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Autumn feed options - buy or grow?

By John Fowler, senior agronomist

Irrigators with stock to feed may well be wondering how to best manage the autumn feed-gap period. Should they sell some water and buy feed or use the water to grow their own? Given the current price of temporary water, the options need to be compared to see which is the most economic.

In order to determine the cost of growing your own feed, you need good data on both autumn pasture production (kg dry matter/ha) and total water use (Ml/ha).  Most irrigators however, probably do not have this information for their own paddocks, so will need to rely on generic data, such as that in the following table.  This data comes from an old experiment conducted by the CSIRO at Deniliquin several decades ago.

Date First
Watering

Pasture Production
mid July (dry matter)
(kg/ha)

Carrying
Capacity
(DSE/ha)

Water
Use
(Ml/ha)

Production
per Ml
(t/Ml)

Dry matter
cost ($/t)
(based on water cost $260/Ml)

28-Feb

5,700

25

3.6

1.6

$164

29-Mar

4,200

17

2.3

1.8

$142

30-Apr

2,200

12

1.7

1.3

$201

A quick evaluation of this data shows that it requires about $142 to $164 worth of water (based on water being $260/Ml) to grow a tonne of pasture, depending on the date of first watering.  It is likely to cost a further $20/t for fertiliser and $10/t for insect and weed control.  Therefore, the cost of growing your own autumn feed is about $175 to $200/t.

This approach allocates all the production costs against autumn pasture production and does not take into consideration the value of the spring production or the rotational benefits of pastures (such as increases in soil organic carbon and nitrogen).

Clover-dominant sub pasture will produce high quality feed.  Therefore, when making a comparison with purchased feed, it needs to be against very good quality feed, such as lucerne or clover hay.

A tonne of feed on the ground however, will not equate to a tonne in the rumen as wastage and spoilage is frequently between 30 – 50%.  Therefore, if you do grow sub, make sure you utilise as much of the growth as possible through higher stocking densities or smaller paddocks. Increasing utilisation can also increase pasture growth and quality

So, even with high water costs, the economics seem to favour growing your own feed rather than purchasing it.  This however assumes good pasture agronomy so that the production target is achieved.  Two of the more important agronomic factors, pasture nutrition and irrigation management, are discussed below:

Pasture nutrition: Legumes pastures have a high phosphorus requirement.  The above production targets would normally require a top dressing of at least 250 kg/ha single superphosphate prior to the first irrigation.

Irrigation management:  The data backs up local experience in suggesting that the optimum time to commence watering sub is about the 1st March.  The second irrigation needs to follow within 7 or 8 days to increase the survival rate of the shallow rooted clover seedlings.   Subsequent irrigations should be scheduled according to crop water use.

Finally, it needs to be understood that this data is for existing sub pastures with a good seed bank (i.e. >300 kg/ha), it will not be achieved by pastures being sown for the first time this season.  Autumn production from sub clover is closely correlated to seedling populations. Maximum production requires a plant population of over 1,500 seedlings/m2, which is not normally achieved in the first year of the pasture.