Effects of nitrogen dosage and urea source on morphological composition and forage accumulation in massai grass

The effects of nitrogen (N) dose and urea source on forage mass (FM), percentage of dry matter of leaf blades (LBDMP), stem (SDMP), and dead material (DMDMP), and the forage accumulation rate (FAR) of Panicum maximum ‘Massai’ (massai grass) were evaluated. We set up an experiment with a completely randomized block design in a factorial arrangement (3×2) + 1, consisting of three doses (100, 200, and 400 kg ha–1 year–1), two urea sources (common and coated with Policote®), and a control treatment, in five consecutive climatic seasons, including the summers of 2011/2012 (summer I), autumn, winter, and spring of 2012, and the summers of 2012/2013 (summer II). We found an interaction effect between N dose, urea source, and season (p < 0.05). LBDMP linearly increased during dry periods (autumn and winter) and SDMP in autumn and DMDMP in winter linearly decreased when coated urea were used. FAR showed a linear increase with the use of both urea sources, except for common urea in autumn, and the increases in the winter were owing to a greater contribution of leaf blades to FM. The use of coated urea for N fertilization linearly increases FAR in all seasons of the year and improves the morphological composition of the forage of massai grass, mainly in dry seasons.