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Planta Daninha

Print version ISSN 0100-8358


NEPOMUCENO, M.P.; VARELA, R.M.; ALVES, P.L.C.A.  and  MARTINS, J.V.F.. Burn-down timing of Urochloa ruziziensis and its effect on RR soybean yield. Planta daninha [online]. 2012, vol.30, n.3, pp.557-565. ISSN 0100-8358.

Two field trials were carried out to evaluate the effects of burn-down timing of Urochloa ruziziensis on transgenic soybean establishment and yield under the no-tillage system. One experiment was conducted in Colina, SP - Brazil, in 2007/2008 season, and the other in Jaboticabal, SP - Brazil, 2009/2010 season. In 2007/2008, the experiment was carried out in a 7-year-old grass pasture of U. ruziziensis, with four burn-down timings of vegetation cover being tested 30, 20, 10, and 0 days in advance to soybean sowing. In 2009/2010, the experiment was conducted in an old grass pasture of U. ruziziensis cropped with maize the summer before. After maize harvesting, a natural re-infestation of U. ruziziensis occurred, corresponding to more than 80% of the vegetation cover. In this experiment, treatments corresponded to six burn-down timings of vegetation cover 25, 20, 16, 7, and 0 days in advance to soybean sowing. In all experiments, 1.44 kg a.e. ha-1 of herbicide glyphosate was applied, and the soybean cultivar M-SOY 7908 RR was used. The experiments were arranged in a randomized block design, with four replicates. The evaluations were carried out by measuring crop stand 20 days after sowing and pre-harvest, plant height, first pod insertion height, number of pods per plant, grain yield, and estimated yield. Data were submitted to ANOVA and the Tukey test at 5% of probability. Burn-down of U. ruziziensis performed at the same day of crop sowing reduced plant height, number of pods per plant, and crop grain yield. Burn-down timing of U. ruziziensis using glyphosate was recommended to be between 10 and 20 days in advance to crop sowing. In conclusion, soybean yield was affected by burn-down timing of U. ruziziensis.

Keywords : Brachiaria ruziziensis; Glycine max; vegetation cover; allelopathy; glyphosate.

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