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Drought tolerance of wheat seedlings

A. Heinrich

Avon Districts Agriculture Centre, Northam WA 6401

Significant yield advantages of very early sown wheat crops (mid to late April) have been clearly demonstrated in the central wheat belt of WA (1). Yield penalties of up to 50 kg/ha/day delay in sowing have been recorded.

Very early sown crops are frequently sown on limited rainfall in mid to late April and as a consequence may be exposed to sub-optimal soil moisture during germination and early growth and development. This work investigated the rainfall requirement of wheat for germination and early growth of early sowings in the central wheat belt of WA.

Methods

Spear wheat was hand sown under a plastic-covered tunnel house on 28 March 1991 on a red brown clay loam (0-15 cm) over red clay (15 mm +) (Dr 2.12) at Northam (31°35'S, 116°42'E). The site was scarified three weeks prior to seeding to a depth of 5-10 cm. Irrigation was applied at rates of 15, 25 and 40 mm, split as 10 mm prior to seeding and the balance immediately after seeding. Plant establishment was recorded on 2 x 0.5 m2 quadrats per plot. Rates of leaf emergence and elongation were recorded on 10 plants per plot.

Results

Ambient temperatures, 1.5 m above ground, exceeding 35°C were recorded on 12 out of the first 21 days after seeding, seven of which exceeded 40°C. Seeds germinated in the 15 mm treatments, but failed to emerge. Plant densities were 73 plants/m2 for the 25 mm plots and 78 plants/m2 for the 40 mm plots two weeks after seeding. Plant death commenced at the end of week 4 in the 25 mm plots.

Leaf emergence and elongation were delayed by water deficit in the 25 mm treatment compared with the 40 mm treatment. Five weeks after seeding, plants in the 25 mm treatment had three leaves and total leaf length of 20.7 mm compared to five leaves and 54.0 cm total leaf length on the 40 mm plots. Tiller emergence was inhibited or very severely delayed compared with the expected time of emergence (1) on both the 25 and 40 mm plots.

Discussion

At the high temperatures experienced with this very early sowing, 15 mm rainfall was insufficient for wheat establishment on the red brown clay loam. This contrasts with the 25 and 40 mm treatments where seeds germinated and plants established. Once established, wheat seedlings were very drought tolerant as their survival under the extreme conditions indicated.

Both the rates of appearance and elongation of main stem leaves were reduced by water deficit in the 25 mm treatment. The appearance of tillers was delayed beyond the expected time of appearance in both treatments. The effects of slower growth and development on potential yield are currently being studied.

Acknowledgment

Funding for this work from the Grain Research and Development Corporation, WA, is gratefully acknowledged.

References

Heinrich, A. 1992. Proc. 6th Aust. Agron. Conf., Armidale (these proceedings).

Klepper, B., Rickman, R.W. and Peterson, C.M. 1982. Agron. J. 74, 789-792.

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