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Light interception and growth by wheat and barley in Western Australia

R.K. Belford, K.H.M. Siddique and E.R. Harvey

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

Ground cover and light interception by crops of wheat and barley were measured in 1987 and 1988 on duplex soils at two locations in Western Australia. The work formed part of a project to compare physiological and morphological characters of old and modern wheats (1).


Measurements of leaf area index (LAI), dry matter production, ground cover, and light interception were made fortnightly up to anthesis on six varieties of wheat and one barley at Merredin in 1987 and 1988; and on four barleys and one wheat at East Beverley in 1988. Results from Merredin in 1987 are considered here. Wheat varieties used were released between 1860 (Purple Straw) and 1986 (Kulin). Ground cover was calculated from photographs taken directly above the crop; interception of photosynthetically active radiation (PAR) was measured on the same area using a Li-Cor line sensor at ground level and above the canopy. PAR interception (i) was derived from fractional ground cover (f) using the procedure of Steven, et al. (2). Values of k1 (the attenuation coefficient for incident PAR) were also calculated from the relationship i = 1 - exp (-ki.L), where L is the green area index.

Results and discussion.

For all varieties of wheat except the oldest (Purple Straw), fractional ground cover was less than fractional radiation intercepted (i.e. ki/kf<l). This suggests that the fewer, more erect leaves of the modern varieties were more efficient at capture of radiation than the larger number of smaller, more prostrate leaves of older varieties, particularly after stein elongation. For the modern wheats, the attenuation coefficients (ki) for intercepted PAR were higher than published values; for older wheats and barley, ki values were similar to published values. For all varieties, the relationships between cumulative PAR and dry matter were logistic. The efficiency of conversion of PAR to above-ground dry matter (DM) (to anthesis) averaged 1.2 g DM/MJ PAR for the six wheats, but there was a trend towards higher values for the modern varieties adapted to the Mediterranean environment of W.A. The difference in conversion efficiency between Purple Straw and Kulin was significant. Values of ki/kf, conversion efficiency, and grain yield of three varieties are shown in Table l.

Table 1. Characteristics of three wheat varieties grown at Merredin, 1987

1. Siddique, K.H.M., Belford, R.K., Perry, M.W., and Tennant, D. (1989), Aust. J. Agric. Res. 40 (3) (in press).

2. Steven, M.D., Biscoe, P.V., Jaggard, K.W., and Paruntu, J. (1986), Field Crops Res., 13, 75 87.

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