NUTRIENT TRANSFER TO THE ATMOSPHERE BY BURNING OF DEBRIS IN EASTERN AMAZONIA

After replacement of tropical primary forests, fire becomes an importa nt management tool. During establishment of plantations with fast-grow ing tree species and within slash-and-bum agriculture, the export of m acronutrients and other elements to the atmosphere by burning was esti mated. Two plots of clearcut 40-year-old and one plot of 7-year-old se condary forest with dry fuel weight 33.5 t ha(-1) (plot Al), 95.2 t ha (-1) (plot A2) and 31.2 t ha(-1) (plot B1) were burnt. Total element l osses including volatilisation, particle and leaching exports ranged f rom 94 to 98% C, 93-98% N, 30-47% P, 30-48% Na, 42-50% K, 13-35% Ca, 2 1-43% Mg and 66-76% S related to the initial nutrient. For the small-h older site (plot B1) where the drying period lasted 4 weeks with a tot al precipitation of 9 mm, this loss was to the atmosphere. Significant preburn losses due to leaching were observed on the moister plots (Al , A2) where the drying period lasted 80 days and 101 days with 250 mm and 296 mm precipitation, respectively. Here, element transfer to the atmosphere due to particle transport and volatilisation were 94-98% C, 95-98% N, 27-33% P, 17-23% Na, 16-31% K, 9-24% Ca, 17-43% Mg, 67-68% S of the initial element stock in the burnt debris.