Poplars (Populus spp.) have been growing as commercial forest crop in southern Brazil since the last decade. To improve soil use and reduce wood cost, poplar has been integrated with grazing cattle. Two major characteristics contribute for the integration of poplar with grazing cattle: the low plant density and the absence of leaves during the winter. Aiming to enhance the quality of food supply and forage to cattle, as well as tree growth within integrated system, a three-year fertilization trial was evaluated, using an eight-year old poplar plantation, located in São Mateus do Sul - PR. Five N rates (0, 20, 40, 80 and 160 kg ha-1. yr), in urea form, were applied to black oat (Avena strigosa Schreb), in 2003, and ryegrass (Lolium multiflorum Lam.), in 2004 and 2005, submitted twice to direct grazing. The N application to the winter crop did not increase poplar growth (tree height and circumference at breast height after two years), suggesting a low residual effect of N. However, the N application promoted a linear increment of dry matter yield for both winter grazing pasture for three years. In addition, an increment of nutrient concentration in the forage was noticed, indicating an improvement in forage quality, especially N. The increment in dry matter yield and/or nutrient concentration in the winter forage increased the nutrient uptake and nutrient cycle. So, the earlier N addition to winter crop was not able to enhance poplar growth, at least in the initial years of evaluation, but the nutrient cycling and the weight gain of livestock with better pasture could bring benefits for poplar culture in the long run.
Poplar; silvopasture system; nitrogen
