In situ ruminal degradation of dry matter and fiber from bermudagrass fertilized with different nitrogen rates and harvested on two dates

Abstract

Nutrient composition and in situ dry matter (DM) and neutral detergent fiber (NDF) degradation of bermudagrass [ Cynodon dactylon (L) Pers.] may vary with different management and environmental factors. This study evaluated nutritional value and in situ degradation characteristics of DM and NDF for bermudagrass, a perennial, warm-season grass. Bermudagrass growing on a poultry layer—litter—amended site was fertilized with ammonium nitrate at four rates (0, 56, 112, and 168 kg N ha −1) on 28 April and 19 July 2000, then harvested on 10 May and 18 August 2000. Five crossbred ruminally-cannulated steers (422±21.0 kg body weight (BW)) were used in a randomized complete block design with a 2×4 (harvest date×N fertilization rate) factorial arrangement to determine in situ DM and NDF degradation kinetics. Quadratic relationships were detected between N fertilization rates and N concentration in the plant when harvested on 30 May ( y=0.0001 x 2+0.009 x+27; P<0.01; R 2=0.99) and 18 August ( y=−0.0001 x 2+0.060 x+18; P<0.01; R 2=0.99), and both the quadratic relationships and intercepts differed ( P<0.05) between harvest dates. Concentrations of NDF decreased linearly ( P=0.01) with increasing N fertilization rate on both harvest dates and the intercept was higher ( P<0.05) on 18 August than on 30 May. Other fiber fraction concentrations did not differ ( P>0.05) across N fertilization rates. The undegraded DM fraction (fraction C) declined ( P<0.01) linearly and the potential extent and DM degradation rate ( k d) increased ( P<0.01) linearly with increasing N fertilization rate across harvest dates. Effective DM degradability increased linearly ( P<0.01) on both dates as N fertilization rates increased, but the rate of increase on 30 May was 64% greater ( P<0.05) than on 18 August. When averaged across N rates, the intercept for DM fraction A and the potential extent of DM degradation was greater ( P<0.05) while that of DM fraction C and k d were smaller on 30 May than on 18 August. Effective NDF degradability and k d increased ( P<0.01) with N fertilization rate, and the intercept for effective NDF degradability was higher ( P<0.05) on 30 May than 18 August. Therefore, N fertilization improved quality of bermudagrass marginally by increasing plant N concentration and by improving the degradation rate and effective ruminal degradability of DM and NDF.