Análise do boro disponível em solos do estado de S. Paulo: I. Crescimento e composição mineral do girassol (Helianthus annuus Mill.)

Sunflower plants were grown in the greenhpuse in five soil series of the Piracicaba Country, S. Paulo, Brazil (Terra Roxa Estruturada, TRE; Roxo Latosol, LR; Red Latosol, LV; Red Yellow Podzolic: PVA- Quartz sand, AQ), under seven rates of B (from 0 to 1 ppm). A visual assessment, based on the age of the plants when first symptoms of B deficiency showed up, disclosed that the PVA had the lowest available B concentration being followed by LV, AQ, TRE and LR. Insolar as growth data are concerned it has been found that plant heightt was the characteristic showing higher correlation with available B in the soil. The tissue concentration of P, Mg, and B consistently increased at low levels of boron in the soil. The leaf concentration of Cu, Fe, Mn, and Zn was unaffected by the B supply, the reverse being true, however, in the case of boron. The concentration of B in young leaves (upper third of the plant), among all organs (roots, stems, older leaves) analysed provided the best correlations with the availability of the micronutrient under study.