EFFECTS OF NITROGEN RATES AND HARVESTING INTERVALS ON DRY MATTER PRODUCTION, TILLERING AND QUALITY OF THE TROPICAL GRASS PANICUM MAXIMUM, JACQ (DEGREE DAYS, APICAL MERISTEM, LEAF: STEM RATIO)

The effect of nitrogen rate and harvesting intervals on dry matter production, tillering and quality of the tropical grass Panicum maximum cv. '68s-5-2' was studied in a greenhouse experiment. Plants were grown in plastic pots with no holes for drainage and containing 3 kg of soil. Demineralized water was added daily to each pot to bring its weight to a point where the water content of the soil was maintained close to 40% of water (V/V) and a pore space around 13% air space. Fertilizer was added to provide an adequate supply or macro and micronutrients except for nitrogen. Three nitrogen rates provided in an ammonium nitrate solution (150, 300 and 1200 mg N/pot) associated with four harvesting intervals (3, 5, 7 and 9 weeks) were the treatments arranged in a complete block design with three replicates.;Increasing the number of harvests and the nitrogen rates significantly increased the number of tillers in Panicum maximum. Dry matter production was not correlated with the number of tillers but it was highly correlated with weight per tiller (r = 0.872). Increased nitrogen rates significantly increased the weight per tiller (r = 0.425) and weight per tiller was highly correlated with percentage of stems in the dry matter produced (r = 0.886). Tillers started growing primarily in the first 8 days after cutting and no additional tillers were initiated after 16 days following cutting. The IVOMD did not correlate with nitrogen rates but it was significantly correlated with the percentage of nitrogen in the plant tops. The IVOMD was inversely and significantly correlated with weight per tiller (r = -0.782), percent of ADF (r = -0.765) and percent of stems (r = -0.697). Degree days showed a positive and significant correlation with dry matter production (r = 0.549) and a negative and significant correlation with IVOMD (r = -0.729). Degree days may be a useful tool to define stage of maturity in tropical grasses that have tillers started in a short period of time after cutting. Rotational grazing is apparently more beneficial to tropical grasses that have early stem elongation and tillers within a short period of time after cutting. The tillering habit of Panicum maximum helps the understanding of localized degradation of pastures established with this forage species in fields of south central Brazil.