September 25, 2002 | By: Laura Skillman

As October approaches, grain farmers will begin planting their winter wheat crop and a properly calibrated drill is the first step towards achieving optimal yield potential.

Selecting and achieving the optimum seeding rate during planting requires that grain drills be calibrated for each seed variety/lot that is used, said Sam McNeill, University of Kentucky College of Agriculture Extension agricultural engineer.

A recent study has shown that individual seed metering/delivery units on drills can vary by more than 10 percent above or below the target seeding rate, which affects costs proportionately. It is best to collect seed from three to five drop tubes across the length of the drill during calibration to obtain an accurate value of the average seeding rate.

Most operator’s manuals provide seeding rate tables that are useful for “coarse tuning” a drill, but these have been found to vary by 10 percent or more from measured values in calibration trials for most soft red winter wheat varieties.

“Operators who calibrate their drills each year and who keep records of their drill settings for a range of seed sizes can reduce the time required to calibrate their equipment, provided that seed of similar size is used,” McNeill said.

Seed rates are generally increased as the planting season progresses to offset less than ideal conditions. No-till operators generally match seed rates to the amount and condition of residue that’s encountered at planting time. The degree of residue

decomposition, soil and residue moisture, and post-harvest residue treatment, (mowed or not mowed) all affect drill performance, stand establishment, final stands, and ultimately yield.

For these reasons a spreadsheet was developed to help farmers calibrate their drills, keep track of seed costs and keep records of their wheat enterprise. The spreadsheet was developed by Shelby County producer Mike Ellis to facilitate drill calibration, McNeill said. It has been expanded to include seed costs and other useful information.

The spreadsheet can be used to compare varieties on a cost per acre. Seed costs per acre vary considerably depending on seed size and quality. Since wheat seed is sold by the pound and seeding rates are based on a specified number of seeds per unit area, the smaller seed of equal quality is the better buy, provided it has the same yield potential with other varieties being compared.

By simply changing the target population on the spreadsheet, the total amount of seed and its cost for a given operation can be quickly calculated. This is a useful feature that helps farmers select profitable target populations, McNeill said.

Using a 500-acre operation as an example, a difference of 50 plants per square yard can change the total seed cost by $1,705. The difference becomes even greater when comparing timely planting and late planting rates and can approach $3,410 or $6.80 per acre, McNeill noted.

The economic implications of whether to use a fungicide seed treatment can also

easily be evaluated with the spreadsheet, he said. For example, suppose a variety is found to have a germination rate of less than 80 percent but could be improved to 90 percent with treatment. The germination difference impacts seeding rate and seed cost, and the $1 treatment cost per bag is easily recovered.

The spreadsheet is provided at no cost and is accessible by the UK Biosystems and Agricultural Engineering department web site, www.bae.uky.eduor through your county Extension office.


Sam McNeill, (270) 365-7541 ext. 213