With increasing global energy demands, the production of biofuels has been gaining economic importance, with the castor oil plant being one option for the production of biofuel. This study was performed on irrigated cultivation of the castor oil plant, variety IAC 2028, from March to October 2011, in Lavras, Minas Gerais, Brazil, with the following aims: a) to characterise and estimate the sub stages and stages of the crop in days after sowing (DAS) and in growing degree days (GDD) and; b) determine a phenological model of development that describes the vegetative and reproductive behavior of the crop cycle. The experiment was conducted under optimal conditions of irrigation and fertilisation. To determine the phenological model, 15 sub stages and 4 stages of the crop were defined and estimated according to the periodic quantification of variables such as the number of leaves, leaf area, soil cover, and periods of floral initiation, anthesis, bean formation, and maturation by raceme order. We concluded that: a) the sub stages were well characterised and estimated, in particular Vo, A2, M2, and M3, which closed stages I, II, III, and IV with nearly 42, 65, 87, and 100% of the thermal power required by the crop during the lifecycle, respectively; b) the phenological model of the sub stages was determined satisfactorily in GDD; and c) the plant and reproductive sub stages were not completely distinguishable, and the maximum soil cover in M1 indicated that greater productivity could occur with a population increase.
Key words: Ricinus communis L., phenological model, phytomass, soil cover fraction, leaf area index.
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