Prediction of the Effect of Deforestation Followed by Intensive Vegetables Cropping Systems on Population Density and invitro Ability of Phosphorhizobacteria in Tropical Highland of Bali Island, Indonesia

Population density of phosphorhizo bacteria known to be different between natural forest and agricultural lands. In the present study, the differences were quantified between natural forest land and the adjacent agricultural lands covered by a fertile Andisolin a tropical highland. The first study on this field of knowledge in Bali and probably Indonesia aimed to determine the effect of either deforestation followed by cropping systems orcropstype onthe population density and in vitro ability of phosphate solubilizing rhizobacteria (PSB)in dissolving phosphor (P). The density of PSB population was enumerated by the pour plate method while dissolving ability of P wasestimated according to either P solubilisation index (SI)or the amount of dissolved P2O5. Rhizosphere of natural forest plantswas inhabited by 26.20x106CFU.g-1 dry soils of PSB with an average Ca3(PO4)2dissolving ability at9.64 ppm P2O5 and SI of 1.94. The decline of PSB population density ofintensive agricultural soils comparedwiththe adjacent natural forests amounted to50.23%, 31.21%, and 26.56%, respectively for the soil in monoculture of lettuce, monoculture of leek and mixed strip intercropping systems. Ability to dissolve P by PSB was generally 29.90-43.47%loweron intensive agricultural soils than natural forest soils. Among the major vegetables types cultivated in the selected agriculture lands, rhizosphere of carrots were colonized by the significant highest number of PSB, while the least was in the rhizosphere of potatoes. The conclusion of this study were (1) deforestation followed by intensive vegetable cultivation activities substantially decrease PSB population density and its ability to dissolve P, (2) monoculture cultivation system with a lower dose of fertilizer as well as mixed stripintercroppingsystems harboring rhizosphere PSB both inhigher population density and in vitro ability to dissolve P, and (3) the carrot planthad the possibility of improving the density of PSB in intensive agricultural land.