Early response of Pinus radiata plantations to weed control and fertilization on metamorphic soils of the Coastal Range, Maule Region, Chile Respuesta temprana de Pinus radiata al control de malezas y la fertilización en suelos metamórficos de la Cordillera de la Costa de la Región del Maule

SUMMARY Management of Pinus radiata plantations in Chile has been intensified in the last decades using site preparation, weed control and fertilization. The lack of information on site-specific responses imposes uncertainty about the biological and economic benefits of these techniques. Early projection of initial tree growth response to intensive culture is extremely important but difficult to estimate unless a clear understanding of limiting resources exists at each site. Based on the three-year development of a weed control and fertilization trial located on metamorphic soils of the Coastal Range of Chile we investigated the site specific limitations at these sites. Fertilization treatments included no fertilization (F0) and fertilized (F1) (26g N + 16.7g K + 2.5g B per plant). Banded weed control treatments on woody vegetation included one (WC1) and two consecutive years (WC2) of release. After 12 months, seedling survival was significantly increased by weed control but not by fertilization. Three years after establishment, weed control increased survival by 13%, and intensive silvicultural treatment gains were 56-103% for root collar diameter (RCD), 53-82% for height (HT), 269-591% for volume index (V=D2H), and 35-77% for crown diameter (CR). Lack of fertilization response suggested that water was the most limiting resource. Weed control responses represented almost one growing season gain in tree growth. No additional gains were obtained by weed control of woody vegetation during the second growing season. A linear relationship was found between log(CR) and log(V), suggesting a simplified method to estimate tree vigor at early stages of plantation development.