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LARA-CABEZAS, Waldo Alejandro Rubén and PADUA, Rodrigo Vieira de. Efficiency and distribution of nitrogen applied on side-dressing in corn intercropped with Brachiaria ruziziensis, cultivated in Santa Fe system. Bragantia [online]. 2007, vol.66, n.1, pp.131-140. ISSN 0006-8705. http://dx.doi.org/10.1590/S0006-87052007000100016.
Within the system of Integrated Cattle Farming, corn intercropping with Brachiaria ruziziensis, Germann & Edvard, the option called Santa Fé system, allow for the production of grains and the production of forrage during the dry season, with the purpose of covering the soil and/or food production for cattle. An experiment was carried out at Fazenda Canadá, Uberlândia, Minas Gerais State, Brazil, in a soil of medium texture (218 g kg-1 of clay), in Santa Fé system with the objectives of: a) to quantify the efficiency of using the N-applied in side-dressing on corn and B. ruziziensis; b) to quantify the SO42--S content distributed on soil profile after the application of N side-dressing and c) dry matter of B. ruziziensis at harvest of corn and 55 days after. An entirely random design was established, with eight treatments with four replications. The treatments were: single corn crop and intercropped with B. ruziziensis without N-applied (controls), single corn crop and intercropped one with urea mixture and ammonium sulphate, at a ratio of 1:1 in nutrient, single corn crop and intercropped with urea and single corn crop and intercropped with ammonium sulphate. Two N-sidedress applications were made, using sources labelled with 15N, in stages from two to three leaves and five to six leaves, applied between rows and incorporated between rows, respectively, using 40 and 64 kg ha-1 of N. The B. ruziziensis was sown at a quantity of 12 kg ha-1 in a single line in the middle of the corn rows, at the stage of five to six leaves. Twenty three days after the second N-sidedressing, the decreasing concentrations of SO42--S in the 20 to 60 cm layer of soil profile went to ammonium sulphate > urea + ammonium sulphate > urea = controls, at the treatments of single corn crop. The average efficiency of N-fertilizer at two to three leaves stage was 45.0% of the N-applied. The average efficiency of N-applied at second stage was 60.7%, the treatment with ammonium sulphate distinguishing itself (73.7 % on average). Up to corn harvest, both cultures assimilated 54.5 kg ha-1 of the N-applied, 97.1 and 2.9% being distributed to the aerial parts of the corn and B. ruziziensis, respectively. There was no grain productivity difference, except in relation to the controls. The B. ruziziensis showed an increasing average of 61.9% dry matter, 55 days after corn harvest. For the purpose of this study, it can be concluded that B. ruziziensis did not affect the efficiency of the N-applied and that ammonium sulphate followed by the mixture of urea + ammonium sulphate contributed to a greater recovery of N-fertilizer by corn plant. High proportion of N-fertilizer assimilated for both cultures was recovery by corn.
Keywords : intercropping corn - B. ruziziensis; 15N isotope; cover crops; forage; out-of season.