An evaluation of seed spacing accuracy of a vacuum type precision metering unit based on theoretical considerations and experiments

Authors: İSMET ÖNAL, ADNAN DEĞİRMENCİOĞLU, ARZU YAZGI

Abstract: Currently the most widely used machine for precision seeding of cotton and maize seed is vacuum type. The capture of seeds by vacuum plate and the release of seeds from the vacuum plate should be performed precisely without missing or doubling. The physical phenomena should be clarified theoretically to understand how the precision seeding mechanism works. To solve these problems, an attempt was made to develop a nomogram using equations describing the technical characteristics of the seeder used in this study and to describe the seed capture mechanism relying on basic principles of fluid mechanics and aerodynamic properties of seeds. Seed spacing accuracy tests were performed to test the theory on a sticky belt in the laboratory. Quality of feed index, miss and multiple indices, and precision have been taken as a set of criteria for seed spacing accuracy. The regression models developed using the data obtained via sticky band tests showed that 16 seeds s^{-1} was the upper limit of seed release frequency (SRF) for cotton and maize seeds. The upper limit of vacuum plate peripheral speed was found to be 0.34 m s^{-1}. The use of 72 holes instead of 26 holes in the vacuum plate at 6.3 kPa created a vacuum band in the width of 10 mm around holes and this increased the multiple index and caused a reduction in seeding performance. For this reason, the use of vacuum plates with 60 or 52 holes is recommended for cotton seed. The forward speed of either 1.0 or 1.5 m s^{-1} was found to be acceptable for the seed spacing of 0.05 and 0.10 m, respectively. Aerodynamic calculations verified that widely used vacuum plates with 26 holes were the appropriate ones for seeding maize seeds. The performance indices, namely the quality of feed, and miss and multiple indices, reduced significantly for cotton and maize seeding when the precision metering unit was run at 20% (11°) slope to the right as compared to the no slope condition.

Keywords: Precision seeding, seeding performance, vacuum plate

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