Development of an automated precision planter for establishment of Miscanthus giganteus
Miscanthus giganteus is a seed sterile crop that has shown potential in the US and Europe as a bioenergy crop. In European trials, M. giganteus yields have ranged from 10-30 Mg dry matter (DM) ha-1 and from 25-38 Mg DM ha-1 in limited US trials. Due to its sterility, M. giganteus is principally propagated by rhizome division. However, limited research has been conducted on the mechanization of the propagation system. Vegetatively propagated crops, planting procedures and commercially available production equipment were reviewed to gain perspective on how to potentially mechanize the process of planting M. giganteus rhizomes. Typical procedures and equipment used for rhizome harvesting were also examined. The review of available technology shows that there are aspects of horticultural equipment that are adaptable for use with M. giganteus. In addition, examination of specialty equipment for M. giganteus shows aspects that are improvable such as uniformity of spacing in row and rhizome singulation. Current equipment for propagation of rhizomes relies on bulk metering of rhizomes into furrows, the key disadvantage of which is non-uniform spacing. Based upon the review and recommendations that were developed, a prototype precision miscanthus rhizome planter was developed from Lockwood Air Cup® row units. The planter uses nozzles under vacuum to singulate rhizomes from a hopper. The planter plants miscanthus rhizomes at fixed in-row spacing of 46, 51, 56, 61 or 76 cm. Based upon the recommendations of previous research a prototype precision miscanthus rhizome planter was developed from Lockwood Air Cup® row units. The planter utilizes vacuum to singulate and plant rhizomes at target in-row spacing. Two field tests were performed where planter performance was quantified by quality of feed, multiple, miss and precision indices. The quality of feed index is the percentage of one or two rhizomes recorded. The multiple index is the percentage of three or more rhizomes recorded. The miss index is the percentage of skips recorded and the precision is the variation in spacing of single and double rhizomes as a percentage of the nominal spacing. The initial field test used rhizome material 0.6-1.3 cm in diameter and 7.0-13.0 cm long. The quality of feed was 61.0% with a multiple index of 17.0% and miss index of 22.0%. The second field test used rhizome material 1.0-1.4 cm in diameter and 7.0-13.0 cm long and tested nominal spacings of 56, 61 and 76 cm. The quality of feed indices were 48.0%, 48.0% and 52.0%, the multiple indices were 1.3%, 1.3 % and 6.7% respectively and the miss indices were 50.7%, 50.7% and 41.3% respectively. The precision was 7.8%, 9.3% and 8.3% respectively. Cup designs were tested to determine if there was a significant difference in the requirements to hold a rhizome. The first design tested was the original conical cup used for potatoes on Lockwood AirCup planters. The second cup was a modified version of the original cup with notches cut into it to help orient rhizomes in the cup and allow the rhizomes to be closer to the nozzle inlet. Testing showed that the modified design required 584 Pa less static pressure, 2.65 m3 hr-1 less flow and an inlet velocity 2.16 m s-1 lower than the original design. The requirements to hold a rhizome against an orifice were investigated for pipe inside diameters of 0.87, 1.20, 1.56, 2.04, 2.62 and 3.64 cm. Models were developed to predict the requirements to hold a rhizome for the diameters tested. Testing showed that flow is positively correlated to pipe diameter according to Q = 3.44D1.94, where Q is the flow (m3 hr-1) and D is pipe inside diameter (cm). Static pressure was found to be negatively correlated to pipe diameter according to Pr = 2200D -2.05 where Pr is static pressure (Pa). The power required was positively correlated to P = 1.70D0.54 where P is power (W). The force exerted on the rhizome is negatively correlated to F = 0.187D-0.74 where F is force (N).
Murphy, Purdue University.
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