IMPACT OF LAND MANAGEMENT ON SOIL MACROFAUNA IN THE ORIENTAL LLANOS OF COLOMBIA

The effect of different types of land management on the soil macrofaun a of the savanna has been assesed using the T.S.B.F. method. Macrofaun a of the forest and savanna has a high density (4293 and 2830 ind.m(2) ) and moderate biomass (13.6 and 15.3 g.m(-2)). Traditional grazing si gnificantly increase earthworm biomass but does not modify biomass (16 .8 g.m(-2)) and density (1971 ind.m(-2)). Burning the savanna leads to a momentarily but important disruption of the soil fauna. After 6 mon ths, soil macrofauna has regained its initial level. When stocking rat e increase, contribution to biomass of different groups is modified. T hese results are probably due to the modification of the soil microcli mate and to the imput of cow dung. Improved pastures have an important earthworm population (22.9 to 51.1 g.m(-2)) composed of native specie s, and a high macrofauna diversity (26 to 32 units). This results from the improving of the quality of the organic matter brought to the soi l (litter and cow dung). Annual high input cultivations results in a s pectacular decrease, both quantitative and qualitative, in the inverte brate populations (3.2 to 4.3 g.m(-2), 429 to 592 ind. m(-2) and 18 un its). This phenomenon may be explained by the effect of the tilling of the soil, the fertilization and by the decrease of the soil organic m atter.