Department of Soil Science, Faculty of Agriculture, Sebelas Maret University, Kentingan, Surakarta, Jawa Tengah 57126 Indonesia

Email: vitaratri@staff.uns.ac.id

Ultisol was characterized as acid soil with high exchangeable-Al that toxic for plant growth. The objective of present research was to analyze the capabillity of some combination of organic matter, calcite and dolomite to neutralize exchangeable-Al on Ultisol Jasinga. Soil sample of Ultisol Jasinga was characterized by pH (H₂O) 4.15 and exchangeable-Al 23 cmol(+).kg^-1. Greenhouse experimental pot used Completely Randomized Design with single factor that consisting of 12 levels: T0 (control), T1 (calcite 100%), T2 (dolomite 100%), T3 (rice straw compost (RSC) 100%), T4 (cow manure (CM) 100%), T5 (dolomite 50% + RSC 50%), T6 (dolomite 50% + CM 50%), T7 (RSC 50% + CM 50%), T8 (dolomite 25% + RSC 75%), T9 (dolomite 25% + CM 75%), T10 (dolomite 25% + RSC 25% + CM 25% + NPK 25%), and T11 (RSC 30% + CM 30% + NPK 30%) with 3 replications. Incubation was conducted for 8 weeks with moisture level at 70% field capacity. The results indicated that the highest effectivity of neutralization of exchangeable-Al was obtained on the treatment of T1 with the pH and exchangeable-Al reached 7,18 and 0 cmol(+).kg^-1, following T2 6.28 and 0.8 cmol(+).kg^-1, T9 5.54 and 2.2 cmol(+).kg^-1, T10 5.51 and 2.3 cmol(+).kg^-1.