Estoques de biomassa e de nutrientes de pousios enriquecidos com Inga edulis Martius em áreas com histórico de agricultura e de pecuária no Assentamento Tarumã-Mirím, Manaus- AM

Abstract

Deforestation rates of primary forests in the humid tropics have been growing intensively in recent years, due mainly to the development of shifting cultivation and extensive pasture. After forest fragmentation and conversion to agricultural use, the cleared areas of rainforest are usually abandoned so there is natural regeneration of vegetation and slow restoration of soil productivity. These courses lead to a progressive reduction in the productive potential of secondary forest, mainly caused by the reduction of standby time. Therefore, it is recommended the activation of areas of disturbed forest through plantation of leguminous species. The objective of this study was to evaluate the production of biomass, the stock and chemistry of accumated litter and improve soil physical, chemical and biological conditions, 15 months after deployment of improved fallow with Inga edulis in areas of previous agriculture and pasture, presently abandoned at the Tarumã-Mirim rural settlement, Manaus, Amazonas. In each site two plots were delimited treatment, with planting of Inga edulis seedling in one of them, leaving the other just under natural regeneration. The biomass accumulated in the 15 months of the experiment, the content and nutrient stocks of Inga edulis and their average height was greater in the area with a history of previous use of improved fallow agriculture. The average stock of litter was increased in the plot of previous use with agriculture. There were no significant difference between treatment and collection times on microbial biomass and mineral-N. Higher density of soil macrofauna was found in the improved fallow land, but greater biomass of soil macrofauna was found in areas with a history of pasture. During the 15 months of experiment, the treatments of improved fallow and natural regeneration did not increase soil fertility. However, the accumulations of plant biomass and nutrients, as well as leaf chemistry, were higher under improved fallow treatment in areas previously used as agriculture. Analyses of the three collection times indicate a consumption of mineral-N by plant species. Physical characteristics of the studied soil bulk density were higher in areas with a history of previous use of pasture and total porosity was higher in areas with a history of previous use agriculture. The biomass, densities and functional groups of soil macrofauna were higher in areas with a history of previous use pasture. These results indicate that positive changes on soil properities, wich were not foun yet in the first 15 months of the experiment, may be expected in the short term under the improved fallow system.