United States Department of Agriculture
Natural Resources Conservation Service		 Montana Go to Accessibility Information
Skip to Page Content




Calibrating a Drill

Plant Materials Technical Note Number MT-30

A printer-friendly version of this technical note is available in Adobe Acrobat format.

Plant Materials Technical Note Number MT-30 (PDF; 40 KB)

1985.

Pure Live Seed

Drills need to be calibrated on the basis of bulk seed. The amount of bulk seed required for a planting is based on the quality of a given seed lot. Therefore, prior to calibrating a drill, seed lot quality must be known. "Pure Live Seed" (PLS) is a means of expressing seed quality. PLS and bulk seed required are determined by using the seed analysis information on the seed tag in the following formulae.

decimal PLS = (percent germination x percent purity) / 100.

bulk seed pounds per acre = PLS seeding rate recommendation pounds per acre / (percent PLS / 100).

Recommended seeding rates provide an adequate amount of PLS seed per acre even though seed lots differ in seed size, shape, weight, viability, etc. The variation in individual seed lots causes the amount of bulk seed planted per acre to vary considerably while the actual PLS seeding rates remain constant.

Properly labeled commercial seed will show germination, hard seed, purity, weed seed, other crop seed and inert material. It Is recommended that seed be purchased on the PLS basis as determined from the label.

If available, certified seed should be recommended and used. Certified seed provides for genetic purity, varietal identity and high seed quality.

Seeding Rates

Recommended standard seeding rates have been established In Technical Guides for all conservation practices involving seed and planting. The attached table provides seed count data for calibration computations on commonly used conservation plants.

The number of live seeds per pound varies depending on the seed production influences placed on each seed lot (environmental, management, processing, etc.). Recommended PLS per square foot varies with number of live seeds necessary to produce an adequate stand of a particular plant. Species differ in their ability to produce adequate stands depending upon their seedling vigor; rate of establishment; management practices; and rate of spread by seed, stolons or rhizomes. Moreover, computing seeding rates on a PLS basis does not assure uniform field emergence. Many other variables influence the seeded stands success or failure under field conditions, such as soils, precipitation, site preparation, cultural and management practices, and so forth. However, purchasing labeled, high quality seed improves the chances of seeding success.

Calibration

Preliminary Steps

  1. Check the drill for proper working order. Become familiar with the drill and its operation. Perform necessary maintenance.
  2. Get an idea from the farmer or rancher about what species, rates and settings he has previously used, or refer to the manufacturers reed chart for settings. This gives you a basis upon which to start your settings.
  3. Always start setting from a wide-open position and close down to desired position.
  4. Check instructions and drill to see that drill gates or flaps are in proper position for the size and kind of seed being planted.
  5. Compute PLS from seed tag.
  6. Determine the standard seeding rate recommendation from the Technical Guide.
  7. Convert PLS seeding rate to bulk seed required for drill calibration.

Methods

There are three general methods of calibration:

  1. Seed-per-foot method--requires a chart showing number of seeds per pound of the species being planted and a tape measure.
  2. Seed weight--distance method--requires small scales and tape measure.
  3. Acreage--weight method--suitable for large field, rough measurement or check on previous two methods. Requires knowledge of weight per sack of seed and acreage gauge or acreage measurement.
Seed per Foot Method
  1. Determine from the seed count data (Montana Plant Materials Technical Note MT-46) the number of seeds per linear foot or square foot required to achieve the desired PLS seeding rate. The data is computed for seeds per square foot at a one pound PLS per acre rate. The number of seeds per linear foot or square foot required for the recommended seeding rate equals:

    recommended seeding rate PLS pounds per acre x seeds per square foot at 1 PLS pound per acre / (percent PLS / 100) = bulk seeds per square foot.

    This will not change with row spacing of 1 foot or wider, but will require proportional reduction for row spacings less than 1 foot.
     
  2. Make initial drill setting based on specie to be seeded and drill seeding rate chart (Montana Plant Materials Technical Note Number MT-46).
  3. Release disk tension and run across a canvas, tarp, burlap or hard road for 20 feet at normal planting speed, (not asphalt or gravel).
  4. Count seed from at least 3 to 5 linear or square foot representative sections and compute average. (Note: Use high quality seed (>80 percent PLS) or only germination percent in order to avoid counting other crop and weed seeds in lots having less than 80 percent purity.)
  5. Compare actual seeds per foot with desired number.
  6. Adjust drill setting up or down and repeat steps 3, 4, and 5 until desired rate is achieved. Within 10 percent of desired rate is adequate. The lower rate is preferred.
  7. Set the acreage gauge or use distance traveled times drill width to determine acreage. Record the mount of seed put into drill box.
  8. After seeding one or more acres, check the quantity of seed used against the acreage and recommended rate.
  9. Adjust accordingly.
  10. Make a record of all settings, counts and other data for future use.

When mixtures are seeded, it is not necessary to count seeds of each species In the mixture provided they have been thoroughly mixed. One or two species in the mix can be counted. If they check out, the others should be correct.

Planting legume and grass in alternate rows Is better than seeding both in the same row. It can be done easily by blocking every other opening in the grain box (grass seed), and alternate openings in the legume box. An alternative is to partition each opening in the grain box and then put a grass-rice hull mixture in every other partition and legume-rice hull mixture in alternate partitions. The volumes of each rice hull mixture must be equal for proper seeding rates of each species.

Drill dial settings indicate approximate seeding rates when all flutes are feeding. Seeding in alternate rows, without changing the setting for a full seeding, will reduce by one-half the pounds of each species needed per acre.

Seed Weight-Distance Methods
A. Catch-All Method
  1. Using the Technical Guide and the following formula, compute bulk weight of seed required for 1/100 acre at the recommended seeding rate:

    Recommended (Montana Plant Materials Technical Note Number MT-46) seeding rate PLS pounds per acre / (percent PLS / 100) = bulk weight in pounds of seed required for 1/100 acre.
     
  2. Select a prepared seedbed of area similar to the site being seeded. Measure and stake off a distance equivalent to 1/100 acre for the width of drill being used. (See following table.)
     
    Drill Width (feet) Distance for 1/100 acre (feet) 1
    6 72.6
    8 54.5
    10 43.6
    12 36.3
    14 31.1
    16 27.2
    18 24.2
    20 21.8

    1) Distance in feet = (.01 acres times 43,560 square feet per acre) divided by drill width in feet.

  3. Seed for at least 6 feet before coming to the first stake. Stop. Remove drill spouts from disks and place canvas or containers underneath all spouts to catch all seed while driving at a constant speed over the measured distance. Stop even with the second stake.
  4. Concentrate seed and weigh on scales.
  5. Check weight of delivered seed with desired amount and make necessary adjustments in drill settings.
  6. When within 10 percent of desired rate, check results with a second trial at the same setting.
  7. Set acreage gauge on the drill. Seed one acre or more and check the quantity of seed used against the acreage and recommended rates, or repeat steps 3, 4, and 5 above the make necessary adjustments.
  8. Record all data accumulated for future use.
B. Representative Sample Method
  1. Repeat steps 1 and 2 as in catch-all method.
  2. Seed for about 6 feet before passing the first stake. Stop. Remove 3 to 5 drill spouts from disks and place paper or plastic sacks or cans under them to catch seed while driving over measured distance. Stop even with second stake.
  3. Weigh seed samples and obtain average per flute. Multiply average seed weight by the total number of flutes on the drill.
  4. The weight in grams divided by 4.5 or the weight in ounces divided by 0.16 equals the amount of bulk seed planted in pounds per acre.
  5. Repeat steps A-5, A-6, A-7 and A-8.
C. Wheel Circumference Method
  1. Jack up the drill drive wheel and measure the circumference in feet.
  2. Determine the number of revolutions the wheel must turn for the distance equivalent of 1/100 acre for the width of drill used:

    Distance in feet* divided by circumference in feet*(C) = Rotations (R)
    * nearest tenth of a foot

    where C equals the circumference of the drive wheel in feet and R equals the number of revolutions to cover required distance and area. The table shown in Step 2 of the catch-all method lists the various distances a given drill width must travel to cover 1/100 acre.
     
  3. Put seed in the drill box and turn drive wheel until all spouts are seeding uniformly.
  4. 4. Remove 3 to 5 drill spouts from disks and place paper or plastic sacks or cans under them. Turn the drive wheel the number of revolutions previously determined.
  5. Weigh the samples and compute average per flute. Multiply average seed weight by the total number of flutes on the drill.
  6. 6. Repeat steps B-4, A-5 through A-8.
D. Acreage Weight Method
  1. Set the acreage gauge on "0" or use the distance traveled times the drill width to determine acreage.
  2. Fill the drill with a known weight of seed and plant a measured area--one acre or less.
  3. Estimate or weigh the mount of seed used and compare with the desired rate. (Option: weigh unused seed and subtract it from the total that was originally poured into drill.)
  4. Make necessary adjustments in the settings. Repeat steps 1 to 3 until desired seeding rate is achieved.
  5. Record all data for future use.

If you have any questions, please contact:

Jim Jacobs, Plant Materials Specialist
Phone: (406) 587-6995
Email: Jim.Jacobs

Ronald Nadwornick, State Resource Conservationist
Phone: (406) 587-6998
Email: Ron.Nadwornick

< Back to Plant Materials Technical Notes

Last Modified: 06/24/2008