RESUMO Objetivou-se avaliar o uso de água residuária do processamento da mandioca como fertilizante orgânico em pastos de Brachiaria brizantha cv. Marandu. Os tratamentos utilizados foram doses de água residuária (0, 15, 30, 60 e 120 m3 ha-1), em blocos ao acaso com quatro repetições. Foram avaliadas as características estruturais e a composição morfológica dos pastos, de julho de 2013 a janeiro de 2014. A adição de água residuária promoveu aumento linear positivo nos três cortes, para altura do dossel, interceptação de luz e índice de área foliar. A máxima produção de matéria seca (MS) foi obtida com 120 m3 ha-1 de água residuária (2796 kg ha-1 de MS no segundo corte). A massa de material senescente nos segundo e terceiro cortes se ajustaram à equação linear positiva. O aumento das lâminas da água residuária promoveu a diminuição de plantas indesejáveis. A dose de água residuária recomendada em pastos de capim-marandu é de 120 m3 ha-1, a qual promove maior massa de forragem e menor de plantas indesejáveis.

ABSTRACT This study aimed to evaluate the use of wastewater from the cassava processing as organic fertilizer on pastures of Brachiaria brizantha cv. ‘Marandu’. The treatments were wastewater doses (0, 15, 30, 60 and 120 m3 ha-1), in a randomized block design with four replicates. The structural characteristics and morphological composition of the pastures were evaluated, from July 2013 to January 2014. The addition of wastewater promoted a positive linear increase in the three cuts for the canopy height, light interception and leaf area index. The maximum dry matter (DM) production was obtained with 120 m3 ha-1 of wastewater (2796 kg ha-1 of DM in the second cut). The mass of senescent material in the second and third cuts fitted to positive linear equation. The increase in wastewater doses promoted the reduction of undesirable plants. The recommended dose of residual water in pastures of ‘Marandu’ grass is 120 m3 ha-1, which promotes a higher mass of forage and lower of undesirable plants.

A theoretical study of the effects of disorder on the Mn-Mn exchange interactions for Ga1-xMn xAs diluted magnetic semiconductors is presented. The disorder is intrinsically considered in the calculations, which are performed using an ab initio total energy density-functional approach, for a 128 atoms supercell, and by considering a variety of configurations with 2, 3 and 4 Mn atoms. Results are obtained for the effective J$^{Mn-Mn}_n$, from first (n = 1) all the way up to sixth (n = 6) neighbors via a Heisenberg Hamiltonian used to map the magnetic excitations from ab initio total energy calculations. One then obtains a clear dependence in the magnitudes of the J$^{Mn-Mn}_n$ with the Mn concentration x. Moreover, we show that, in the case of fixed Mn concentration, configurational disorder and/or clustering effects lead to large dispersions in the Mn-Mn exchange interactions. Also, calculations for the ground-state total energies for several configurations suggest that a proper consideration of disorder is needed when one is interested in treating temperature and annealing effects.