Produção e concentração de nutrientes via deposição de liteira na Floresta Nacional do Tapajós, Belterra-PA

Abstract

The litter is the most superficial layer in forest soils formed by leaves, twigs, flowers, fruits, animal waste, among others. This material is configured on a site of intense interaction between the cycling of elements and the transfer of energy, because it is the primary means of displacement of the nutrients to the soil. One of the climatic variables that can influence on your contribution and nutrient availability are temperature and precipitation. It should be noted, too, that the type of vegetation and environmental conditions become determining factors for its quantity and quality, because depending of the characteristics of each ecosystem, a particular factor can prevail over the other. Therefore, this research aimed to estimate the production of litter and establish the concentration of macronutrients in it contained, calculating the efficiency of utilization of nutrients in the Tapajós national forest, located in the city of Belterra, para. Litter sampling was given in four transects (1000 m x 50 m), where they were systematically distributed in each transect, 10 plastic circular collectors with 0.22 m2 area each and background consisting of nylon fabric with 4 mm2 mesh, totaling 40 collectors. The collections were accomplished biweekly, from January 2002 to December 2004, where the material deposited in the baskets was collected and taken to a laboratory for drying in an oven at 65 °C and subsequently segregated into four fractions: sheets, wood, reproductive and miscellaneous. The amount of litter deposited in the collector was quantified to kg ha-1 month-1 and kg ha-1 year-1, and also determined the concentrations and the contents of macronutrients (N, P, K, Ca, Mg) contained in leaf litter and nutrient use efficiency. It was used ANOVA (analysis of variance) of type factorial of repeated measurements for the comparison of each fraction of production in seasons (dry and rainy) and years (2002 to 2004), considering the monthly figures. For determining the possible differences between the productions over the years and in rainy and dry periods, it was considered that can generate influence the three years and the two seasons (periods). The litter deposition was seasonal, with higher production in the dry season and lower air temperatures, producing per year average of 7154.98 kg ha-1 of litter. The larger fraction was the deposition of leaves, being greater than 70%, being this and the miscellaneous fraction the ones that demonstrated the greatest contributions of nutrients. Nitrogen and calcium were the macronutrients found in higher concentrations and contents in all fractions studied. In general the litter production and nutrient concentration showed the following order: leaves > Wood > Miscellaneous > reproductive and N > Ca > Mg > K > P, respectively.