The effect of slash and burn agriculture on plant nutrients in the Tertiary Region of Central Amazonia ()

SUMMARY The slash and burn method was studied with respect to changes on the chemical composition in the top-soil layer (upper 20 cm) of yellow latosols (about 85% of the total area) and hydromorphic soils (about 1% of the total area) before and after fire was set on the cleared forest. The obtained analytical data prove the following result : 1) the soil fertility of latosols and hydromorphic soils is considerably low as far as natural conditions are concerned, 2) after burning a considerable amount of plant nutrients normally bound to the standing crop is lost in the form of volatiles and particles during the burning procedures, 3) a great amount of plant nutrients is rapidly released to the soil after burning, 4) great quantities of temporarily available nutrients are lost by leaching as the nutrient uptake capacity of the crops is not able to match the excess of available plant nutrients, 5) strong nutrient fixation will reduce the availability of present plant nutrients remarkably, 6) the nutrient return from standing crop bound nutrients by means of fire is not able to guarentee long-term tropical agriculture, 7) correction of soil pH by means of heavy liming and the application of fertilizers is a basic need in tropical landuse systems, 8) the treatment with herbicides, insecticides and fungicides is indispensable to reduce root competion and plant deseases and 9) favourable conditions as far as the impact of atmospheric agents on the crops is concerned has to be set up by means of crop specific shelter-wood systems.