Overseeding of annual ryegrass (Lolium multiflorum Lam.) in natural pastures increases the availability and quality of forage in cold periods in the subtropics. We measured the effects of N fertilization (zero, 100 and 200 kg ha-1 of nitrogen) on tiller dynamics, density, stability and biomass of ryegrass overseeded on natural pasture grazed by cattle. We used a randomized block design with three replicates. Forage biomass was estimated visually on a monthly basis using a double sampling technique. Tiller dynamics were evaluated using the marked tillers technique. Results indicated that nitrogen is critical for the early establishment of ryegrass populations. The number of tillers m-² observed in the first measurement (August) were 1153 (zero), 3078 (N100) and 4537 (N200). Initial tiller density was adversely affected by the amount of dead biomass of native vegetation, which depended on the amount of nitrogen added. Higher concentrations of nitrogen resulted in reduced dead biomass at the time of ryegrass establishment due to greater cold tolerance, thus favoring the initial increases in ryegrass tiller density. Initial tiller density directly affected vegetative biomass of ryegrass. Nitrogen fertilization is an appropriate tool to maintain stability and survival of annual ryegrass overseeded on native pastures.
Key words: Fertilization, Lolium multiflorum, pasture establishment, tiller dynamics.
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