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Effect of Plant Density and Growth Duration on Grain Sorghum Yield under Limited Water Supply¹

In one experiment, three experimental grain sorghum (Sorghum bicolor L. Moench.) hybrids (heading 55, 60, and 70 days from emergence) were planted at 12 plant densities (from 2.9 to 27.9 plants/m²) in a systematic design. Plants were grown under conditions of 302 mm available soil water, as determined at emergence, with no additional water supply.

It was found that the grain yield of the late maturing hybrid was highest under the low plant density and that of an early maturing hybrid was highest under the high density. The superiority of low density in the late maturing hybrid and of high density in the early maturing hybrid was also consistent regarding yield per plant, number of heads per plant and number of grains per panicle.

The highest yield in the experiment was obtained with the earliest maturing hybrid planted at the densest plant population. All grain yield components were operative in the determination of inter-hybrid differences under moderate competition. The expression of components was suppressed by increased competition, and at the highest plant density grain yield was determined only through the interaction between the number of grains per panicle and the weight per grain. The superiority of the early maturing hybrid at the highest density was attained through its ability to maintain larger grains in spite of increased interplant competition for water.

In a second experiment an early maturing hybrid used less water than a later maturing hybrid, at all stages of growth, beginning on 30 days from emergence. Water use was increased by increased plant density.

Key Words: Competition • Water stress • Water use • Duration of growth • Grain yield components • Sorghum bicolor L. Moench • Hybrid sorghum

² Research Agronomist, Division of Field Crops, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Presently, F.A.O. André Mayer Fellow, Department of Agronomy, University of Nebraska, Lincoln, Nebr. 68503.

Received for publication December 31, 1969.