The approach for the present experiment was based on the following points: 1. Amorphus shica present in rice hull ashes reacts with aluminium compounds present in the soil diminishing aluminium activity, 2. Amorphous silica added to the soil could decrease the amount of phosphate sorbed by the soil, 3. An increase in nutrient content of the soil could occurs when rice hull ashes are applied, and 4. Amorphus silica could form differentty pes of clay. The two soil samples used in the experiment were taken from the top soil )0.25· c) of two fields (liLa Reserva and Lote Experimental) on the Carimagua Experimental Station of the Centro Internacional de Agricultura Tropical CIAT located at the Llanos Orientales, Meta (Colombia). According to the New Classification System the two soils are classified as Typic Haplustox (Lote Experimenta) and Tropeptlc Haplustox (liLa Reserva); they are representative of a large portion of soHs in the East area of the Llanos Orientales. A factorial desing with two repetitions was used. Plastic pots capped were located on open wire netting shelves in a dark constant temperature room (25°C ± 1) of the Soils Laboratory of the Soil Science Departarment of the University of Reading, Reading England. The variables were: a.-Amount of ashes equivalent to O, 4, 8, and 16 ton. hr 1,b. Humidity conditions: field capacity and flooded. c-Sampling times: 1,3,8, 15,30, 60,90,150,210 and 300 days. The soil samples taken from the pots every time of sampling were tested for the following determinations. 1. Silicon water soluble, extracted by 0,01M CaC12. (Oliver, R. 1971). 2. Free Iron Oxides extracted with sodium dithionite. 3. Aluminium oxides treated twice with HN03 and H202 and H20. 4. Exchangeable aluminium extracted with 1N KCL, determined by Aluminon Me· thod in Automated Auto Analiser. 5. Available phosphorus determined by the Olsen Method and determined by using the Auto Analiser. 6. pH 1:1 (soil:CaC12) measured using a ION-86 Analuser pl+meter. 7. Calcium, Magnesium and Manganese extracted by KC1 1N and determined using a Perkin-Elmer 3030. 8. Phosphate absortion adding solutions of P (KH2P02 in CaC12 0,01 M) shaking for 24 hs. and determined in the Auto Analiser. 9. Mineral determinations: for X-ray diffraction analysis only the clay fraction was used Mg-glycol saturated using a Philips PW 1050 diffractometer. The information obtained from the present experiment allows the following conclusions: Application of rice hull ashes had a significant effect increasing the amount of calcium, magnesium and maganese in both sampies mainly on flooded conditions and increase phosphate content particularly under field capacity conditions. Application of rice hull ashes had not been effective for diminishing AI3 activity or Feoxides content nor the amount of-P-sorbed. Further work with rice hull ashes must be conducted through field trials using crops such as rice, corn or grasses and their residual effects obtained from three consecutive crops at least. Only significant results will be mentionated in this paper.