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Castorbean Yield and Quality as Influenced by Irrigation Schedules and Fertilization Rates¹

Irrigation of the growing crop in addition to preplant irrigation did not significantly increase yields of castorbeans (Ricinus communis L.) in 2 of 3 years. In 1963 one irrigation on July 25 produced yields that were significantly higher than either no postplant irrigation or six weekly irrigations. Delay of first irrigation 14 days reduced yields significandy. High nitrogen (180 kg/ha) significantly increased yields of ‘Baker 296’ variety, but not of ‘Lynn,’ grown only in 1963. Irrigation treatments had a significant effect on field loss of seed of Lynn. Highest field losses were from treatments receiving the earliest irrigation. Baker 296 seed losses were lower and differences between treatments were not significant. Nitrogen level had no significant effect on field loss. Weight per 100 seeds and oil content were inversely related to amount of irrigation water applied. Added nitrogen significantlty reduced Alternaria leaf spot infection. In the no-irrigation treatment soil moisture approached the permanent wilting point in the 30- to 61-cm depth of soil in late August, in the 91- to 122-cm depth in late September, and significant utilization of soil moisture in the 152- to 183-cm depth was evident in early September.

Key Words: Ricinus communis L. • Alternaria leaf spot • Alternaria ricini (Yoshii) hansford • blue capsule mold • field loss • germination • nitrogen • oil content • seed weight

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

Received for publication April 10, 1967.