Growers have been reporting a big variation in thousand grain weights (TGW) in winter cereal varieties this planting season.

In many cases, a larger than average variation in TGW can be found between different batches of the same variety.

The thousand grain weight is a measure of seed size. It is the weight in grams of 1,000 seeds.

The figure is used when calculating the seeding rate and can often vary from one crop to another, between the same variety, between growing years and can even vary from one area of the field to another.

Therefore, it is important to be conscious of the potential in variability in TGW in any given year.

As growers have been making headway with winter barley planting, a larger than average variation in TGW in the same variety has been noticed in places this year.

Variation between varieties and between batches

TGW will generally vary a number of grams between each batch, but some growers have noticed a greater variation between batches this year.

One grower reported a difference in TGW of 15 grams between batches of Tower winter barley seed, ranging from 49 to 64.

The TGW is generally stated on the label, but a recommended grain weight can also be found for each variety on the Department of Agriculture recommended variety list.

The Department’s figures are based on an average TGW for that variety over the past three years.

While these weights serve as a good guide, growers should always check the TGW of each individual batch of seed. If this is not available on the label, contact your merchant.

The variation in TGW this year in particular is in part explained by difficult growing season drought pressure and high temperatures experienced earlier in the season.

Know your seeding rates

Growers have reported the need to adjust seeding rates in their drills much more often this season, as seeding rate is in part determined by TGW.

Seeding rate calculation = TGW x target plant population per square metre / % establishment = required seeding rate (kg/ha)

If, for example, a grower is drilling winter barley at 350 seeds/m2 with the aim of establishing 300 plants/m2 at 85% establishment, the TGW can make a big difference to the required seeding rate - see Table 1.

The key message from this is not to rely on average variety TGW stated in the recommended list when setting your drill and to check the TGW of every batch of seed sown.

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