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Effects of Sulfur Fertilization on Composition and Digestion of Phenolic Compounds in Tall Fescue and Orchardgrass

University of Illinois, Urbana 61801 and North Carolina State University, Raleigh 27695

Abstract

Tall fescue was fertilized with S at 0 or 132 kg/ha (TF and FTF, respectively) and orchardgrass was fertilized with S at 0 or 132 kg/ha (OG and FOG, respectively). Total S concentration of tall fescue and orchardgrass was increased by 21.2 and 27.6%, respectively, when fertilized with S. Steer metabolism trials showed that digestion coefficients for neutral detergent fiber (NDF), acid detergent fiber (ADF) and permanganate lignin were not different between TF and FTF, but were greater (P<.01) for FOG vs OG. Acid detergent lignin (ADL) concentration was less than permanganate lignin in all grasses. There were no treatment effects on ADL digestibility. Supplemental S (.15% of dry matter) did not improve in vitro NDF or ADF digestion of either OG or FOG, indicating that increased digestion of FOG vs OG was not due to a microbial S deficiency. Concentrations of NDF alkali-labile phenolic monomers were similar between TF and FTF, but FOG contained 12.8% less p-coumaric acid and 15.3% less ferulic acid than did OG. Concentrations of phenolic monomers obtained after nitrobenzene oxidation of alkali-extracted NDF residues were similar for TF and FTF but were 26.4% less in FOG than in OG. Greater (P<.05) apparent in vivo digestibilities of alkali-labile phenolics were found for protocatechuic acid from FOG vs OG and p-hydroxybenzoic acid from FTF vs TF. Greater (P<.05) apparent digestibilities of phenolic aldehydes (p-hydroxybenzaldehyde, vanillin and syringaldehyde) obtained after nitrobenzene oxidation were observed for FOG vs OG. Benzoic acid excreted in urine was related to apparent disappearance of cinnamic acids. Sulfur fertilization had no effect on phenolic constituents of tall fescue, but lowered concentrations and increased apparent digestibilities of some phenolics in orchardgrass.

¹ Dept. of Anim. Sci., Univ. of Illinois.

² Dept. of Anim. Sci., North Carolina State Univ.