| Summary: | This study was conducted to determine the effects of different nitrogen (N) fertilizer levels on botanical composition, dry matter (DM) yield, chemical composition, in situ ruminal DM and NDF degradability and net energy lactation (NEL) of a native legume-grass mixture pasture. Field and degradability trials were arranged in a Complete Randomized Block Design with three replicates. Pasture was fertilized at six levels of N fertilizer (ammonium nitrate, N0, N50, N100, N150, N200 and N250 kg/ha). Three rumen cannulated Holstein Friesian heifers (3-4 year old) were used. Feed samples were incubated for 0, 8, 12, 24, 36, 48, 72 and 96 h. Application of nitrogen fertilizer results indicated that nitrogen fertilizer decreased the legumes ratio (LR) of pasture, approximately 22.4%, Although N fertilizer increased the grass ratio (GR) of pasture approximately 55.8%. Dry matter (DM), Net energy lactation (NEL, Mcal/kg) and ash contents of pasture were increased by increasing N fertilizer level. However, when N fertilizer level increased acid detergent fiber (ADF) concentration of pasture decreased. Application of the different rate of nitrogen fertilizer had no effect on in situ rumen degradability of DM and NDF of pasture. It was also found that there was the significant positive relationship between effective NDF degradability at 48 h. rumen incubation period and different level of N fertilizer. In addition, it was determined that there was a linear and quadratic positive relationship between DM yield and different nitrogen doses. In conclusion, different rates of nitrogen application changed botanical composition, decreased ADF content and increased NEL and effective rumen degradability of neutral detergent fiber (EDNDF 48 h.) of pasture.
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