Carbono e nutrientes na biomassa e no solo em povoamento de Anadenanthera peregrina (L.) Speg. var. peregrina em diferentes espaçamentos

Abstract

The study aimed to describe changes in soil attributes and evaluate the effect of planting spacing on soil carbon and nitrogen stocks, aboveground biomass and nutrients, as well as nutrient use efficiency in Anadenanthera peregrina (L.) Speg. var. peregrina stands. The study was carried out in an area from the Federal Institute of Espírito Santo (Ifes), in Alegre, Espírito Santo, Brazil, with previous use for grazing pasture. The stands were settled in June 2011. Three blocks were allocated, where three planting spacings were evaluated: 3 m x 3 m, 4 m x 4 m and 5 m x 5 m. For the aboveground biomass sampling at 7.5 years, 30 trees were measured, which were divided into stem, bark, leaves, thin branches and thick branches, and further biomass prediction models were adjusted. Chemical analysis was performed to determine the nutrients (N, P, K, Ca and Mg) and carbon concentrations and calculate stocks in biomass. For soil chemical and physical sampling at 8.2 years, nine trenches of 100 cm depth were used. The stocks of C and nutrients were calculated. The biological utilization coefficients and possible nutrient export scenarios were estimated. The soil from the 8,2 years old stands have medium to low fertility, with low levels of exchangeable bases and P, medium soil organic matter and low pH. Planting spacings do not alter soil carbon and total nitrogen stocks. The 5 m x 5 m spacing promotes greater allocation of individual aboveground biomass, mostly into thick branches. There is no spacing influence on biomass and carbon stocks per hectare, except for bark. Trees within 5 m x 5 m spacing have larger individual nutrient stocks and smaller nutrient stock per hectare. Most of it is stored into leaves and thick branches. Stands in wider spacings are more efficient using nutrients. There are nutritional limitations for upcoming production cycles in non-conservational harvest systems. The use of 5 m x 5 m spacing is recommended for A. peregrina var. peregrina stands, as it produces the same amount of biomass per hectare at a lower cost of implantation and greater nutritional efficiency. It is recommended to exploit only the stem. In this sense, there is an opportunity for reduction of the initial cost of implantation and multiple use of the biomass. The maintenance of the soil fertility is strongly recommended, as well as testing prunning and thinning effects on the development of the stand. The growth and production under these practices depend on new scientific investigations.