Fontes de nitrogênio e caule decomposto de Mauritia flexuosa na nodulação e crescimento de Enterolobium contortsiliquum

Nitrogen sources (N) and proportions of decomposed stem from 'buritizeiro' (Mauritia flexuosa L.f.) on nodulation, growth and biometric indexes of 'tamboril' [Enterolobium contortsiliquum (Vell.) Morong] seedlings were evaluated in the Southwestern region of Piaui State, Brazil. The experimental design was a completely randomized factorial 3x5, with five replications. Three sources of N were tested (mineral N fertilization, N in the substrate, inoculation with the strain Bradyrhizobium elkanii BR 4406), with five proportions of "buritizeiro" decomposed stem: soil (v/v, %): 0: 100; 10: 90; 20: 80; 40: 60; 80: 20. Seedling emergence was evaluated daily until the thirteenth day after sowing. At 80 days, seedlings were collected for determining biometric indexes and nodulation. The seedlings grown in substrates containing "buritizeiro" decomposed stem showed higher growth and nodulation compared to those grown on the substrate 0: 100 (stem decomposed of "buritizeiro": soil). Maximum Dickson Index of Quality was obtained with the proportion 57: 43. Thus, we recommend this proportion of waste compost and soil for the production of "tamboril" seedlings. Regarding to nitrogen sources, strain BR 4406 was not effective in promoting gains in nitrogen content and shoot dry matter, compared to the treatment with mineral-N. The native populations of diazotrophic bacteria present on the substrate, which did not receive mineral-N neither inoculation, could efficiently nodulate "tamboril" since they led to an increase in the nitrogen content and on shoot dry matter, similar to the observed on seedlings treated with mineral N.