Influência dos resíduos vegetais de exploração florestal nos estoques de carbono e nutrientes em Latossolos Amarelos das clareiras formadas por exploração florestal, Itacoatiara (AM)

Abstract

Usually, residues from logging(i.e., logged tree’s crown), remainon site. However, forest managers have considered using those wastes for energy generation. But, harvesting residues represents an additional nutrient exportation to those nutrients in commercial tree trunks. Therefore, the objective of this study is to evaluate the influence of harvesting residues from logging on soil (Oxisols) physical and chemical properties 18 months after gaps formation by tree fall. The study was carried out on the Annual Production Unit ITP23, situated on Farms Itapiranga II and III that belong to Precious Woods Amazon Ltda.(Itacoatiara –Amazon State). Five soils samples were taken in 0-5, 5-10, 10-20, 20-30, 30-40, 40-100 and 100-150 cm depths in each treatment: mature undisturbed forest (FLOR), gaps with residues remaining on site (CCR) and gaps with removal of logged tree’s large branches (CSR). Physical (texture and bulk density) and chemical (pH, contents and stocks of C, N, P, K, Ca, Mg, Fe, Zn, Mn and Cu) analysis were performed. Until 20 cm deep, clay contents were higher in CCR and CSR’s soils than FLOR’s soils, but all soils remained clayey. No differences were founded on soil’s bulk density between treatments. In general, carbon and nutrients levels were higher in 0-5 and 5-10 cm soil layers of CCR. Above those, contents of all nutrients but phosphorus were higher in CSR’s soils. This indicates higher decomposition rates in remaining residues (mainly, fragmented small branches and leaves) and nutrient leaching to deeper layers in those soils, especially potassium. Nutrients stocks were higher in ≤ 30 cm layers in all treatments (which represents 40-60% of total nutrient stock in 150 cm depth). No differences were founded in soil nutrient’s stock proportions between treatment’s soil layers. This means an advanced nutrient transportation in CCR and CSR soils and those nutrients may be reaching deeper layers than those studied (> 150 cm). Macronutrients stocks were higher in CSR’s soils, while micronutrients were higher in CCR’s soils. Even micronutrients stocks in FLOR’s soils were higher than CSR’s soils. The nutrient exported/soil nutrient stocks were higher with large branches harvest (CSR). This would result in a faster nutrient depletion in soils compared to residues remaining on site.