Soil that has a high degree of weathering, with more inorganic P bound to Fe and Al oxides, has less P availability to plants. Thus, the critical element of a plant refers to the level below which the growth rate and plant production decreases, demonstrating the need for supplementary fertilization. Accordingly, an experiment was conducted in a greenhouse at Embrapa Algodao with the objective of evaluating the response of castor plants to five doses of P in four types of soil with different adsorption characteristics and critical levels of foliar P. The experimental design was completely randomized in a 4 x 5 factorial design, four types of soil and 5 levels of P with four replications. For TCo, there was an increase in height growth, with dose of 229.6 mg dm(-3) responsible for maximum plant height (74.3 cm). The largest diameter stem (17.58 mm) was observed in CXve with an application of 229.6 mg dm(-3) of P; a decrease was seen when using higher doses. The increase in leaf area was smaller in RY (4724.8 cm(2)), where it was obtained with a dose of 280.2 mg dm(-3). In general, critical levels of P in the plant shoots did not vary much between the soils. The critical level of P in castor bean shoot dry mass was higher (4.61 g kg(-1)) in TCo, this result being directly related to the low clay content of the soil.Dr Empresa Brasileira Pesquisa Agr, EMBRAPA, Ctr Nacl Pesquisa Algodao, Campina Grande, PB, BrazilFCA UNESP, Fac Ciencias Agron, Botucatu, SP, BrazilEMBRAPA, Ctr Nacl Pesquisa Algodao, Campina Grande, PB, BrazilFCA UNESP, Fac Ciencias Agron, Programa Pos Grad Agr, Botucatu, SP, BrazilFCA UNESP, Fac Ciencias Agron, Botucatu, SP, BrazilFCA UNESP, Fac Ciencias Agron, Programa Pos Grad Agr, Botucatu, SP, Brazil