Substâncias húmicas do solo e alelopatia de leguminosas arbóreas na germinação e no crescimento do milho (Zea Mays L.)

Abstract

The allelopathy is a phenomenon in which products of the secondary metabolism of vegetal determined one are set free, resulting in chemical interactions that affect, beneficially or harmfully, the germination and the development of other plants. The humic and fulvic acid of the soil are importants abiotic components of the organic substance of the soil. Ample evidences exist of that these substances are absorbed by the plants and incorporated to its tissues, where they can intervene directly with diverse metabolic processes being able to reduce the allelopathics effect on the cultures. The research was divided in two experiments. The first one, with the objective to investigate the allelopathic potential of the leguminous sombreiro (Clitoria fairchildiana) and leucaena (Leucaena leucocephala) on the germination of seeds and the growth of corn seedlings. The second, with intention to try to inhibit the allelopathic effect of the sombreiro already proven on the corn, using humic substances of the soil. For the evaluation of the allelopathic potential, aqueous leaf extracts had been used of both the leguminous, in different concentrations (0%, 25%, 50%, 75% and 100%). In both the experiments, the tests of germination and growth had been carried through with the seeds of corn made use in trays, being 50 seeds for tray. The experimental design was totally randomized, with 9 treatments and 4 repetitions, totalizing 36 trays and 1800 seeds. For the test of inhibition of the allelopathy, the aqueous extract of the sombreiro was used, in concentrations 0%, 50% and 100%, mixed the different concentrations of fulvic and humic acid of the soil (20%, 30% and 40%). The experimental design also was totally randomized, with 21 treatments and 3 repetitions, in a total of 63 trays and 3150 seeds. The leucaena extract did not indicate significant differences in the normal, abnormal percentages of seedlings and in the length of seedlings. However, a light stimulaton in the germination and the growth of the corn was observed. Moderate harmful effect had been evidenced only in high concentrations of the extract and only in the length of the radicle and the dry weight of seedlings and radicle. The sombreiro extract exerted inhibitory allelopathic effect on the germination of the seeds and the growth of corn seedlings, in all the tested concentrations. The determinative factor of this effect was the abnormality of seedlings, evidenced, mainly, in the atrophied roots. In the generality, the fulvic and humic acid of the soil had revealed efficient in inhibiting the allelopathic action of the sombreiro on the corn. However, in some variable analyzed, the fulvic acid had demonstrated inhibitory potential greater of this phytotoxic action.