Nirialuce Rezende
Abstract:
The experiment was conducted at the UFG - Jataí Campus, aimed to evaluate five nitrogen levels - NL (0, 80, 160, 240, 320 kg N/ha) on andropogon and brachiaria decumbens dry matter (DM) and crude protein (PB) percentage and production and neutral detergent fiber (NDF) and acid (ADF) percentage in a DBC arrangement and two 2x5 factorial design (Factorial 1: andropogon vs. brachiaria decumbens and Factorial 2: pioneer vs. mombasa), with five replications and four cuts. The data were analyzed and the NL averages were compared by orthogonal contrasts using F test at 5%. There was an interaction (P <0.05) between species in factorial 1 and NL for DM and ADF percentage and DM production and for species and NL in PB percentage and PB and DM production and only between species for NDF percentage. The responses of andropogon to NL was linear for DM production and cubically for the FDA, with average productivity increase of 5.56 t/ha and fiber reducing of 11.76%. Andropogon had 4.6% NDF higher than decumbens (81.46%). The andropogon DM average production was 0.62 t/ha higher than decumbens (3.58 t/ha). The PB decumbens was 0.92% higher than andropogon (8.42%) and associated to the DM resulted in 0.328 and 0.362 t CP/ha production for brachiaria and andropogon, respectively. Nevertheless, brachiaria was more responsive to NL than andropogon, reaching 10.63% PB when fertilized with 320 kg N/ha, while andropogon reached 8.87%. At factorial 2 the results showed that nitrogen fertilization increased forage CP content from 8.32 to 10.63% in Mombasa grass and from 11.94 to 12.77% in Pioneer grass, resulting in PB productions of 0.330 and 0.578 kg/ha, respectively. The increased in N supply also reduced the Mombasa FDA concentration form 28.79 to 17.03%. Between the species, Pioneer grass was the most productive showing total DM production of 25.71 t/ha (4.62 t DM/ha/cut), 37% more productive than Mombasa, which produced 16.18 t DM/ha (3.58 t DM/ha/cut). In more extensive systems management brachiaria decumbens is more responsive to nitrogen fertilization, producing grass with the best nutritional value. When species was very demanding where used, it was concluded that it is necessary to use annual nitrogen doses above 240 kg/ha for the grasses productive capacity maintenance with better nutritional value.
