By Romulo Lollato,
Extension Wheat and Forages Specialist

The decisions taken prior to wheat planting can account for much of the success or failure of the wheat crop.

These decisions include selecting a variety well adapted to the area and with a good yield stability record, soil sampling to determine fertility needs, pre-plant fertilization (N, P, K, lime), either tillage for weed control and seedbed preparation or using a contact herbicide in no-till situations, and proper drill calibration.

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.

The stationary method, which is a simple 5-step method to calibrate a wheat drill prior to planting, is described below. 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 the result to a targeted seed weight by length of drill-row.

The five steps are as follows:

1 — Determine seeding density. Targeted seeding density varies within Kansas based on annual precipitation. A target range of seeds per acre based on current K-State recommendations (based on recommended pounds per acre for a variety with an average 15,000 seeds per pound) is shown in Table 1:

2 — Determine the number of seeds to be placed in 50 drill-row feet based on row spacing and targeted seeding density. Determine the linear row feet of actual planted seed per acre based on the drill’s row width (Table 2). With narrower row spacings, there will be more linear row feet of planted seed than at wide row spacings.

Afterwards, 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 emergence (for instance, 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.

Considering 85% emergence, this number increases to 912 seeds (Table 2). Count and weight 912 seeds from each variety. If no scale is available, place the 912 seeds in a clear graduate cylinder such as a rain gauge and mark the level for each variety.

3 — Determine the number of wheel revolutions needed for 50 drill-row ft. Hook 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 drive wheel’s circumference to determine how many times the drive wheel needs to be rotated to account for 50 drill-row feet.

For instance, 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 a tape (i.e. duct tape) to facilitate counting how many times the wheel is being turned.

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 be calibrated 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 evaluated, the more accurate will the calibration be. Weigh the collected seed (or pour it in the marked graduate cylinder from step 2) and compare to the target weight of seed per 50 drill-row feet as determined in step 2. If the collected seed weighs too little or too much compared to the target, adjust the metering system to deliver more or less seed, respectively.

It is recommended to 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 on step 2.

Table 2. Seeds per 50 dril-ow feet, as a function of row width, and target number of seeds per acre. Feed of linear row per acre, as a function of row width, is also shown.