Tropical soils are naturally acidic, that is, with low pH values, high levels of aluminum that are toxic to plants, and low levels of Ca and Mg. The acidity of tropical soils occurs most often due to high rainfall, which causes the leaching of exchangeable bases from the soil. This acidity causes damage to agricultural crops, preventing their proper development and consequently resulting in lower productivity. Liming is one of the management practices used to increase pH values and make nutrients available to plants. In Brazil, there is no official method for determining liming doses. Therefore, several studies have been carried out to estimate liming in several Brazilian states. In many countries, the SMP buffer method has been increasingly used due to its practicality, speed, and efficiency in determining potential soil acidity and determining liming doses. This study aimed to evaluate the pH SMP method for recommending liming for forest soils in the southern region of Amazonas. The experiment was set up to incubate soils with limestone doses. Ten soil samples were collected under native forest vegetation in southern Amazonas, in the 0 to 20 cm depth layer. The experiment was conducted in a greenhouse at IEAA/UFAM, where the soils were broken up, sieved through a 4 mm mesh, separated into samples of 1 kg of air-dried soil and placed in 1000 mL plastic pots with lids and no drainage pores, totaling 200 experimental units. The soils were placed for incubation with corresponding doses of 0.0; 1.0; 2.0; 4.0; 6.0; 8.0 and 10.0 t/ha-1, treatments resulting from 10 soil types under 7 different doses and 3 replicates. With the results, analysis of variance was performed using the F test at 5%, and the pH results in H2O were illustrated graphically according to the limestone doses and adjusted to the polynomial regression model. It is noted that there was no good relationship between the SMP pH and the liming requirements in all the soils evaluated. The liming estimate by the SMP method presented satisfactory data, to raise the pH of the forest soils in southern Amazonas to the desired values of 5.5; 6.0 and 6.5, according to the incubation curve.
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