The Effect of Lime Application on Emergence and Growth of Castor Oil Plants

Castor oil (Ricinus communis) has been cultivated for centuries and its production is currently being scrutinized because of the ricin content of the plant and its possible use in terrorist activities. The objective of this study was to measure the effects of lime application on the emergence, growth and development of castor accessions under greenhouse conditions. Lime was applied to a Norfolk Sandy loam soil and incubated for three months. Castor oil seeds were planted into a soil with a pH of either 5.3 or 5.9. The five accessions used in the study were obtained from: Tanzania (TZ1, TZ2), Guyana (GY-PAR), and Jamaica (JA2, JA4). The study was conducted in the greenhouse facilities at the G. W. Carver Agricultural Experiment Station at Tuskegee University. Data were collected on plant emergence, height, and vigor, as well as dry matter yield. Four weeks after emergence, TZ2 and GY-PAR had the highest percent germination (96%), while JA2 exhibited the lowest (80%) when limed. One week later, the highest percent germination remained the same, and JA2 had the lowest percent germination (88%). When soil was left unlimed (pH 5.3) TZ1 had the highest percent germination (88%), while only 76 % of JA4 seeds had germinated. One week later, TZ1 remained the same, and all other accessions exhibited 80% germination. At 4 weeks only JA2 plants showed increased foliage production when limed. However, 8 weeks after emergence, JA2 and JA4 produced more foliage when limed. After 8 weeks, the results also indicated that plants that were limed had higher dry weights (66.1 g/pot) than unlimed plants (63.3 g/pot). At 12 weeks only JA2 had increased foliage production under limed conditions. It is possible that both the Tanzania and the Guyana accessions produced more dry matter at 4 and 8 weeks, when no lime was applied, because the soil types in both locations were predominantly acid. On the other hand, the Jamaican accessions give higher dry weights under limed conditions because they were taken from soils that were calcareous. Further studies are needed to identify accessions that are suitable for the southern US.