Drill calibration: one shot at getting the seed rate right

The planting of spring cereals at the correct rate, seeding depth and in good ground conditions is critical to the successful establishment of the crop. There is only one shot at this task; patchy or uneven crops cause management headaches all year and ultimately reduce yield and profit.

Calibration and pre-sowing checks are the only way an operator can confidently go about the job of sowing for themselves or other contracting clients.

Every seed drill on the market will have a different method for calibration and the manufacturer’s manual will have the details on their individual procedure.

The common element is how much seed is needed per hectare to give the desired plant population for a full crop.

The seeding rate depends on a number of factors that need to be considered:

From the following formula, the expected seeding rate can be calculated:

Seeding rate (kg/ha) = Thousand grain weight (g) X Target plant population (m2) / % crop establishment

See Table 1 for example calculations.

Expected establishment

At home, I calibrated our Accord seed drill, which is the baseline DA model. The steps are common to many similar drills that may be using a comparable metering system.

Some machines will have more technology that will aid the process. For example, if the seed rate is initially checked once and the result entered in the control box, the machine can determine the new setting for the seed drill to give the desired seeding rate.

Calculate required rate

When sowing propino spring barley, the information needed to go ahead with calibration is the thousand grain weight, target plant population and the expected establishment. The expected establishment can range from 50% to 95%, depending on the field conditions, rotation, time of sowing and a number of other factors that may influence the germination of the crop.

The target plant population we are aiming for is 300 plants/m², giving an expected establishment of 90% and 50g thousand grain weight.

From the formula, the seeding rate needed was calculated to be 167kg/ha or 10.6 stones per acre. The higher the thousand grains weight, the higher the seeding rate per hectare.

Seed drill calibration

On the Kverneland Accord DA drill, calibration is a simple task, but awkward to get at on the drill.

The first check is to set the machine’s metering unit to the recommended internet/ book setting of 167kg/ha.

Next, remove the band connecting the air supply to the metering unit and place the collection bag underneath.

The land-wheel drive connection is then uncoupled using a simple R key. The calibration turning handle is fitted then to turn the metering unit for calibration. Eighty-five turns of the metering unit gives one tenth of a hectare of seed in the collection bag.

Adjustments

In my own calibration, after the first check with the metering unit set at 53, 14.5kg of seed was collected, giving 145kg/ha seeding rate.

The process was repeated twice and changed to 57 and then 60 on the metering unit, giving 157kg/ha and then 165kg/ha respectively.

The calibration shows that the book setting on the machine was out by 22kg/ha or 3.4 stones per acre. The reasons for this are grain size, seed dressings used and perhaps how well the seed is cleaned in the case of home-saved seed.

Checking delivery system

Checking seeding pipes and the distributor head is advisable as partial blockages can affect the flow of seed. Pipes that are kinked or moist will cause the problems. Also, the seed labels can end up in the distributor head and some unwelcome tenants over the winter months may have taken up residence.

The tramline pipes should be checked to ensure the electric solenoids are opening and closing the flaps for diverting the seed away from the coulters.

If slipping or stretched, the V belts driving the fan (photo above) will reduce the airflow and this may block the pipes with seed. Hydraulically driven fans have the advantage of keeping the air flowing even if the power harrow slip clutch goes.

The land-wheel on the drill turns the metering mechanism in line with the ground speed to deliver the seed into the venture and up to the distributor head. Ideally, it is best to check that this is working before starting work.

Sensors on the wheel will indicate if the wheel has stopped turning during work. However, a slipping cog in the metering device or jumped chain are more difficult to spot.

Drill component checks

The coulters themselves need to be inspected for wear and damage. The spacing of the coulters on the machine may have moved during the previous year’s work, giving incorrect row spacing that may affect the establishment of the crop and cause disease pressure over the growing season.

Suffolk coulters can be prone to blocking, especially in sticky conditions where the drill rolls back. Worn coulter tips will add to the problem. The cover flaps on the coulters should be checked or replaced if lost. Disc coulters may also block, with wear on the disc being the major culprit.

The after-harrow, if fitted on the drill, may need adjustment if seeds are visible on the ground after sowing.

Setting the sowing depth

Seeding depth, in relation to the size and type of crop sown, can be set by adjusting the coulter pressure. Sowing seed too deep can reduce the vigour of seed, while shallow sowing may leave the emerging seed vulnerable to bird damage and also cause poor soil-to-seed contact, which is essential for germination.

Power harrow checks

The power harrow itself will need the gearbox oil levels checked and also the recommended oil grease mixture for the bed of the harrow. Oil weeps found underneath the harrow or on the tines themselves are signs that the seals or bearings may need attention. The bed might just need a top-up for the season until a winter overhaul can be conducted.

The skids on the side of the harrow need adjustment downwards or upwards, depending on the operating depth, as they wear.

Skids that are not set right can cause visible ridges between the passes of the machine up and down the field. These ridges can cause uneven emergence and problems later on for the combine.

The slip clutch on the shaft of the power harrow should have enough tension to provide the torque to drive the machine, while giving protection to the tractor and the power harrow.

Worn scrapers on the packer roller are easy to spot, as soil build-up on the packer is evident (photo below).

A packer roller that has soil caked on it is not functioning correctly in consolidation of the seed bed and may also cause smearing of the soil.