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Calculating seeding rate with 1000 grain weights

BCG highlight the importance each year of correctly calculating seeding rate, but this year with record high prices for all grains, it is more important than ever to know exactly how much seed to sow to achieve your target plant densities.

Target Plant Density: the table below provides a guide to the target plant densities for various rainfall zones.

  

Target Plants/m2 for annual rainfall zone

Crop

250-350mm

350-450mm

450-550mm

Wheat

150-180

160-200

160-220

Barley

130-160

160-180

160-180

Oaten hay

250

250

250

Canola

40-70

50-80

50-80

Lentils

110-120

110-120

110-120

Faba beans

15-30

20-35

20-35

Field peas

35-70

40-70

60-80

Lupins

45-60

45-55

35-45

Vetch grain

40-50

40-50

50-60

Thousand grain weights can be a bit of extra work but this year they are worth it. The example shown in the table below is from actual seed stored on an eastern Mallee farm and shows the difference grain weight can make to sowing rate.

  

Thousand grain weight
(g)

Sowing rate (kg) for 150plants/m2 target

No. plants/m2 at 60kg/ha sowing rate

Silverstar

24

45

200

Clearfield JNZ

32

60

150

Yitpi

40

75

121

How to do your own grain weights:

  1. Buy or borrow a reputable digital electric kitchen scale that weighs +/- 1g. An added bonus is that it can be used to accurately weigh herbicides such as Glean and Ally.
  2. Grade and pickle seed grain if this is to be done. The grain count can be made while the grader is running so that the amount of seed to be graded can be calculated to more accurately match the area to be sown.
  3. Select a representative sample of seed.
  4. Place some seed on an A4 sheet of paper near the edge of a table.
    Place ice cream container on knees under edge of table.
    Using a skewer/knife, scrape 5 grains at a time over the edge of the table into the container.
    Do this 20 times (which equals 100 grains).
    Make a mark on the paper at the end of each group of 20. Repeat these groups of 20, 10 times in all, which means you have counted 1000 grains. It doesn't take all that long and it is a very easy way to make/save money.
  5. Place small container on kitchen scale and tare.
  6. Tip in counted grains and record the reading this is your thousand grain weight.
  7. Finally to calculate sowing rate use the following formula:

Sowing rate (kg/ha) = 1000 grain weight (g) x desired plants /m2 germination percentage

For example: Yitpi weighs 40g (1000 seeds), target plant population 150plants/m2, approx establishment = 80%
Sowing rate (kg/ha) = 40 x 150 80 = 75kg/ha

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