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Effects of Plant Population on Castorbean Yield¹

Plant population effects on yield and growth of irrigated and non-irrigated castorbeans (Ricinus conttnunis L.) was tested for 3 years. The optimum plant population of irrigated dwarf-internode castorbeans was about 58,000 plants per ha. Row spacings from 0.5 m to 1.0 m did not significantly affect yields, if plant population was held constant. The optimum plant population for nonirrigated castorbeans was near or higher than the highest population in our tests. It was clearly higher than the current recommendation of 20,000 plants per ha. Linear regression of yield on plant population was significantly different among cultivars and among tests for the nonirrigated castorbeans. Cultivars with bushy growth and small racemes had greater yield depression from low populations than did more erect cultivars with large racemes. Plant population effect on yield was reduced as the yield level of the nonirrigated tests decreased.

Low plant population in nonirrigated tests increased plant height, hypocotyl diameter, length of primary raceme, number of racemes per sequential set, and yield of all sets of racemes. Low population reduced height of the primary raceme from the soil. Population had no effect on nodes to the primary raceme. Oil content of the seed or test weight were not affected by plant population of nonirrigated castorbeans.

Key Words: Ricinus communis L. • Oil content • Plant morphology • Stand density • Seeding

² Formerly Assistant Professor (now Research Agronomist, Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, University of Arizona Cotton Research Center, Phoenix, 85040) and Associate Professor, University of Nebraska, Lincoln 68503.

Received for publication December 23, 1969.