Mixed stands of Eucalyptus urograndis and Acacia mearnsii in an agroforestry system: I - Biomass production

Objetivou-se com o presente estudo quantificar a biomassa de um plantio misto de Eucalyptus urograndis e Acacia mearnsii em sistema agroflorestal com milho ( Zea mays L.) no munic\uedpio de Bag\ue9, RS. O delineamento utilizado foi blocos ao acaso com cinco tratamentos e tr\ueas repeti\ue7\uf5es (T1- 100E; T2-100A; T3-50E:50A; T4-75E:25A e T5-25E:75A), com espa\ue7amento de 4,0 m x 1,5 m. Foram plantadas tr\ueas linhas de milho, entre as fileiras de eucalipto e/ou ac\ue1cia-negra. Aos 10 meses de idade, foi quantificada a biomassa das esp\ue9cies florestais, que foram separadas por fra\ue7\uf5es (folha, galho e tronco). A biomassa do milho foi coletada no final do ciclo e tamb\ue9m separada por fra\ue7\uf5es (folha, palha, gr\ue3o, sabugo e colmo). Em plantio misto o tratamento T5 (25E:75A) apresentou o maior ac\ufamulo de biomassa, sendo 35,1% nas folhas, 25,8% nos galhos e 39,1% no tronco. A ac\ue1cia-negra apresentou maior crescimento inicial do que o eucalipto, tanto em monocultivo como em plantio misto. A produtividade do milho ficou entre 1,01 a 1,26 Mg ha-1, n\ue3o diferindo estatisticamente (p < 0,05) entre os tratamentos.This study aimed to evaluate a mixed stand of Eucalyptus urograndis and Acacia mearnsii in an agroforestry system with corn ( Zea mays L.) in Bag\ue9, RS. The design entailed a randomized block with five treatments and three replicates (T1- 100E; T2- 100A; T3- 50E:50A; T4- 75E:25A e T5- 25E:75A), with 4.0 m x 1.5 m planting space. Three lines of corn were planted, between the eucalyptus and/or black-wattle lines. Ten months after the installation, the biomass from forest species were quantified and separated in fractions (leaf, branch and stem). Corn biomass was collected at the end of the cycle and separated in fractions (leaf, straw, grain, corn cob and stem). In mixed stands, the treatment T5 (25E:75A) showed the highest biomass accumulation, being 35.1% in the leaves, 25.8% in branches and 39.1% in stem. The black wattle showed higher growth than the initial eucalyptus, both alone and in the mixed stand. The yield of corn was between 1.01 to 1.26 Mg ha-1, which was not statistically different (p<0.05) between treatments