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In an irrigated wheat experiment two Australian varieties and two introduced semi-dwarf varieties were compared in growth and yield, each at three levels of nitrogen fertilizer. The semi-dwarf wheats yielded more grain than Heron and Olympic in the sampling harvest, the increase over Heron being 26 per cent for Mexico 120 and 15 per cent for Chile 1B. This higher yield resulted from a longer duration of grain growth, probably associated with earlier flowering. The semi-dwarfs produced fewer tillers, both at the maximum and at maturity. Their higher yield was derived not from increased total dry matter production but from an increased harvest index. Nitrogen fertilizer stimulated tillering and early growth and increased the weight of grain set at flowering. Relative growth rates at each fertilizer level then remained approximately equal until maturity. Although there was a large response to nitrogen, there was no varietal interaction, possibly because of the relatively low level of production and absence of severe lodging. |
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