Determinação da capacidade de troca catiônica das raízes de plantas forrageiras e sua relação com os teores de potássio, de cálcio e de magnésio na parte aérea

Resumo

Experiments were carried out to determine the cation exchange capacity of roots of selected forage plants and to study the relationship betwen the cation exchange capacity of the roots and the contents of nutrients in the aerial parts of the plants. The study was corried out in greenhouse, and samples of taken from the campus of the Federal University of Viçosa, Viçosa, Minas Gerais, Brazil. The study was corried out in greenhouses, and samples of a Red-Yellow Latosol taken from the campus of the Federal University of Viçosa, Viçosa, Minas Gerais, Brazil, were used.

The experiment consisted of eight completely randomized treatments with four repetitions. Species studied were the grasses capim-coloniao (Panicum maximum Jacq.), capim-buffel (Cenchrus ciliaris L. cv. ‘Gayndah'), capim-jaragua (Hyparhenia rufa (Ness) Stapf) and capim-gordura (Centrosema pubescens Benth.), calopogonium (Calopogonium mucunoides Desv.), perennial soybean (Glycine wightii C.V. Cooper) and stylosanthes (Stylosanthes guyanensis C. V. Oxley). Forty days after planting, the plants were harvested and the cation exchange capacity of the roots and the levels of potassium, calcium and magnesium of the aerial portions were determined.

The results showed that the cation exchange capacity of the roots of the legumes was higher than that of the grasses, and specific differences existed among both the legumes and the grasses. The percentages of calcium in the dry matter of both grasses and legumes were directly proportional to the cation exchange capacity of the roots, while the amounts of potassium (mg/pot) decreased in quadratic relationship with increase in cation exchange capacity of the roots.