Definition, Properties and Characteristics of Volcanic Soil
According to Tan (1984), volcanic soils in Indonesia generally originate from the Quaternary or Quaternary-Tertiary period with a variety of parent materials originating from volcanic eruptions. Allen and Hajek (1989) suggested that more than 60% of the material spewed by volcanoes is in the form of dust, cinder, volcanic glass and pyroclastics. The chemical, morphological, and physical properties of these volcanic soils are closely related to the behavior and origin of active Al and/or Fe consisting of non-crystalline clay minerals such as allophane and ferrihydrite as well as paracrystalline clay minerals ‘imogolite’ (Wada, 1989). The presence of a large number of active compounds Al and Fe in the soil causes P to be strongly adsorbed on this mineral structure or bound to the positively charged OH or H functional groups (Shoji et al., 1993).
Allophane is the most reactive clay mineral because it has a very large surface area and many active functional groups (Farmer et al., 1991). The presence of allophane gives the soil characteristic properties. This is because allophane has a large variable charge, is amphoteric, CEC is between 20 to 50 cmol(+)/kg while KTA is between 5 to 30 cmol (+)/kg, the structure is random and open and can bind large amounts of phosphate. (Wada, 1989; Tan, 1992; Van Ranst, 1995). Due to the strong fixation of phosphate by this mineral, the availability of soluble phosphate will soon decrease and according to Egawa (1977) only 10% of the given P fertilizer can be used by plants. The high percentage of loss of P fertilizer is a serious problem that is often found in volcanic soils.
Volcanic Soil Pictures
Other characteristics of volcanic soils are low volume weight (BV), loose, greasy feel (smeary) with large water holding capacity and high phosphate fixation. The uniqueness of this volcanic soil is due to its mineral composition which contains a lot of active colloids Al and Fe, both in non-crystalline and para-crystalline forms (Shoji et al., 1993), such as allophane and ferrihydrite as well as paracrystalline clay minerals ‘imogolite’ (Wada et al., 1993). 1989). The presence of a large number of active compounds Al and Fe in the soil causes P to be strongly adsorbed on this mineral structure or bound to the positively charged OH or H functional groups (Shoji et al., 1993).