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Yield, Chemical Composition and Digestibility by Sheep of Orchardgrass Fertilized with Different Rates of Nitrogen and Sulphur or Associated Red Clover¹

Virginia Polytechnic Institute and State University, Blacksburg 24061

Abstract

The effects of red clover (Trifolium pratense L.) or three rates of N (0, 224 and 448 kg·ha^–1·yr^–1) in split application, and two rates of S (0 and 34 kg·ha^–1·yr^–1) on yield, chemical composition and dry matter digestibility of orchardgrass (Dactylis glomerata L.) by sheep were studied. Thus, a 2 x 4 factorial was used. Treatments were replicated three times in a randomized-block design with a split-plot arrangement of treatments. Three metabolism trials, each involving 16 wether lambs (35 kg avg body weight), were conducted. The herbage was fed as chopped sun-cured hay. A 7-d preliminary period preceeded a 7-d collection period during each trial. Inclusion of red clover had no effect on composition of orchardgrass forage, probably due to a low proportion of red clover (8%) in the mixed sward. Crude protein (CP) content, in vitro dry matter digestibility (IVDMD) and dry matter (DM) yield were increased (P<.01) but S content was decreased (P<.05) with increasing levels of N fertilization. Application of S increased (P<.05) S content of orchardgrass and decreased N:S ratio at the low and high N application rates. Sulphur increased (P<.05) CP content and IVDMD and decreased contents of neutral detergent fiber (NDF), lignin and hemicellulose (P<.05). In vivo dry matter digestibility was increased (P<.01) by N fertilization. Inclusion of red clover in orchardgrass increased (P<.01) the digestibility of DM and hemicellulose. Interactions occurred between N and S with regard to the digestibility of DM and CP (P<.01). Digestibility of DM was increased by the low rate of N fertilization (224 kg N/ha) regardless of S application, but a response to the high rate (448 kg/ha) occurred only when S was applied. Apparent digestibility of CP was not affected by N fertilization in forage not fertilized with S, but increased with level of N application when the sward was fertilized with S. Sulphur fertilization of grass appears to be most beneficial when high levels of N are applied, or when available S in soil is low.

¹ Research supported in part by United States Agency for Int. Devel. Project and the Sulphur Inst., Washington, DC.

² Dept. of Anim. Sci.

³ Present address: Dept. of Anim. Sci., Univ. of Peradeniya, Peradeniya, Sri Lanka.

⁴ Dept. of Agron.