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Soil evaporation, transpiration and transpiration efficiency estimates for old and modern varieties of wheat

D. Tennant, R.K. Belford and K.H.M. Siddique

Department of Agriculture Baron-Hay Court, South Perth, 6151, W.A.

In a detailed study of old and modern varieties of, wheat to identify. morphological and physiological attributes associated with high grain yield, water use efficiencies were found to increase from old to modern varieties, but were little different between varieties released in the past ten years. To see how this was reflected in soil evaporation (SE), transpiration (T) and transpiration efficiency (TE), we used procedures outlined by Cooper, et al. (1) to partition evapotranspiration.


Dry matter, leaf area and soil water were measured on ten varieties of wheat, representing a chronological sequence of economically significant releases between the 1860s and the present day. Data used to estimate SE and T included bare soil evaporation measured from uncropped plots at either end of the experimental area, variety attenuation coefficients (k) calculated from sequential light intensity measurements made above and below the variety canopies, leaf area index and evapotranspiration.

Results and discussion

Variety attenuation coefficients increased progressively from 0.74 with Purple Straw, the oldest variety, to 1.33 with Kulin, the most recently released variety (Table 1), suggesting more efficient capture of radiation by the modern than the old varieties. Reasons for this are not clear, but may be associated with greater mutual leaf shading with the old prostrate and tall variety types when compared to the modern semi-dwarf erect plant type. SE was less with the modern than the old varieties.

Evapotranspiration (ET) was higher with the old varieties due to rain between maturity of the modern (early flowering) and old (late flowering) varieties. T obtained by difference from ET reflected this. SE was of the order of 38-44% of ET. Grain yield TEs were highest with the modern varieties of wheat, but showed no gains when comparing varieties released since 1960.

Table 1. Soil evaporation (SE), transpiration (T) and transpiration efficiency (TE) estimates made for ten varieties of wheat, grown at Merredin in 1987

1. Coopet, P.J.M., Keatinge, J.D.H. and Hughes, G. (1983). Field Crop Research 7:299-312

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