DEVELOPMENT OF A PRECISION METERING SYSTEM FOR PREGERMINATED SEED.

摘要

Scope and Method of Study. This study was undertaken to develop a method of accurately metering pregerminated seed. In recent years, research with pregerminated seed has shown it to have many advantages over the conventional methods of crop establishment, direct seeding and transplanting. Transplanting and the thinning required with direct seeding are both expensive and labor intensive operations. The use of pregerminated seed offers the advantages of both methods since live growing seed can be planted in the soil without handling each plant individually. For maximum success, this process requires a metering device which could accurately space the seed. A successful metering system would allow the planting of crops directly to stand.; A study was made of water swellable gels which could serve as carriers for the pregerminated seed in a metering system. The gels were evaluated for rheological properties and ability to hold seed in suspension. An analysis of the spacing distribution from an unmetered mixture of seed and gel was made and the results were compared to theoretical predictions. A microcomputer controlled system was developed for metering pregerminated seed. The system utilized a gel as a seed carrier, photoelectric cells as seed detection devices, stepping motors for driving motion of the metering mechanism and an optical encoder to sense travel speed. The metering system was tested with four different seed: cabbage, tomato, lettuce and cucumber. The system performance was analyzed at four gel/seed concentrations, 4.0, 3.0, 2.0 and 1.0 ml/seed, and four metering rates, 0.5, 1.0, 2.0, and 3.0 seed/sec. The results were analyzed for spacing uniformity and metering error.; Findings and Conclusions. Two water swellable gels, Viterra II and CLD were found to be pseudoplastic or shear thinning in nature. In addition the Viterra II was found to have thixotropic properties. Both gels were analyzed for their ability to hold seed in suspension during vibration. Viterra II did not hold the seed in suspension. However, the CLD could hold the seed in suspension at higher concentrations. CLD was determined to be unsuitable for use as a seed carrier because free water would separate from the gel under certain conditions.; Cucumber seed were mixed in Viterra II gel at varying rates and the mixture was extruded onto an endless belt in order to determine the resulting spacing distribution. Prediction equations developed by previous researchers fit the measured distributions well. In addition a predictor of the mean spacing was derived and found to be in agreement with the measured values. The measured spacing distributions were found to be unsatisfactory for use in applications where precision planting is necessary.; The developed metering system proved to have unacceptably high levels of metering error at all metering rates and gel/seed concentrations. Spacing uniformity was good at slow metering rates and gradually decreased as the metering rate was increased. Causes of metering error in the system were identified and design improvements were suggested.