Proper drill calibration can increase the chances of success of the wheat crop by ensuring the amount of seed planted per acre is close to the target.
There are several methods to calibrate seed drills. In this article, we discuss the stationary method, which is a simple 4-step method to calibrate a wheat drill prior to planting. In stationary drill calibration, a drill operation is simulated by turning the drive wheel freely above ground, weighing the seeds delivered from the drill spouts, and comparing to a targeted seed weight by length of drill-row. Note: some drills are designed so that using the stationary drill calibration method cannot be easily done and the drill needs to be operated to calibrate.
1. Determine seeding density.
Targeted seeding density varies within the State of Kansas based on annual precipitation. A target range of seeds per acre based on current K-State recommendations is shown in Table 1.
Table 1. Target seeding density for Kansas when the wheat crop is planted at the optimum sowing date, based on annual precipitation.
Annual precipitation (inches) |
Target seeding density |
> 20 in |
675,000 - 900,000 |
20 - 30 in |
900,000 - 1,125,000 |
>30 in |
1,125,000 - 1,350,000 |
Irrigated |
1,350,000 - 1,800,000 |
2. Determine the number of seeds in 50 drill-row feet based on row spacing and targeted seeding density.
Determine the number of linear row feet per acre based on the drill’s row width (Table 2). Next, estimate the number of seeds to be collected in 50 drill-row feet based on row width and the target seeds per acre. This can be done by dividing the number of target seeds per acre by the number of linear row feet per acre based on row width and multiplying the result by 50. Percent emergence can be accounted for by dividing the result by the fraction of emergence (for example, dividing by 0.85 for 85% emergence). Table 2 shows calculations for selected row widths and targeted number of seeds per acre considering 85% emergence.
After determining the number of seeds to be collected from 50 drill-row feet, weigh the equivalent amount of seed of each variety you intend to plant. For instance, if the target is 675,000 seeds per acre and row width is 12 inches, a total of 775 seeds need to be planted in a 50 drill-row feet. Assuming 85% emergence, this number increases to 912 seeds (Table 2). Count and weigh 912 seeds from each variety. If no scale is available, place the 912 seeds in a clear graduated cylinder (i.e. a rain gauge) and mark the level for each variety.
Table 2. Seeds per 50 drill-row feet as function of row width and target number of seeds per acre. Feet of linear row per acre as a function of row width is also shown.
Row width |
Feet of linear row per acre |
Target number of seeds per acre |
|||||
675,000 |
750,000 |
900,000 |
1,125,000 |
1,350,000 |
1,800,000 |
||
Seeds per 50 drill-row feet |
|||||||
6 |
87,120 |
456 |
506 |
608 |
760 |
912 |
1,215 |
7 |
74,674 |
532 |
591 |
709 |
886 |
1,063 |
1,418 |
7.5 |
69,696 |
570 |
633 |
760 |
950 |
1,139 |
1,519 |
8 |
65,340 |
608 |
675 |
810 |
1,013 |
1,215 |
1,620 |
10 |
52,272 |
760 |
844 |
1,013 |
1,266 |
1,519 |
2,026 |
12 |
43,560 |
912 |
1,013 |
1,215 |
1,519 |
1,823 |
2,431 |
3. Determine the number of wheel revolutions needed for 50 drill-row ft.
First, attach the seed drill to a tractor and raise the drill off the ground. Measure the drive wheel’s circumference using a tape measure, and divide 50 drill-row feet by the length of the circumference to determine how many times the drive wheel needs to be rotated to account for 50 drill-row feet. For example, if the drive wheel’s circumference is 7 feet, dividing 50 by 7 indicates that the wheel needs to be rotated 7.15 times to account for 50 drill-row feet. Mark a starting point in the wheel with tape (i.e. duct tape) to facilitate counting how many times the wheel is being turned. If the drill design won’t allow turning the drive wheel, then measure and flag a 50’ distance and catch the seed out of the seed tube as the drill is operated the measured distance.
4. Calibrate the drill.
Adjust the seed meter using the rate chart provided by the manufacturer for the desired seeding rate, which should result in a first approximation of final calibration. Add enough seed of the variety to ensure seed cups will remain covered throughout the calibration process. Rotate the wheel the number of revolutions needed to cover 50 drill-row feet as calculated in step 3 and collect the seed from each spout in a bucket or similar container. The more spouts and longer distance evaluated, the more accurate the calibration. Weigh the collected seed (or pour it in the marked graduated cylinder from step 2) and compare to the target seed per 50 drill-row feet as determined in step 2. If the collected seed weighs too low or too heavy compared to the target, adjust the metering system to deliver more or less seeds, respectively. Keep a record of the different seeding rates achieved at each setting for future reference. Repeat this process until the number of seeds delivered from the drill spouts matches the target established in step 2.
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
John Holman, Cropping Systems Agronomist, Southwest Research-Extension Center
jholman@ksu.edu