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Increasing wheat yields on the south coast of Western Australia

W.R. Smith and W.K. Anderson

Department of Agriculture, Esperance Agriculture Centre Esperance, Western Australia 6450

In the major cropping areas of Western Australia lack of rainfall is often considered to be the major limitation to yield. However the high rainfall, south coastal region receives three to five times the rainfall of these areas but produces similar average yields (1-1.5 t/ha). A project was commenced in 1986 to examine ways of increasing wheat yields on the south coast towards the theoretical potential of 5-10 t/ha.

Methods

Factorial experiments employing various levels and combinations of cultivar, N rate, seed rate, and fungicide at a range of sites (rotations, drainage, sowing times) were used.

Results and discussion

Examples of the major factors influencing yield (t/ha) are illustrated below:

1. Open cut drains. 2. > 80% clover dominant pasture, grass control in lupins not complete. 3. Data from adjacent experiments. 4. Tilt at 750 mL/ha at elongation and booting. 5. Mean of 13 sites. 6. Mean of 7 sites.

The response to drainage illustrates the importance of site and soil type selection to minimize the risk of waterlogging. The use of 'grass-free' rotations usually involving lupins as the previous crop minimized the incidence of take-all. Yield increases from nitrogen applied at 80 kg/ha compared to 40 kg/ha were not found in these experiments. Sowing in May using the mid-season cultivar Aroona outyielded later sowings where all other factors were favourable. Yield reduction with later sowing was sometimes also related to increased aphid attack and barley yellow dwarf virus. Two fungicide sprays increased yield where Septoria diseases (n major limiting factor. The winter cultivar Osprey was not well adapted to the south coast and a better adapted, long season cultivar is still required. Doubling seed rate to 100 kg/ha increased yield at seven out of thirteen sites.

In these experiments yields of Aroona wheat approached the rainfall limited yield potential when seasonal rainfall was about 400 mm, root diseases were minimized, and 100 kg/ha of seed was sown in May. Scope still exists however to improve yields using longer season, Septoria resistant cultivars.

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