Root system characteristics of Marandu palisadegrass supplied with nitrogen and magnesium rates

The development of root system of forage grasses is influenced by the supply of mineral nutrients. The experiment was carried out in a greenhouse in Piracicaba, São Paulo State, with the objective of evaluating the effect of nitrogen and magnesium rates on dry mass yield, total length and surface, specific length and surface, and concentrations of nitrogen, magnesium, calcium and potassium in the root system of Brachiaria brizantha Stapf. cv. Marandu. It was studied five rates of nitrogen (2, 9, 16, 23 and 30 mmol L-1) and five rates of magnesium (0.05, 0.70, 1.35, 2.00 and 2.65 mmol L-1) in nutrient solutions in an incomplete 5² factorial arrangement, which resulted in the following combinations: 2/0.05; 2/1.35; 2/2.65; 9/0.70; 9/2.00; 16/0.05; 16/1.35; 16/2.65; 23/0.70; 23/2.00; 30/0.05; 30/1.35 and 30/2.65. The experimental design was a randomized block with four replications. Plants had two growth periods, and after the second harvest the roots were separated from the plant tops. Combination of the high rates of nitrogen and magnesium resulted in expressive increases in rooty dry matter yield, in the length and in the root surface of marandu palisadegrass. High rates of nitrogen and magnesium resulted in short root specific length and surface. Combinations of high rates of nitrogen and magnesium increased nitrogen concentration or decreased potassium concentration in the roots. Calcium concentration in the roots was increased by nitrogen rates and decreased by magnesium rates. Magnesium rates resulted in increase in magnesium concentration in the roots of marandu palisadegrass