While nutrients such as calcium, magnesium and sulphur are required by plants in lower amounts than the amounts required of nitrogen, phosphorus, and potassium, these nutrients are as important as those required for the growth and development of plants. Varying concentrations of calcium and magnesium can be found in wood ash as residue, which may have a high percentage of these nutrients. This study aims to evaluate the concentration of calcium, magnesium and sulphur in Brachiaria brizantha, a genus of tropical grasses, as a function of the levels of wood ash. The experiment was conducted in a greenhouse. The experimental design was completely randomized in a factorial of 6 × 2, corresponding to 6 doses of wood ash (0, 3, 6, 9, 12 and 15 g dm-3) and 2 cultivars of B. brizantha (Marandu and Xaraes), and was completed with 6 replicates. Experimental characteristics included the concentrations of calcium, magnesium and sulphur in the dry mass of the shoots and roots of Marandu and Xaraes. The variance of the results was analyzed using an F test at a 5% probability. For wood ash, we performed a regression analysis, and for tropical grasses, we performed a Tukey test at a 5% probability. In the three sections, the highest concentrations of calcium, magnesium and sulphur in the shoots and roots of Marandu and Xaraes are between the wood ash doses of 7.72 and 11.79 g dm-3, respectively. The wood ash influences the nutritional characteristics of the grasses by increasing the concentrations of calcium and magnesium in the shoots of Marandu and Xaraes, respectively, in excess of 42 to 29% and greater than 77 and 39% increments for the roots. The average concentrations of magnesium in shoots of Marandu and Xaraes were 0.87 and 0.94 g kg-1, respectively, while the roots had concentrations of 0.94 and 0.95 g kg-1, respectively. Wood ash as a fertilizer promotes significant changes in the nutritional characteristics of the grasses Marandu and Xaraes when planted in Cerrado Oxisol.
Key words: Brachiaria brizantha, mineral nutrition, solid residue.
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