Accuracy Then and Now
Twenty-five years ago, when farmers went to the field to plant, the planting monitor on the tractor was typically equipped with simple indicator lights showing seeds were actually getting to the ground. If a seed tube became plugged, the monitor alarm would sound, and the problem could be resolved. However, this “data” only monitored activity and did not actually measure anything — seed populations were still a function of using the correct combination of gears on the ground drive system, and digging in the dirt to confirm.
In the late 1990s, significant improvements were made to seed tube sensors and monitors, and the actual number of seeds planted could be counted. For the first time, real-time data was being delivered to the farmer so that corrections to seed population could be made quicker and easier. Population accuracy is expressed as a percentage by dividing the actual seed population by the target population.
Then in the mid-2000s, seed tube sensors and monitoring systems are further improved and skips and doubles can be measured. Singulation, or how well the meter drops seeds one-by-one becomes the new data to gather. Accuracy percentage, measured in real-time, takes into account the number of skip and doubles.
Today, faced with increasing planter speeds, more irregular seed shapes, and higher populations, meters must singulate seed almost perfectly AND deliver consistent spacing between seeds. To accurately measure the new demands on planter performance, the Coefficient of Variation has become the preferred measurement of planting accuracy.
Coefficient of Variation (COV)
Broadly defined, Coefficient of Variation (COV) is a measurement of overall planter performance, which affects the variation of seed spacing, as influenced by the following:
- Meter singulation
- Seed release from the seed disc
- Seed bounce in seed tube
- Row unit bounce
- Seed trench shape and cleanliness
- Planter speed
- Field conditions.
However, more narrowly defined as an indicator of meter accuracy, COV is the measurement of how well the meter is releasing seed and the variation of seed spacing that results. A meter can have perfect singulation (no skips or doubles), but a perfectly spaced “picket fence stand” may not result if the seed is not releasing from the seed disc uniformly. The lower the COV value (expressed as a decimal) the better, with ‘0’ being a perfect value.
Testing Seed Meter Coefficient of Variation
While COV is a measurement of overall planter performance, seed meters are where the seed's journey to the ground all starts. Poor performance of a meter will only be amplified, not lessened, by the bouncing and motion of a planter, so it is important that meters be removed from the planter and tested individually to ensure their peak performance.