Grain weights and volumes
When feed budgeting, or deciding on supplementary feeding rates, it is often necessary to convert the feeding rate (in kilograms or tonnes) to a volume for the feed-out bin. Therefore, it is important to know the density of the grain and the volume of your feed bin so that accurate amounts of feed are used. Just as important is the feed out rate if only a proportion of the bin is to be fed to a particular mob.
Grains have variable bulk densities — usually given in kilograms(kg)/hectolitre or tonnes/cubic metre (t/m3) — and can often be lighter than expected. This affects the amounts actually fed out.
| Grains | Bulk density (t/m3) | Bulk density (kg/hectolitre) | Bulk density (kg/litre) |
|---|---|---|---|
| Barley | 0.65 | 65 | 0.65 |
| Oats | 0.50 | 50 | 0.50 |
| Wheat | 0.75 | 75 | 0.75 |
| Lupins | 0.78 | 78 | 0.78 |
A quick and easy method of determining the bulk density of a grain is to weigh a 20 litre (L) container of the grain. Divide the weight of the grain by the 20L to give a bulk density in t/m3 (note; it is the same as kg/L) or to get the answer in kg/hectolitres multiply the answer by 100. For example, a 20L container of barley which weighs 10.8kg has a bulk density of 0.54t/m3 or 54kg/hectolitre.
Converting grain weight to volume
If the feed requirement for a mob of sheep is given in kilograms, it is a simple calculation to convert it into a volume for use with a feed bin if you know the grain's bulk density.
For example, a mob of sheep needs to be fed 500kg of oats (bulk density = 0.50t/m3) and the feed bin holds 3m3.
volume needed = 500kg oats/0.5t/m3 = 1m3
or
volume needed = 500kg/50kg/hectolitres = 10 hectolitres
This means one third of the bin capacity should be filled.
When feeding out two grains at a time (for example lupins and oats), both volumes need to be calculated so that accurate amounts are fed.
For example, a mob of sheep needs to be fed 500kg of a 25/75 lupin:oats mix. Lupins at 0.78t/m3 and oats at 0.50t/m3 bulk densities and the feed bin holds 3m3.
volume of lupins needed = 25% of 500kg = 0.125t (125kg)/0.78t/m3 = 0.16m3
and
volume of oats needed = 75% of 500kg = 0.375t (375kg) / 0.5t/m3 = 0.75m3
= 0.16 + 0.75 = 0.91m3 total
The volume of lupins is about one third less than an equivalent amount, in weight, of oats.