Effect of Plant Age and Nitrogen Fertilization on the Chemical Composition and In Vitro Cellulose Digestibility of Tropical Grasses1

Abstract

AbstractThis study was conducted in the state of Minas Gerais, Brazil, on a sandy loam soil low in fertility and a pH of 5.1. The mean monthly rainfall ranged from near zero during the 5‐ to 6‐month winter dry season and up to 330 mm in the mid‐summer wet season. The percentages of dry matter, crude protein, cellulose, crude fiber, and in vitro digestibility were determined on six tropical grass species: Melinis minutiflora Beauv., Digitaria decumbens Stent., Pennisetum purpureum Schum., Pennisetum clandestinum Hochst, Cynodon dactylon Pers., and Panicum maximum Jacq. var. Gongylodes Doell. Samples were taken with advancing age every 4 weeks beginning at the outset of the wet summer seasons in each of 2 years, 1964 and 1965, and each sampling period continued for 36 weeks. Lime, N, P, and K were applied as a basal application. In addition, N was applied each year at the rates of 0, 100, and 200 kg/ha. The increase in dry matter percentage was linear over time with an increase of 21.2 to 51.4% for all grasses. P. purpureum had the lowest dry matter percentage and C. dactylon the highest. Application of N fertilizer resulted in decreased dry matter percentage during the early growth stages but not at the more mature stages. The crude fiber percentage increased with age and the in vitro cellulose digestibility decreased. The cellulose percentage of three of the grasses increased with age while the other three remained almost constant during the sampling period.