Mini-Horhizotron: A Non-destructive Technique for Observing and Measuring Growth of Developing Root Systems during Production

There are several techniques used to measure/assess plant root growth and development, however most current methods are destructive and may not accurately quantify root systems.  Two common practices often used include subjective root ratings and root washing to determine root dry mass, both of which alter the natural position/architecture of root systems. Subjective ratings are highly variable and are only qualitative while root washing often looses large amounts of fine roots and root hairs.  The mini-Horhizotron is a new non-destructive technique developed to study root growth of small plant material (e.g. seeds, liners and plugs) during crop production.  The mini-Horhizotron is designed with three quadrants extending away from the center of the box, allowing for lateral root growth to occur. Shade panels cover the quadrants to exclude light from the root zone. Each of the three quadrants have two clear sides which allows visible measurements to be taken from a plant growing in the center. Measurements include root length, speed of root growth, presence and quantity of root hairs, and root architecture/branching.  The objective of this study was to use the mini-Horhizotron to quantify root growth patterns and observe the effects of different substrates on root growth development of Rudbeckia.  Rudbeckia hirta ‘Becky Yellow’ plugs were grown in peat-based substrates amended with either 20%, 30%, or 40% pine-wood-chip (PWC) aggregates.  The PWC was produced by hammermilling freshly chipped loblolly pine trees (Pinus taeda) through a 6.35 mm screen.  Three mini-Horhizotrons were filled with each individual substrate resulting in nine mini-Horhizotrons used.  The three longest Rudbeckia roots were measured on each quadrant face for each substrate, every four days from 15 to 67 days after planting (DAP).  From 15 to 39 DAP root growth of Rudbeckia was not different among the three substrates.  At 43 DAP root length of Rudbeckia in 40% PWC substrate was longer compared to plants grown in 30 or 20% PWC substrates. At 51 DAP plants grown in both 30% and 40% PWC had longer root lengths compared to plants in the 20% PWC substrate.  The general increase in root growth of Rudbeckia with increasing rates of PWC is likely attributed to the increase in air space of the substrates as the percent aggregate (PWC) increased.