Changes in natural vegetation cover and cultural practices have given rise to alterations in the chemical properties of soils. It can improve or degrade them and this depends, mainly, of the nature of the soil. The aim of this research was to evaluate chemical alterations in an Ultisol used for pasture and to plant Brachiaria brizantha, Coffea canephora, Saccharum officinarum L., taking tro- pical forest soil as the point of reference, and to characterize the nutritional status of the crop systems. The study was carried out in a rural area in Ji-Parana city, in the Brazilian State of Rondonia. A completely randomized design was used, with ten replicates. Soil samples were collected at three depths (0-0.1, 0.1-0.2 and 0.2-0.4 m) for the chemical analysis and leaves from the agricultural systems were collected for nutritional analysis. The soil with tropical forest presented greater P concentration down to a depth of 0,2 m, while sugar cane and coffee plantations presented, respectively, the highest and the lowest levels of organic carbon. The system with sugar cane had a positive effect on the chemical properties of the soil, while the coffee and pasture systems produced the highest level of degradation of these properties, when compared to native forest. The agroecosystems with sugarcane and coffee presented low foliar concentrations of Ca and Mg and high values of micronutrients (Cu, Mn, Fe and Zn). Rev. Ci. Agra., v.53, n.2, p.143-149, Jul/Dez 2010