Biological Systems Engineering


Date of this Version



Chapter in PRECISION AGRICULTURE (1996), P.C. Robert, R.H. Rust and W.E. Larson (eds.), p. 369-377.


Copyright © 1996 ASA-CSSA-SSSA


Agricultural machines used in precision fanning must adjust application rates according to the needs of each cell within a field. Changing from an initial application rate to a new rate while the machine travels from one cell to another in the field is accompanied with some misapplication. The severity of this misapplication depends on the down-the-row delivery characteristics of the metering system and the magnitude of the rate change from cell to cell.

On-the-go rate change tests evaluated the down-the-row performance of an operator controlled metering system when increasing and decreasing wheat seeding rates by 10 and 20 kg/ha steps. The transition time from one cell to another ranged from 3 to 9 s depending upon the magnitude of the application rate change.

The difference between the initial and final seeding rate was based on a simple index. This separation index was based upon the initial and final down-the-row seeding rate distributions. When the separation index was greater than or equal to zero, the difference between the initial and final application rate was considered to be suitable for precision fanning. The separation criterion was always satisfied with 20 kg/ha rate changes. For 10 kg/ha rate changes, the separation index was negative in most cases. This indicated that rate changes of 10 kg/ha or less were unlikely to provide detectable rate differences as the metering rate variability exceeded the magnitude of the 10 kg/ha rate change.