Aporte e decomposição da serapilheira e atributos do solo no contexto socioambiental da Amazônia

Abstract

The objective of the present work was to obtain information on the contribution of litter forming material, its decomposition rate and soil attributes in forest, cerrado and cerradão environments in the Amazon. For the evaluation of litter input in each studied area, ten conical collectors were installed. Samples were collected monthly from March 2018 to March 2019. After each collection, fractions of leaves, branches, reproductive material and bark were screened and then the samples were dried and weighed to estimate the percentage of each. of the burlap fractions. To evaluate the decomposition rate, 40 litter bags were installed in each area. Litter bag collections were performed at intervals of 30, 60, 90, 120, 150, 180, 210, 240, 270 and 300 days, with four repetitions. Based on the obtained masses, the remaining mass percentage, the decomposition rates (k) and the half-life time (t1 / 2) were estimated. To evaluate the effect of seasonality on the dynamics of soil attributes, in each area four sampling points were chosen. The collections were performed in two periods of the year: dry and rainy. The evaluated attributes were: pH, power acidity, exchangeable aluminum, organic carbon, carbon stock, macroporosity, microporosity, gravimetric humidity, soil density, total pore volume, texture and aggregate stability. The attributes MaP, MiP, Pt, UG, pH, CO, Ds, DMG, DMP and Al3 + did not induce significant differences between environments and depths evaluated in the dry period of the year. The attributes with the highest values during the rainy season were MiP, Pt, UG, pH and Est. C in the forest area, most of them in the 0 - 5, 5 - 15 cm depth. Seasonal variation of precipitation induced changes in 15 of the 16 evaluated attributes, and only the MPD did not change between the dry and rainy periods. However, the modifications did not occur simultaneously for all areas and depths. The attributes that suffered the most changes between the dry and rainy periods were: MiP, Pt, Ds, MO and CO, which presented reduced values in the rainy season. The forest and cerradão environments did not present statistical difference in litter production, but presented higher deposition when compared to the cerrado environment. The months with low rainfall indices coincide with the period of highest litter deposition. Leaf fraction was the largest contributor to total litter production, followed by twigs, reproductive material and bark fractions. Among the evaluated environments, the forest presented the highest decomposition speed and the lowest cerrado. It was evidenced that the decomposition process for all studied environments occurred with greater intensity in the rainy season. During the studied period, the cerrado environment presented the lowest constant k (0.0017 g g-1 day-1) and consequently the longest half-life (407 days), followed by the cerradão (0.0023 g g -1 day-1 and 301 days) and forest (0.0036 g g-1 day-1 and 192 days). Among the evaluated environments, the forest presented higher decomposition speed and the lower cerrado, which shows that the cerrado will require more time for the nutrients to be available to the soil.