Organic Matter Application Improves Posttransplant Root Growth of Three Native Woody Shrubs

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The need for reliable planting techniques that encourage posttransplant root growth in adverse conditions has prompted research into planting above soil grade (above-grade). Container-grown Morella cerifera (L.) Small (syn. Myrica cerifera L.) (wax myrtle), Illicium floridanum Ellis (Florida anise tree), and Kalmia latifolia L. (mountain laurel) plants were planted in Horhizotrons (root observation chambers) in a greenhouse in Auburn, AL, on 1 Mar. 2006, 6 June 2006, and 3 Jan. 2007, respectively. The experiment was repeated with all three species being planted 18 June 2007. Horhizotrons contained four glass quadrants extending away from the root ball providing a nondestructive method for measuring root growth of the same plant into different rhizosphere conditions. Each quadrant was filled with a native sandy loam soil in the lower 10 cm. The upper 10 cm of the quadrants were filled randomly with: 1) milled pine bark (PB); 2) peat (P); 3) cotton gin compost (CGC); or 4) more native soil with no organic matter (NOM). Horizontal root lengths (HRL, length measured parallel to the ground from the root ball to the root tip) of the five longest roots visible along each side of a quadrant were measured weekly for M. cerifera and I. floridanum and biweekly for K. latifolia. These measurements represented lateral growth and penetration of roots into surrounding substrates on transplanting. When roots of a species neared the end of the quadrant, the experiment was ended for that species. M. cerifera had the fastest rate of lateral root growth followed by I. floridanum and then by K. latifolia. In most cases, roots grew initially into the organic matter rather than the soil when organic matter was present. In general, HRL and root dry weight (RDW) of I. floridanum and K. latifolia were greatest in PB and P, whereas for M. cerifera, these were greatest in P. Differences in root growth among substrates were not as pronounced for M. cerifera as for the other species, perhaps as a result of its rapid increase in HRL. Increased root growth in PB and P may be attributed to the ideal physical and chemical properties of these substrates. Results suggest that planting above soil grade with organic matter may increase posttransplant root growth compared with planting at grade with no organic matter.