Andisols is a variable charge soil where fertilizations to the soil do not give the same result as that to
the soils with permanent charges. Therefore, amelioration is needed to improve the soil chemical properties.
The purpose of this research was to find out the influence of nanoparticles of volcanic ash and rock
phosphate as ameliorants on pHw, pH0, P-retention and available P on variable charge Andisols, Indonesia.
This research used a complete randomized experimental design on factorial pattern with two factors. The
first factor was nanoparticle of volcanic ash consisting of four levels i.e. 0, 2.5, 5.0 and 7.5% of soil weight
(w/w). The second factor was nanoparticle rock phosphate, also consisting of 4 levels like nanoparticle of
volcanic ash. The treatments were repeated 3 times. The results showed that there was an interaction
between nanoparticle of volcanic ash and rock phosphate in increasing pHw to 5.37 and increasing
availbale P to 330 mg kg-1. However, there was no interaction in pH0 and P-retention. Nanoparticle of
volcanic ash and rock phosphate was found effective to improve some soil chemical properties after one
month of incubation
