An experiment under greenhouse conditions was carried out with Tanzania guineagrass supplied with combined rates of nitrogen and calcium in nutrient solutions during the spring season. A randomized block design was used, with four replicates, in an incomplete 5² factorial scheme with five nitrogen rates (2; 9; 16; 23 e 30 mmol L-1) and five calcium rates (0.50; 1.75; 3.00; 4.25 e 5.50 mmol L-1) resulting in 13 nitrogen:calcium combinations (mmol L-1): 2:0.50; 2:3.00; 2:5.50; 9:1.75; 9:4.25; 16:0.50; 16:3.00; 16:5.50; 23:1.75; 23:4.25; 30:0.50; 30:3.00 and 30:5.50. Macronutrient concentrations were determined in the two recently expanded leaf blades (diagnostic leaves) collected in the three harvests of Tanzania guineagrass. The results showed that, in the first harvest of the plants, calcium rates did not interact with nitrogen for any of the nutritional traits, except for sulphur concentration in the diagnostic leaves. The interaction nitrogen × calcium was significant for concentrations of calcium and sulphur in the diagnostic leaves at the second and third samplings of the grass. Nitrogen rates and, not calcium rates, are determinant for nitrogen, phosphorus, and potassium concentrations in the diagnostic leaves of Tanzania guineagrass. The concentration of calcium at the first harvest of the grass depends only on the supply of this nutrient. Concentration of magnesium in plant tissue decreases as nitrogen or calcium supply increases. Reduction of calcium to 40% of that one used in the nutrient solution does not reduce nutritional parameters of this grass, even with the supply of high nitrogen rate.
forage plant; leaf diagnosis; mineral nutrition; nutrient solution; Panicum maximum
