A greenhouse experiment was carried out during the Spring 2004 aiming to evaluate Panicum maximum cv. Tanzania root system as related to the combined supply of K and Mg in nutrient solutions. A randomized block design was used, with four replications, in an incomplete 5² factorial experiment with 13 combinations between K and Mg fertilization rates, in mmol/L: 0.4K/0.05Mg; 0.4K/1.35Mg; 0.4K/2.65Mg; 3.2K/0.70Mg; 3.2K/2.00Mg; 6.0K/0.05Mg; 6.0K/1.35Mg; 6.0K/2.65Mg; 8.8K/0.70Mg; 8.8K/2.00Mg; 11.6K/0.05Mg; 11.6K/1.35Mg, and 11.6K/2.65Mg. Roots were collected after the second harvest of the plants, by washing with tap and deionized water and using 0.25 and 1.00 mm screens. Potassium and magnesium rates combinations highly influenced root dry weight, specific root length and surface, and root K concentration. Increasing Mg rates also increased root surface, but decreased calcium concentration in the grass roots. Maximum responses of Tanzania guineagrass roots were found when K was supplied between 6.0 and 8.8 mmol/L and Mg between 1.4 and 2.0 mmol/L. Root K concentration ranged between 35 and 53% and root Mg concentration about 20% to the total concentration of potassium, magnesium and calcium in the grass roots.
forage grass; macronutrients; nutrient solution; root length; root surface
