiments involved boxes using either observation windows or micro-rhizotron observation tubes between trees. A third experiment utilized 45-gallon containers (171,457 cm3) joined by innovative observation windows. The container rhizotrons reduced labor and material costs, were more effective at monitoring roots, were more convenient than field measurements, and more closely simulated orchard growing conditions. This method provides several advantages to better study and manipulate the rooting environment of orchard-grown trees.

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Kevin Fort, Joaquin Fraga, Daniele Grossi, and M. Andrew Walker

-free and even-textured soil media, as were performed by Carbonneau (1985) and Natali et al. (1985) . In the present study, a rhizotron container system was used with the abovementioned rootstocks ‘Ramsey’, ‘110R’, ‘Riparia’, and ‘101-14Mgt’, and sought

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Lisa E. Richardson-Calfee, J. Roger Harris, Robert H. Jones, and Jody K. Fanelli

selected as the date when twig extension had stopped on at least four of five preselected twigs on non-transplanted trees. Rhizotrons for the non-transplanted trees were located in the PIP system and nursery bed and could not be randomized in the same bed

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Matt Kelting, J. Roger Harris, Jody Fanelli, and Bonnie Appleton

Application of biostimulants, humate-based products marketed as aids to plant establishment, may increase early post-transplant root growth and water uptake of landscape trees. We tested three distinct types of biostimulants on root growth and sapflow of balled and burlapped red maple (Acer rubrum L. `Franksred') trees. Treatments included: humate, 1) as a wettable powder formulation, applied as a soil drench; 2) as a liquid formulation to which various purported root growth—promoting additives had been added, also applied as a soil drench; 3) as a dry granular formulation, applied as a topdress; and 4) a nontreated control. Root growth was monitored through single-tree rhizotrons, and sap flow was measured with a heat balance sapflow system. Roots were first observed in the rhizotron windows 38 days after planting. No biostimulant-treated trees had more root length than nontreated controls, and the two soil drench treatments had the lowest root length throughout the 20 weeks of post-transplant observation. All biostimulants increased sapflow.

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J. Roger Harris, Nina L. Bassuk, Richard W. Zobel, and Thomas H. Whitlow

The objectives of this study were to determine root and shoot growth periodicity for established Fraxinus pennsylvanica Marsh. (green ash), Quercus coccinea Muenchh. (scarlet oak), Corylus colurna L. (Turkish hazelnut), and Syringa reticulata (Blume) Hara `Ivory Silk' (tree lilac) trees and to evaluate three methods of root growth periodicity measurement. Two methods were evaluated using a rhizotron. One method measured the extension rate (RE) ofindividual roots, and the second method measured change in root length (RL) against an observation grid. A third method, using periodic counts of new roots present on minirhizotrons (MR), was also evaluated. RE showed the least variability among individual trees. Shoot growth began before or simultaneously with the beginning of root growth for all species with all root growth measurement methods. All species had concurrent shoot and root growth, and no distinct alternating growth patterns were evident when root growth was measured by RE. Alternating root and shoot growth was evident, however, when root growth was measured by RL and MR. RE measured extension rate of larger diameter lateral roots, RL measured increase in root length of all diameter lateral roots and MR measured new root count of all sizes of lateral and vertical roots. Root growth periodicity patterns differed with the measurement method and the types of roots measured.

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Shengrui Yao, Ian A. Merwin, and Michael G. Brown

Rhizotron observations enabled us to compare the performance of three apple (Malu ×domestica) rootstock clones following different pre-plant soil treatments in an apple replant study at Ithaca, NY. Trees were planted in Nov. 2001, with one minirhizotron tube per tree in three replicate plots of three rootstocks (M7, CG30, and CG6210), three pre-plant soil treatments (fumigation, compost amendment, and untreated controls), and two planting positions (within the old tree rows, or in the old grass lanes). Monthly root observations were conducted during the 2003 and 2004 growing seasons. There were substantially fewer new roots observed in the first bearing year (2004) than the previous nonbearing year (2003), for all three rootstocks. A root-growth peak in early July accounted for more than 50% of all new roots in 2003, but there was no midsummer root growth peak in 2004. Neither pre-plant soil treatments nor old row or grass-lane planting positions had much influence on root growth. The median lifespan for roots of CG6210 was twice as long as that of CG30 and M7 in 2004. Also, CG6210 had more roots below 30-cm depth, while M7 had more roots from 11–20 cm. Trees grafted on CG6210 were bigger and yielded more fruit in the third year after planting, compared with trees on CG30 and M7 rootstocks. Crop load severely inhibited new root development and changed root-growth dynamics during the first cropping year, with a surge in root growth after fruit harvest in Oct. 2004. Rootstock genotype was the dominant influence on root lifespan and distribution, compared with pre-plant soil fumigation, compost amendments, or replanting positions within the previous orchard rows or grass lanes.

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H. Khatamian and R. J. Hilton

Abstract

The relationship between shoot growth and area of trunk cross-section was curvilinear for apple, peach, pear, plum, and hybrid Carolina poplar trees grown in rhizotron compartments in Fox sandy loam under natural conditions. The coefficient of determination (R2) values ranged from 0.86 to 0.99, indicating trunk diameter, transformed to area of cross-section, may be substituted for shoot growth in estimating tree vigor.

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J. Roger Harris, Jody Fanelli, and Paul Thrift

Description of early post-transplant root growth will help formulate best transplanting strategies for landscape trees. In this experiment, the dynamics of early root system regeneration of sugar maple (Acer saccharum Marsh. `Green Mountain') and northern red oak (Quercus rubra L.) were determined. Field-grown 4-year-old trees were transplanted bare-root into outdoor root observation containers (rhizotrons) in Oct. 1997, Nov. 1997, or Mar. 1998. All trees were grown in the rhizotrons until Oct. 1998 and then transplanted, with minimally disturbed rootballs, to field soil and grown for an additional two years. October-transplanted trees of both species began root regeneration earlier and regenerated more roots, as judged by accumulated root length on rhizotron windows, than Nov.- or March-transplanted trees. Median date for beginning root extension for sugar maples was 48, 22, and 0 days before budbreak for October-, November-, and Marchtransplanted trees, respectively. Median date for beginning root extension for northern red oak was 4, 21, and 14 days after budbreak for October-, November-, and Marchtransplanted trees, respectively. Height and trunk diameter growth were similar for all treatments within each species for 3 years after application of treatments. Early fall transplanting will result in earlier first season post-transplant root growth for sugar maple and northern red oak. Earlier post-transplant root growth will likely increase resistance to stress imposed by harsh landscape environments.