Some chemical and mineralogical properties of cocoa soils in Brazil. In: Theobroma v. 6 p. 15-30, 1976.

Abstract

Soil samples were collected from the traditional cocoa producing zone of Southern Bahia as well as from areas potentially avaitable for cocoa production both in Bahia State and in the Amazonian region. The pH of the soits ranged from 3.8 to 6. 7. The pH's determined in water were in ali cases higher than in KCI. The decrease in pH with depth agreed with the trend observed for KCI extractable acidity. Most of the soita showed rather low values for base contént but only in few casea was aluminum the dominant cation. The CEC by neutral KaOAc varied from 2.64 to 16.20 me /100 g and decreased with depth. Organic carbon showed the same trend. Considerable positive charge was present, _ especially in lhe B horizons, giving low efective net negative charge. In spite of the low nega tive charge measured at the field pH, a large pH dependent charge was present. X-ray analysis of the clay « 2 p.) fraction revealed that differences in fertility among soits tested were mainly due to differences in clay mineralogy. 'Ibe Amazonian soit. apparently have less phosphate fixing capacity than the Southem Bahian soits, as indicated by their lower leveIs of iron oxides, and this can have practical significance relative to phosphate fertilizer practices.