Factors limiting the growth of Panicum maximum cv. Tanzania-1 in an agrosilvopastoral system with eucalypt, in the Cerrados of Minas Gerais, Brazil

A study was conducted in an agrosilvopastoral system, constituted by Eucalyptus urophylla and Panicum maximum ev. Tanzania-1, to verify the hypothesis that there were other factors, besides the low light availability, affecting the normal growth of the grass, four years after its introduction in the system. A NPK fertilization field trial was carry out, using the randomized block design, with the treatments in the 23 factorial outline, with two doses of nitrogen (0 and 100 kg/ha of N), phosphorus (0 and 70 kg/ha of P2O5) and potassium (0 and 100 kg/ha of K2O). The grass did not respond to P nor K fertilization, in spite of the low original P and K availability in the soil. However, with the application of nitrogen the rate of herbage accumulation was twice superior compared to control, showing that the grass growth was being restricted by the low N availability in the soil. The high response to the N fertilization showed that the shading was not the only factor limiting the understorey productivity and, also, that the established Panicum maximum plants were not being negative and significantly affected by allelopathic substances produced by eucalypts.