The knowledgement of the nutritional sustainability of the practices used in
plantations is necessary for its adequate management, mainly when used in low fertility
sites, with slash-burning, and with no fertilizer application, like P.taeda plantations in
south of Brazil. Given the increasing importance of the species, a study was done to
investigate the nutritional sustainability of cenarios, based on eight representatives sites
of Parana and Sao Paulo States. These sites, within 19 to 29 years-old, were measured
and the nutrient stocks was determined by sampling 4 tress per site, plus the forest floor.
Soil nutrient stocks were also established based on soil profiles description and analysis.
Yield and nutrient stocks were adjusted for a 25-years cycle, together with the nutrient
rainfall inputs. The studied cenarios were: i) harvesting (removing just debarked logs or
the hole trees), ii) salsh-management (minimum cultivation or burning), iii) erosion (none
or 2 cm per cycle). The number of nutrient cycles (N, P, K, Ca and Mg) to zero the soil-
forest system stocks were used as the sustainability indicator. Simulations were carried
out with a VBA implementd program. Mean annual increments ranged from 11 to 27 m3
ha-1 yr-1, with site index from 18 to 29 m (base age of 25 years). MAI was positively
correlated with minerable N (r2 = 0,722) and available P (r2 = 0,702). These two nutrients
also differ from the others due to their higher concentarion on the aboveground part of
the soil-forest (50 and 66%, respectively). The cycle number analysis showed that N is
the only nutrient that never has a positive balance. For all nutrients the most impactant
practice is the burning, followed by the hole tree harvesting and then by erosion. The
average nutritional limitation risk was: N > P > Mg > K,Ca, based on positive balances
and number of cycles. Taking N as the best indicator for sustainability, the most
productive sites tend to be the less sustainables, considering their growth rate. The long
term sustainability of P.taeda palantations depends on the use of conservacionist
practices together with fertilization practices in some cases.
