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Development of a Low-Cost Root Collar Diameter Measurement System for Pine Seedlings

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  035003,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14113) @2003
Authors:   Tony E. Grift
Keywords:   Seedling, Root Collar Diameter, Measurement, Optical

To assess the growth stage of the crop in the field, every year seedling nurseries measure the Root Collar Diameter (RCD) of a large number of seedlings. This is traditionally done manually using a slide micrometer and registration of data on paper, a tedious and error-prone practice. As an alternative, an optical system was developed that measures the RCD of a pine seedling semiautomatically.

As a proof of concept, a system was devised where objects of constant diameter were mounted on the rim of a wheel spinning at a constant speed. The diameters of the objects were measured with optical sensors, producing a maximum error of 2.85 %.

Two realistic versions of a semi-automatic RCD measurement system were developed, 1) a system where the user slides the seedling along an edge and 2) a system where the user places the seedling on a table after which the system measures and stores the RCD at the push of a button. The first version produced errors less than 0.7%, sufficiently accurate, but operator dependent and not very user-friendly. The second version had an accuracy better than 0.2%, virtually independent of operator skill.

The concept of measuring the RCD on-the-fly using an optical method could be used to develop a seedling yield monitor on a seedling harvester (lifter) in the near future, although the transition from laboratory to field conditions will require redesign and intensive testing.

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