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Effects of nitrogen application on the light interception and radiation use efficiency of sunflower, helianthus annuus l.

R.M. Kamona and B.T. Steer

University of Western Australia, School of Agriculture, Nedlands WA 6009

The amount of photosynthetically active radiation (PAR) intercepted by the crop canopy and the efficiency with which the crop utilizes that light in the production of new dry matter (RUE) determines the crop growth rate (4). Studies on the effect of nitrogen (N) on the extinction coefficient (K), which is one of the determinants of light interception, and the RUE in sunflower are limited.


An experiment was carried out in 1989/90 at The University of Western Australia to determine the effects of N on light interception and the RUE using sunflower cv. Hysun 33 planted at 10 plants/in' under irrigation. The N application rates were at 130 (high N) and 60 (low N) kg/ha N, given in split applications.

Results and discussion

The proportion of incident PAR intercepted by the canopy reached a maximum of 94% and 70% under high and low N respectively. The increase in light interception was due to a higher leaf area index of 3.45 compared to 2.08 at low N. The distribution of light in the plant canopy was better under low N as the K values were 0.77 and 0.53 for high and low N respectively.

The RUE based on the above ground dry matter reached a maximum of 2.93 g/MJ PAR under high N compared to 2.16 g/MJ PAR under low N. The significant effect of N on RUE is in support of findings in wheat (Triticum aestivum L.) (1), sorghum (Sorghum bicolor (L) Moench) and maize (Zea mays L.) (2). The high RUE with high N could have been due to differences in the partitioning of dry matter between root and shoot, the increase in the photosynthetic rate and/or increased utilization of intercepted PAR (3).


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Muchow, R.C. and Davies, R. 1988. Field Crops Res. 18, 17-30

Novoa, R. and Loomis, R.S. 1981. Plant Soil 58, 177-204

Warren Wilson, J. 1971. In: Transition from extensive to intensive agriculture with fertilizers. Proc. 7th Colloqium Inter. Potash Inst. IPI,Beme. pp. 34-56.

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