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

Irrigation management
Three years of demonstration work on a border check
layout in the Murray Valley of NSW showed a 0.75 t/ha
response to irrigating at early flowering, which reduced to
0.3 t/ha by waiting until mid flowering.
If there has not been substantial winter rainfall (soil profile
is dry to 60–80 cm) and the crop is showing early signs of
moisture stress, irrigate in early August if water is available.
Growers with access to a bore or river allocation have a
distinct advantage over irrigators on company schemes.
From these water sources crops can be watered before
August in very dry years with relatively low risk on raised bed
layouts or spray irrigation.
Be prepared to irrigate for the target yield. Between
two and four spring irrigations are usually needed to finish
the crop but this depends on soil water holding capacity.
These irrigations will normally require 1.5–3 ML/ha in total
depending on the efficiency of the irrigation layout and the
amount of spring rainfall.
In fully irrigated crops the final irrigation needs to be
applied to supply enough soil moisture for the crop up until
physiological maturity as seed is still filling and gaining weight.
Physiological maturity usually occurs about 25–30 days after
the end of flowering (end of flowering date is recorded when
five per cent of plants still have flowers). So, the last irrigation
in a crop with high yield potential crop needs to be applied
about 10–15 days after the end of flowering date.
Crops grown under spray irrigation need to be irrigated
earlier in the spring than those under flood irrigation, mainly
because smaller amounts of water are applied at each
irrigation and the time it takes to get to a full soil profile is
longer. Starting irrigation earlier will provide a soil moisture
buffer in the event of hot, dry weather. Spray irrigated crops
need to be irrigated even closer to maturity as smaller
amounts are applied in each irrigation. About 30–40 mm
applied in each of three or four irrigations is usually required.
The total irrigation requirement (establishment plus spring) for
a spray irrigation system will vary from 1.2–2 ML/ha.
Irrigation scheduling
To time irrigations precisely, the irrigation supply system must
have the capacity to deliver sufficient water. Growers should
use a locally developed and tested irrigation scheduling
system to aid their irrigation management decisions. Two
practical systems are available for canola, based on either
the measurement of weather conditions or the measurement
of soil water. The NSW Department of Primary Industries
provides a weather-based water use information service
called Water Watch in some irrigation areas of NSW. Water
Watch evapo-transpiration values can be related to any type
of crop and used in a manual water balance calculation
system.
Soil moisture monitoring equipment is in demand as
irrigators strive for maximum efficiency with limited water.
Technology to meet this demand is developing rapidly.
Neutron probes perform well when used with a consultant.
Newer technology using four to six gypsum blocks
connected to data loggers is proving very popular. They are
relatively cheap, easy to install and interpret. The Hansen
logger allows data to be viewed in the field, while the GBug
operates on a wireless connection to download data, which
can then be uploaded into computer software for analysis.
Other similar devices are commercially available.
Some irrigation companies are establishing data handling
services for growers to help manage the advanced soil
moisture systems where new capacitance probes are
completely sealed and buried below the cultivation depth.
Soil moisture monitoring equipment is proving its worth,
especially for timing the critical first spring irrigation, when
growers are hesitant to irrigate if rain is forecast in the near
future.
Figure 12.1 Relationship between moisture stress during
flowering and applied nitrogen on canola seed yield at
Condobolin, NSW
Seed yield (t/ha)
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0
0
Water stressed
50 100 150
Nitrogen rate (kg N/ha)
Irrigated
SOURCE: Tony Bernardi, NSW DPI
Soil moisture monitoring technology
can improve decision making for
irrigation timing. Here, data stored in
the Hansen logger is being read in
the field. Photo: R. Hoogers, NSW DPI
74 Canola best practice management guide