best practice management guide for south-eastern Australia - Grains ...

Irrigation management
12. Irrigation management
Don McCaffery, NSW DPI
Canola is an important irrigation crop, grown in rotation
with a range of winter and summer crops. While rice is the
major break crop in continuous crop rotations involving
winter cereals, canola and faba beans have gained in
popularity in recent years. Irrigated production is mostly
confined to the inland river valleys of central and southern
NSW and the irrigation districts of northern Victoria.
The largest area of production is in the Murrumbidgee
and Murray Valleys of southern NSW, where yields are
typically 2–2.5 t/ha. However, yields of 3.0–3.5 t/ha and
higher are achievable with high levels of management,
paying particular attention to paddock selection and soil
type, irrigation method and establishment technique,
sowing time, nutrition management, and spring irrigation
scheduling.
An achievable water use efficiency (WUE) target for
canola on a good flood irrigated layout is 8–10 kg/ha/mm,
that is, for each millimetre of growing season water (rainfall
plus irrigation). Note that starting soil water is not included
in the calculation of WUE as it is presumed to be negligible
in most years in southern Australia. A water budget
undertaken at the start of the irrigation season, or before
sowing, will help with decisions on crop inputs and yield
targets. The water budget should be reviewed on a monthly
basis. The planted area must be matched to the supply rate
by calculating peak water requirements during flowering and
pod filling.
Salinity
Canola has a similar salinity tolerance to wheat and much
better than soybeans and maize. Overseas research indicates
that canola has a soil salinity threshold of around 6.5 deci
Siemens per metre (dS/m) averaged in the rootzone. The
impact of soil salinity is highly dependent on soil texture. To
ensure salinity does not affect yields, avoid paddocks with
high watertables (within 1 metre of the soil surface) which
are also saline. Canola can also tolerate more saline irrigation
water than some other crops, but specialist advice should be
sought from an experienced irrigation agronomist or irrigation
officer. The published threshold for irrigation water salinity for
canola is about 2 dS/m for a slow draining soil. However,
without a leaching component, irrigation water of this salinity
will make the soil more saline over time.
Irrigation systems
Canola yields best in moderate to highly fertile self-mulching
grey or brown soils. These soils are generally the best for
irrigated cropping.
Raised beds
Raised beds are ideal for irrigated canola, especially where
the slope is 1:1500 or flatter. The optimum slope depends
on the soil type and structure which dictate the water
movement from the furrow into the bed (subbing ability).
Raised beds are the preferred flood irrigation method in the
Raised beds are the
preferred method for
growing canola under
flood irrigation.
Photo: D. McCaffery, NSW DPI
Canola best practice management guide
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