EFFECTS OF AMMONIUM NITRATE AND POTASSIUM SULFATE FERTILIZATION ON RATES OF RUMINAL IN SITU DISAPPEARANCE OF TALL FESCUE AND ORCHARDGRASS NITROGEN AND SULFUR

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Abstract
Tall fescue (TF) and orchardgrass (OG) were fertilized with 0, 294 or 882 kg NH4NO3/ha and 0 or 833 kg K2SO4/ha to determine the effect on rates of apparent ruminal disappearance of herbage dry matter (DM), nitrogen (N) and sulfur (S) using the in situ nylon bag technique. Losses of water-soluble and filtrable DM, N and S differed significantly due to herbage species, NH4NO3 and K2SO4 fertilization levels. After 24-h ruminal incubation, there was no difference between herbages in residual DM, N or S expressed as a proportion of original nutrient. Increasing level of NH4NO3 fertilization reduced (P < 0.001) 24-h residual DM and N and increased (P < 0.001) residual S. Potassium sulfate fertilization reduced (P < 0.001) residual herbage S after 24-h incubation. Rates of insoluble herbage DM and N disappearance (kd) did not differ between herbages but increasing level of NH4NO3 fertilization increased (P < 0.001) insoluble DM and N disappearance rates. Rate of insoluble S disappearance was lower (P < 0.05) for TF than OG but unaffected by fertilization. Effective ruminal degradability (ERD) of DM (P < 0.01) and release (ERR) of N (P < 0.001) and S (P < 0.05) were lower for OG than TF. Increasing NH4NO3 fertilization increased (P < 0.001) ERD and ERR of DM and N, respectively. Furthermore, NH4NO3 fertilization reduced (P < 0.001) while K2SO4 application increased (P < 0.001) ERR of herbage S. Simple correlation coefficients between kd of DM, N and S and original herbage total N concentration were r = 0.59 (P < 0.001), r = 0.51 (P < 0.001) and r = 0.36 (P < 0.05), respectively. The relationships between ERR of herbage S and total N or nonprotein S concentration in herbage were r = −0.74 (P < 0.001) and r = 0.70 (P < 0.001), respectively. Key words: Tall fescue, orchardgrass, sulfur, nitrogen, ruminal in situ disappearance