Optimisation of Design and Operational Parameters of a Pneumatic Seed Metering Device for Planting Cottonseeds

The performance of the seed-metering device of a pneumatic planter was investigated under laboratory and field conditions to optimise the design and operating parameters for cottonseed planting. The effect of operational speed of the disc, vacuum pressure and shape of the entry of seed hole were evaluated by examining the mean seed spacing, precision in spacing (coefficient of variation), miss index, multiple index, and highest quality of feed index. For picking single seeds, the planter disc had a seed hole of 2·5 mm in diameter. The entry cone angle of the hole was varied from 90 to 150°, the speed varied from 0·29 to 0·69 m/s, and the vacuum pressure from 1 to 2·5 kPa. The metering system of the planter was set to place the seeds at 250 mm spacing. It was observed that the planter disc with a 120° entry cone angle gave superior performance at all speeds and operating pressures. However, there was no conclusive statistical evidence to identify a single value of disc speed or vacuum pressure. Lower miss indices were observed at higher pressures and lower speeds, and lower multiple indices at lower pressure and higher speeds. The metering system with a speed of 0·42 m/s, and a vacuum pressure of 2 kPa produced superior results with a feed index of 94·7% and a coefficient of variation in spacing of 8·6%, recording a mean seed spacing of 251 mm. Optimisation of the regression equations incorporating speed of the disc and operating vacuum pressure through iteration further revealed that a disc, operating at speeds from 0·34 to 0·44 m/s and a vacuum pressure of 2 kPa, yielded similar performance. Based on the optimised operational parameters, performance indices of the pneumatic planter were determined under field condition by measuring the distribution of cotton plants spacing. A mean plant spacing of 298 mm was found in the field with a 19·1% precision (coefficient of variation). Within the range of 210–300 mm, 49% cotton plants were distributed compared to 88% seeds spacing distribution observed on the laboratory test rig. Displacement of seeds in the field (due to rolling and bouncing) can affect the plant spacing distribution in the field.