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Castorbean Production as Related to Length of Growing Season I. Effect of Date of Plant Desiccation¹

Castorbean plants (Ricinus communis L.) were killed by chemical desiccant at weekly intervals during the fall in four tests in 2 years in Nebraska. Effects of desiccation on total yield and germination were determined. Yield, weight per 100 seeds, and germination were also determined for sequential racemes. Natural freeze was the check treatment. Yield increased at a uniform rate with delay of desiccation except in one test severely affected by Alternaria leaf spot disease. The average weekly increase in yield for the four tests was 199 kg per ha. Primary racemes were mature at the time of first treatments. The contribution of secondary, tertiary and quaternary racemes to yield increased during the entire course of the treatments.

Seed weight from secondary and tertiary racemes increased with maturity. Germination was positively and significantly correlated with seed weight. The highest percentage germination was obtained from late September and early October desiccation treatments. Freezing of immature seeds and weathering of mature seeds reduced germination. Drying of seed following plant desiccation required about 10 days and did not reduce germination. Yield loss from 10 days' growth prior to freeze was calculated to be 284 kg per ha. On basis of low seed germinations obtained in these tests, the feasibility of castorbean production for seed in Nebraska would be questioned.

Key Words: Ricinus communis L. • sequential racemes • germination • Alternaria leaf spot • seed weight • Alternaria ricini (Yoshii) Hansford

² Formerly Assistant Professor (now Research Agronomist, Crops Research Division, ARS, USDA, University of Arizona Cotton Research Center, Phoenix) and Associate- Professor, University of Nebraska, Lincoln.

Received for publication March 16, 1967.