Although acid soils with low pH are always of interest to farmers in the farming process, the use of amendments to control pH can affect some other components of the soil. Soil quality index (SQI) and soil parameters including pH(H2O), electrical conductivity (EC), total organic carbon content (TOC), available phosphorus (Pav) and ammonium nitrogen (NH4+) were monitored during short-term incubation (60 days) with amendments (lime, solid biochar and liquid biochar extract derived from macadamia husk) under laboratory conditions. The SQI estimation was based on the simple addition method. The results showed that soil parameters such as pH, EC, TOC, available P, and NH4+ did not change in a clear trend over the incubation times. However, the results showed that the SQI of acid soil amended with biochar extract was evaluated as more optimal than the other two amendments at all incubation times and maintained at good and very good levels for 35 days of incubation. The findings of the study provide a basis for potential applications of biochar as well as for improving the efficient use of agricultural by-products.